HYDROGRAPHIC DICTIONARY - International Hydrographic

INTERNATIONAL HYDROGRAPHIC ORGANIZATION
HYDROGRAPHIC DICTIONARY
Part I
Volume I, English
Special Publication No. 32
FIFTH EDITION
MONACO
1994
600-XII-1994
S-32
INTERNATIONAL HYDROGRAPHIC ORGANIZATION
HYDROGRAPHIC DICTIONARY
Part I
Volume I, English
Special Publication No. 32
FIFTH EDITION
MONACO
1994
PREFACE
The preparation of the Fifth Edition of the Hydrographic Dictionary was undertaken by a Working
Group established in accordance with the Bureau's Circular Letter CL 45/1984 of 13 December 1984.
The Working Group was comprised of staff members of the Hydrographic Offices of Argentina,
Croatia (associate member), France, and the United States of America (NOS). It carried out its work under
the chairmanship of Captain H.-P. Rohde, IHB.
The Hydrographic Dictionary is published in two parts. Part I contains terms and definitions in the
two official IHO languages and is published in separate volumes for each language. The definitions are
intended to give concise explanations of terms, without necessarily considering specific applications or
interpretations as, for example, for legal matters. Definitions of terms in Part I which were taken from
publications of other authorities, are given without quoting these authorities. Other IHO publications
containing glossaries were consulted to ensure consistency.
Part II will consist of separate supplements that provide a translation of the terms into various
languages other than the official IHO languages. In each supplement, the terms will be listed alphabetically in
English, with their equivalent in the other language, but without a translation of the definition. Each
supplement will also contain an alphabetical listing of the terms in the other language, giving the relevant
index number of the term in the English volume of Part I.
The English text in Volume I of this Dictionary has been modified to ensure maximum agreement
with the French text and also to take into account certain more recent sources which have become available
since the date of the Fourth Edition.
Valuable advice has been received from the Hydrographic Offices of a number of Member States
and from other users of the Hydrographic Dictionary which sent the Bureau lists of proposed amendments to
the 1990, Fourth Edition.
__________
INTRODUCTION
Terms and expressions are listed alphabetically in English, according to standard dictionary
practice, and assigned index numbers to be used as reference for the translation of terms from one language to
another.
The definitions are given in English, one of the two official languages of the IHO.
The work is cross-referenced in the following manner:
a) Most of the terms and expressions appearing in the definitions when defined under another
heading are printed in capital letters. Terms or expressions consisting of several words may be
listed under a heading with a different word order. In some cases reference is only made to the
generic term.
b) Attention is drawn to related terms by the words 'see', or 'see also' followed by the term (in
capital letters).
c) When synonyms exist, they are usually given at the end of a definition and printed in italics.
Abbreviations
adj.
adv.
n.
v.t.
v.i.
pl.
adjective
adverb
noun
verb transitive
verb intransitive
plural
__________
A
1
abeam. In a line approximately at right angles to the ship's keel; also: the waist or middle part of the ship.
2
aberration of light. In ASTRONOMY, the apparent displacement in position of a HEAVENLY BODY caused by the
combination of the VELOCITY of light and that of an observer on the surface of the EARTH. Aberration of light due to
the ROTATION of the EARTH on its AXIS is termed diurnal aberration. That due to the REVOLUTION of the EARTH
around the SUN is termed annual aberration. In optics, failure of an OPTICAL SYSTEM to bring all LIGHT RAYS
received from a point object to a single IMAGE POINT or to a prescribed geometric position. Spherical aberration is
caused by RAYS from various zones of a LENS or MIRROR coming to FOCUS at different distances from the LENS or
MIRROR. Chromatic aberration (or chromatism) is due to the differences in REFRACTION of the coloured RAYS of the
SPECTRUM; those of each colour having a different FOCUS.
3
abrasion. The wearing away or rounding of surfaces by friction.
4
abscissa. See COORDINATES: PLANE RECTANGULAR.
5
absolute accuracy. See ACCURACY: ABSOLUTE.
6
absolute error. See ERROR.
7
absolute orientation. See ORIENTATION.
8
absolute stereoscopic parallax. See PARALLAX.
9
absorption: atmospheric. Transformation of RADIANT ENERGY into thermal, mechanical, electrical, etc. energy, by
interaction with atmospheric constituents.
10
abyssal(adj.). Belonging to the lowest DEPTHS of the OCEAN, generally below 3,700 METRES (2,000 FATHOMS).
11
abyssal gap. A gap in a sill, ridge, or rise that lies between two abyssal plains.
12
abyssal hills. A tract of small elevations on the deep-sea floor.
13
abyssal plain. An extensive, flat, gently sloping or nearly level region at abyssal depths.
14
acceleration. The rate of change of VELOCITY.
15
acceleration: angular. The rate of change of ANGULAR VELOCITY.
16
acceleration of gravity. The ACCELERATION of a freely falling body caused by the force of GRAVITY.
17
accidental error. See ERROR.
18
acclivity. An upward SLOPE of GROUND; as opposed to DECLIVITY.
19
accommodation. The faculty of the human eye to adjust itself to give sharp IMAGES for different object distances. In
STEREOSCOPY, the ability of the eyes to bring two IMAGES into superimposition for stereoscopic viewing.
20
accretion. The gradual building up of LAND over a long period of time, solely by the action of the forces of nature, on a
BEACH by deposition of water or air-borne material. Artificial accretion is a similar build-up of LAND by reason of an
act of man. Also called aggradation.
21
accuracy. The extent to which a measured or enumerated value agrees with the assumed or accepted value. See
PRECISION.
22
accuracy: absolute. The evaluation of all errors encountered in defining the position of a single feature or point on a
GEODETIC DATUM or system.
23
accuracy: relative. The evaluation of the RANDOM ERRORS in determining the positional orientation of one point or
feature with respect to another.
24
accuracy: repeatable. See REPEATABLE ACCURACY.
7
25
achromat. See ACHROMATIC LENS.
26
achromatic lens. A compound LENS that has been partly corrected for chromatic aberration. Such a LENS is
customarily made to bring green and red LIGHT RAYS to approximately the same point focus. Also called achromat. See
ABERRATION OF LIGHT.
27
aclinic line. See EQUATOR: MAGNETIC.
28
acoustic. Science of sound, including its production, transmission and effects.
29
acoustic bearing. See BEARING: SONIC.
30
acoustic line of position. See SONIC LINE OF POSITION.
31
acoustic navigation. See NAVIGATION: SONIC.
32
acoustic sounding. See ECHO SOUNDING.
33
acoustic wave. See WAVE: SOUND.
34
active satellite. 1. An artificial satellite which transmits an electromagnetic signal. A satellite with the capability to
transmit, repeat, or retransmit electromagnetic information as contrasted with passive satellite.
2. As defined by the International Telecommunication Union (ITU), an earth satellite carrying a station intended to
transmit or retransmit radiocommunication signals.
35
active system. Any electromagnetic or sonic position fixing system operating with an interrogation-response procedure.
See also PASSIVE SYSTEM.
36
active tracking system. A satellite system which operates by transmission of signals to and receipt of responses from the
satellite.
37
adiabatic process. A thermodynamic change of state of a system in which there is no transfer of heat or mass across the
BOUNDARIES of the system. In an adiabatic process, compression always results in warming, expansion in cooling.
38
adiabatic temperature change. RISE or fall of temperature due to compression or expansion without gain or loss of heat
to the surroundings.
39
adjacent coasts. The coasts lying either side of the land boundary between two adjoining States.
40
adjusted position. See POSITION.
41
adjustment. The determination and application of CORRECTIONS to OBSERVATIONS or MEASUREMENTS, for the
purpose of reducing ERRORS or removing internal inconsistencies in observed results. Adjustment may either refer to
mathematical procedures or to CORRECTIONS applied to instruments.
42
aerial. See ANTENNA.
43
aerial camera. See CAMERA.
44
aerial navigation. See NAVIGATION: AIR.
45
aerial photogrammetry. See PHOTOGRAMMETRY.
46
aerial photograph. See PHOTOGRAPHY.
47
aerial photography. See PHOTOGRAPHY.
48
aerial survey. See SURVEY.
49
aerial triangulation. See PHOTOTRIANGULATION.
50
aerology. Study of the FREE ATMOSPHERE.
51
aeromarine light. See LIGHT.
8
52
aeronautical beacon. See BEACON.
53
aeronautical chart. See CHART.
54
aeronautical ground light. See LIGHT.
55
aeronomy. Term proposed for the study of the chemistry and physics of the high ATMOSPHERE.
56
aerotriangulation. See PHOTOTRIANGULATION.
57
affluent. A STREAM flowing into a larger STREAM or LAKE; a TRIBUTARY.
58
afloat. Floating, as opposed to being AGROUND.
59
age of diurnal inequality. The time interval between the maximum semi-monthly north or south declination of the moon
and the maximum effect of the declination upon the range of tide or the speed of the tidal current, this effect being
manifested chiefly by an increase in the height or speed difference between the two high (low) waters or flood (ebb)
currents during the day. The tides occurring at this time are called TROPIC TIDES. Also called diurnal age.
60
age of parallax inequality. The time interval between perigee of the moon and the maximum effect of parallax upon the
RANGE OF TIDE or the speed of the TIDAL CURRENT.
61
age of phase inequality. The time interval between new or full moon and the maximum effect of these phases upon the
range of tide or the speed of the tidal current.
62
age of the moon. The elapsed time since the last new moon; usually expressed in DAYS and fractions of a DAY. See
PHASES OF THE MOON.
63
age of tide. See AGE OF PHASE INEQUALITY.
64
agger. See TIDE: DOUBLE.
65
aggradation. See ACCRETION.
66
agonic line. The line through all points on the EARTH's surface at which the MAGNETIC VARIATION is zero.
67
aground(adj. and adv.). Touching, resting or lodged on the BOTTOM of shallow water. The opposite is AFLOAT.
68
ahead. Bearing approximately 000° relative. The term is often used loosely for dead ahead or bearing exactly 000°
relative. The opposite is ASTERN.
69
aid to navigation. BUOYS, BEACONS, FOG SIGNALS, LIGHTS, RADIO BEACONS, LEADING MARKS, radio
position fixing systems, and generally any charted or otherwise published device serving the interests of safe
NAVIGATION. See NAVIGATIONAL AID.
70
aiming line. See COLLIMATION: LINE OF.
71
air almanac. See under ALMANAC.
72
air base. In PHOTOGRAMMETRY, the line joining two AIR STATIONS, or the length of this line; also, the distance (at
the SCALE of the STEREOSCOPIC MODEL) between adjacent PERSPECTIVE CENTRES as reconstructed in the
plotting instrument. See also PHOTO BASE.
73
air camera. A CAMERA specially designed for use in flying craft.
74
air mass. Ensemble of air particles whose PATHS and physical properties exhibit, in the horizontal, only small and
continuous differences. The mass may extend over an area of several million square miles and over a depth of several
kilometres.
75
air navigation. See NAVIGATION.
76
air photograph. See PHOTOGRAPH: AERIAL.
77
air photography. See PHOTOGRAPHY: AERIAL.
9
78
air sextant. See SEXTANT.
79
air speed. The SPEED of an aircraft relative to the surrounding ATMOSPHERE. As opposed to GROUND SPEED.
80
air station. In PHOTOGRAMMETRY, the point in space occupied by the camera lens at the moment of EXPOSURE.
Also called exposure station or camera station.
81
albedo. The ratio of radiant energy reflected to that received by a surface, usually expressed as a percentage.
82
alga. A plant of simple structure which grows chiefly in water, such as the various forms of seaweed.
83
aliasing. An occurence in tidal analysis when the sea level varies with a period that is less than the sampling period. Due
to the varying position of the samples on the curve, a spurious tidal frequency appears in the analysis. It is usually only
possible when there is a seiche at the observation site or observations are taken at intervals greater than one hour.
84
alidade. Pivoted sight bar that moves over a graduated arc. The upper part of a THEODOLITE. The alidade used in
topographic SURVEYING consists of a straight-edge ruler carrying a TELESCOPE or other sighting device and used in
recording a DIRECTION on the plane table sheet. The term is also used to describe a BEARING CIRCLE fitted with a
TELESCOPE to facilitate OBSERVATION of BEARINGS. If a TELESCOPE is used, the instrument is often termed a
telescopic alidade.
85
alignment. The placing of objects along a straight line. In NAVIGATION, the bringing into line of two or more
conspicuous objects, such as LIGHTS, BEACONS, etc. Also their BEARING as seen by an observer from seaward.
86
alignment correction(tape). See TAPE: ALIGNMENT CORRECTION.
87
alignment of base. The laying out of a BASE LINE in correct ALIGNMENT by means of a THEODOLITE and range
poles, before the length of the line is measured.
88
alkalinity. The number of milliequivalents of hydrogen ions that are neutralized by 1 KILOGRAM of SEA WATER at
20°C when a large excess of acid is added.
89
almanac. A periodical publication of astronomical data useful to a navigator. It contains less information than an
ephemeris, and values are generally given to less precision. If information is given in a form and to a precision suitable for
air navigation, it is called an air almanac.
90
almanac: air. A periodical publication containing various computed astronomical DATA primarily intended for use in
AIR NAVIGATION. See also EPHEMERIS.
91
almanac: nautical. An annual publication containing various computed astronomical DATA primarily intended for use in
MARINE NAVIGATION. See also EPHEMERIS.
92
almucantar. Any SMALL CIRCLE on the CELESTIAL SPHERE parallel to the HORIZON. Also called parallel of
altitude.
93
alphanumeric. Contraction of alphabetic-numeric. Characters including letters of the alphabet and numbers.
94
alt-azimuth instrument. An instrument equipped with both horizontal and vertical graduated CIRCLEs, for the
OBSERVATION of horizontal and vertical DIRECTIONS or angles.
95
altimeter. An instrument that indicates directly the HEIGHT above a reference surface.
96
altimeter: barometric. A sensitive ANEROID BAROMETER calibrated to read the HEIGHT above a pressure datum
according to the standard atmospheric pressure-to-height relationship.
97
altimeter: pulse radio. See ALTIMETER: RADIO.
98
altimeter: radar. See ALTIMETER: RADIO.
99
altimeter: radio. Any instrument used for determining an aircraft's flight altitude by the measurement of time intervals
between the emission and return of electromagnetic PULSES. Also called pulse radio altimeter or radar altimeter. See
ALTITUDE: FLIGHT.
100 altimetry. The process of determining the difference of ELEVATION by the use of ALTIMETERS.
10
101 altitude. The vertical distance of a LEVEL, a point or an object considered as a point, measured from a given datum,
usually MEAN SEA LEVEL. See also ELEVATION. In ASTRONOMY, the vertical angle between the plane of the
HORIZON and the line to a CELESTIAL BODY. See also ANGLE OF DEPRESSION and ANGLE OF ELEVATION.
102 altitude: apparent. The SEXTANT ALTITUDE of a CELESTIAL BODY corrected for INDEX ERROR, DIP (HEIGHT
of EYE), and (for SUN or MOON only) SEMIDIAMETER. Also called rectified altitude.
103 altitude: ex-meridian. An ALTITUDE of a CELESTIAL BODY near the CELESTIAL MERIDIAN of the observer, to
which a CORRECTION is to be applied to determine the MERIDIAN ALTITUDE. Also called circummeridian altitude.
104 altitude: flight. The vertical distance above a given DATUM, usually MEAN SEA LEVEL, or an aircraft in flight.
105 altitude: meridian. The ALTITUDE of a CELESTIAL BODY when it is on the CELESTIAL MERIDIAN of the
observer.
106 altitude: observed. The SEXTANT ALTITUDE of a CELESTIAL BODY after all corrections (see ALTITUDE:
APPARENT) have been applied. In American terminology the term is usually employed in the place of TRUE
ALTITUDE.
107 altitude: rectified. See ALTITUDE: APPARENT.
108 altitude: sextant. The ALTITUDE as indicated by a SEXTANT before CORRECTIONS are applied.
109 altitude: true. The APPARENT ALTITUDE of a CELESTIAL BODY after all corrections have been applied. In
American terminology usually referred to as OBSERVED ALTITUDE.
110 altitude difference. See INTERCEPT.
111 altocumulus. See CLOUD GENERA.
112 altostratus. See CLOUD GENERA.
113 aluminium sheet. An aluminium-mounted paper sheet occasionally used for BOAT-SHEETS, SMOOTH SHEETS, or
plane table boards.
114 ambient noise. The erratic electromagnetic or sonic background noise emitted by natural or artificial sources
contaminating the proper signal.
115 ambiguity. Uncertainty of value or meaning because of the possibility of two or more interpretations. The condition when
navigational COORDINATES define more than one POSITION, DIRECTION, LINE OF POSITION, or SURFACE OF
POSITION.
116 Amici prism. A prism which deviates the RAYS of light through 90°and because of its shape inverts the IMAGE. See
ROOF PRISM.
117 amidships. At, near, or toward the middle of a ship.
118 ampere. The unit of density of electric current in the SI SYSTEM.
119 amphidromic point. A no-tide point, from which COTIDAL LINES radiate.
120 amplitude. In ASTRONOMY, the arc of the HORIZON, between a CELESTIAL BODY at rising or setting and true east
or west point. In tide terminology, the semi-range of the HARMONIC CONSTITUENT. In physics, the maximum
departure of a WAVE or other periodic PHENOMENON from the average or zero position.
121 amplitude modulation. See MODULATION.
122 anaglyph. A STEREOGRAM in which the two views are printed or projected superimposed in complementary colours,
usually red and green. By viewing through filter spectacles of corresponding complementary colours a STEREOSCOPIC
IMAGE is formed.
123 anaglyphic map. See under MAP.
11
124 analemma. A SCALE of the SUN's daily DECLINATION drawn from TROPIC OF CANCER to TROPIC OF
CAPRICORN on TERRESTRIAL GLOBES. An ORTHOGRAPHICAL PROJECTION of the sphere made on the plane
of the MERIDIAN, the eye being supposed to be an infinite distance and in the east or west point of the HORIZON.
125 anallatic lens. A convergent LENS fitted between the OBJECTIVE LENS and the DIAPHRAGM of TELESCOPES of
instruments for direct measurements of distances between the OPTICAL CENTRE of the instrument and a graduated staff
called STADIA.
126 analogue. The way of representing information by continuous data.
127 analogue computer. See under COMPUTER.
128 analytical (or analytic) photogrammetry. See under PHOTOGRAMMETRY.
129 anastigmatic(adj.). Free from ASTIGMATISM. Corrected for ASTIGMATISM.
130 anchorage. An area in which vessels anchor or may anchor.
131 anchorage buoy(s). BUOY(S) marking the limits of an ANCHORAGE.
132 anchor buoy. A BUOY marking the position of an anchor.
133 anchor ice. ICE which is attached to the BOTTOM, irrespective of the nature of its formation. Also called bottom ice,
depth ice, ground ice, lappened ice and underwater ice.
134 anemometer. Instrument used in the measurement of wind speed or of wind speed and direction. See also
ANEMOGRAPH.
135 anemogram. Record of the ANEMOGRAPH.
136 anemograph. An instrument which records WIND speed and direction. See also ANEMOMETER.
137 aneroid barometer. See BAROMETER.
138 aneroid capsule. Metallic capsule, of thin sides, partially evacuated by a fixed amount, carrying an arrangement to prevent
its collapsing under ATMOSPHERIC PRESSURE, and whose shape changes in accordance with changes of this pressure.
139 angle: check. See CHECK ANGLE.
140 angle: concluded. In a TRIANGULATION, the third angle of a triangle, not measured, but computed from the other two
angles.
141 angle: conversion. See ARC TO CHORD CORRECTION.
142 angle: crossing. The angle at which two LINES OF POSITION intersect. Also called angle of cut.
143 angle: danger. See DANGER ANGLE.
144 angle: drift. See DRIFT ANGLE.
145 angle: hour. See HOUR ANGLE.
146 angle: masthead. See MASTHEAD ANGLE.
147 angle: parallactic. See PARALLACTIC ANGLE.
148 angle: phase. See PHASE ANGLE.
149 angle: slope. See SLOPE ANGLE.
150 angle: vectorial. See COORDINATES: PLANE POLAR and COORDINATES: POLAR.
151 angle of convergence. See PARALLACTIC ANGLE.
12
152 angle of cut. See ANGLE: CROSSING.
153 angle of depression. The angle in the VERTICAL PLANE between the horizontal and the line to an object below the
HORIZON. Also called negative altitude.
154 angle of elevation. The angle in the VERTICAL PLANE between the horizontal and the line to an object above the
HORIZON. Also called positive altitude.
155 angle of incidence. The angle between the line of motion of a RAY and the perpendicular to a surface at the point of
impingement.
156 angle of reflection. The angle between the line of motion of a reflected RAY and the perpendicular to a surface at the
point of REFLECTION.
157 angle of refraction. The angle between a refracted RAY and the perpendicular to the refraction surface.
158 angstroem. A unit of length, used especially in expressing the length of light waves, equal to one ten-thousandth of a
8
MICRON or one hundred-millionth of a centimetre (1 x 10- cm).
159 angular acceleration. See ACCELERATION.
160 angular distance. The angular difference between two directions, numerically equal to the angle between two lines
extending in the given directions. The arc of the GREAT CIRCLE joining two points, expressed in angular units.
161 angular distortion. See DISTORTION.
162 angular parallax. See PARALLACTIC ANGLE.
163 angular rate. See SPEED: ANGULAR.
164 angular speed. See SPEED.
165 angular velocity. See SPEED: ANGULAR.
166 annotation. Any marking on illustrative material for the purpose of clarification, such as numbers, letters, symbols, and
signs.
167 annual aberration. See ABERRATION OF LIGHT.
168 annual change. See MAGNETIC ANNUAL CHANGE.
169 annual inequality. Seasonal variation in water level or tidal current speed, more or less periodic, due chiefly to
meteorological causes.
170 annual parallax. See PARALLAX.
171 annual variation. See MAGNETIC ANNUAL VARIATION.
172 annular eclipse. See ECLIPSE.
173 anomalistic month. See MONTH.
174 anomalistic year. See YEAR.
175 anomaly. Deviation from the normal or natural characteristics of a PHENOMENON. Abnormality. In ASTRONOMY,
true anomaly is the angle at the SUN between lines connecting the SUN with a PLANET and with the PLANET's
PERIHELION. Mean anomaly and eccentric anomaly are also considered.
176 anomaly: gravity. See GRAVITY ANOMALY, BOUGUER ANOMALY, FREE AIR ANOMALY, ISOSTATIC
ANOMALY.
177 anomaly: magnetic. See LOCAL MAGNETIC DISTURBANCE.
178 Antarctic circle. The GEOGRAPHIC PARALLEL having a south LATITUDE equal to the complement of the
o
DECLINATION of the WINTER SOLSTICE (lat. = 66 33' S app.).
13
179 antenna. A conductor or system of conductors for radiating or receiving RADIO WAVES. Also called aerial.
180 antenna: directional. An ANTENNA for transmitting or receiving SIGNALS in, or from, a given direction.
181 antenna: omnidirectional. An ANTENNA having essentially uniform response in AZIMUTH and a directional pattern in
ELEVATION.
182 antenna: screened. Any ANTENNA which is screened in some way to counteract disturbances.
183 antenna: unidirectional. An ANTENNA having a single well-defined direction of maximum radiation intensity or
maximum GAIN.
184 anthelion. Pure white, rounded spot, but sometimes iridescent or surrounded by coloured rings or arcs, which appears on
very rare occasions opposite the SUN and at the same HEIGHT above the HORIZON.
185 anticline. An arch of stratified ROCK in which the LAYERS bend downward in opposite directions from the CREST.
186 anticyclone. Region of the ATMOSPHERE where the pressure is high relative to the surrounding region at the same
LEVEL. It is represented on a SYNOPTIC CHART by a system of ISOBARS at a specified LEVEL or of CONTOURS at
a specified pressure which enclose relatively high values of pressure or LEVEL. Also called high.
o
187 antimeridian. The MERIDIAN which is 180 of LONGITUDE from a given MERIDIAN. One MERIDIAN with its
antimeridian constitute a complete GREAT CIRCLE.
188 antipode(s). Place(s) on the surface of the EARTH directly opposite to each other.
189 antiselena. Luminous PHENOMENON analogous to ANTHELION, the luminary being the MOON.
190 anti-trade. Air current with a westerly component which in various subtropical regions of either hemisphere sometimes
blows above the TRADE WIND.
191 aperture: relative. For a photographic or telescopic LENS, the ratio of the EQUIVALENT FOCAL LENGTH to the
diameter of the ENTRANCE PUPIL. Expressed as f: 4.5; also called f-number, f-stop, or speed of lens.
192 aperture of antenna. The diameter of a reflector antenna, usually expressed in units of WAVE LENGTH.
193 aperture stop. The physical element (such as a DIAPHRAGM, or lens periphery) of an OPTICAL SYSTEM which limits
the size of the PENCIL of RAYS traversing the system. Also called the stop. Diameter of that part of the LENS actually
used.
194 apex. The top, PEAK, or highest point of something, as of a MOUNTAIN. See also VERTEX.
195 apex: solar. The point of the CELESTIAL SPHERE towards which the SOLAR SYSTEM as a whole is moving. It lies in
the CONSTELLATION of Hercules.
196 aphelion. That orbital point farthest from the SUN when the SUN is the centre of attraction, as opposed to PERIHELION.
197 aphotic(adj.). Without light.
198 apochromatic lens. A LENS that has been corrected for CHROMATIC ABERRATION for at least three colours.
199 apogean tide(s). See under TIDE.
200 apogee. That orbital point farthest from the EARTH when the EARTH is the centre of attraction, as opposed to PERIGEE.
201 apparent altitude. See ALTITUDE: APPARENT.
202 apparent horizon. See HORIZON.
203 apparent motion. See RELATIVE MOTION.
204 apparent noon. See NOON.
14
205 apparent position. See POSITION.
206 apparent precession. Apparent change in the direction of the axis of rotation of a spinning body, as a GYROSCOPE, due
to the ROTATION of the EARTH.
207 apparent shoreline. The seaward limit of marine vegetation, such as mangrove, marsh grass, or trees in water that would
reasonably appear to the mariner from a distance to be the fast shoreline. The seaward limit of kelp, low grass in water,
and other low-lying vegetation normally does not constitute an apparent shoreline.
A line drawn on the chart in lieu of the mean high water line or the mean water level line in areas where either may be
obscured by marsh, mangrove, cypress, or other type of marine vegetation. This line represents the intersection of the
appropriate datum with the outer limits of vegetation and appears to the navigator as shoreline.
208 apparent solar day. See DAY: SOLAR.
209 apparent solar time. See TIME.
210 apparent sun. See SUN.
211 apparent time. See TIME: APPARENT SOLAR.
212 apparent wind. See RELATIVE WIND.
213 approximate position. A position that is considered to be less than third-order accuracy, but is generally considered to be
within 100 feet (30.5 metres) of its correct geographic location. The method of location may be an indication of the
recorded accuracy.
214 apron. 1. A gently dipping featureless surface, underlain primarily by SEDIMENT, at the base of any steeper SLOPE.
2. The area of wharf or quay for handling cargo.
3. A sloping underwater extension of an iceberg.
4. An outwash plain along the front of a glacier.
215 apsis(pl. apsides). See LINE OF APSIDES.
216 arc: astronomical. The apparent arc described above (diurnal arc) or below (nocturnal arc) the HORIZON by the SUN
or another CELESTIAL BODY.
217 archipelagic apron. A gentle SLOPE with a generally smooth surface on the SEA FLOOR, particularly found around
groups of ISLANDS or SEAMOUNTS.
218 archipelagic baseline(s). See BASELINE.
219 archipelagic sea lane. Sea lanes designated by an ARCHIPELAGIC STATE for the passage of ships and aircraft.
220 archipelagic state. A State constituted wholly by one or more archipelagos, eventually including other islands.
221 archipelagic waters. The waters enclosed by ARCHIPELAGIC BASELINES.
222 archipelago. A group of ISLANDS.
223 arc of triangulation. See TRIANGULATION: ARC OF.
224 arc of visibility. The arc of a LIGHT SECTOR designated by its limiting BEARINGS in which a LIGHT is visible as
viewed from a vessel.
225 Arctic circle. The GEOGRAPHICAL PARALLEL having a north latitude equal to the complement of the
o
DECLINATION of the SUMMER SOLSTICE (lat. = 66 33' N app.).
226 arc to chord correction. The quantity used by seamen to correct a GREAT CIRCLE BEARING of a point B from a point
A to a MERCATOR BEARING, and usually referred to as the half convergency. On the MERCATOR PROJECTION,
this quantity is equal to half the convergency, on the SPHEROID, of the MERIDIANS through the two points being
considered. Also called conversion angle. See CONVERGENCE OF THE MERIDIANS.
227 Area. In United Nations Law of the Sea terminology the sea-bed and ocean floor and subsoil thereof, beyond the limits of
national jurisdiction.
15
228 area clearance. The effective depth, within specified limits, obtained by a WIRE DRAG SURVEY.
229 area to be avoided. A routing measure comprising an area within defined limits in which either navigation is particularly
hazardous or it is exceptionally important to avoid casualties and which should be avoided by all ships, or certain classes
of ships.
230 area survey. A method of BOTTOM RELIEF SURVEY consisting of surveying overlapping strips which allow
soundings to be obtained with a specified accuracy at any position of the area under survey.
231 argillaceous(adj.). Applied to all ROCKS or SEDIMENTS composed partly or completely of CLAY.
232 arming. Tallow or other substance placed in the recess at the lower end of a SOUNDING LEAD for obtaining a sample of
the BOTTOM. See BOTTOM SAMPLE.
233 arm of the sea. A narrow portion of the SEA projecting from the main body. The expression is often shortened to 'arm'.
234 array(s). The order in which equipment (antenna, oceanographic equipment) or mathematical quantities are ordered.
235 articulated beacon. A vertical pipe structure that oscillates around a universal coupling connected to a sinker. The
structure is kept upright by the buoyancy of a submerged floating chamber. Primarily designed to mark narrow channels
with greater precision than conventional buoys.
236 articulated light. See ARTICULATED BEACON.
237 artificial horizon. See HORIZON.
238 artificial intelligence. 1. The capability of a device to perform functions that are normally associated with human
intelligence, such as reasoning, learning, and self-improvement.
2. Research and study in methods for the development of a machine that can improve its own operations. The development
or capability of a machine that can proceed or perform functions that are normally associated with human intelligence, as
learning, adapting, reasoning, self-correction, automatic improvement.
3. The study of computer and related techniques to supplement the intellectual capabilities of man. As man has invented
and used tools to increase his physical powers, he now is beginning to use artificial intelligence to increase his mental
powers. In a more restricted sense, the study of techniques for more effective use of digital computers by improved
programming techniques.
239 artificial installation. See INSTALLATION OFFSHORE.
240 artificial island. See INSTALLATION OFFSHORE.
241 artificial satellite. See SATELLITE.
242 ascending node. See NODE.
243 ashore(adj. and adv.). On the SHORE, on LAND or AGROUND.
244 assumed position. See POSITION.
245 astenosphere. See MANTLE.
246 astern. Bearing approximately 180°relative. The term is often used loosely for DEAD ASTERN, or bearing exactly 180°
relative. The opposite is AHEAD.
247 asteroid. One of the many small PLANETS revolving around the SUN, most of the ORBITS being between those of Mars
and Jupiter. Also called PLANETOID or MINOR PLANET.
248 astigmatism. An aberration affecting the sharpness of IMAGES for objects off the AXIS, in which the RAYS passing
through different meridians of the LENS come to FOCUS in different planes.
249 astro compass. See under COMPASS.
250 astrolabe. An instrument formerly used for measuring ALTITUDES of CELESTIAL BODIES. See ASTROLABE:
PRISMATIC.
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251 astrolabe: prismatic. An ASTROLABE consisting of a TELESCOPE in a horizontal position, with a prism and
ARTIFICIAL HORIZON attached at its objective end, used for determining ASTRONOMIC POSITIONS.
252 astrometry. That branch of ASTRONOMY dealing with the determination of POSITIONS and motions of CELESTIAL
BODIES, including the EARTH.
253 astronautics. The science of locomotion and travel outside the EARTH's ATMOSPHERE, involving the problems of
ARTIFICIAL SATELLITES and of interplanetary journeys.
254 astro-navigation. See NAVIGATION: CELESTIAL.
255 astronomic(al) arc. See ARC.
256 astronomic(al) azimuth. See AZIMUTH.
257 astronomic(al) control. See CONTROL.
258 astronomic(al) day. See DAY.
259 astronomic(al) equator. See EQUATOR.
260 astronomic(al) latitude. See LATITUDE.
261 astronomic(al) longitude. See LONGITUDE.
262 astronomic(al) meridian. See MERIDIAN.
263 astronomic(al) observation(s). See OBSERVATION.
264 astronomic(al) parallel. See PARALLEL.
265 astronomic(al) position. See POSITION.
266 astronomic(al) refraction. See REFRACTION.
267 astronomic(al) station. See STATION.
268 astronomic(al) tide. See TIDE.
269 astronomic(al) time. See TIME.
270 astronomic(al) transit. See TRANSIT.
271 astronomic(al) traverse. See TRAVERSE.
272 astronomic(al) triangle. The triangle on the CELESTIAL SPHERE formed by arcs of GREAT CIRCLES connecting the
CELESTIAL POLE, the ZENITH and the CELESTIAL BODY. Also called navigational triangle.
273 astronomic(al) twilight. See TWILIGHT.
274 astronomic(al) year. See YEAR: TROPICAL.
275 astronomy. The science which deals with the size, constitution, motions, RELATIVE POSITIONS, etc. of CELESTIAL
BODIES, including the EARTH. See also ASTROMETRY.
276 astronomy: geodetic. ASTRONOMY as applied to GEODESY.
277 astronomy: nautical (or navigational). ASTRONOMY as applied to NAVIGATION.
278 atlas. A collection of CHARTS or MAPS to be kept (loose or bound) in a volume.
279 atmosphere. Gaseous envelope which surrounds the EARTH. The gaseous envelope surrounding any STAR, PLANET,
etc. A unit of pressure, equal to the pressure exerted per square centimetre by a column of mercury 760 mm high at a
2
temperature of 0°C when the ACCELERATION OF GRAVITY is 980.665 centimetres per SECOND .
17
280 atmosphere: free. That part of the ATMOSPHERE above the FRICTION LAYER, in which the air motion is affected to
a negligible degree by surface friction.
281 atmosphere: ICAO. STANDARD ATMOSPHERE adopted by the International Civil Aviation Organization (ICAO). Its
o
main features are mean sea-level pressure of 1013.25 mb, and a temperature lapse rate of 6.5 C/km from surface to the
TROPOPAUSE situated at 11 km.
282 atmosphere: standard. Conventional reference atmosphere, chosen to represent in a simple way the approximate average
condition in the VERTICAL.
283 atmospheric. ELECTROMAGNETIC WAVE resulting from an electric discharge (LIGHTNING) in the
ATMOSPHERE.
284 atmospheric drag. A major perturbation of close artificial satellite orbits by the resistance of the atmosphere.
285 atmospheric pressure. See PRESSURE.
286 atmospheric refraction. See REFRACTION.
287 atmospheric window. The region in the radiation spectrum containing wavelengths between 8.5 and 11 micrometers,
which are not absorbed to any great extent by atmospheric gases. In the absence of cloud, terrestrial radiation of this
wavelength is lost to space, enabling the cooling of the earth to take place. Other narrower wavebands also do not absorb
long-wave radiation, but these are of less importance in this context.
288 atoll. A coral ISLAND consisting of a ring-shaped REEF nearly or entirely surrounding a central LAGOON.
289 atom. The smallest particle of an element which can enter into a chemical combination.
290 atomic clock. See CLOCK.
291 Atomic Time: International. The time reference coordinate established by the Bureau International de l'Heure on the
basis of atomic clocks.
292 attenuation. A lessening in amount, particularly the reduction of the AMPLITUDE of a WAVE or the intensity of light or
SOUND with distance from the origin.
293 audiofrequency. A FREQUENCY within the audible RANGE, about 20 to 20.000 CYCLES per SECOND. Also called
sonic frequency.
294 aurora. Luminous PHENOMENON which appears in the high ATMOSPHERE, mainly in high LATITUDES, in the
form of RAYS, arcs, bands, draperies, or CORONA. Also called polar aurora.
295 aurora australis. AURORA of the southern hemisphere.
296 aurora borealis. AURORA of the northern hemisphere.
297 autocollimator. See COLLIMATOR.
298 automated cartography. The performance of cartographic functions in a fully automatic mode.
299 automatic floating station. A BUOY equipped with instruments automatically recording oceanographic and
meteorological DATA. Also called automatic buoy.
300 automatic gain control. A circuit which automatically maintains a constant output volume regardless of input signal
strength. Also called automatic volume control.
301 automatic plotter. See PLOTTER.
302 automatic tide gauge. See GAUGE: TIDE.
303 automatic volume control. See AUTOMATIC GAIN CONTROL.
304 automation. The technique of improving human productivity in the processing of materials, energy and information, by
utilizing in various degrees elements of automatic CONTROL, and of automatically executed product programming.
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305 autopositive. A material which gives a positive copy from a positive TRANSPARENCY (or a negative from a negative)
by direct processing.
306 autumnal equinox. See EQUINOX.
307 avulsion. Rapid EROSION of shoreland by WAVES during a STORM.
308 awash (adj. and adv.). Flush with, or washed by the WAVES.
309 axis. The line, real or imaginary, about which something centres or revolves.
310 axis: horizontal. In a THEODOLITE or TRANSIT, the AXIS about which the TELESCOPE of the instrument rotates
when moved vertically. Also called trunnion axis, or transit axis.
311 axis: optical. See AXIS OF LENS.
312 axis: polar. In a system of POLAR or SPHERICAL COORDINATES, the primary AXIS of DIRECTION.
313 axis: principal. See AXIS OF LENS.
314 axis: trunnion. See AXIS: HORIZONTAL.
315 axis: vertical. In a THEODOLITE or TRANSIT, the line through the centre of the instrument about which the ALIDADE
rotates.
316 axis of camera. A line perpendicular to the FOCAL PLANE of the CAMERA and passing through the emergent nodal
point of the LENS SYSTEM. Also called camera axis. See NODAL POINT.
317 axis of channel. The centre line of a CHANNEL. See also TALWEG.
318 axis of collimation. See COLLIMATION AXIS.
319 axis of homology. In PHOTOGRAMMETRY, the intersection of the plane of the PHOTOGRAPH with the horizontal
plane of the MAP or the plane of reference of the GROUND. Corresponding lines in the PHOTOGRAPH and map planes
intersect on the axis of homology. Also called the axis of perspective, or map parallel.
320 axis of lens. The straight line which passes through the centres of curvature of the lens surfaces. Also called principal
axis, optical axis or lens axis.
321 axis of optical system. The line formed by the coinciding principal axes of the series of optical elements.
322 axis of perspective. See AXIS OF HOMOLOGY.
323 axis of spirit level. The line tangent to the surface of a spirit level tube against which the bubble forms, at the centre of the
graduated SCALE of the LEVEL, and in the plane of the tube and its centre of curvature. Also called level axis or spirit
level axis.
324 axis of tilt. In PHOTOGRAMMETRY, a line through the PERSPECTIVE CENTRE perpendicular to the PRINCIPAL
PLANE.
325 azimuth. A horizontal angle reckoned clockwise from the meridian. The horizontal direction of a celestial point from a
terrestrial point, expressed as the angular distance from a reference direction. It is usually measured from 000° at the
reference direction clockwise through 360°. An azimuth is often designated as true, magnetic, compass, grid, or relative as
the reference direction is true, magnetic, compass, or grid north, or heading, respectively. Unless otherwise specified, the
term is generally understood to apply to true azimuth which may be further defined as the arc of the horizon, or the angle at
the zenith, between the north part of the celestial meridian or principal vertical circle and a vertical circle, measured from
000° at the north part of the principal vertical circle clockwise through 360°. When the angle is measured in either
direction from north or south, and labelled accordingly, it is properly called azimuth angle; when measured either direction
from east or west, and labeled accordingly, it is called AMPLITUDE.
326 azimuth (of a celestial body). The angle between the observer's MERIDIAN and the VERTICAL CIRCLE through the
body, measured in the plane of the HORIZON. There is no universally accepted manner of reckoning the AZIMUTHS.
Quadrantal, half-circle, and whole-circle methods are being used. In the latter, the AZIMUTH is measured preferably
clockwise from north. See also AZIMUTH ANGLE.
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327 azimuth: astronomic(al). The angle between the astronomic meridian plane of the observer and the plane containing the
observed point and the VERTICAL of the observer.
328 azimuth: astronomic(al) determination of. The determination of the AZIMUTH of a line or BASE LINE by
ASTRONOMICAL OBSERVATIONS.
o
329 azimuth: back. An AZIMUTH 180 from a given AZIMUTH. In GEODESY, the DIRECTION of the line BA as
distinguished from the forward azimuth AB. The two differ by 180° plus the amount of CONVERGENCE OF THE
MERIDIANS between points A and B. Also called reverse azimuth. See AZIMUTH: GEODETIC.
330 azimuth: forward. See AZIMUTH: GEODETIC.
331 azimuth: geodetic. For the GEODESIC LINE from A to B, the angle between the tangent to the MERIDIAN at A and the
tangent to the GEODESIC LINE at A. This AZIMUTH is called the forward azimuth for the line AB. See AZIMUTH:
BACK.
332 azimuth: grid. The angle in the plane of PROJECTION between a straight line and the Y-AXIS of a PLANERECTANGULAR COORDINATE system. See BEARING: GRID.
333 azimuth: Laplace. A GEODETIC AZIMUTH derived from an ASTRONOMIC AZIMUTH by means of the LAPLACE
EQUATION.
334 azimuth: magnetic. At the point of OBSERVATION, the angle between the VERTICAL PLANE through the observed
object and the VERTICAL PLANE in which a freely suspended symmetrically magnetized NEEDLE, influenced by no
transient artificial magnetic disturbance, will come to rest.
335 azimuth: reverse. See AZIMUTH: BACK.
336 azimuth: true. AZIMUTH relative to TRUE NORTH.
337 azimuthal equidistant projection. See PROJECTION.
338 azimuthal orthomorphic projection. See PROJECTION: STEREOGRAPHIC.
339 azimuthal projection. See PROJECTION.
340 azimuth angle. AZIMUTH measured from 0°at the north or south reference direction clockwise or counter-clockwise
through 90°or 180°. It is labelled with the REFERENCE DIRECTION as a prefix and the DIRECTION of measurement
from the REFERENCE DIRECTION as a suffix.
341 azimuth circle. See BEARING CIRCLE.
342 azimuth diagram. A DIAGRAM for obtaining graphically rather than by computation the AZIMUTHS of observed
CELESTIAL BODIES.
343 azimuth mark. A MARK set at a significant distance from a TRIANGULATION or TRAVERSE STATION to mark the
end of a line for which the AZIMUTH has been determined, and to serve as a starting or reference azimuth for later use.
20
B
344 back azimuth. See AZIMUTH.
345 backbeach. Also written as two words. See BACKSHORE.
346 backing wind. Counter-clockwise change of wind direction, in either hemisphere.
347 backrush. The seaward return of water following UPRUSH of WAVES on a BEACH.
348 backrush current. See CURRENT: BACKRUSH.
349 backshore. That part of a BEACH which is usually dry, being reached only by the highest TIDES. Also called backbeach.
See also FORESHORE.
350 backsight. In NAUTICAL ASTRONOMY, an OBSERVATION of a CELESTIAL BODY made by facing 180°from the
AZIMUTH of the body. In LEVELLING, a reading on a LEVELLING ROD held on a point whose ELEVATION has
been previously determined and which is not the closing SIGHT of a level circuit. Also written as two words. See also
FORESIGHT.
351 backwash. Water or WAVES thrown back by an obstruction such as a ship, BREAKWATER, CLIFF, etc.
352 backwater. Water turned back by an obstruction, opposing CURRENT, etc. Water held back from the main FLOW.
353 ballistic camera. See CAMERA.
354 band of colour. See STRIPES (OF COLOUR)
355 band of frequency. The RANGE of FREQUENCY between two specific limits. Also called frequency band.
356 bandwidth. The number of units (HERTZ, kilohertz, etc.) of FREQUENCY required for transmission.
357 bank. An ELEVATION of the SEA FLOOR located on a CONTINENTAL (or an ISLAND) SHELF, over which the
DEPTH of water is relatively shallow but sufficient for safe SURFACE NAVIGATION. A shallow area of shifting
SAND, GRAVEL, MUD, etc. as a sand bank, mud bank, etc. The sloping margin of a RIVER or STREAM; the
GROUND bordering upon a RIVER. A raised margin of a POND, LAKE, etc. See LEFT BANK and RIGHT BANK.
358 bar. A RIDGE or succession of RIDGES of SAND or other substances extending across the MOUTH of a RIVER or
HARBOUR and which may obstruct NAVIGATION. Derived pressure in the CGS SYSTEM. See also MILLIBAR.
359 bar buoy. A BUOY marking the location of a BAR.
360 bar check. An on-site calibration method for echo sounders.
361 bar scale. See SCALE.
362 bar sweeping. A sweeping procedure using a beam suspended horizontally under a vessel. The sweep passing over the
bottom may be equipped with rockers or other sensors to record contact with the bottom.
363 baroclinity. The condition and type of motion in which pressure is not constant on surfaces of constant density, e.g.
internal waves.
364 barogram. Record made by a BAROGRAPH.
365 barograph. RECORDING BAROMETER.
366 barometer. Instrument for measuring ATMOSPHERIC PRESSURE.
367 barometer: aneroid. BAROMETER whose sensitive element comprises one or a series of ANEROID CAPSULES.
368 barometer: marine. MERCURY BAROMETER used on board ships, characterized by a constriction in the tube in order
to damp out OSCILLATIONS of the mercury caused by the movements of the ship.
21
369 barometer: mercurial (or mercury). A BAROMETER in which ATMOSPHERIC PRESSURE is balanced against the
pressure exerted by a column of mercury.
370 barometer: recording. BAROMETER which gives a continuous graphic representation of the atmospheric pressure
variations with TIME.
371 barometric altimeter. See ALTIMETER.
372 barometric elevation. See ELEVATION.
373 barometric gradient. See PRESSURE GRADIENT.
374 barometric levelling. See LEVELLING.
375 barometric pressure. See PRESSURE: BAROMETRIC.
376 barotropy. The condition and type of motion in which pressure is constant on surfaces of constant density, e.g. surface
tides.
377 barrel buoy. See BUOY.
378 barrier reef. A CORAL REEF fronting the SHORE, at some distance from it, and separated from it by a LAGOON or a
navigable CHANNEL of moderate DEPTH. See also FRINGING REEF.
379 barye. Pressure unit in the CGS SYSTEM.
380 barysphere. See CENTROSPHERE.
381 basal coplane. See COPLANE: BASAL.
382 basal orientation. See ORIENTATION.
383 basal plane. See EPIPOLAR PLANE.
384 base. In a TRIANGULATION, the side of one of a series of connected triangles, the length of which is measured directly
and with prescribed ACCURACY and PRECISION, and from which the lengths of the other triangle sides are obtained by
computation. Also called base line or triangulation base line. See also BASE TERMINALS.
385 base apparatus. Any apparatus designed for use in measuring with ACCURACY and PRECISION the length of a BASE
in TRIANGULATION, or the length of a line in TRAVERSE.
386 base course (of a vessel). The true course between a vessel's point of departure and arrival.
387 base direction. See DIRECTION.
388 base extension triangulation (British terminology). A part of a TRIANGULATION NET starting with a measured BASE
and expanding that relatively short distance to a larger distance comparable to the average length of the triangulation sides.
Called base net in U.S. terminology.
389 base height ration. In PHOTOGRAMMETRY, the ratio between the AIR BASE and the FLIGHT ALTITUDE of a
STEREOSCOPIC PAIR of PHOTOGRAPHS.
390 base line. The line from which the outer limits of the territorial sea and certain other outer limits are measured. In
RADIOLOCATION, the GEODESIC LINE between two stations operating in conjunction for the determination of a
LINE OF POSITION. Also written as one word. See also BASE.
391 baseline: archipelagic. Archipelagic baselines are straight lines joining the outermost points of the outermost islands and
drying reefs of an archipelago.
392 baseline: normal. The low-water line along the coast as marked on large-scale charts officially recognized by the coastal
State.
393 baseline: straight. Straight baselines are a system of straight lines joining specified or discrete points on the low-water
line, usually known as straight baseline turning points. Straight baselines are used in DELIMITATION.
22
394 base line extension. In RADIOLOCATION, the extension of the BASE LINE beyond the TRANSMITTERS.
395 base map. See MAP.
396 base net. See BASE EXTENSION TRIANGULATION.
397 basepoint. A basepoint is any point on a baseline.
398 base tape (or wire). A tape or wire of metal or alloy, so designed and graduated that it is suitable for measuring the
lengths of BASES. See also TAPE: INVAR, TAPE: STEEL and WIRE: INVAR.
399 base terminals. The two extremes of a BASE LINE. Usually marked on a MONUMENT or metal stake buried beneath a
visible SURFACE MARK. See also REFERENCE MARK.
400 base tilt. See TILT.
401 basic control. See CONTROL.
402 basic survey. A hydrographic survey so complete and thorough that it does not need to be supplemented by other surveys,
and is adequate to supersede, for charting purposes, all prior hydrographic surveys of the area.
403 basin. Sheltered body of water available for port operations connecting either with the SEA or with an outer PORT or with
another basin, sometimes by means of a LOCK or PASSAGE. In geography, the tract of country drained by a RIVER and
its TRIBUTARIES or which drains into a particular LAKE or SEA. In OCEANOGRAPHY, a DEPRESSION of the SEA
FLOOR more or less equidimensional in form and of very variable extent.
404 basin: tidal. A BASIN affected by tidal forces in which water can be kept at a desired LEVEL by means of a gate.
405 bathymeter. An instrument primarily designed for measuring DEPTH of water.
406 bathymetric (adj.). Of or pertaining to BATHYMETRY.
407 bathymetric chart. See CHART.
408 bathymetric map. A topographic map of the ocean floor, or the bed of a lake.
A topographic chart of the bed of a body of water, or a part of it. Generally, bathymetric maps show depths by contour
lines and gradient tints.
409 bathymetry. The determination of ocean depths. The general configuration of SEA FLOOR as determined by profile
analysis of depth data.
410 bathyscaphe (or bathyscaph). A free, manned vehicle for exploring the deep OCEAN.
411 bathysphere. A diving sphere for deep-sea observations.
412 bathythermogram. The record of temperature versus DEPTH made by a BATHYTHERMOGRAPH. Rarely used.
413 bathythermograph. A device for obtaining a record of temperature against DEPTH in the OCEAN, from a ship
underway.
414 bay. Wide INDENTATION in the COASTLINE generally smaller than a GULF and larger than a COVE.
For the purposes of the United Nations Convention on the Law of the Sea, a bay is a well-marked indentation whose
penetration is in such proportion to the width of its mouth as to contain land locked waters and constitute more than a mere
curvature of the coast. See also HISTORIC BAY.
415 bay closing line. A line dividing the internal waters and territorial seas in a bay.
416 bay ice. Level FAST ICE of more than one winter's growth, which may be nourished by surface layers of SNOW.
Thickness of ICE and SNOW up to about 2 m above SEA LEVEL. When bay ice becomes thicker than this, it is called an
ICE SHELF.
417 bayou. A minor sluggish WATERWAY or estuarial CREEK, generally tidal or characterized by a slow CURRENT, with
a COURSE generally through LOWLANDS or SWAMPS, TRIBUTARY to or connecting with other bodies of water.
Various specific meanings have been implied in different parts of the Southern United States. Sometimes called SLOUGH.
23
418 beach. On a SHORE, the area on which the WAVES break and over which shore debris, such as SAND, SHINGLE,
PEBBLES accumulate. A beach includes BACKSHORE and FORESHORE.
419 beach comber. See COMBER.
420 beacon. A prominent specially constructed object forming a conspicuous MARK as a fixed AID TO NAVIGATION, or
for use in HYDROGRAPHIC SURVEY. Also called day beacon or DAYMARK.
421 beacon: aeronautical. An AERONAUTICAL GROUND LIGHT visible at all AZIMUTHS, either continuously or
intermittently, to designate a particular point on the surface of the EARTH. A radiobeacon may be coterminous with the
aeronautical beacon.
422 beacon: hazard. A BEACON marking an OBSTRUCTION or hazard.
423 beacon: identification. An AERONAUTICAL and/or RADIO and/or LIGHT BEACON emitting a coded SIGNAL by
means of which a particular REFERENCE POINT can be identified.
424 beacon: light (or lighted). A BEACON from which a LIGHT is exhibited.
425 beacon: omnidirectional. See OMNIRANGE.
426 beacon: radio. See RADIOBEACON.
427 beacon: responder. See TRANSPONDER BEACON.
428 beacon: transponder. See TRANSPONDER BEACON.
429 beaconage. A system of BEACONS. See BUOYAGE.
430 beam. RADIANT ENERGY confined to a particular shape.
431 beam compass. An instrument consisting of a beam or rod with sliding sockets that hold pencil, pen, or steel points, used
together with a SCALE for plotting exact lengths or for drawing large circles.
432 beam sea. WAVES moving in a direction approximately 90°from the HEADING.
433 beam width. The angular measure of the transverse section of a beam (usually in the main lobe) lying within directions
corresponding to specified values of field strength relative to the maximum.
434 beam wind. WIND blowing in a direction approximately 90°from the HEADING.
435 bearing. The horizontal DIRECTION of one terrestrial point from another, expressed as the ANGULAR DISTANCE
from a REFERENCE DIRECTION. It is usually measured from 0°at the REFERENCE DIRECTION clockwise through
360°. The terms bearing and AZIMUTH are sometimes used interchangeably, but in NAVIGATION the former
customarily applies to terrestrial objects and the latter to the DIRECTION of a point on the CELESTIAL SPHERE from a
point on the EARTH. A bearing is designated as true, MAGNETIC, or compass as the REFERENCE DIRECTION is
TRUE, MAGNETIC, or COMPASS NORTH.
436 bearing: acoustic. See BEARING: SONIC.
437 bearing: compass. See BEARING.
438 bearing: danger. The maximum or minimum BEARING of a point for safe passage of an offlying danger.
439 bearing: great circle. The initial DIRECTION of a GREAT CIRCLE through two terrestrial points, expressed as
ANGULAR DISTANCE from a REFERENCE DIRECTION. BEARINGS obtained by any form of RADIANT ENERGY
are great-circle bearings.
440 bearing: grid. BEARING relative to GRID NORTH. See also AZIMUTH: GRID.
441 bearing: magnetic. BEARING relative to MAGNETIC NORTH. COMPASS BEARING corrected for MAGNETIC
DEVIATION.
442 bearing: Mercatorial (or Mercator). See BEARING: RHUMB.
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443 bearing: polar. In a system of POLAR or SPHERICAL COORDINATES, the angle formed by the intersection of the
reference MERIDIONAL PLANE and the MERIDIONAL PLANE containing the point.
444 bearing: radar. A BEARING obtained by RADAR.
445 bearing: radio. The angle between the apparent direction of a definite source of emission of ELECTRO-MAGNETIC
WAVES and a REFERENCE DIRECTION, as determined at a RADIO DIRECTION-FINDING STATION.
446 bearing: reciprocal. A BEARING differing by 180°from a given BEARING.
447 bearing: relative. BEARING relative to the HEADING of a craft.
448 bearing: rhumb. The direction of a RHUMB LINE through two terrestrial points expressed as ANGULAR DISTANCE
from a REFERENCE DIRECTION. Also called mercatorial (or mercator) bearing.
449 bearing: sonic. A BEARING determined by measuring the direction from which a SOUND WAVE is coming. Also
called acoustic bearing.
450 bearing: transit. A BEARING taken of two objects when in line.
451 bearing: true. See BEARING.
452 bearing circle. A ring designed to fit snugly over a COMPASS or COMPASS REPEATER, and provided with VANES
for observing BEARINGS. A similar ring provided with means for observing AZIMUTH of the SUN is called an azimuth
circle.
453 bearing plate. See PELORUS.
454 beat. The periodic variation that results from the superposition of two OSCILLATIONS whose FREQUENCIES differ by
a small amount.
455 Beaufort wind scale. A numerical scale for indicating wind speed, devised by Admiral Sir Francis Beaufort in 1805.
Beaufort numbers (or forces) range from force 0 (calm) to force 12 (hurricane).
456 bed. The GROUND upon which a body of water rests.
457 bedrock. Any solid ROCK underlying SOIL or unconsolidated SEDIMENTS.
458 bel. A dimensionless unit for expressing the ratio of two values of power, the number of bels being the logarithm to the
base 10 of the power ratio. In practice decibel is commonly used, the number of decibels being 10 times the logarithm to
the base 10 of the power ratio.
459 bell buoy. See BUOY: SOUND.
460 belt. In ice terminology, a long area of PACK ICE from a few kilometres to more than 100 kilometres in width.
461 bench. See TERRACE.
462 bench mark (benchmarks). A permanent, stable object containing a marked point of known ELEVATION with respect
to a DATUM used as a REFERENCE LEVEL for TIDAL OBSERVATIONS or as a control point for LEVELLING.
463 beneaped (or neaped). Said of a vessel left aground following a spring high tide.
464 benthic division. In the classification of the marine ENVIRONMENT and its inhabitants, a primary division of the SEA
which includes all of the ocean floor. The other primary division of the SEA is the PELAGIC DIVISION.
465 benthos. The category of marine organisms that live on, in, or close to the BOTTOM of the OCEANS.
466 berg. Short for ICEBERG.
467 bergy bit. A massive piece of SEA ICE or disrupted HUMMOCKED ICE; also medium-sized piece of floating
GLACIER ICE. Generally less than 5 m above SEA LEVEL, and not more than about 10 m across.
25
468 berm. A narrow, raised path or EMBANKMENT along a STREAM, CANAL, or BEACH. On a BEACH it may be
formed by the deposit of material by WAVES and marks the limit of HIGH TIDES.
469 berm line. In CARTOGRAPHY, the outer edge of vegetation shown as SHORELINE on CHARTS in marsh or mangrove
areas.
470 berth. Place in which a ship is moored at WHARF.
471 beset(adj.). Of a ship when surrounded so closely by SEA ICE that steering control is lost. The term does not imply
pressure. See also ICEBOUND, NIPPED.
472 Bessel's spheroid. See REFERENCE SPHEROID.
473 between-the-lens shutter. See SHUTTER.
474 bias. The distortion of a result through negligence of a factor usually introducing a systematic error of unchanging
magnitude and sign throughout a given series of observations.
475 bifurcation. A division into two branches.
476 bifurcation buoy. See BUOY: BIFURCATION.
477 bight. A bend or curve in the COASTLINE, a bend in a RIVER, etc. In ice terminology, an extensive crescent-shaped
indentation in the ICE EDGE formed either by WIND or CURRENT.
478 Bilby steel tower. A demountable and transportable TRIANGULATION TOWER for elevating a THEODOLITE and
LUMINOUS SIGNALS above the GROUND, designed by J.S. Bilby, USC&GS.
479 billow. A great WAVE.
480 binary. The number system using 2 as the base for number representation. Binary numbers are composed of BITS.
Generally any element capable of only two mutually exclusive states is called binary.
481 binnacle. The stand in which a COMPASS is mounted and in which lighting and compensatory units are carried.
482 binocular(s). An optical instrument consisting of a pair of TELESCOPES joined so as to be adaptable to the use of both
eyes simultaneously.
483 binocular vision. Simultaneous vision with both eyes.
484 biology: marine. The study of the life, history and ECOLOGY of marine and brackish water plants and animals.
485 bioluminescence. The emission of light by living organisms. See also NOCTILUCA.
486 biosphere. Spherical terrestrial LAYER comprising the lower part of the ATMOSPHERE, the SEAS and the upper
LAYERS of the SOIL within which living organisms can exist naturally.
487 bissextile year. See YEAR: CIVIL.
488 bit. Short for "binary digit", the digit in binary number representation. A bit can only assume the binary values "0" and "1".
A binary number representation is composed of bits just as a decimal number is represented by decimal digits.
A unit of 8 bits is called a BYTE.
It also stands for "basic indissoluble information unit", a unit used for measuring the information content in information
theory.
489 blind rollers. Long, high SWELLS which have increased in HEIGHT, almost to the breaking point, as they pass over
SHOALS or run in shoaling water. Called blind seas in some localities.
490 blind seas. See BLIND ROLLERS.
491 blind zone. An area within or from which little or no radio SIGNAL is received. Also called zone of silence.
492 blip. Indication of a SIGNAL on the SCOPE of an electronic instrument, produced by a short sharply-peaked PULSE of
voltage.
26
493 blizzard. Violent and very cold WIND which is laden with SNOW, some part, at least, of which has been raised from
snow-covered GROUND. This term originated in North America but has been extended to include similar WINDS in other
countries.
494 block correction. See CHARTLET.
495 blow up. Enlarge photographically.
496 bluff. A CLIFF or HEADLAND with an almost perpendicular face.
497 blunder. See ERROR: GROSS.
498 boat compass. See COMPASS.
499 boat grid. See CAREENING GRID or GRIDIRON.
500 boat sheet (U.S. terminology). The work sheet used by the HYDROGRAPHER in the field for plotting the details of a
HYDROGRAPHIC SURVEY as it progresses. See also FIELD BOARD.
501 boat slip. A SLIPWAY designed specifically for boats.
502 bog. Wet spongy ground consisting of decaying vegetation, which retains stagnant water, too soft to bear the weight of any
heavy body.
503 bold coast. A prominent land mass that rises steeply from the SEA.
504 bollard. Small shaped post, mounted on a wharf or dolphin used to secure ship's lines. Also see MOORING.
505 boom. A floating barrier used to protect a river or harbour mouth or to create a sheltered area for storage purposes.
506 boomer. Seismic instrument for shallow penetration work. The boomer TRANSDUCER produces acoustic pulses by the
motion of a metal plate in the water.
507 border. The district lying along the edge of a country or territory; a frontier. The boundary line which separates one
country from another, the frontier line.
508 border break. A cartographic technique to extend cartographic detail of a map or chart beyond the neatline into the
margin to show important features. This technique eliminates the necessity of producing an additional CHART. Also
called Blister.
509 border of chart. The NEATLINE defining the limits of the area charted.
510 borderland. A region adjacent to a CONTINENT, normally occupied by or bordering a SHELF, that is highly irregular
with DEPTHS well in excess of those typical of a SHELF.
511 border scale. See SCALE.
512 bore. A high breaking WAVE of water, advancing rapidly up an ESTUARY. Bores can occur at the MOUTHS of shallow
RIVERS if the TIDE RANGE at the MOUTH is large. They can also be generated in a RIVER when TSUNAMIS enter
shallow coastal water and propagate up the RIVER. Also called eager, mascaret, or tidal bore.
513 boring. Forcing a vessel under power through ICE.
514 bottom. Any GROUND covered by water.
515 bottom: nature of. The feature of the BOTTOM including the material of which it is composed and its physical
characteristics. Also called character (or characteristics) of the bottom, or quality of the bottom.
516 bottom characteristics. Designations used on survey and nautical charts to indicate the consistency, colour, and
classification of the sea bottom. Also called NATURE OF THE BOTTOM, CHARACTER OF THE BOTTOM.
517 bottom contour chart. A chart designed for surface and sub-surface bathymetric navigation seaward of the 100-fathom
contour. Bottom configuration is portrayed by DEPTH CONTOURS and selected soundings.
27
518 bottom friction. The force resulting from the interaction between the ocean bottom and water particle motion over it.
519 bottom ice. See ANCHOR ICE.
520 bottom profiler. An ECHO SOUNDER for precision surveys of the sea bottom surface.
521 bottom relief survey. A survey conducted to obtain information on the spatial characteristics of the sea bottom relief.
522 bottom sample. A portion of the sea bottom material brought to the surface for examination. See also CORE.
523 bottom sampler. Any device for obtaining a BOTTOM SAMPLE. See also CORER, DREDGE, DRIVER ROD, GRAB
and SNAPPER.
524 bottom sampling. The process of collecting bottom samples.
525 bottom sediments. See SEDIMENTS: BOTTOM.
526 Bouguer anomaly. A difference between an observed value of GRAVITY and a theoretical value at the point of
observation, which has been corrected for the effect of the TOPOGRAPHY and ELEVATION only, the TOPOGRAPHY
being considered as resting on a plane of indefinite extent.
527 boulder. A rounded ROCK with a diameter of 256 millimetres (about 10 INCHES) or larger.
528 boulder clay. See TILL.
529 boundary. Anything marking a limit; bound; BORDER.
530 boundary layer. The LAYER of fluid in the immediate vicinity of a bounding surface. It is the LAYER in which
frictional forces are not negligible.
531 boundary monument. A material object placed on or near a boundary line to preserve and identify the ground location of
the boundary line. Where it is impracticable to establish a monument on or very close to a boundary line, the position of
the boundary line on the ground is preserved by means of reference marks. The term monument is sometimes used to
include both the mark on the boundary and the reference mark.
532 boundary wave. See WAVE: INTERNAL.
533 Bourdon tube. Closed, curved, flexible tube of elliptic cross-section which is deformed, according to type, by variations
of ATMOSPHERIC PRESSURE or temperature and so provides a measurement of the particular element.
534 Bowditch rule. A method of ADJUSTMENT of TRAVERSES.
535 box compass. See DECLINATOIRE.
536 box gauge. See GAUGE: FLOAT.
537 box sextant. A small portable instrument used for approximate measurement of angles.
538 brackish water. Water in which salinity values range from approximately 0.50 to 17.00 parts per thousand.
539 brash ice. Accumulation of FLOATING ICE made up of small fragments not more than 2 metres across; the wreckage of
other forms of ICE.
540 breaker. A WAVE breaking on the SHORE, over a REEF, etc. Breakers may be roughly classified into three kinds,
although the categories may overlap: spilling breakers break gradually over a considerable distance; plunging breakers
tend to curl over and break with a crash; and surging breakers peak up, but then instead of spilling or plunging they surge
up on the beach face. The French word 'brisant' is also used for the obstacle causing the breaking of the WAVE.
541 breaking of waves. Disintegration of a WAVE which breaks with foam in SHALLOWS whose gradient is more or less
regular. An incomplete breaking can likewise result from a sudden reduction in DEPTH.
28
542 breakwater. A structure protecting a shore area, HARBOUR, ANCHORAGE, or BASIN from WAVES. See also
FLOATING BREAKWATER.
543 breeze. A WIND of moderate strength. See LAND and SEA (or LAKE) BREEZE.
544 bridge. 1. An elevated structure extending across or over the weather deck of a vessel, or part of such a structure. The term
is sometimes modified to indicate the intended use, such as navigating bridge or signal bridge.
2. A structure erected over a depression or an obstacle such as a body of water, railroad, etc., to provide a roadway for
vehicles or pedestrians.
545 bridge: bascule. A counterpoise bridge rotated in a vertical plane about an axis at one or both ends. Also called balance
bridge.
546 bridge: draw. A general name for bridges of which part or the entire span of the bridge may be raised or drawn aside to
allow ships to pass through.
547 bridge: lift. A movable bridge which is capable of being lifted vertically to allow vessels to pass beneath.
548 bridge: swing. A movable bridge which rotates in a horizontal plane about a vertical pivot to allow the passage of vessels.
549 bridge clearance. See CLEARANCE.
550 bridging. See STEREOTRIANGULATION.
551 broad on the beam. Bearing 090°relative (broad on the starboard beam) or 270°relative (broad on the port beam). If the
bearings are approximate, the expression on the beam or abeam should be used. See also ON THE BEAM.
552 broad on the bow. Bearing 045°relative (broad on the starboard bow) or 315°relative (broad on the port bow). If the
bearings are approximate, the expression on the bow should be used. See also ON THE BOW.
553 broad on the quarter. Bearing 135°relative (broad on the starboard quarter or 225°relative (broad on the port quarter). If
the bearings are approximate, the expression on the quarter should be used. See also ON THE QUARTER.
554 broadcast. Communication by RADIO intended for reception at any point within a specified area.
555 broadcast ephemeris. Ephemeris transmitted by a satellite which describes its position and orbital parameters.
556 broadside on. Beam on, as to the wind or sea.
557 broken telescope transit. See TRANSIT.
558 broken water. An area of small WAVES and EDDIES occurring in what otherwise is a calm SEA.
559 brook. A small STREAM; a RIVULET. Also called run.
560 bubble: spirit (or sensitive). See LEVEL: SPIRIT.
561 bubble sextant. See SEXTANT.
562 bucket temperature. Temperature of surface sea water trapped and measured in a bucket or similar receptacle.
563 bulkhead. On land, a structure or partition built to retain or prevent sliding of the land. A secondary purpose is to protect
the upland against damage from wave action. Bulkheads are frequently backfilled thereby increasing the utility of the
adjacent land area.
564 bull's eye level. See LEVEL: SPIRIT.
29
565 buoy. A floating object moored to the BOTTOM in a particular (charted) place, as an AID TO NAVIGATION or for
other specific purposes. Navigational buoys may be classified according to:
(a) their shape, appearance, or construction, such as barrel, CAN, cask, CONICAL, cylindrical, DAN, KEG, NUN,
PILLAR, SPAR, spherical, or TOPMARK BUOY;
(b) their colour, such as black, chequered, green, red buoy;
(c) their location, such as BIFURCATION, FAIRWAY, JUNCTION, MID-CHANNEL, MIDDLE-GROUND, or
TURNING BUOY;
(d) the various kinds of hazards or dangers to NAVIGATION which they mark, such as BAR, ISOLATED DANGER,
FISH TRAP, OBSTRUCTION, SPOIL GROUND, TELEGRAPH or WRECK BUOY;
(e) their particular purpose or use, such as ANCHOR, ANCHORAGE, COMPASS ADJUSTMENT, DREDGING,
FAREWELL (or landfall), MARKER, QUARANTINE, STATION (or watch), or WARPING BUOY.
566 buoy: automatic. See AUTOMATIC FLOATING STATION.
567 buoy: bifurcation. A distinctive lateral BUOY used to indicate both the point at which a channel divides and the channel
that has been designated as preferred channel.
568 buoy: cable. A BUOY used to indicate the run of a SUBMARINE CABLE.
569 buoy: cardinal. A BUOY used to indicate that the best navigable water is to be found in one particular of the quadrants
that are bounded by the four bearings NW, NE, SE and SW taken from the position of the mark.
570 buoy: fairway. A BUOY intended to be the first to be seen during an approach from the open sea to a FAIRWAY.
571 buoy: lateral. A BUOY used to indicate a lateral limit of NAVIGABLE water.
572 buoy: life. A BUOY intended to keep persons afloat. Also called life jacket.
573 buoy: light (or lighted). A BUOY with a LIGHT having definite characteristics for detection and identification during
darkness. See CHARACTERISTICS OF LIGHT.
574 buoy: lighted sound. A LIGHT BUOY provided with a SOUND SIGNAL.
575 buoy: mooring. A BUOY secured to the BOTTOM by permanent moorings with means for mooring a vessel by use of its
anchor chain or mooring lines.
576 buoy: radar. A BUOY with a cluster of RADAR REFLECTORS.
577 buoy: radiobeacon. A BUOY equipped with a MARKER RADIOBEACON.
578 buoy: sound. A BUOY equipped with a characteristic SOUND SIGNAL. Sound buoys may be further classified
according to the manner in which the SOUND is produced, such as bell, gong, horn, trumpet, or whistle buoy.
579 buoy: special. A BUOY primarily used to indicate an area or feature referred to in nautical documents rather than to assist
navigation.
580 buoy: super. A very large BUOY designed to carry a signal light of high luminous intensity at a high elevation. See also
LARGE AUTOMATIC NAVIGATION BUOY (LANBY).
581 buoy: survey. A BUOY used by SURVEY SHIPS to control HYDROGRAPHIC SURVEYS. See also BUOYCONTROL METHOD.
582 buoyage. A system of, or providing with, BUOYS, serving the purpose of indicating NAVIGABLE waters. See
BEACONAGE.
583 buoyancy. Force resulting from the upward pressure of water, acting upon the immersed volume of a body, set against the
total WEIGHT of such body. If the volume immersed is such that the upward pressure counterbalances the WEIGHT of
the body, the buoyancy is said to be positive and the body floats on the surface; if the volume immersed is insufficient, the
weight of the body is greater than the upward pressure, the buoyancy is negative, and the body sinks.
584 buoyancy: centre of. CENTRE OF GRAVITY of liquid displaced by a floating body.
585 buoyant beacon. See ARTICULATED LIGHT.
30
586 buoy-control method. A system of accurately located BUOYS on which THREE-POINT FIXES could be observed, or to
which distances could be measured by radio acoustic methods, for extending HYDROGRAPHIC SURVEYS beyond the
VISIBILITY of shore control.
587 butte. An isolated flat-topped HILL, similar to, but smaller than a MESA.
588 byte. A unit consisting of 8 BITS, frequently used for measuring the capacity of storage devices.
10
1 Kbyte = 2 byte = 1.024 byte (kilo-byte)
20
1 Mbyte = 2 byte = 1.048.576 byte (mega-byte)
30
1 Gbyte = 2 byte = 1.073.741.824 byte (giga-byte)
31
C
589
cable. A unit of distance originally equal to the length of a ship's anchor cable, but now generally considered to be about
600 FEET. In the British Navy it is 608 FEET, or exactly one-tenth of a NAUTICAL MILE. In the United States Navy
it is 720 FEET but is infrequently used. Sometimes called cable length. A chain or very strong fibre or wire rope used to
anchor or moor vessels or BUOYS. A stranded conductor or an assembly of two or more electric conductors insulated
from each other, but laid up together with a strong, waterproof covering.
590
cable: coaxial. A transmission cable consisting of two concentric conductors insulated from each other.
591
cable: degaussing. CABLE carrying an electric current for degaussing a vessel.
592
cable: leader. CABLE lying on the BOTTOM and carrying an electric current by which ships equipped with
appropriate instruments, can be guided.
593
cable: submarine. An insulated, waterproof wire or bundle of wires for carrying an electric current under water.
594
cable buoy. See BUOY.
595
cable length. See CABLE.
596
cable sign. A sign on a post marking the point from which a cable runs under water.
597
C/A Code. The standard (Coarse/Acquisition, or Clear/Access) GPS code; a sequence of 1023 pseudo-random binary
biphase modulations on the GPS carrier at a chip rate of 1.023 MHz, thus having a code repetition period of one
millisecond. See also P-CODE.
598
cadastral map. See MAP.
599
cadastral survey. See SURVEY.
600
cadastre. A public record of the extent, value, and ownership of LAND for purposes of taxation.
601
cairn. A mound of STONES, usually conical or pyramidal, raised as a LANDMARK or to designate a point of
importance in SURVEYING.
602
caisson. A steel structure used for closing the entrance of LOCKS, WET and DRY DOCKS. See also LOCK GATE.
603
calcareous (adj.). Composed of or containing calcium or calcium carbonate.
604
calculator. A machine for performing arithmetical operations usually more complex than that done by an adding
machine; a calculating machine, which may be mechanical, electrical, electronic or a combination of all three. A person
who calculates.
605
calendar line. See DATE LINE.
606
calibrate (v.t.). To fix, check or correct the GRADUATIONS of a measuring instrument. To determine the calibre of.
607
calibrated focal length. See FOCAL LENGTH.
608
calibration. The act or process of determining certain specific measurements in an instrument or device by comparison
with a STANDARD, for the purpose of correcting or compensating ERRORS or for purposes of record.
609
calibration: direct base. The calibration of a positioning system with the help of one or more baselines of known
length, which is determined with an instrument having an accuracy superior to that of the positioning system.
610
calibration: direct simultaneous. The calibration of a positioning system at the same time when the distances used for
calibration are measured using another system or instrument of superior accuracy.
32
611
calibration: indirect position. The calibration of a positioning system using positions of the survey vessel at different
locations which were determined independently of the positioning system. True distances can be derived from these
positions and by comparison with the data rendered by the positioning system, calibration values can be deduced.
612
calibration: indirect variation. The calibration of a positioning system by obtaining redundant observations so that
calibration values can be deduced mathematically from the discrepancies between uncalibrated values at different
locations.
613
calibration of compass. See SWINGING SHIP.
614
calling-in point. Point at which vessels are required to report to a traffic control center.
615
calling the soundings. Announcement made by LEADSMAN when heaving the LEAD.
616
calm. WIND with a SPEED zero or less than 2 KNOTS (BEAUFORT SCALE wind force 0). The state of sea when
there are no WAVES.
617
calorie. A unit of quantity of heat, originally defined as the amount of heat required to raise the temperature of one
GRAM of water through one DEGREE C. The 15-degree gram-calorie is the amount of heat required to raise the
temperature of one GRAM of water from 14°.5 C to 15°.5 C, and is equal to 4.1855 JOULES.
618
calving. The breaking away of a mass of ICE from a GLACIER, ICE FRONT, or ICEBERG.
619
camber. A small BASIN, usually with a narrow ENTRANCE, situated inside a HARBOUR.
620
camera. A lightproof chamber or box in which the IMAGES of exterior objects are projected upon a sensitized PLATE
or film, through an opening usually equipped with a LENS or LENSES, SHUTTER and variable aperture.
621
camera: aerial. A CAMERA specially designed for use in aircraft.
622
camera: ballistic. A precision terrestrial camera usually employing glass plates, used at night to photograph such
objects as ROCKETS or SATELLITES against a star background. If the CAMERA is mounted so that it tracks the
STARS or the object, it may be called a tracking camera.
623
camera: continuous-strip. A CAMERA in which a continuous-strip exposure is made by rolling the film continuously
past a narrow slit opening at a SPEED proportional to the GROUND SPEED of the aircraft.
624
camera: deep sea. A camera system specially designed for obtaining PHOTOGRAPHS of the ocean bottom.
625
camera: multiple lens. A CAMERA with two or more LENSES, with the AXES of the LENSES systematically
arranged at fixed angles in order to cover a wide field by simultaneous EXPOSURES in all chambers.
626
camera: photogrammetric. A general term applicable to CAMERAS used in any of the several branches of
PHOTOGRAMMETRY.
627
camera: stereometric. A combination of two CAMERAS mounted with parallel OPTICAL AXES on a short rigid
base; used in TERRESTRIAL PHOTOGRAMMETRY for making PHOTOGRAPHS in STEREOSCOPIC PAIRS.
628
camera: surveying (or mapping). A CAMERA specially designed for the production of PHOTOGRAPHS to be used
in SURVEYING. The prefix 'mapping' or 'surveying' indicates that the CAMERA is equipped with means for
maintaining and indicating the INTERIOR ORIENTATION of the PHOTOGRAPHS with sufficient ACCURACY for
surveying purposes. A mapping camera may be an aerial mapping camera or a terrestrial mapping camera.
629
camera: terrestrial. A CAMERA designed for use on the GROUND. See PHOTOTHEODOLITE.
630
camera: tracking. See CAMERA: BALLISTIC.
631
camera axis. See AXIS OF CAMERA.
632
camera station. See AIR STATION.
633
canal. An artificial WATERCOURSE. A long narrow ARM OF THE SEA extending inland between ISLANDS, or
between ISLANDS and the MAINLAND.
33
634
can buoy. A BUOY the above-water part of which is in the shape of a cylinder. Sometimes called cylindrical buoy.
635
candela. The unit of LUMINOUS INTENSITY in the SI SYSTEM.
636
candlepower. LUMINOUS INTENSITY expressed in CANDELAS. Also written as two words.
637
cantilever extension. PHOTOTRIANGULATION from a controlled area to an area of no CONTROL. Also, the
connection by RELATIVE ORIENTATION and scaling of a series of PHOTOGRAPHS in a strip to obtain STRIP
COORDINATES.
638
canyon. A relatively narrow, deep depression with steep sides, the bottom of which generally has a continuous slope.
639
canyon: submarine. A relatively narrow, deep DEPRESSION with steep SLOPES, the BOTTOM of which grades
continuously downward.
640
cap. A feature with a rounded cap-like top.
641
capacitor. See CONDENSER.
642
cape. A piece of LAND projecting into a body of water.
643
capillary wave. See WAVE.
644
card. See COMPASS CARD.
645
cardanic suspension. See GIMBALS.
646
cardinal points. The four points of the HORIZON at the intersections of the HORIZON with the MERIDIAN and the
PRIME VERTICAL; the north, south, east and west points.
647
cardinal system. A buoyage system generally used to indicate dangers where the COAST is flanked by numerous
ISLANDS, ROCKS and SHOALS as well as to indicate dangers in the open sea. In this system the BEARING (TRUE)
of the MARK from the danger is indicated to the nearest CARDINAL POINT. A system of BUOYAGE in which the
aids are assigned shape, colour, and number distinction in accordance with location relative to the nearest
OBSTRUCTION. The CARDINAL POINTS delineate the sectors for buoy location.
648
careen. Causing a vessel to lie over on one side.
649
careening grid. A timber structure in the intertidal zone serving as a support for vessels at low stages of the tide to
permit work on the exposed portion of the vessel's hull.
650
carrier. See WAVE: CARRIER.
651
carrier wave. See WAVE.
652
cartogram. A MAP showing geographical statistics by means of lines, dots, shaded areas, etc.
653
cartographer. Person employed in drawing and constructing CHARTS or MAPS.
654
cartography. The art and science of expressing graphically, by MAPS and CHARTS, the known physical features of
the EARTH, or of another CELESTIAL BODY. Often includes the works of man and his varied activities.
655
cartouche. A panel on a MAP, often with decoration, enclosing the TITLE or other LEGENDS, the SCALE, etc.
656
Cassini projection. See PROJECTION.
657
cast. In OCEANOGRAPHY, a single lowering of a series of WATER BOTTLES or other oceanographic instruments at
an OCEANOGRAPHIC STATION. Also referred to as oceanographic cast.
658
catenary. The curve formed by a uniform CABLE, CHAIN, or TAPE supported only at its ends.
659
catenary correction (tape). See TAPE: SAG CORRECTION.
34
660
cathode-ray tube. A vaccum tube in which electrons emitted by a hot cathode are formed into a narrow BEAM,
accelerated at high VELOCITY and directed towards a specially prepared SCREEN which fluoresces at the point where
the electrons strike.
661
catoptric light. See LIGHT.
662
causeway. A raised way across low or wet GROUND or water.
663
cautionary (or caution) note. Information calling special attention to some fact, usually a DANGER AREA shown on
a CHART, or other publication.
664
cavitation. The turbulent formation, generally mechanically induced, including growth and collapse of bubbles in a
fluid, and occurring when the static pressure at any point in fluid flow is less than fluid vapour pressure.
665
cay (also kay, key). A low, flat ISLAND of SAND, CORAL, etc. awash or drying at LOW WATER; a term originally
applied to the coral islets around the COAST and ISLANDS of Caribbean Sea.
666
ceiling. See HEIGHT OF CLOUD BASE.
667
celestial body. Any body pertaining to the heavens, constituting a unit for astronomical study, such as the SUN, the
MOON, the PLANETS, FIXED STARS, COMETS, etc. Also called heavenly body.
668
celestial concave. See CELESTIAL SPHERE.
669
celestial coordinates. See COORDINATES.
670
celestial equator. See EQUATOR.
671
celestial equator system of coordinates. A set of CELESTIAL COORDINATES based on the CELESTIAL
EQUATOR as the PRIMARY GREAT CIRCLE. Usually DECLINATION, RIGHT ASCENSION and HOUR
ANGLE, or SIDEREAL HOUR ANGLE. Also called equinoctial system of coordinates.
672
celestial globe. See STAR GLOBE.
673
celestial horizon. See HORIZON.
674
celestial latitude. See LATITUDE.
675
celestial line of position. A LINE OF POSITION determined by means of one CELESTIAL BODY.
676
celestial longitude. See LONGITUDE.
677
celestial meridian. See MERIDIAN.
678
celestial navigation. See NAVIGATION.
679
celestial pole. See POLE.
680
celestial sphere. An imaginary sphere of infinite radius, concentric with the EARTH, on which CELESTIAL BODIES
are imagined to be projected. Also called celestial concave.
681
cellular wave. See WAVE.
682
Celsius temperature scale. A thermodynamic scale of temperature (t°C) defined as a function of the KELVIN
TEMPERATURE SCALE (T°K) by the relationship t°C = T°K 273.15. Name for Anders Celsius (1701-44), Swedish
astronomer who first described, in 1742, the centigrade temperature scale.
NOTE. According to a resolution of the Ninth International Conference on Weights and Measures (1948), temperature
should be designated 'degrees Celsius' and the designation 'degrees centigrade' should be discontinued.
683
centering (or centring). The placing of an instrument with its VERTICAL AXIS in the VERTICAL through the
ground mark. The setting of LENSES of an optical instrument in such a manner that their OPTICAL AXES are in the
same straight line.
684
centigrade temperature scale. See CELSIUS TEMPERATURE SCALE.
35
685
centimetre-gram-second (CGS) system. The system of physical units in which the fundamental units of length, mass
and TIME are the centimetre, GRAM and SECOND, respectively.
686
central meridian. See MERIDIAN: INITIAL.
687
central processing unit (CPU). In computers in general the unit that comprises the arithmetic logic unit and the control
unit.
688
centre: reduction to. See REDUCTION.
689
centre of buoyancy. See BUOYANCY.
690
centre of gravity. See GRAVITY.
691
centrifugal force. The force with which a body moving under constraint along a curved PATH reacts to the constraint.
Equal and opposite to the CENTRIPETAL FORCE.
692
centripetal force. The force directed towards the centre of curvature which constrains a body to move in a curved
PATH. Equal and opposite to the CENTRIFUGAL FORCE.
693
centrosphere. The central CORE of the EARTH, composed of dense material, and making up most of its mass. Also
called barysphere or CORE.
694
cesium clock. See CLOCK: CESIUM.
695
cesium magnetometer. See MAGNETOMETER.
696
C-factor (U.S.A.). In PHOTOGRAMMETRY, an empirical value which expresses the vertical measuring capability of
a given stereoscopic system; generally defined as the ratio of the flight height to the smallest CONTOUR INTERVAL
accurately plottable. The C-factor is not a fixed constant but varies over a considerable RANGE, according to the
elements and conditions of the photogrammetric system. In planning for AERIAL PHOTOGRAPHY, the C-factor is
used to determine the flight height required for a specified CONTOUR INTERVAL, CAMERA, and instrument system.
697
CGS system. See CENTIMETRE-GRAM-SECOND (CGS) SYSTEM.
698
chain. A group of TRANSMITTERS broadcasting the same programme. In ELECTRONIC NAVIGATION, several
related transmitting stations in geographic proximity (Decca chain, Loran chain, etc.). In DIGITAL data, a sequence of
one or more line segments.
699
chaining. See TAPING.
700
chain adjustment. A mathematical adjustment of a whole series of figures, for example, a CHAIN OF
TRIANGULATION.
701
chain of triangulation. See TRIANGULATION: ARC OF.
702
challenger. See INTERROGATOR.
703
change of tide. A reversal of the direction of motion (rising or falling) of a TIDE. The expression is also sometimes
applied to a reversal in the SET of a TIDAL CURRENT. Also called turn of the tide. See also STAND OF TIDE.
704
channel. That part of a body of water (sometimes dredged) deep enough for NAVIGATION through an area otherwise
not navigable. It is usually marked by a single or double line of BUOYS and sometimes by RANGES. The deepest part
of a STREAM, BAY or STRAIT through which the main CURRENT flows. See also STRAIT.
705
channel: frequency. A continuous portion of the frequency spectrum appropriate for a transmission utilizing a
specified class of emission.
706
channel: sea. A long, narrow, U-shaped or V-shaped shallow depression of the SEA FLOOR usually occurring on a
gently sloping PLAIN or FAN. A continuously sloping, elongated DEPRESSION commonly found in CONES or
ABYSSAL PLAINS and customarily bordered by levees on one or both sides.
36
707
character. As pertains to typography, a graphic symbol such as a letter of the alphabet, figure, punctuation mark or sign
employed in recording language.
In data processing, an element of a CODE set used for representing information.
708
characteristics of light. All particularities of a LIGHT, such as colour, PERIOD, group number, VISIBILITY,
HEIGHT above SEA LEVEL and CHARACTER. Also called light characteristics. See also GROUP.
709
character of light. The distinct character, such as fixed, flashing, or occulting, which is given to each LIGHT to avoid
confusion with neighbouring ones.
710
character (or characteristics) of the bottom. See BOTTOM: NATURE OF.
711
chart. A special-purpose MAP generally designed for NAVIGATION or other particular purposes. See CHART:
NAUTICAL, PAPER.
712
chart: aeronautical. A representation of a portion of the EARTH, its CULTURE and RELIEF, specifically designed to
meet the requirements of AIR NAVIGATION.
713
chart: bathymetric. A topographic CHART of the BED of a body of water, or a part of it. Generally, bathymetric
charts show DEPTHS by CONTOUR LINES and GRADIENT TINTS.
714
chart: blank. A chart with a reduced amount of detail serving as cartographic basis for graphical documents of all
kinds and for the depiction of reference data.
715
chart: coast (or coastal). A NAUTICAL CHART intended for inshore COASTWISE NAVIGATION.
716
chart: cotidal. A CHART showing COTIDAL LINES.
717
chart: current. A CHART on which current data are graphically depicted.
718
chart: datum. A CHART depicting the undulations of the GEOID.
719
chart: fair. See FAIR CHART.
720
chart: field. A NAUTICAL CHART prepared at the survey site, usually contains limited, and/or unedited information.
721
chart: fishery. A chart with additional details required for the exploitation of marine natural resources.
722
chart: general. A NAUTICAL CHART intended for offshore COASTWISE NAVIGATION.
723
chart: gnomonic. A CHART on the GNOMONIC PROJECTION. Also called great circle chart.
724
chart: geophysical. A chart which primarily shows parameters of geophysical nature.
725
chart: gravity anomaly. A CHART on which current GRAVITY ANOMALIES are graphically depicted.
726
chart: great circle. See CHART: GNOMONIC.
727
chart: grid. A chart only showing a cartographic grid on its inner border.
728
chart: harbour. A NAUTICAL CHART intended for NAVIGATION and ANCHORAGE in HARBOURS and small
WATERWAYS.
729
chart: hydrographic. See CHART: NAUTICAL.
730
chart: index. An outline CHART showing the limits and identifying designation of navigational CHARTS, volumes of
SAILING DIRECTIONS, or LIST OF LIGHTS.
731
chart: layer depth. A chart showing the synoptic distribution of LAYER DEPTHS.
732
chart: magnetic. A CHART showing for an established EPOCH the values of such magnetic elements as
VARIATION, DIP, HORIZONTAL and VERTICAL INTENSITY of the EARTH'S MAGNETIC FIELD, and TOTAL
MAGNETIC INTENSITY.
37
733
chart: marine. See CHART: NAUTICAL.
734
chart: Mercator. A CHART on the MERCATOR PROJECTION. This is the CHART commonly used for MARINE
NAVIGATION. On a Mercator chart, a RHUMB LINE is a straight line.
735
chart: nautical. A CHART specifically designed to meet the requirements of MARINE NAVIGATION, showing
DEPTHS of water, NATURE OF BOTTOM, ELEVATIONS, configuration and characteristics of COAST, dangers and
AIDS TO NAVIGATION. Also called marine chart, hydrographic chart, or simply CHART.
736
chart: new. The first publication of a CHART.
737
chart: new edition. See NEW EDITION (OF CHART).
738
chart: original. A CHART which has been drawn up as a result of direct SURVEY.
739
chart: pilot. A CHART containing information required for safe NAVIGATION, including OCEAN CURRENTS, ICE
at SEA, WIND ROSES, storm tracks, ISOTHERMS, MAGNETIC VARIATION, great circle routes, limits of TRADE
WINDS, etc.
740
chart: polar. A CHART of the polar areas, or one on a polar PROJECTION.
741
chart: provisional. A special CHART, usually for which there is an urgent need. The chart is compiled from approved
source materials and may be drafted for direct reproduction. All charted information is usually combined on the black
printing plate and no other colours are shown.
742
chart: radar. A CHART designed primarily for use with RADAR, or one suitable for this purpose.
743
chart: radionavigational. A chart with additional details for the determination of a vessel's position with the aid of
radionavigation systems.
744
chart: route (or routeing). A CHART showing routes between various places, usually with distances indicated.
745
chart: sailing. A small scale nautical chart for OFFSHORE NAVIGATION.
746
chart: sea bottom sediment. A chart primarily showing information on the types and characteristics of sea bottom.
747
chart: star. A representation, on a flat surface, of the CELESTIAL SPHERE or a part of it, showing the POSITIONS
of the STARS and sometimes other features of the CELESTIAL SPHERE.
748
chart (or map): synoptic. See CHART (or MAP): WEATHER.
749
chart: tidal current. A CHART showing by arrows and numbers the average direction and SPEED of TIDAL
CURRENTS at a particular part of the current cycle.
750
chart (or map): weather. Geographical MAP on which meterological conditions or elements are represented by
figures, SYMBOLS, or ISOPLETHS. Also called synoptic chart (or map).
751
chart: working. In HYDROGRAPHIC SURVEY, a working document (CHART or PROJECTION) by means of
which a survey programme can be broadly planned.
752
chart amendment patch. See CHARTLET.
753
chart comparison unit. A device which provides simultaneous, superimposed views of a CHART and radar scope.
754
chart compilation. The production of a new or revised map or chart, or portions thereof, from existing maps, aerial
photographs, surveys, new data and other sources or the selection, assembly, and graphic representation of all relevant
information required for the preparation of a map or chart.
755
chart datum. See DATUM: CHART.
756
charted depth. See DEPTH.
38
757
chart evaluation survey. The Chart Evaluations Surveys (CES) program is designed to:
1. Resolve all deficiencies reported or discovered. (A deficiency is defined as charted information that can be made
more complete through field examination, or information which should be charted but is not.)
2. Evaluate the adequacy/accuracy of hydrographic information on existing charts.
3. Verify or revise information published in the appropriate Coast Pilot.
4. Conduct user evaluation and public relations efforts to provide an awareness of products and obtain user input.
758
chartlet. A small auxiliary CHART giving new details on a particular area, to be added to the CHART after
publication. Also called block correction or chart amendment patch. A small CHART, such as one showing the
coverage area of electronic navigational systems, with the distribution of its LINES OF POSITION, CORRECTIONS to
be applied to readings, location and identification of TRANSMITTERS, etc.
759
chart portfolio. A systematic grouping of nautical charts covering a specific geographical area.
760
chart production. All processes in the design, compilation, draughting and reproduction of a chart.
761
chart projection. See PROJECTION.
762
chart reading. Interpretation of the symbols, lines, abbreviations, and terms appearing on charts. May be called map
reading when applied to maps generally.
763
chart scale. See SCALE.
764
chart sounding datum. The tidal datum to which soundings and drying heights on a chart are referred. It is usually
taken to correspond to a low water stage of the tide. Often shortened to CHART DATUM, especially when it is clear
that reference is not being made to a horizontal datum.
765
chart symbol. A character, letter, or similar graphic representation used on a chart to indicate some object,
characteristic, etc. May be called map symbol when applied to any map.
766
check angle. A third angle taken to a fourth point as a check to a THREE-POINT FIX.
767
check lines of sounding. SOUNDING LINES run after completing the main system of SOUNDING LINES for the
purpose of checking them. See also CROSS LINES OF SOUNDING.
768
chlorinity. The total amount in GRAMS of chlorine, bromine and iodine contained in one KILOGRAM of SEA
WATER, assuming that the bromine and the iodine had been replaced by chlorine. See SALINITY.
769
chlorophyll. The green pigment contained in the leaves of plants. See PHOTOSYNTHESIS.
770
chlorosity. The property of SEA WATER corresponding to the CHLORINITY expressed as GRAMS per LITRE at
20°.
771
choppy (adj.). Of the SEA, having short, abrupt, breaking WAVES dashing against each other.
772
choppy sea. The state of the sea caused by interaction of waves running in different directions.
773
chromatic aberration. See ABERRATION OF LIGHT.
774
chromatism. See ABERRATION OF LIGHT.
775
chromosphere. The reddish LAYER of incandescent gases around the SUN, visible at a TOTAL ECLIPSE. A similar
LAYER surrounding a STAR.
776
chronograph. An instrument for measuring and recording TIME or time intervals.
777
chronometer. A portable timekeeper with a compensated balance, capable of showing TIME with extreme
PRECISION and ACCURACY.
778
chronometer: sidereal. A CHRONOMETER that indicates SIDEREAL TIME at a given place, or that corresponding
to a given MERIDIAN.
779
chronometer: standard. The CHRONOMETER with which the others aboard a vessel are compared and to which all
OBSERVATIONS involving TIME are referred.
39
780
chronometer correction. The amount to be added algebraically to the TIME of the CHRONOMETER to obtain the
correct TIME.
781
chronometer rate. The amount gained or lost by a CHRONOMETER in a unit of TIME. It is usually expressed in
SECONDS per 24 HOURS, and is sometimes called daily rate.
782
chronometric method. A former method of determining LONGITUDE by transporting CHRONOMETERS between
STATIONS whose DIFFERENCE OF LONGITUDE was to be determined.
783
cinders. Fragments formed when MAGMA is blown into the air; larger in size than VOLCANIC ASH. Cinders are a
constituent of certain marine sediments.
784
circle. In a surveying instrument, the graduated disk which is perpendicular to and centered about an AXIS of
ROTATION and is calibrated to read the amount of ROTATION.
785
circle: dip. See DIP CIRCLE.
786
circle: fundamental. See PRIMARY GREAT CIRCLE.
787
circle: great. The intersection of a sphere and a plane through its center. See also ORTHODROME.
788
circle: horizontal. In a surveying instrument, the graduated CIRCLE used for measuring horizontal angles.
789
circle: hydrographic. A double-reflecting instrument intended primarily for use in HYDROGRAPHIC SURVEY;
enables measurement of angles up to 180°. See also SEXTANT: SOUNDING.
790
circle: small. The intersection of a sphere and a plane which does not pass through its center.
791
circle: vertical. A GREAT CIRCLE on the CELESTIAL SPHERE passing through the ZENITH and NADIR. Vertical
circles are perpendicular to the HORIZON. In a surveying instrument, the graduated CIRCLE used for measuring
vertical angles.
792
circle of declination. See HOUR CIRCLE.
793
circle of equal altitude. A SMALL CIRCLE on the surface of the EARTH at every point of which, at the instant of
OBSERVATION, the observed CELESTIAL BODY (SUN, STAR, or PLANET) has the same ALTITUDE and,
therefore, the same ZENITH DISTANCE.
794
circle of latitude. A GREAT CIRCLE of the CELESTIAL SPHERE through the ecliptic poles, and hence
perpendicular to the plane of the ECLIPTIC.
795
circle of position. The SMALL CIRCLE on the surface of the EARTH on which an OBSERVATION shows the
observer to be. The expression is most frequently used to indicate the CIRCLE OF EQUAL ALTITUDE. Also called
position circle.
796
circle of right ascension. See HOUR CIRCLE.
797
circle of uncertainty. A circle having as its centre a POSITION, however determined, and as its radius the maximum
PROBABLE ERROR of the POSITION; a circle within which a craft is considered to be located.
798
circle of visibility. That circle surrounding an AID TO NAVIGATION and in which the aid is visible. See RANGE OF
VISIBILITY.
799
circle sheet (U.S. terminology). A BOAT SHEET or a SMOOTH SHEET on which intersecting systems of curves are
drawn, each curve corresponding to the LOCUS of some angle between two STATIONS. POSITIONS are plotted on
circle sheets at the intersection of the LOCI of two observed angles, each LOCUS being found by INTERPOLATION
between the curves drawn on the sheet. Circle sheets are prepared and employed in HYDROGRAPHIC SURVEYS for
plotting FIXES without the use of PROTRACTOR. Also called standard circle sheet; formerly called sextant chart.
See also FIXED ANGLE PLOT, and LATTICE.
800
circular fix. See FIX.
801
circular level. See LEVEL: SPIRIT.
40
802
circular radiobeacon station. A RADIO STATION which needs not necessarily be manned, the emissions of which,
radiated around the HORIZON, enable its BEARING to be determined by means of the RADIO DIRECTION FINDER
of a ship.
803
circum-meridian altitude. See ALTITUDE: EX-MERIDIAN.
804
circumpolar (adj.). Revolving about the ELEVATED POLE without setting. A CELESTIAL BODY is circumpolar
when its POLAR DISTANCE is approximately equal to or less than the LATITUDE of the observer. The actual limit is
extended somewhat by the combined effect of REFRACTION, SEMIDIAMETER, PARALLAX, and the HEIGHT of
the observer's eye above the HORIZON.
805
cirrocumulus. See CLOUD GENERA.
806
cirrostratus. See CLOUD GENERA.
807
cirrus. See CLOUD GENERA.
808
civil day. See DAY.
809
civil time. See TIME.
810
civil twilight. See TWILIGHT.
811
civil year. See YEAR.
812
clamping error. See ERROR.
813
clamp (or clamping) screw. A screw for holding in place a moving part of an instrument as during an
OBSERVATION or reading with a THEODOLITE or SEXTANT.
814
clamshell snapper. See SNAPPER.
815
clapotis. The French equivalent for a type of STANDING WAVE.
816
Clarke's spheroid. See REFERENCE SPHEROID.
817
clay. Mineralogically, a hydrous aluminium silicate material with plastic properties and a crystal structure. As a size
term, refers to sediment particles ranging from 0.0039 to 0.00024 millimeter, in which case it includes rock flour,
calcareous muds, aragonite, etc.
818
clean (adj.). Free from OBSTRUCTIONS, unevenness, imperfections, as a clean ANCHORAGE.
819
clear (v.t.). To make such distance from an object as to have open sea-room.
820
clearance. In NAVIGATION, a safe distance off a danger. In METEOROLOGY: a) decrease of total CLOUD
AMOUNT when the latter is large; b) TIME at which this decrease takes place; c) gap in a cloud layer covering the
entire sky. Also called clearing.
821
clearance: bridge. Minimum vertical or horizontal space available for passage.
822
clearance: overhead pipeline. Minimum vertical or horizontal space available for passage.
823
clearance: safe overhead. The HEIGHT above the VERTICAL CONTROL DATUM at which the highest points of a
ship can pass under an overhead power CABLE without risk of electrical discharge from the cable to the ship or without
making contact with a BRIDGE.
824
cleared depth. The effective depth over a feature, obtained by a wire drag survey.
825
clearing. See CLEARANCE.
826
clearing line. A straight line, on a CHART, that marks the BOUNDARY between a safe and a dangerous area; or that
passes clear of a navigational danger. Sectors of lighthouse lights are usually bounded by them.
827
clearing marks. Selected MARKS, natural or otherwise, used to help vessels keep clear of dangers.
41
828
clear sweeping. A form of BAR SWEEPING. A sweep, set at a predetermined depth, and passed over an area to ensure
that no obstructions have been missed.
829
cliff. LAND rising abruptly for a considerable distance above the water or surrounding LAND.
830
climate. Fluctuating aggregate of atmospheric conditions characterized by the states and developments of the
WEATHER of a given area.
831
climatology. Study of CLIMATES (causes, variations, distributions, types, etc.).
832
clinometer. An instrument for indicating the degree of SLOPE or the angle of ROLL or PITCH of a vessel, according
to the plane in which it is mounted.
833
clock. Instrument for measuring TIME and recording HOURS.
834
clock: atomic. A precision clock that depends for its operation on an electrical OSCILLATOR regulated by the natural
vibrational FREQUENCY of an atomic system (such as a beam). The combination of two (or more) radionuclides
whose activities can be utilized to ascertain time intervals.
835
clock: cesium. An atomic clock using the properties of cesium.
836
clock: crystal. A precision clock essentially consisting of a generator of constant FREQUENCY controlled by a
resonator made of quartz crystal with suitable methods for producing continuous ROTATION to operate time-indicating
and related mechanisms. Also called quartz clock.
837
clock: quartz. See CLOCK: CRYSTAL.
838
closed traverse. See TRAVERSE.
839
close pack ice. PACK ICE composed of FLOES mostly in contact, such that NAVIGATION becomes difficult even for
specially constructed vessels. ICE CONCENTRATION 7/10th to 9/10th.
840
closing error. See ERROR OF CLOSURE.
841
closing line. A line that divides the internal waters and territorial seas of a coastal State or the archipelagic waters of an
archipelagic State.
842
closing the horizon. See HORIZON.
843
closure: error of. See ERROR OF CLOSURE.
844
closure of triangle. See ERROR OF CLOSURE OF TRIANGLE.
845
cloud. Visible aggregate of minute particles of liquid water or ICE, or of both together, in suspension in the
ATMOSPHERE. This aggregate may include larger particles of liquid water or ICE, non-aqueous particles or solid
particles, originating for example from industrial gases, smoke or DUST.
846
cloud amount. The fraction of the sky covered by the CLOUDS of a certain genus, certain species, certain variety,
certain layer, or of a certain combination of CLOUDS. Also called 'partial cloud amount'. See CLOUD GENERA.
847
cloud classification. System of distinguishing and grouping CLOUDS according to one or more of the following
criteria: a) appearance, b) process of formation, c) common HEIGHT, d) particulate composition.
848
cloud genera. Main characteristic mutually exclusive forms of CLOUDS, constituting the basis of the CLOUD
CLASSIFICATION included in the International Cloud Atlas, 1956. The cloud genera are ten in number: cirrus,
cirrocumulus, cirrostratus, altocumulus, altostratus, nimbostratus, stratocumulus, stratus, cumulus, cumulonimbus.
849
clutter. Confused unwanted ECHOES on a radar display.
850
coast. The edge or margin of the LAND next to the SEA; the SEASHORE. Sometimes defined as the meeting of the
LAND and SEA considered as the BOUNDARY of the LAND.
851
coast (v.t.). To sail along or near a COAST.
852
coastal chart. See CHART: COAST.
42
853
coastal current. See CURRENT.
854
coastal refraction. See REFRACTION.
855
coastal survey. See SURVEY.
856
coast chart. See CHART.
857
Coast Guard station. See LIFE-SAVING STATION.
858
coastline. See SHORELINE.
859
coastlining. The process of obtaining DATA from which the COASTLINE can be drawn on a CHART.
860
coast pilot (U.S.A.). A descriptive book for the use of mariners, containing detailed information of coastal waters,
harbour facilities, etc., of an area. Such books are prepared by the National Ocean Service for waters of the U.S.A. and
its possessions. See also SAILING DIRECTIONS.
861
coastwise navigation. See NAVIGATION.
862
coaxial cable. See CABLE.
863
cobble. A naturally rounded STONE larger than a PEBBLE.
864
cocked hat. Triangle on CHART, formed by three POSITION LINES that do not cross at one point. Also called
triangle of error.
NOTE. This expression is seldom used by American navigators.
865
cocurrent line. A line through places having the same tidal current hour.
866
code. A method of information representation by mapping it into a machine-readable alphabet; e.g. textual information
may be represented in computer memory by the ASCII or the EBCDIC alphabet.
867
codeclination. 90°minus the DECLINATION. See POLAR DISTANCE.
868
coding delay. An arbitrary time delay in the transmission of pulse signals. In the LORAN system this is inserted
between the transmission of master and slave signals to prevent zero or small readings, and aid in distinguishing
between master and slave station signals.
869
coefficient of refraction. See REFRACTION: COEFFICIENT OF.
870
coelenterate. One of a phylum of two-staged (sessile and free-floating) organisms. The sessile stage basically is
cylindrical and is called a polyp; the free-swimming stage is disc or bell shaped and is called a medusa or JELLYFISH.
871
coherent electromagnetic wave. See WAVE: ELECTROMAGNETIC.
872
col. A marked DEPRESSION in the summit line of a MOUNTAIN CHAIN, generally affording a PASS from one
SLOPE to the other. In METEOROLOGY, a saddle-backed region of almost uniform pressure which appears between
two DEPRESSIONS and two ANTICYCLONES arranged alternately in a cross.
873
colatitude. The complement of the LATITUDE, or 90°minus the LATITUDE.
874
cold front. Any non-occluded FRONT which moves in such a way that colder air replaces warmer air.
875
cold wave. Marked cooling of the air, or the invasion of very cold air, over a large area.
876
collector tracing. A comprehensive record of the work compiled while the HYDROGRAPHIC SURVEY is in
progress.
877
collimate (v.t.). In physics and ASTRONOMY, to render parallel to a certain line or direction; to render parallel, as
RAYS of light; to adjust the LINE OF SIGHT of an optical instrument so that it is in the proper position relative to the
other parts of the instruments. In PHOTOGRAMMETRY, to adjust the FIDUCIAL MARKS of a CAMERA so that
they define the PRINCIPAL POINT.
43
878
collimation: line of. The line through the OPTICAL CENTRE of the OBJECTIVE LENS of a TELESCOPE and the
centre of the RETICLE. Also called LINE OF SIGHT, sight line, pointing line or aiming line of the instrument.
879
collimation adjustment. The process of bringing the LINE OF COLLIMATION of a TELESCOPE into close
agreement with the COLLIMATION AXIS.
880
collimation axis. The line through the OPTICAL CENTRE of the OBJECTIVE LENS perpendicular to the AXIS of
ROTATION of the TELESCOPE. Also called axis of collimation.
881
collimation error. See ERROR OF COLLIMATION.
882
collimator. An optical device for artificially creating a TARGET at infinite distance (a BEAM of parallel RAYS of
light) used in testing and adjusting certain optical instruments. It usually consists of a converging LENS and a TARGET
(a system or arrangement of CROSS HAIRS) placed at the principal FOCUS of the LENS.
883
collimator: auto. A COLLIMATOR provided with a means of illuminating its CROSS HAIRS so that, when a
reflecting plane is placed normal to the emergent LIGHT BEAM, the reflected IMAGE of the CROSS HAIRS appears
to be coincident with the CROSS HAIRS themselves. This device is used in calibrating optical and mechanical
instruments.
884
collimator: vertical. A TELESCOPE so mounted that its COLLIMATION AXIS can be made to coincide with the
VERTICAL (or direction of PLUMB-LINE). The vertical collimator serves as an optical PLUMB-LINE, and may be
designed for use in placing a MARK on the GROUND directly under an instrument or in centering an instrument
directly over a MARK on the GROUND.
885
colour of sea water. See SEA WATER.
886
colour proof. The final proof for checking before printing utilizing all of the negatives involved to produce a copy of
the final product with all of the required colours. See also PROOF.
887
colour plate. A general term for a pressplate from which any given colour is printed.
888
colour separation. Either the process of preparing a separate drawing, engraving or negative for each colour required in
the production of a chart or a photographic process or electronic scanning procedure using colour filters to separate a
multi-coloured copy into separate images of each of the three primary colours.
889
colure: equinoctial. The HOUR CIRCLE through the EQUINOXES.
890
colure: solsticial. The HOUR CIRCLE through the SOLSTICES.
891
coma. An aberration affecting the sharpness of IMAGES off the AXIS, in which RAYS from a point object off the
AXIS passing through a given circular zone of the LENS, come to a FOCUS in a circle rather than a point, and the
circles formed by RAYS through different zones are of different sizes and are located at different distances from the
AXIS. Therefore, the IMAGE of a point object is comet-shaped. The foggy envelope surrounding the nucleus of a
COMET.
892
comb: micrometer. See MICROMETER.
893
comber. A deep water WAVE whose crest is pushed forward by a strong WIND and is much larger than a
WHITECAP. Also called beachcomber. A long-period SPILLING BREAKER. See also ROLLER.
894
comet. A HEAVENLY BODY having a starlike nucleus with a luminous foggy envelope (see COMA), and usually
developing a long luminous tail when near the SUN.
895
common (or vulgar) establishment. See ESTABLISHMENT.
896
compact pack ice. Pack ice in which the concentration is 10/10 (8/8) and no water is visible.
897
compacted ice edge. A close, clear-cut ice edge compacted by wind or current. It is usually on the windward side of an
area of pack ice.
898
compacting. Pieces of sea ice are said to be compacting when they are subjected to a converging motion, which
increases ice concentration and/or produces stresses which may result in ice deformations.
44
899
comparator. An instrument for measuring a dimension in terms of a STANDARD. An optical instrument for
measuring RECTANGULAR or POLAR COORDINATES of points on any plane surface, such as a photographic
PLATE.
900
comparing watch. See WATCH.
901
compass. An instrument consisting of two legs jointed by a PIVOT used for describing circles or transferring
measurements. Also referred to as pair of compasses. An instrument for indicating a horizontal REFERENCE
DIRECTION relative to the EARTH.
902
compass: astro. An instrument which, when oriented to the horizontal and to the CELESTIAL SPHERE, indicates a
horizontal REFERENCE DIRECTION relative to the EARTH. This COMPASS is designed primarily for the
OBSERVATION of CELESTIAL BODIES to determine the ORIENTATION of an aircraft relative to the AZIMUTH
of a CELESTIAL BODY.
903
compass: boat. A small portable COMPASS mounted in a box for convenient use in small water craft.
904
compass: box. See DECLINATOIRE.
905
compass: deadbeat. An aperiodic COMPASS; one that, when deflected, returns by one direct movement to its proper
reading.
906
compass: dipping. See DIP CIRCLE.
907
compass: dry (or dry card). A COMPASS without a liquid-filled bowl, particularly a MAGNETIC COMPASS
having a very light COMPASS CARD. Such a MAGNETIC COMPASS is seldom used in modern practice. See
COMPASS: LIQUID.
908
compass: dumb. See PELORUS.
909
compass: gyroscopic. A COMPASS having one or more GYROSCOPES as the directive element, and tending to
indicate TRUE NORTH. Also called gyro compass.
910
compass: hanging. A COMPASS having its BINNACLE overhead and its graduated card facing downward. Also
referred to as overhead compass, or inverted compass.
911
compass: inverted. See COMPASS: HANGING.
912
compass: liquid. A MAGNETIC COMPASS having a bowl completely filled with liquid in order to damp the swinging
of the card. Sometimes called spirit compass, or wet compass.
913
compass: magnetic. A COMPASS depending for its directive force upon the attraction of the MAGNETISM of the
EARTH for a MAGNET free to turn in an horizontal direction.
914
compass: master. A COMPASS controlling one or several REPEATERS.
915
compass: master gyro. A GYROSCOPIC COMPASS for controlling one or several remote indicators, called GYRO
REPEATERS.
916
compass: overhead. See COMPASS: HANGING.
917
compass: pocket. A portable COMPASS (employed in COASTLINING or RECONNAISSANCE SURVEY).
918
compass: sky. A type of ASTRO COMPASS which utilizes the POLARIZATION of sunlight in the sky, designed for
use in the arctic during long periods of TWILIGHT. It operates whenever the ZENITH is clear whether or not the SUN
is visible, but when the SUN is more than about 6.5°below or 10°above the HORIZON, readings are uncertain.
919
compass: spirit. See COMPASS: LIQUID.
920
compass: standard. A COMPASS designated as the STANDARD for a vessel. It is located in a favourable position
and is accurately calibrated.
921
compass: steering. The COMPASS placed next to the steering wheel, by which the COURSE is steered. See also
STEERING REPEATER.
45
922
compass: sun. A form of ASTRO COMPASS utilizing the shadow of a GNOMON.
923
compass: surveyor's. An instrument for determining a MAGNETIC BEARING of a LINE OF SIGHT by the use of a
sighting device, a graduated HORIZONTAL CIRCLE and a pivoted NEEDLE.
924
compass: trough. See DECLINATOIRE.
925
compass: tubular. A COMPASS supplied for attachment to certain types of LEVELS and THEODOLITES.
926
compass: wet. See COMPASS: LIQUID.
927
compass adjustment. See COMPENSATION OF MAGNETIC COMPASS.
928
compass adjustment buoy. A BUOY placed at a favourable location to assist a vessel to adjust its COMPASS or
swing ship. Also called swinging buoy. See also SWINGING SHIP.
929
compass bearing. See BEARING.
930
compass bowl. That part of a COMPASS in which the COMPASS CARD is mounted. A magnetic compass bowl is
usually filled with liquid. The compass bowl turns with the craft while the COMPASS CARD remains essentially in a
north-south direction.
931
compass calibration. See SWINGING SHIP.
932
compass card. That part of a COMPASS on which the direction graduations are placed. Also referred to as card.
933
compass compensation. See COMPENSATION OF MAGNETIC COMPASS.
934
compass corrector. See COMPENSATOR: MAGNETIC.
935
compass course. See COURSE.
936
compasses: pair of. See COMPASS.
937
compass meridian. See MERIDIAN.
938
compass needle(s). Magnetized steel needle(s) of high RETENTIVITY that tends to keep north-south line of
COMPASS CARD in MAGNETIC MERIDIAN.
939
compass north. See NORTH: COMPASS.
940
compass points. The 32 divisions of a COMPASS, at intervals of 11°1/4.
941
compass repeater. A device for repeating at a distance the indications of the MASTER COMPASS.
942
compass rose. A circle graduated in DEGREES clockwise from 0°(north) to 360°printed on a CHART for use as a
PROTRACTOR. Compass roses are also placed at other convenient locations to facilitate measurements of directions.
They may be oriented to the TRUE or the MAGNETIC NORTH.
943
compensate (v.t.). To counteract an ERROR, as in an instrument; to counterbalance.
944
compensating coils. The coils placed near a MAGNETIC COMPASS to neutralize the effect of the vessel's degaussing
system on the COMPASS.
945
compensation depth. See DEPTH.
946
compensation of magnetic compass. The process of neutralizing or reducing to a minimum the magnetic effects the
vessel itself exerts on a MAGNETIC COMPASS. It is based on the principle that the magnetic effect of the iron and
steel of the vessel can be counterbalanced by means of MAGNETS and SOFT IRON placed near the COMPASS. Also
called compass adjustment, compass compensation, or magnetic compensation. See also COMPASS ADJUSTMENT.
947
compensator: magnetic. A MAGNET, piece of SOFT IRON such as a sphere or iron bar, placed in a BINNACLE or
in vicinity of a MAGNETIC COMPASS for reducing MAGNETIC DEVIATION to a minimum. Also called compass
corrector or corrector magnet. See FLINDERS BAR, HEELING MAGNET, QUADRANTAL CORRECTORS.
46
948
compilation. In CARTOGRAPHY, the production of a new or improved MAP or CHART (or portion thereof) from
existing MAPS or CHARTS, AERIAL PHOTOGRAPHS, SURVEYS, new DATA, and other sources. In
PHOTOGRAMMETRY, the production of a MAP (or portion of a MAP) from AERIAL PHOTOGRAPHS and
geodetic control data, by means of photogrammetric instruments. Sometimes called stereocompilation.
949
compilation diagram. See SOURCE DIAGRAM.
950
compiler. A program that translates programs from one programming language (source program) into another
programming language (object program). Typically the compiler translates from a higher, user understandable language
to a lower, machine interpretable language.
951
component. See HARMONIC CONSTITUENT.
952
composite electronic navigational system. One contrived in such a way that the POSITION is determined by lines of
different types, for instance, by a LATTICE of circles and a LATTICE of HYPERBOLAE.
953
composite path. A wave track which lies partly over LAND and partly over water.
954
composite photograph. See PHOTOGRAPH.
955
composite sailing. See SAILING.
956
compound tide. See TIDE.
957
compression (of the earth). See FLATTENING OF THE EARTH.
958
compression ratios. See FLATTENING OF THE EARTH.
959
compressional wave. See WAVE.
960
computer. A person who performs calculations.
A device capable of accepting DATA, processing it according to stored instruction that are followed in automatic
sequence, and supplying the results in some form. It usually consists of input and output devices, STORAGE, arithmetic
and logical units, and a control unit.
961
computer: analogue. A physical device or system which behaves in a manner analogous to some system under study,
simulating the processes and producing results which are measured in terms of physical quantities. Often an electrical
system.
962
computer: digital. A machine for carrying out mathematical processes by operations based on counting, as distinct
from an ANALOGUE COMPUTER.
963
computer-assisted (computer-aided) cartography. A system which is used to perform specific cartographic function
by means of computer hardware and software which aids humans to make decisions and/or perform their functions.
Because of the graphic nature of cartography, such a system always contains, or makes use of, a computer graphics
system.
964
computer graphics. All methods and techniques used in computer sciences to represent data in graphical form and to
process images.
965
concentration: ice. See ICE.
966
concluded angle. See ANGLE.
967
condenser. In optics, a LENS or LENS SYSTEM designed to concentrate the ILLUMINATION from a light source on
a limited area. In electricity, a device for receiving and storing an electric charge. Also called a capacitor.
968
condition equation. See EQUATION.
969
conductivity. The ability to transmit, as electricity, heat, sound etc.
970
cone. See FAN.
971
configuration of terrain. The TOPOGRAPHY of a region.
47
972
confluence. Flowing together. The place where two or more RIVERS, STREAMS, etc. unite. In METEOROLOGY,
progressive drawing together of the STREAMLINES in the direction of FLOW.
973
conformality. The special property of CONFORMAL PROJECTION, i.e. that of having correct relationship about a
point.
974
conformal projection. See PROJECTION.
975
conic (or conical) projection. See PROJECTION.
976
conical buoy. A BUOY the above water part of which is in the shape of a cone.
977
conical projections. The map projections produced by projecting the geographic meridians and parallels onto a cone
which is tangent to or intersects the surface of a sphere, and then developing the cone into a plane.
978
conjunction. In ASTRONOMY, the situation of two CELESTIAL BODIES having the same CELESTIAL
LONGITUDE or the same sidereal HOUR ANGLE. For a SUPERIOR PLANET, it occurs when the SUN is between
the EARTH and the PLANET.
979
conjunction: inferior. The CONJUNCTION of an INFERIOR PLANET and the SUN when the PLANET is between
the EARTH and the SUN.
980
conjunction: superior. The CONJUNCTION of an INFERIOR PLANET and the SUN when the SUN is between the
EARTH and the PLANET.
981
connection: geodetic. OBSERVATIONS on one or more STATIONS common to the two different geodetic schemes of
TRIANGULATION to be incorporated.
982
console. The housing of the main operating unit of electronic equipment, in which INDICATORS and general
CONTROLS are located. A portion of a COMPUTER used to control the machine manually.
983
consolidated pack ice. Pack ice in which the concentration is 10/10 (8/8) and the floes are frozen together.
984
conspicuous (adj.). Term applied to an object either natural or artificial which is distinctly and notably visible from
seaward.
985
constant deviation. See DEVIATION.
986
constant error. See ERROR.
987
constellation. Formerly a number of FIXED STARS grouped within an imaginary outline. Now, a region of the
CELESTIAL SPHERE marked by arbitrary boundary lines.
988
constituent. See HARMONIC CONSTITUENT.
989
constituent day. See DAY.
990
contact glass. See FOCAL PLANE PLATE.
991
contact plate. See FOCAL PLANE PLATE.
992
contact print. See PRINT.
993
contiguous zone. A zone contiguous to a coastal state's territorial sea, which may not extend beyond 24 nautical miles
from the baselines from which the breadth of the territorial sea is measured. The coastal state may exercise certain
control in this zone subject to the provisions of International Law.
994
continent. One of the main continuous bodies of LAND on the EARTH's surface. The main LAND, as distinguished
from outlying ISLANDS; MAINLAND.
995
continental borderland. A region adjacent to a CONTINENT, normally occupied by or bordering a CONTINENTAL
SHELF, highly irregular, with DEPTHS well in excess of those typical of a CONTINENTAL SHELF.
48
996
continental margin. The zone, generally consisting of SHELF, SLOPE and RISE, separating the CONTINENT from
the ABYSSAL PLAIN or DEEP OCEAN FLOOR.
997
continental rise. A gentle RISE with a generally smooth surface lying between the CONTINENTAL SLOPE and the
DEEP OCEAN FLOOR.
998
continental (or island) shelf. A zone adjacent to a CONTINENT (or around an ISLAND), extending from the LOW
WATER LINE to the DEPTH at which there is usually a marked increase of SLOPE to greater DEPTH. See SHELF.
999
continental shelf limit. The limit of the continental shelf or continental margin determined in accordance with the
provisions of the United Nations Convention on the Law of the Sea.
1000
continental (or island) slope. The zone of DECLIVITY from the outer EDGE of a CONTINENTAL (or ISLAND)
SHELF into greater DEPTH. See SLOPE.
1001
continuous strip camera. See CAMERA.
1002
continuous wave. See WAVE.
1003
contour (or contour line). A line connecting points of equal ELEVATION or equal DEPTH. See also FORM LINE,
HACHURES, ILLUMINATED CONTOURS, INDEX CONTOURS.
1004
contour: depression. A closed CONTOUR inside of which the GROUND is at lower ELEVATION than outside. See
also FORM LINE.
1005
contour: depth. See DEPTH CURVE.
1006
contouring. The process of establishing lines representing equal values of a quantity on a map or chart.
1007
contour interval. The difference in ELEVATION between adjacent CONTOURS.
1008
contour line. See CONTOUR.
1009
contour map. See MAP.
1010
contour sweeping. A form of BAR SWEEPING. A sweep, set at a predetermined depth, and passed over the bottom at
right angles to the depth contours. When contact is made the position is recorded.
1011
contrast. In PHOTOGRAPHY, the actual difference in DENSITY between the highlights and the shadows on a
NEGATIVE or POSITIVE. Contrast is not concerned with the magnitude of DENSITY but only with the difference in
DENSITIES. Also the rating of a photographic material corresponding to the relative density difference which it
exhibits.
1012
control. A system of points with established POSITIONS or ELEVATIONS, or both, which are used as fixed
references in positioning and correlating map features. Control is generally classified in four orders (with first order
denoting highest quality) according to the PRECISION of the methods and instruments used in establishing it, and the
ACCURACY of the resultant POSITIONS and ELEVATIONS. Often called basic control.
Regulation or direction of a machine, electronic equipment, etc.; or the DIAL, knob, switch, etc. for performing this
function.
The exercise of directing influence over the movements of a craft or missile, with particular reference to changes in
direction and SPEED.
1013
control: astronomical. CONTROL determined from ASTRONOMICAL OBSERVATIONS.
1014
control: basic. See CONTROL.
1015
control: geodetic. A system of CONTROL STATIONS established by geodetic methods. See SURVEY: GEODETIC.
1016
control: ground. CONTROL established by GROUND SURVEYS, as distinguished from CONTROL established by
photogrammetric methods.
1017
control: horizontal. CONTROL that is determined in horizontal POSITION. The POSITION may be referred to any
recognized geographic or plane coordinate system.
1018
control: minor. See CONTROL: PHOTOGRAMMETRIC.
49
1019
control: photogrammetric. CONTROL established by photogrammetric methods, as distinguished from CONTROL
established by ground methods. Also called minor control.
1020
control: supplemental. Points established by subordinate SURVEYS, to relate AERIAL PHOTOGRAPHS used in
mapping with the system of GEODETIC CONTROL. The points must be positively photoidentified, that is, the points
on the GROUND must be positively correlated with their IMAGES on the PHOTOGRAPHS.
1021
control: vertical. CONTROL determined in ELEVATION relative to a DATUM PLANE.
1022
controlled mosaic. See MOSAIC.
1023
controlling depth. See DEPTH.
1024
control mark. A specific object on the ground whose position and/or elevation has been determined or is to be
determined.
1025
control point. In PHOTOGRAMMETRY, any STATION in a horizontal and vertical control system that is identified
on a PHOTOGRAPH and used for correlating the DATA shown on that PHOTOGRAPH. More specific terms are
photo-control point, picture control point and ground control point. A CONTROL STATION.
1026
control station. A point on the GROUND whose POSITION (horizontal and vertical) is used as a base for a dependent
SURVEY. Also referred to as CONTROL POINT.
1027
convection. In general, mass motions within a fluid resulting in TRANSPORT and mixing of the properties of that
fluid.
In the ATMOSPHERE, organized internal motions within a LAYER of air, leading to vertical transport of heat,
momentum, etc.
1028
convection: forced. In the ATMOSPHERE, CONVECTION caused by mechanical forces, such as those arising from
air motion over a rough or sloping surface.
1029
convection: free. In the ATMOSPHERE, CONVECTION caused by density differences within the air.
1030
convergence. In OCEANOGRAPHY, a situation whereby waters of different origins come together at a point or, more
commonly, along a line known as a convergence line. Along such a line the denser water from one side sinks under the
lighter water from the other side. See SINKING.
1031
convergence of the meridians. The angular drawing together of the GEOGRAPHIC MERIDIANS in passing from the
EQUATOR to the POLES. The difference between the two angles formed by the intersection of a GREAT CIRCLE
with two MERIDIANS. The difference between the RECIPROCAL BEARINGS of two points. At any point of a
cartographic PROJECTION, the angle between the MERIDIAN, as represented on the plane of the PROJECTION and
GRID in use, and the GRID NORTH line.
1032
convergence zone. In OCEANOGRAPHY, region of CONVERGENCE. The region in the deep OCEAN where
SOUND RAYS, refracted from the DEPTHS, arrive at the surface in successive intervals of 30 to 35 NAUTICAL
MILES.
1033
conversion. Determination of the rhumb line direction of one point from another when the initial great circle direction is
known, or vice versa.
1034
conversion angle. See ARC TO CHORD CORRECTION.
1035
conversion factor. That factor by which the numerical value made in one system of units must be multiplied to arrive at
the numerical value in another system of units.
1036
conversion scale. A SCALE for the conversion of units of one measurement to equivalent units of another
measurement. See NOMOGRAM.
1037
conversion table. A TABLE for the conversion of units of one measurement to equivalent units of another
measurement. See NOMOGRAM.
1038
coordinate axes. See COORDINATES: PLANE RECTANGULAR.
1039
coordinated universal time (UTC). See UNIVERSAL TIME COORDINATED.
50
1040
coordinates. Linear or angular quantities which designate the POSITION of a point in relation to a given reference
system.
1041
coordinates: celestial. Any set of COORDINATES used to define a point on the CELESTIAL SPHERE. The
HORIZON, CELESTIAL EQUATOR and ECLIPTIC SYSTEMS of celestial coordinates are based on the
CELESTIAL HORIZON, CELESTIAL EQUATOR and ECLIPTIC respectively, as the PRIMARY GREAT CIRCLE.
1042
coordinates: false. GRID COORDINATES obtained by adding fixed numerical quantities to all grid values. These
quantities are so large that none of the resultant false coordinates are negative. Such a procedure introduces a false
origin to the south and west of the true ORIGIN. See COORDINATES: ORIGIN OF.
1043
coordinates: geocentric. COORDINATES that define the POSITION of a point with respect to the centre of the
EARTH. See LATITUDE: GEOCENTRIC. The term 'geocentric longitude' is never used, as the quantity which it would
designate is the same as GEODETIC LONGITUDE.
1044
coordinates: geodetic. Quantities which define the horizontal POSITION of a point on the SPHEROID OF
REFERENCE with respect to the planes of GEODETIC EQUATOR and of a selected GEODETIC MERIDIAN. See
LATITUDE: GEODETIC and LONGITUDE: GEODETIC.
1045
coordinates: geographic(al). A system of SPHERICAL COORDINATES for defining the POSITIONS of points on
the EARTH.
1046
coordinates: grid. A plane rectangular coordinate system based on, and mathematically adjusted to, a MAP
PROJECTION, so that GEOGRAPHIC POSITIONS in terms of LATITUDE and LONGITUDE can be readily
transformed into PLANE COORDINATES, and the computation relating to them made by the ordinary methods of
PLANE SURVEYING.
1047
coordinates: origin of. The point of intersection of the COORDINATE AXES, from which the COORDINATES are
reckoned. In mathematical treaties, this ORIGIN is usually given the COORDINATES 0,0; in SURVEYING, however,
it is standard practice to give this ORIGIN, COORDINATES having large positive numerical values, thereby avoiding
the use of negative COORDINATES. Also called point of origin. See COORDINATES: FALSE.
1048
coordinates: photograph. A system of COORDINATES, either RECTANGULAR or POLAR, to define the
POSITION of a point on a PHOTOGRAPH.
1049
coordinates: plane. See COORDINATES: PLANE RECTANGULAR.
1050
coordinates: plane polar. The distance and DIRECTION from a central point of reference to a point whose POSITION
is being defined. The point of reference is termed the POLE or ORIGIN; the line (distance) connecting the ORIGIN
with the point whose POSITION is being defined is the radius vector; and the angle between the fixed line (POLAR
AXIS) which the DIRECTION is referred to and the radius vector is the vectorial angle.
1051
coordinates: plane rectangular. A system of COORDINATES in a HORIZONTAL PLANE used to describe the
POSITIONS of points with respect to an arbitrary ORIGIN by means of two distances perpendicular to each other. The
two REFERENCE LINES at right angles to each other passing through the ORIGIN are called the coordinate axes. The
distances parallel to the true (or arbitrarily assigned) north-south axis are called the ordinates, or the y coordinates. The
distances parallel to the true (or arbitrarily assigned) east-west axis are called the abscissae, or the x coordinates. The
north and east directions are usually taken as positive, and the south and west directions are usually taken as negative.
Also referred to as plane coordinates.
1052
coordinates: polar. A system of COORDINATES used to describe the POSITION of a point in space with respect to
an arbitrarily chosen ORIGIN by means of two DIRECTIONS and one distance; i.e., the vectorial angles and radius
vector magnitude.
1053
coordinates: rectangular. COORDINATES on any system in which the axes of reference intersect at right angles.
1054
coordinates: space. In PHOTOGRAMMETRY the term may refer to any general three-dimensional coordinate system
used to define the POSITION of a point in the object space, as distinguished from the IMAGE of the same point on a
PHOTOGRAPH.
1055
coordinates: spherical. A system of POLAR COORDINATES in which the ORIGIN is the centre of a sphere and the
points all lie on the surface of a sphere. The POLAR AXIS of such a system cuts the sphere at its two POLES.
1056
coordinates: strip. The COORDINATES of any point in a strip, whether on the GROUND or actually an AIR
STATION, referred to the ORIGIN and axes of the air coordinate system of the first OVERLAP.
51
1057
coordinate system. A fixed system of lines used to define the position of a point, line, or plane.
1058
coordinatograph. An instrument used to plot in terms of PLANE RECTANGULAR COORDINATES. It may be an
integral part of a STEREOSCOPIC PLOTTING INSTRUMENT whereby the planimetric motions (x and y) of the
FLOATING MARK are plotted directly.
1059
coplane: basal. In PHOTOGRAMMETRY, the condition of EXPOSURE of a pair of PHOTOGRAPHS in which the
two PHOTOGRAPHS lie in a common plane parallel to the AIR BASE. If the AIR BASE is horizontal, the
PHOTOGRAPHS are said to be exposed in horizontal coplane.
1060
copper plate. Polished PLATE on which manuscript drawings were formerly engraved for the printing of CHARTS.
1061
coral. Hard calcareous skeletons of many tribes of marine polyps.
1062
coral head. A massive mushroom or pillar shaped coral growth.
1063
coral reef. A REEF, often of large extent, composed chiefly of CORAL and its derivatives.
1064
co-range line. A line through points of equal TIDE RANGE.
1065
cordillera. A RANGE or system of MOUNTAINS.
1066
core. The central or innermost part of anything. See CENTROSPHERE. In OCEANOGRAPHY, a vertical, cylindrical
sample of the BOTTOM SEDIMENTS from which the nature and stratification of the BOTTOM may be determined.
Also called core sample or sediment core.
1067
core barrel. The tubular section of a core sampling device. Bottom sediment samples are collected either directly in the
core barrel or in a plastic liner placed inside it. Also called coring (or core) tube.
1068
core catcher. A mechanical device located at the bottom of a CORE BARREL to retain a BOTTOM SAMPLE.
1069
corer. A device for obtaining a CORE; a hollow tube that is driven into the ocean floor. Also called coring instrument
or coring device. See CORER: HYDROPLASTIC, CORER: PISTON, PIGGOT GUN and VACUUM LEAD.
1070
corer: hydroplastic. A deep sea coring device, developed at the U.S. Naval Oceanographic Office, to obtain 3 1/2-inch
diameter cores up to 12 FEET in length. The barrel is constructed of high-impact grade polyvinyl chloride plastic
without an inner liner. Also called polyvinyl corer.
1071
corer: piston. A CORER equipped with a piston inside the core tube that is connected to the lowering cable. When the
CORER penetrates the ocean bottom the stopped cable and piston, in effect, provides a suction which overcomes the
frictional forces acting between the SEDIMENT and the interior wall of the coring tube.
1072
corer: polyvinyl. See CORER: HYDROPLASTIC.
1073
core sample. See CORE.
1074
coring instrument (or device). See CORER.
1075
coring (or core) tube. See CORE BARREL.
1076
Coriolis force. Composite CENTRIFUGAL FORCE, due to the ROTATION of the EARTH, which acts on moving
particles, whose motion is considered relative to that of the EARTH.
1077
corona. PHOTOMETEOR formed by one or more sequences (seldom more than three) of coloured rings of relatively
small radius, centred on the SUN or MOON.
1078
corrected establishment. See LUNITIDAL INTERVAL.
52
1079
correction. A quantity which is applied to an OBSERVATION or function thereof, to diminish or eliminate the effects
of ERRORS and obtain an improved value of the OBSERVATION or function. It is also applied to reduce an
OBSERVATION to some arbitrary STANDARD. The correction corresponding to a given ERROR is of the same
magnitude but of opposite sign. See CHRONOMETER CORRECTION, DIP CORRECTION, INDEX CORRECTION,
INSTRUMENTAL CORRECTION, LEAD LINE CORRECTION, PARALLAX CORRECTION, PERSONAL
CORRECTION, POLARIS CORRECTION, REFRACTION CORRECTION, SEMIDIAMETER CORRECTION,
SEXTANT ALTITUDE CORRECTION, SKY WAVE CORRECTION, ORTHOMETRIC CORRECTION, TIDAL
DIFFERENCE.
1080
correction: atmospheric. The statistical removal of meteorological effects from mean sea level changes.
1081
correction: ionospheric. A correction for errors introduced by ionospheric refraction occuring when signals travel
through the ionosphere.
1082
correction: relativistic. A correction for errors introduced by relativistic effects of the clock rates of positioning
systems.
1083
correction: sky-wave. The correction to be applied to the signals received via the ionosphere to convert them to their
groundwave equivalent.
1084
correction(s): tape. See TAPE CORRECTION(S).
1085
correction of soundings. The CORRECTION of the observed DEPTHS for any departure from true DEPTH due to the
method of SOUNDING or to a fault in the measuring apparatus. See also REDUCTION OF SOUNDINGS.
1086
corrector magnet. See COMPENSATOR: MAGNETIC.
1087
correlate equation. See EQUATION: CORRELATE.
1088
correlation. The removal of discrepancies that may exist among survey data, so that all parts are interrelated without
apparent error.
1089
correspondence. In STEREOSCOPY, the condition that exists when corresponding IMAGES on a pair of
PHOTOGRAPHS lie in the same EPIPOLAR PLANE; the absence of Y-PARALLAX.
1090
cosmic dust. Very fine particles of solid matter in any part of the universe, including METEORIC DUST and zodiacal
light particles in the SOLAR SYSTEM, interstellar matter of uncertain origin in the Milky Way Galaxy, and
accumulation of dark matter in other galaxies.
1091
cosmic radiation. RADIATION, of very high energy and great penetrative power, which emanates from cosmic
regions.
1092
cotidal chart. See CHART.
1093
cotidal line. A line on a CHART passing through all points where HIGH WATER occurs at the same TIME.
1094
coulomb. The unit of electric charge in the SI SYSTEM.
1095
counter. An indicator on a machine, for keeping count of turns, strokes, etc., of the machine or its parts.
1096
counter current. A secondary CURRENT setting in a direction opposite to that of a main CURRENT.
1097
course. The intended horizontal direction of travel. It is measured from 0°at the REFERENCE DIRECTION clockwise
through 360°; strictly for MARINE NAVIGATION, the term applies to the direction to be steered, which sometimes
differs from the direction intended to be made good over the GROUND (see DRIFT ANGLE). The course is designated
as true, magnetic, compass, or grid as the REFERENCE DIRECTION is TRUE, MAGNETIC, COMPASS or GRID
NORTH respectively. See COURSE MADE GOOD and TRACK.
The channel in which water flows. See also WATERCOURSE.
1098
course: compass. See COURSE.
1099
course: great circle. The direction of the GREAT CIRCLE through the point of departure and the destination,
expressed as the ANGULAR DISTANCE from a REFERENCE DIRECTION, usually north, to the direction of the
GREAT CIRCLE. The angle varies from point to point along the GREAT CIRCLE. At the point of departure it is called
Initial Great-Circle Course; at the destination it is called Final Great-Circle Course.
53
1100
course: grid. See COURSE.
1101
course: magnetic. See COURSE.
1102
course: recommended. See TRACK: RECOMMENDED.
1103
course: true. See COURSE.
1104
course line. A LINE OF POSITION approximately parallel to the COURSE.
1105
course made good. The actual TRACK MADE GOOD over the ground (seabed); the direction of the point of arrival
from the point of departure. Course made good is the direction component of the resultant ship's velocity and the water
current. Course made good should not be confused with HEADING, or ship's head.
1106
course over ground. The direction of the path over the ground actually followed by a vessel. It is normally a somewhat
irregular line. This is a misnomer in that courses are directions steered or intended to be steered through the water with
respect to a reference meridian. Also called track over ground.
1107
course recorder. A device which makes an automatic record of the HEADINGS of a vessel. See DEAD RECKONING
TRACER.
1108
cove. A small BAY.
1109
coverage. The actual area covered (by CHARTS, PHOTOGRAPHS, etc.).
The area controlled by a radiolocation system.
1110
covariance. The arithmetic mean or expected value of the product of the deviations of corresponding values of two
variables from their respective mean values.
1111
covers and uncovers (or discovers). Expression intended to indicate an area of a REEF or other projection from the
BOTTOM of a body of water which periodically extends above and is submerged below the surface. Also referred to as
dries or uncovers.
1112
crab. The condition caused by failure to orient a CAMERA with respect to the TRACK of the airplane. In vertical
PHOTOGRAPHY, crab is indicated by the edges of the PHOTOGRAPHS not being parallel to the airbase lines.
1113
crack. Any fracture or RIFT in SEA ICE not sufficiently wide to be described as a LEAD.
1114
crag. A steep or precipitous rugged ROCK.
1115
crater. Bowl-shaped cavity, at the SUMMIT or on the side of a volcano.
1116
creek. A comparatively narrow INLET, of fresh or salt water, which is tidal throughout its whole course. A small
TRIBUTARY.
A small, narrow BAY which extends farther inland than a COVE.
1117
crescent (adj.). See PHASES OF THE MOON.
1118
crest. The highest part of a WAVE, SWELL, RIDGE, etc.
1119
crib. A permanent marine structure usually designed to support or elevate pipelines; especially a structure enclosing a
screening device at the offshore end of a potable water intake pipe. The structure is commonly a heavy timber enclosure
that has been sunken with rocks or other debris.
1120
critical sounding. The least depth in proximity to a known or potential navigational route.
1121
cross bearings. Two or more BEARINGS used as intersecting LINES OF POSITION for fixing the POSITION of a
craft.
1122
cross hairs. See CROSS WIRES.
1123
crossing angle. See ANGLE.
1124
crosslines. Sounding lines that cross the main system of lines at either right angles or at an oblique angle to serve as a
check on the accuracy of the work.
54
1125
cross lines of sounding. SOUNDING LINES run approximately at right angles to those of normal direction, frequently
useful when examining SHOALS. Cross lines are also run after completing the main system of SOUNDING LINES,
with the purpose of checking them.
1126
cross sea. A series of WAVES or SWELL crossing another wave system at an angle.
1127
cross section lines of soundings. SOUNDING LINES run in a SURVEY perpendicular to the FLOW of a STREAM
and from BANK to BANK in a RIVER.
1128
cross wind. WIND which blows in a direction perpendicular to that of the motion of a moving object, relative to the
EARTH's surface.
1129
cross wires (or hairs). Wires or etched lines, at right angles, held at the FOCAL PLANE of an astronomical or sighting
TELESCOPE. See also RETICLE.
1130
cruise line of sounding. See TRACK LINE OF SOUNDING.
1131
cruising radius (or range). The distance a craft can travel at a given SPEED without refueling.
1132
crust. In GEOLOGY, the outer LAYER of the solid EARTH; the LITHOSPHERE. Also called earth's crust.
1133
crystal clock. See CLOCK.
1134
ctd probe. Instrument for measuring electrical CONDUCTIVITY, TEMPERATURE and DEPTH of the SEA
WATER. See PROBE.
1135
culmination. The position of a HEAVENLY BODY when at highest APPARENT ALTITUDE. Also, for a
HEAVENLY BODY which is continually above the HORIZON, the position of lowest APPARENT ALTITUDE.
Culmination occurs when the body transits the LOCAL MERIDIAN. See MERIDIAN TRANSIT.
1136
culture. All features constructed on the surface of the EARTH by man, such as cities, railways, CANALS, etc.
1137
cumulonimbus. See CLOUD GENERA.
1138
cumulus. See CLOUD GENERA.
1139
cupola. A small dome-shaped tower or turret rising from a building.
1140
current. Water or other fluid in essentially horizontal motion.
In British terminology, a non-periodical movement of water, generally horizontally, due to many causes such as
different temperatures and prevalent WINDS. Some may be temporary, others permanent.
1141
current: backrush. A GRADIENT CURRENT caused by the rise of water level near shores and in SEA REACHES.
1142
current: coastal. A relatively uniform DRIFT usually flowing parallel to the SHORE in the deeper water adjacent to
the SURF ZONE.
1143
current: density. A GRADIENT CURRENT caused by the horizontal gradient of water density.
1144
current: diurnal. The type of TIDAL CURRENT having only one FLOOD and one EBB period in a TIDAL DAY.
1145
current: drift. A wide, slow-moving OCEAN CURRENT principally caused by WINDS.
1146
current: drift angle. The angle between the true heading and the track of a vessel caused by the action of current.
1147
current: earth. See CURRENT(S): TELLURIC.
1148
current: ebb. See EBB STREAM.
1149
current: flood. See FLOOD STREAM.
1150
current: geostrophic. A current existing when the horizontal pressure gradient and the Coriolis force are in balance.
1151
current: gradient. A current due to the horizontal component of the hydrostatic pressure gradient.
55
1152
current: mixed. The type of TIDAL CURRENT characterized by a conspicuous difference in SPEED and duration
between the two FLOOD CURRENTS or two EBB CURRENTS occurring each TIDAL DAY.
1153
current: nontidal. Any CURRENT that is caused by other than TIDE PRODUCING FORCES. See also STREAM.
1154
current: ocean/sea. A movement of ocean water characterized by regularity, either of a cyclic nature or as a continuous
STREAM flowing along a definable PATH.
1155
current: periodic. An oscillating CURRENT the values of which recur at somewhat regular intervals.
1156
current: permanent. A CURRENT which continues with relatively little periodic or seasonal change.
1157
current: rectilinear. See CURRENT: REVERSING.
1158
current: residual. The mean CURRENT without periodic components.
1159
current: reversing. A TIDAL CURRENT which flows alternately in approximately opposite directions, with SLACK
WATER at each reversal. Such CURRENTS occur principally in areas where motion is largely restricted to relatively
narrow CHANNELS. Also called rectilinear current or rectilinear stream.
1160
current: rip. The return flow of water piled up on SHORE by incoming WAVES and WIND.
1161
current: rotary. A TIDAL CURRENT that flows continually, with the direction of FLOW changing through 360°
during a TIDAL CYCLE. Called rotary stream in British terminology.
1162
current: seasonal. A CURRENT which has large changes in SPEED or direction due to seasonal WINDS.
1163
current: semidiurnal. The type of TIDAL CURRENT having two flood and two ebb periods of nearly the same
duration during a TIDAL DAY.
1164
current: stream. A narrow, deep, and fast-moving CURRENT as opposed to a relatively wide and weak DRIFT
CURRENT.
1165
current: subsurface. A CURRENT usually flowing below the THERMOCLINE generally at slower SPEEDS and
frequently in a different direction from the CURRENTS near the surface.
1166
current: surface. A CURRENT that does not extend more than a few (2-3) METRES below the surface.
1167
current: surge. The coastal CURRENT influenced by remote waves.
1168
current(s): telluric. Natural electric currents that flow on or near the EARTH's surface in large sheets. Also called
earth current.
1169
current: tidal. The alternating horizontal movement of water associated with the RISE and fall of the TIDE caused by
TIDE-PRODUCING FORCES. Also called tidal stream.
1170
current: turbidity. A highly turbid, relatively dense CURRENT carrying large quantities of CLAY, SILT and SAND
in suspension which flows down a submarine SLOPE through less dense SEA WATER.
1171
current: wind driven. A CURRENT formed by the force of the WIND.
1172
current chart. See CHART.
1173
current cycle. A complete set of tidal current conditions, as those occurring during a tidal day, lunar month, or Metonic
cycle.
1174
current difference. The difference between the TIME of SLACK WATER or STRENGTH OF CURRENT at a
SUBORDINATE STATION and at its REFERENCE STATION.
1175
current direction. See DIRECTION OF CURRENT.
1176
current line. See CURRENT POLE.
56
1177
current meter. An instrument for the measurement of either SPEED alone or of both direction and SPEED of a
CURRENT. See CURRENT POLE, EKMAN CURRENT METER, PRICE-GURLEY CURRENT METER,
ROBERTS RADIO CURRENT METER, SWALLOW FLOAT, SAVONIUS ROTOR CURRENT METER,
WOLLASTON CURRENT METER.
1178
current pole. A pole used to determine the direction and SPEED of a SURFACE CURRENT. The direction is
determined by the direction of motion of the pole, and the SPEED by the amount of an attached graduated line (called
current line or log line) paid out in a specified TIME.
1179
current station. The geographic location at which current observations are conducted. Also, the facilities used to make
current observations. These may include a buoy, ground tackle, current meters, recording mechanism, and radio
transmitter. See CONTROL current STATION and SUBORDINATE current STATION.
1180
current tables. TABLES listing predictions of the TIMES and SPEEDS of TIDAL CURRENTS at various places, and
other pertinent information. Also called tidal current tables.
1181
cursor. A device used with an instrument, to provide a movable reference, as the runner of a SLIDE RULE, or the
rotatable bearing indicator on a radar scope.
In computer systems, a highlighted point on the DISPLAY which indicates the actual working position. For graphical
editing special cursors (e.g. crosses, cross-hairs) can be selected. On output the cursor is moved automatically by the
computer; on input it is under user control by means of a manual controlling device.
A cursor may also be a manually positionable device, sometimes magnifying lens and a reticula to be used in connection
with a DIGITIZER.
1182
curvature correction. In ASTRONOMY, a CORRECTION applied to the mean of a series of OBSERVATIONS on a
STAR or PLANET to take account of the divergence of the apparent PATH of the STAR or PLANET from a straight
line.
In GEODESY, the CORRECTION applied in some geodetic work to take account of the divergence of the surface of
the EARTH (SPHEROID) from a plane.
1183
curve: depth. See DEPTH CURVE.
1184
customhouse. The office, especially in harbours, at which customs are collected.
1185
Cust protractor. See PROTRACTOR.
1186
cut: angle of. See ANGLE: CROSSING.
1187
cutter. A boat belonging to a warship.
1188
cycle. One complete series of events or PHENOMENA that recur regularly in the same sequence. See also
FREQUENCY, HERTZ, PERIOD.
1189
cycle per second. A unit of FREQUENCY more and more superseded by the HERTZ.
1190
cycloidal wave. See WAVE.
1191
cyclone. See DEPRESSION.
1192
cylindrical buoy. See CAN BUOY.
1193
cylindrical projection. See PROJECTION.
57
D
1194
daily rate. See CHRONOMETER RATE.
1195
daily retardation. The amount of time by which corresponding tidal PHASES grow later day by day (averages
approximately 50 MINUTES).
1196
dam. A barrier to check or confine anything in motion; particularly one constructed to hold back water and raise its
level to form a RESERVOIR, or to prevent flooding.
1197
damped wave(s). See WAVE.
1198
damping. The dissipation of energy with TIME or distance.
The progressive reduction of AMPLITUDE of OSCILLATIONS, WAVES, etc.
1199
dan buoy. A BUOY consisting of a ballasted FLOAT carrying a staff which supports a flag or LIGHT.
1200
danger angle. The maximum (or minimum) angle between two points, as observed from a craft, indicating the limit of
safe approach to an offlying danger.
1201
danger area. An area designated by a proper authority, in which a danger to craft exists. Also called danger zone.
1202
danger bearing. See BEARING.
1203
danger buoy. See ISOLATED DANGER MARK.
1204
danger line. A line drawn on a CHART, to indicate the limits of safe NAVIGATION for a vessel of specific DRAFT.
A dotted line on a CHART to emphasize the presence of an OBSTRUCTION.
1205
dangerous rock. A SUNKEN ROCK of a small area (PINNACLE), at such a DEPTH as to be considered dangerous to
SURFACE NAVIGATION.
1206
dangerous semicircle. Region of a TROPICAL CYCLONE, situated to the right of its PATH in the northern
hemisphere and to the left of its PATH in the southern hemisphere, in which the SEAS are higher and the WINDS more
violent and tend also to carry shipping forward on to the CYCLONE's PATH. The other half of the CYCLONE is
termed the navigable semicircle.
1207
dangerous wreck. A WRECK submerged at such a DEPTH as to be considered dangerous to SURFACE
NAVIGATION.
1208
danger sounding. See SOUNDING.
1209
danger to navigation. Any feature or condition that might hinder, obstruct, endanger or otherwise constitute danger to
safe navigation.
1210
danger zone. See DANGER AREA.
1211
dark slide. See SLIDE: DARK.
1212
data. A representation of facts, concepts or instructions in a formalised manner suitable for communication,
interpretation or processing.
1213
data bank. A collection of DATA in a common location, relating to a given set of subjects. Usually comprised of
several DATA BASES considered as an entity.
1214
data base. An organised collection of DATA stored so as to be capable of use by relevant applications with the DATA
being accessed by different logical paths. It should be application independent.
1215
data base management system. A set of software for creating, maintaining and accessing the DATA of a DATA
BASE.
1216
data processing. Any operation carried out with data usually with the help of a computer.
58
1217
data retrieval. The extraction of data which meet certain criteria from a FILE or DATA BANK.
1218
data set. A logical entity of data consisting of several elements (fields) grouped under one criterion.
1219
data telemetry. Measuring a quantity, and transmitting the measured value to a distant station where further processing
takes place.
1220
date line. The line coinciding approximately with the 180th MERIDIAN, at which each calendar day first begins, the
BOUNDARY between the -12 and +12 TIME ZONES. The date on each side of this line differs by one DAY, but the
TIME is the same in these two ZONES. Sometimes called calendar line or international date line.
1221
datum. Any numerical or geometrical quantity or set of such quantities which may serve as a reference or base for other
quantities. In geodesy a datum is defined by a set of parameters specifying the reference surface or the reference
coordinate system. Therefore two types of datums are required: a horizontal datum which forms the basis for
computations of horizontal control surveys in which the curvature of the earth is considered, and a vertical datum to
which elevations are referred.
1222
datum: chart. A permanently established surface from which SOUNDINGS or tide heights are referenced, usually
LOW WATER. Also called DATUM, datum level, DATUM PLANE, hydrographic datum, reference level, reference
plane. See DATUM: TIDAL.
1223
datum: geodetic. A set of parameters specifying the reference surface or the reference coordinate system used for
geodetic control in the calculation of coordinates of points on the earth. Commonly datums are defined as horizontal and
vertical datums separately.
For a local geodetic datum the reference surface is defined by five parameters: the LATITUDE and LONGITUDE
of an INITIAL POINT, the AZIMUTH of a line from this point, and the parameters of the REFERENCE SPHEROID.
Absolute datums specify the INITIAL POINT of the REFERENCE ELLIPSOID to be (ideally) located at the earth's
centre of mass. For modern reference systems using datum information given by satellites additional parameters are
defined, e.g. gravity models.
See also HORIZONTAL CONTROL DATUM.
1224
datum: levelling. See DATUM: VERTICAL CONTROL.
1225
datum: sounding. The horizontal plane or TIDAL DATUM to which the SOUNDINGS on a HYDROGRAPHIC
SURVEY are reduced. Also called datum for sounding reduction.
1226
datum: tidal. A LEVEL of the SEA defined by some PHASE of the TIDE, from which water depths and HEIGHTS OF
TIDE are reckoned.
1227
datum: vertical control. Any LEVEL SURFACE (e.g., MEAN SEA LEVEL) taken as a surface of reference from
which to reckon ELEVATIONS. Also called datum level, reference level, reference plane, levelling datum, datum for
heights. See also DATUM PLANE.
1228
datum for heights. See DATUM: VERTICAL CONTROL.
1229
datum for sounding. See DATUM: SOUNDING.
1230
datum for sounding reduction. See DATUM: SOUNDING.
1231
datum level. See DATUM: VERTICAL CONTROL and DATUM: CHART.
1232
datum line. See REFERENCE LINE.
1233
datum of tide predictions. The LEVEL from which the HEIGHTS OF TIDE are referenced in the TIDE TABLES. See
also DATUM: CHART.
1234
datum plane. A VERTICAL CONTROL DATUM. Although a LEVEL SURFACE is not a plane, the VERTICAL
CONTROL DATUM is frequently referred to as the datum plane.
1235
datum point. See REFERENCE POINT.
59
1236
day. The duration of one ROTATION of the EARTH, or occasionally another CELESTIAL BODY, on its AXIS. It is
measured by successive TRANSITS of a reference point on the CELESTIAL SPHERE over the MERIDIAN, and each
type takes its name from the reference used.
The period of daylight, as distinguished from night.
1237
day: apparent solar. See DAY: SOLAR.
1238
day: astronomical. A MEAN SOLAR DAY beginning at NOON.
1239
day: civil. A MEAN SOLAR DAY beginning at MIDNIGHT.
1240
day: constituent. The duration of one ROTATION of the EARTH on its AXIS, with respect to a fictitious STAR
representing one of the periodic elements in the tidal forces. It approximates the length of a LUNAR or SOLAR DAY.
The expression is not applicable to a long-period constituent.
1241
day: lunar. The duration of one ROTATION of the EARTH on its AXIS, with respect to the MOON. Its average length
h
m
is about 24 50 of MEAN SOLAR TIME. Also called TIDAL DAY.
The duration of one ROTATION of the MOON on its AXIS, with respect to the SUN.
1242
day: mean solar. See DAY: SOLAR.
1243
day: sidereal. The duration of one ROTATION of the EARTH on its AXIS, with respect to the VERNAL EQUINOX
over the UPPER BRANCH of a MERIDIAN. Because of the PRECESSION OF THE EQUINOXES, the sidereal day
thus defined is slightly less than the PERIOD of ROTATION with respect to the STARS, but the difference is less than
h
m
s
0.01 SECOND. The length of the sidereal day is 24 HOURS of SIDEREAL TIME or 23 56 04.091 of MEAN
SOLAR TIME.
1244
day: solar. The duration of one ROTATION of the EARTH on its AXIS, with respect to the SUN. This may be either a
mean solar day, or an apparent solar day, as the reference is the MEAN or APPARENT SUN, respectively.
The duration of one apparent ROTATION of the SUN.
1245
day: tidal. See DAY: LUNAR and TIDAL DAY.
1246
daybeacon. An unlighted BEACON. A daybeacon is identified by its colour, shape, and number of its daymark. The
simplest form of daybeacon consists of a single pile with a daymark affixed at or near its top.
1247
daylight saving time. See TIME.
1248
daymark. 1. The identifying characteristics of an aid to navigation which serve to facilitate its recognition against a
daylight viewing background. On those structures that do not by themselves present an adequate viewing area to be seen
at the required distance, the aid is made more visible by affixing a daymark to the structure. A daymark so affixed has a
distinctive colour and shape depending upon the purpose of the aid.
2. An unlighted navigational mark.
1249
day number. The sequentially numbered day of the year, usually starting with day number 1 on 1st January.
1250
dead ahead. Bearing 000°relative. If the bearing is approximate, the term ahead should be used.
1251
dead astern. Bearing 180°relative. If the bearing is approximate, the term astern should be used. Also called right
astern.
1252
deadbeat (adj.). Aperiodic, or without a PERIOD.
1253
deadbeat compass. See COMPASS.
1254
deadhead. 1. A block of wood used as anchor buoy.
2. A BOLLARD.
1255
dead reckoning. A method of NAVIGATION utilizing only the SPEED and HEADING of the craft, without reference
to external aids.
In AIR NAVIGATION, the best estimate of COURSE and SPEED over the GROUND is used, i.e., dead reckoning
incorporates wind vector.
1256
dead reckoning position. See POSITION.
60
1257
dead reckoning tracer. A device that automatically provides a graphical record of the DEAD RECKONING TRACK.
See COURSE RECORDER.
1258
dead reckoning track. See TRACK.
1259
dead water. The PHENOMENON which occurs when a ship of low propulsive power negotiates water which has a
thin LAYER of fresher water over a deeper LAYER of more saline water. As the ship moves, part of its energy goes
into generation of an INTERNAL WAVE which causes a noticeable drop in efficiency of propulsion.
1260
debris. See DETRITUS.
1261
deceleration. Negative ACCELERATION.
1262
decibar. One-tenth of a BAR.
1263
decibel. See BEL.
1264
decimetre. One-tenth of a METRE.
1265
declination. In ASTRONOMY, the angle at the centre of the CELESTIAL SPHERE between the radius passing
through a CELESTIAL BODY and the plane of the CELESTIAL EQUATOR. Declination is measured by the arc of the
HOUR CIRCLE between the CELESTIAL BODY and the CELESTIAL EQUATOR. It is plus when the body is north
of the EQUATOR, and minus when south of it.
1266
declination: grid. See GRID.
1267
declination: magnetic. See VARIATION.
1268
declinational inequality. See DIURNAL INEQUALITY.
1269
declination circle. See HOUR CIRCLE.
1270
declinatoire. A combined MAGNETIC COMPASS and STRAIGHT EDGE, suitable for use on a PLANE TABLE to
mark the MAGNETIC MERIDIAN. Also known as a box compass or trough compass. See also COMPASS:
TUBULAR.
1271
declinometer. A magnetic instrument similar to a SURVEYOR'S COMPASS, but arranged so that the LINE OF
SIGHT can be rotated to conform with the NEEDLE or to any desired setting on the HORIZONTAL CIRCLE. Used in
determining the magnetic declination. See VARIATION.
1272
declivity. A downward SLOPE or sloping of a HILL; as opposed to ACCLIVITY.
1273
deep. In OCEANOGRAPHY, an obsolete term which was generally restricted to DEPTHS greater than 6,000 m.
An unmarked fathom point on a LEAD LINE.
1274
deep-draught route. A route which is primarily selected for use by ships which, because of their deep DRAUGHT,
may not be able to navigate safely outside such route.
1275
deep ocean floor. The surface lying at the bottom of the deep ocean.
1276
deep scattering layer (DSL). See PHANTOM BOTTOM.
1277
deep-sea camera. See CAMERA.
1278
deep-sea lead. See LEAD.
1279
deep-sea thermometer. See THERMOMETER.
1280
deep water route. A route in a designated area within defined limits which has been accurately surveyed for clearance
of sea bottom and submerged obstacles to a minimum indicated depth of water.
1281
defile. A narrow PASS or GORGE between MOUNTAINS.
1282
definition. In PHOTOGRAPHY, and electronic equipment, the degree of clarity and sharpness of an IMAGE. See
RESOLUTION and RESOLVING POWER.
61
1283
deflection of the plumb line. See DEFLECTION OF THE VERTICAL.
1284
deflection of the vertical. The angle at a point on the EARTH (GEOID) between the VERTICAL (direction of the
PLUMB LINE) and the direction of the NORMAL to the SPHEROID OF REFERENCE through the point. Also called
deflection of the plumb line, deviation of the vertical, or station error.
1285
deflector. An instrument for measuring the directive force acting on a MAGNETIC COMPASS on different
HEADINGS, for use in COMPASS ADJUSTMENT.
1286
degaussing. Neutralization of the strength of the MAGNETIC FIELD of a vessel, by means of suitably arranged
electric coils permanently installed in the vessel. See also CABLE: DEGAUSSING.
1287
degaussing cable. See CABLE.
1288
degree. A unit of angular or circular-arc measurement, equal to 1/360 of a circle.
A unit of measurement of temperature in any SCALE.
1289
Delambre's spheroid. See REFERENCE SPHEROID.
1290
delimitation. The process of establishing the LINE(S) OF DELIMITATION in the context of the United Nations' Law
of the Sea Convention.
1291
delineation. In CARTOGRAPHY, the visual selection and distinguishing of mapworthy features on various possible
source materials by outlining the features on the source material, or on a map manuscript (as when operating a
STEREOSCOPIC PLOTTING INSTRUMENT); also a preliminary step in COMPILATION.
1292
delta. An area of alluvial DEPOSIT, usually triangular in outline, near the MOUTH of a RIVER.
1293
demagnetize (v.t.). To remove MAGNETISM. The opposite is MAGNETIZE.
1294
densitometer. An electric instrument designed to accurately measure optical DENSITY or tone values and used in
place of the human eye for such purposes.
1295
density. In PHOTOGRAPHY, a measure of the degree of blackening of an exposed film, PLATE or paper after
development, or the direct IMAGE (in the case of a print-out material). It is defined strictly as the logarithm of the
optical OPACITY.
In OCEANOGRAPHY, density is equivalent to SPECIFIC GRAVITY and represents the ratio, at ATMOSPHERIC
PRESSURE, of the WEIGHT of a given volume of SEA WATER to that of an equal volume of distilled water at 4.0°C.
1296
density layer. A LAYER of water in which DENSITY increases with DEPTH enough to increase the BUOYANCY of
a submarine.
1297
density of soundings. Intervals between LINES OF SOUNDING and SOUNDINGS in the same line. Density of
soundings mostly depends on the SCALE and nature of the SURVEY. Also called frequency of soundings.
1298
departure. The distance between two MERIDIANS at any given PARALLEL OF LATITUDE expressed in linear
units, usually NAUTICAL MILES. The distance to the east or west made good by a vessel in proceeding from one point
to another.
1299
departure: point of. The point from which the initial COURSE to reach the point of destination begins.
1300
deposit. Accumulations of solid material (of any type or from any source) on the sea bottom which eventually may
become compacted and consolidated and form sedimentary ROCK.
1301
depressed pole. See POLE.
1302
depressor. A device to maintain a towfish at a given depth.
1303
depression. Any HOLLOW or relatively sunken area.
In METEOROLOGY, a region of the ATMOSPHERE in which the pressure is low relative to the surrounding
region at the same level. It is represented on a WEATHER CHART by a system of ISOBARS at a specified level or of
CONTOURS at a specified pressure which enclose relatively low values of pressure or level. Also called low or
cyclone.
62
1304
depression: angle of. See ANGLE OF DEPRESSION.
1305
depression contour. See CONTOUR.
1306
depression of the horizon. See DIP.
1307
depth. The vertical distance from a given water level to the BOTTOM.
1308
depth: charted. The vertical distance from the CHART DATUM to the BOTTOM.
1309
depth: compensation. The DEPTH at which the light intensity is just sufficient to bring about a balance between the
oxygen produced by ALGAE through PHOTOSYNTHESIS and that consumed by them through respiration.
1310
depth: controlling. The least DEPTH in the approach or CHANNEL to an area, such as a PORT or ANCHORAGE,
governing the maximum DRAFT of vessels that can enter.
1311
depth: standard. A DEPTH below the sea surface at which water properties should be measured and reported,
according to the proposal by the International Association of Physical Oceanography in 1936.
1312
depth: thermometric. The DEPTH, in METRES, at which paired protected and unprotected THERMOMETERS
attached to a NANSEN BOTTLE are reversed. The difference between the corrected readings of the 2
THERMOMETERS represents the effect of the HYDROSTATIC PRESSURE at the DEPTH of reversal. This DEPTH
may then be determined by formula or from a DEPTH ANOMALY GRAPH. DEPTHS obtained by this means are of
greatest value when a WIRE ANGLE occurs.
1313
depth anomaly graph. A graph constructed to determine the difference between the computed or THERMOMETRIC
DEPTH and the ideal or assumed DEPTH of reversal of THERMOMETERS attached to a NANSEN BOTTLE.
1314
depth contour. See DEPTH CURVE.
1315
depth curve. A depth curve is a line connecting points of equal water depth which is sometimes significantly displaced
outside of soundings, symbols, and other chart detail for clarity as well as generalization. Depth curves therefore often
represent an approximate location of the line of equal depth as related to the surveyed line delineated on the source.
1316
depth differences. Those differences in DEPTH which may be encountered in HYDROGRAPHIC SURVEYS at
crossing of CROSS LINES and principal LINES OF SOUNDINGS.
1317
depth finder. An instrument for the measurement of the DEPTH of water, particularly an ECHO SOUNDER.
1318
depth gauge. See GAUGE.
1319
depth ice. See ANCHOR ICE.
1320
depth of the sea. The vertical distance from the water surface to the sea bottom.
1321
derelict. Any property abandoned at SEA, often of sufficient size as to constitute a menace to NAVIGATION;
especially an abandoned vessel. See WRECK.
1322
derrick. A tall pyramid of latticed steel mounted over a borehole.
1323
descending node. See NODE.
1324
detached position. See POSITION.
1325
detached sounding. See SOUNDING.
1326
detail(s). In CARTOGRAPHY, the items or particulars of information (shown on a MAP by lines, SYMBOLS, and
lettering) which, when considered as a whole, furnish the comprehensive representation of the physical and cultural
features of the EARTH's surface.
1327
detection threshold. The lowest or highest level of a parameter above or below which sensing equipment can detect the
parameter.
63
1328
detritus. In GEOLOGY, material removed by disintegration and other processes from the surface of ROCKS. There is a
general tendence to use debris.
In MARINE BIOLOGY, suspended matter of organic origin permanently incapable of reproduction organic detritus
may often 'collect' a considerable amount of inorganic material.
1329
deviation. See DEVIATION: MAGNETIC.
1330
deviation: constant. DEVIATION which is the same on any HEADING, which may result from certain arrangements
of asymmetrical horizontal SOFT IRON.
1331
deviation: magnetic. The angle between the COMPASS NEEDLE and the MAGNETIC MERIDIAN, expressed in
degrees east or west of MAGNETIC MERIDIAN. Also called deviation.
1332
deviation: quadrantal. DEVIATION which changes its sign (E or W) approximately each 90°change of HEADING.
It is caused by INDUCED MAGNETISM in horizontal SOFT IRON.
1333
deviation: residual. DEVIATION of a MAGNETIC COMPASS after COMPENSATION.
1334
deviation: semicircular. DEVIATION which changes sign (E or W) approximately each 180°change of HEADING.
1335
deviation: standard. See ERROR: STANDARD.
1336
deviation of the vertical. See DEFLECTION OF THE VERTICAL.
1337
deviation table. A TABLE of the DEVIATION of a MAGNETIC COMPASS on various HEADINGS, magnetic or
compass.
1338
dew. Deposit of water drops on objects at or near the GROUND, produced by the condensation of water vapour from
the surrounding clear air.
1339
dew-point. The temperature to which air must be cooled at constant pressure and constant water vapour content to reach
saturation.
1340
diagenesis. The chemical and physical changes that SEDIMENTS undergo after their deposition, by LITHIFICATION.
1341
diagram. A graphic representation of certain DATA.
1342
dial. The face of a WATCH or CLOCK. The clockwise face of an instrument for indicating, as by a moving pointer, the
amount of something; face of a COMPASS, GAUGE or METER.
A SUNDIAL.
1343
diaphone. A device operated by compressed air for producing a distinctive FOG SIGNAL.
1344
diaphragm. In a TELESCOPE, a thin glass disk on which etched lines forming a RETICLE are placed. See also
RETICLE, and APERTURE STOP.
1345
diapositive. A positive PHOTOGRAPH on a transparent medium. One which has a right reading image when viewed
through the base support.
1346
difference: tidal. See TIDAL DIFFERENCE.
1347
difference of latitude. The ANGULAR DISTANCE between the PARALLELS of two places measured on a
MERIDIAN.
1348
difference of longitude. The angle at the POLE or intercepted arc of EQUATOR between the MERIDIANS of two
places.
1349
differential GPS. Differential GPS is implemented by placing a GPS monitor receiver at a precisely known location.
Instead of computing a navigation fix, the monitor determines the range error to every GPS satellite it can track. These
ranging errors are then transmitted to local users where they are applied as corrections before computing the navigation
result.
1350
differential levelling. See LEVELLING.
64
1351
differential mode. A method of accurate positioning; transmissions of an electromagnetic position fixing system are
received at known positions ashore and the offsets between absolute known positions and system positions are
transmitted to the ship in the vicinity. The offsets are applied to the measurements of the ship's receiver.
1352
differential shrinkage. In mapping, the difference in unit contraction along the grain structure of the material as
compared to the unit contraction across the grain structure; frequently refers to photographic film and papers and to map
materials in general.
1353
diffraction. The bending of the RAYS of RADIANT ENERGY around the edges of an obstacle, or when passing near
the edges of an opening, or through a small hole or slit, resulting in the formation of a SPECTRUM, or arrangement by
WAVE LENGTH of component WAVES, producing, for visible WAVE LENGTHS, the chromatic SPECTRUM.
The bending of a WAVE as it passes an obstruction.
1354
digital. A method of representing information by combinations of discrete and discontinuous data.
1355
digital chart. See ELECTRONIC CHART.
1356
digital computer. See COMPUTER.
1357
digital imagery processing system. A system which processes images which are stored in digital form.
1358
digital terrain model (DTM). A model representing the terrain surface by a collection of digital data, mainly
coordinates in three dimensions, x, y, and z, and a digitally defined method to interpolate arbitrary terrain heights in
between the stored values. Not to be confused with digital cartographic model which may also contain digital data
representing terrain, but in a form suitable for the drawing of a particular kind of map.
1359
digitization (or digitisation). The process of converting analog data to digital data.
1360
digitizer. A computer aided device equipped with a digitizing table and a CURSOR for digitally capturing graphical
data (pictures, charts), usually based on vector-techniques (as opposed to a SCANNER). The digitizing table consists of
a gridded electrical network under the table's surface which allows an automatic computation of the planar x/y
coordinates of a cursor's position. Lines are sequentially scanned by moving the cursor along the position and
identifying the appropriate symbol on a menu.
1361
dike (or dyke). An artificial ditch to hold, or control the FLOW of water.
An artificial EMBANKMENT to contain or hold back water.
In GEOLOGY, a tabular body of IGNEOUS ROCK molded from molten ROCK within a fissure.
1362
dilution of precision (DOP). A parameter relating the precision of the position (and/or an unknown auxiliary) provided
by a positioning system to that of the "observed quantities" directly measured by the system. DOP is a measure of the
influence of the geometry of loci on the precision of position fixing. DOP is frequently used with a qualifying term such
as geometric (GDOP), horizontal (HDOP), vertical (VDOP) etc. to indicate that DOP is related to all or some unknown
quantities.
1363
diopter. A unit of refractive power of an optical system in the SI system.
1364
dioptric light. See LIGHT.
1365
dip. The vertical angle, at the eye of an observer between the horizontal and the LINE OF SIGHT to the APPARENT
HORIZON. Also called dip of the horizon or depression of the horizon.
The angle between the horizontal and the LINES OF FORCES of the EARTH's MAGNETIC FIELD at any point.
Also called magnetic dip or magnetic inclination.
1366
dip circle. An instrument for measuring MAGNETIC DIP. It consists essentially of a DIP NEEDLE or MAGNETIC
NEEDLE, suspended in such manner as to be free to rotate about a horizontal AXIS. Also called INCLINOMETER, or
dipping compass. See also EARTH INDUCTOR.
1367
dip correction. That CORRECTION to SEXTANT ALTITUDE due to the DIP OF THE HORIZON. Also called
height of eye correction.
1368
dip (or dipping) needle. A MAGNETIC NEEDLE suspended in such a manner as to be free to rotate about a
horizontal AXIS. See DIP CIRCLE.
65
1369
dip of a sea horizon. The vertical angle, at the eye of an observer, between the horizontal and the line of sight to the sea
horizon.
1370
dip of the horizon. See DIP.
1371
dipping compass. See DIP CIRCLE.
1372
dipsey lead. See LEAD: DEEP SEA.
1373
direction. In SURVEYING and mapping, the angle between a line or plane and an arbitrarily chosen REFERENCE
LINE or PLANE.
1374
direction: base. In PHOTOGRAMMETRY, the DIRECTION of the vertical plane containing the AIR BASE which
might be expressed as a BEARING or an AZIMUTH.
1375
direction: grid. Horizontal DIRECTION expressed as ANGULAR DISTANCE from GRID NORTH.
1376
directional antenna. See ANTENNA.
1377
directional gyroscope. See GYROSCOPE.
1378
directional (or directed) radiobeacon station. A special type of radiobeacon station the emissions of which are
intended to provide a definite TRACK for GUIDANCE.
1379
direction finder. See RADIO DIRECTION FINDER.
1380
direction (or directional) light. See LIGHT.
1381
direction method of observation. A method of observing angular relationships wherein the graduated CIRCLE is held
in a fixed position, and the DIRECTIONS of the various SIGNALS are observed around the HORIZON. Thus,
DIRECTIONS are pointings whereby angles are found by the differences in DIRECTION.
1382
direction of current. The direction toward which a CURRENT is flowing, called the SET of the CURRENT. Also
called current direction.
1383
direction of gravity. See GRAVITY.
1384
direction of movement of the waves. Direction from which the WAVES arrive at a fixed point.
1385
direction of relative movement. See RELATIVE MOTION.
1386
direction of the force of gravity. See GRAVITY: DIRECTION OF.
1387
direction of tilt. The DIRECTION (AZIMUTH) of the PRINCIPAL PLANE of a PHOTOGRAPH. Also, the
DIRECTION of the PRINCIPAL LINE on a PHOTOGRAPH.
1388
direction of traffic flow: established. A traffic flow pattern indicating the directional movement of traffic as
established within a traffic separation scheme.
1389
direction of traffic flow: recommended. A traffic flow pattern indicating a recommended directional movement of
traffic where it is impractical or unnecessary to adopt an established direction of traffic flow.
1390
direction of wind. Direction from which the WIND blows. Also called wind direction.
1391
direction theodolite. See THEODOLITE.
1392
direct levelling. See LEVELLING.
1393
direct wave. See WAVE.
1394
disc (U.S. disk). Rotating storage medium composed of one or two usable surfaces or a vertical assembly of such discs
with a common axis. Typically discs combine high storage volumes and short access time allowing fast access to data
which is distributed randomly over the medium.
66
1395
discoloured water. Unnatural coloured areas in the SEA due to the existence of SHOALS.
SEA WATER having a colour other than the blues and greens normally seen. Variations of the colours red, yellow,
green and brown, as well as black and white, have been reported. Discolorations may appear in patches, streaks, or large
areas and may be caused by concentrations of inorganic or organic particles or PLANKTON. See RED TIDE.
1396
discontinuity layer. See THERMOCLINE.
1397
discrepancy. A difference between results of duplicate or comparable measures of a quantity. The difference in
computed values of a quantity obtained by different processes using DATA from the same SURVEY.
1398
discrepancy in position. The difference between a reckoned and an observed position at the same time.
1399
discriminator. A radar circuit that produces a RESPONSE which depends upon the FREQUENCY of the input signal.
A transponder beacon circuit which accepts PULSES of proper duration and rejects others.
That part of a frequency modulation receiver which converts the modulated SIGNALS directly into audiofrequency
signals.
1400
dish aerial. A parabolic aerial for the receipt and transmission of high frequency radio signals.
1401
dispersion. The separation of RADIANT ENERGY into its various components.
In optics, the separation of light into its component colours by its passage through a diffraction grating or by
REFRACTION such as that provided by a prism.
In OCEANOGRAPHY, the separation of a complex surface gravity wave disturbance into its component parts.
1402
displacement. In RADIOLOCATION, the half of the band of uncertainty having as its centre line an ELECTRONIC
LINE OF POSITION.
In PHOTOGRAMMETRY, any shift in the position of an IMAGE on a PHOTOGRAPH which does not alter the
perspective characteristics of the PHOTOGRAPH (i.e. shift due to TILT of the PHOTOGRAPH, scale change in the
PHOTOGRAPH, and RELIEF of the objects photographed).
1403
displacement drafts. See DRAFT.
1404
display. A visual presentation of data.
1405
distance finding station. A RADIOBEACON equipped with a synchronized SOUND SIGNAL to provide a means of
determining distances from the source of the SOUND, by measuring the difference in the time of reception of the
SIGNALS.
1406
distance measuring equipment (DME). See ELECTRONIC DISTANCE MEASURING EQUIPMENT.
1407
distance reduction. See REDUCTION TO SEA LEVEL.
1408
distortion. An undesired change in WAVEFORM.
In optics, an aberration affecting the position of the IMAGES off the AXIS, in which objects at different
ANGULAR DISTANCES from the AXIS undergo different MAGNIFICATIONS. Also called lens distortion.
In PHOTOGRAPHY, any shift in the position of an IMAGE on a PHOTOGRAPH which alters the perspective
characteristics of the PHOTOGRAPH. Causes of image distortion include lens aberration, DIFFERENTIAL
SHRINKAGE of film or paper, and motion of the film or CAMERA.
1409
distortion: angular. In CARTOGRAPHY, DISTORTION in a PROJECTION because of non-conformality. See
CONFORMALITY.
1410
distortion: lens. See DISTORTION.
1411
distortion: radial. A lens aberration that is corrected on the PHOTOGRAPH by displacing the IMAGE along a radial
line from the PRINCIPAL POINT.
1412
distortion of medium. Changes in the dimensions of SURVEYS or CHARTS due to expansion or contraction of the
paper on which the SURVEY or CHART is drawn or printed. See also DIFFERENTIAL SHRINKAGE.
1413
distributary. A river branch which flows away from the main STREAM without returning to it, as in a DELTA.
1414
diurnal aberration. See ABERRATION OF LIGHT.
67
1415
diurnal arc. See ARC: ASTRONOMICAL.
1416
diurnal current. See CURRENT.
1417
diurnal inequality. The difference between the HEIGHTS of the two HIGH TIDES (high water inequality) or the two
LOW TIDES (low water inequality) during a TIDAL DAY, or the difference in SPEED between the two FLOOD or the
two EBB CURRENTS during a TIDAL DAY. The average diurnal inequality is called tropic high water inequality and
tropic low water inequality when referred to the HIGH WATERS and LOW WATERS, respectively, of TROPIC
TIDES. Mean diurnal high water inequality is half the average difference between the HEIGHTS of the two HIGH
WATERS of each TIDAL DAY over a 19-year period. Mean diurnal low water inequality is half the average difference
between the HEIGHTS of the two LOW WATERS for a similar period. Also called declinational inequality.
1418
diurnal motion. The apparent daily motion of a celestial body.
1419
diurnal parallax. See PARALLAX.
1420
diurnal range. See RANGE.
1421
diurnal tide. See TIDE.
1422
diver. A person skilled in the practice of diving.
1423
divergence. In OCEANOGRAPHY, a horizontal FLOW of water, in different directions, from a common centre or
zone; often associated with UPWELLING.
1424
divider(s). Measuring COMPASSES having both legs pointed, used principally for measuring distances and
COORDINATES.
1425
dock. The space between two PIERS. Also called slip.
1426
dock: dry. An artificial BASIN fitted with a gate or CAISSON, into which vessels can be floated and the water pumped
out to expose the vessel's bottom. Also called graving dock.
1427
dock: floating. A form of DRY DOCK consisting of a floating structure of one or more sections which can be partly
submerged by controlled flooding to receive a vessel, then raised by pumping out the water so that the vessel's bottom
can be exposed.
1428
dock: graving. See DOCK: DRY.
1429
dock: wet. A DOCK in which water can be maintained at any level by closing a gate when the water is at the desired
level.
1430
dock sill. The foundation at the bottom of the entrance to a dry dock or lock against which the caisson or gates close.
The depth of water controlling the use of the dock or lock is measured from the sill to the surface.
1431
dog leg. A LEG which does not lead directly to the destination or way point.
1432
doldrums. Zone of calm or light variable WINDS, in the lower atmospheric LAYERS, situated near the THERMAL
EQUATOR; the zone follows, with slight time lag, the annual meridional fluctuation of the THERMAL EQUATOR.
1433
dolphin. A post or group of posts, used for mooring or warping a vessel, or as an AID TO NAVIGATION. The dolphin
may be in the water, on a WHARF or on the BEACH.
1434
dolphin beacon. A minor light structure consisting of a number of piles driven into the bottom in a geometric or random
pattern and drawn together, with a light mounted at the top.
1435
Doppler effect. The apparent change in WAVE LENGTH, and therefore in FREQUENCY of RADIANT ENERGY,
when the distance between the source and the observer or RECEIVER is changing. This effect is exploited in
underwater acoustics and satellite positioning.
1436
Doppler navigation. See NAVIGATION.
1437
double high water. See HIGH WATER.
68
1438
double low water. See LOW WATER.
1439
double meridian distance. See MERIDIAN DISTANCE.
1440
double tide. See TIDE.
1441
double zenith distance. See ZENITH DISTANCE.
1442
doubtful sounding. See SOUNDING.
1443
Dove prism. A prism which reverts the IMAGE but does not deviate nor displace the BEAM. A given angular
ROTATION of the prism about its longitudinal AXIS causes the IMAGE to rotate through twice the angle. Also called
a rotating prism.
1444
down. An area of high, treeless GROUND, usually undulating and covered with grass. See also DUNE.
1445
downstream (adj. and adv.). In the direction of FLOW of a CURRENT or STREAM. The opposite is UPSTREAM.
1446
downwind(adj. and adv.). In the direction toward which the WIND is blowing. The opposite is UPWIND.
1447
dracontic month. See MONTH: NODICAL.
1448
draft (or draught). The vertical distance, at any section of a vessel from the surface of the water to the bottom of the
keel. When measured at or near the bow, it is referred to as draft forward and when measured at or near the stern as
draft aft. The mean draft is the mean of the drafts forward and aft. These drafts are more specifically described as
displacement drafts as opposed to navigational drafts which are measured to the lowest appendage to the hull as
opposed to the keel.
1449
draft aft. See DRAFT.
1450
drafted original. A scribed or drafted CHART or portion of a CHART on stable base material, which may be
processed for final REPRODUCTION.
1451
draft forward. See DRAFT.
1452
drafting. The art of drawing from given specifications.
1453
draft marks. Numerals at the bow and stern of a vessel that indicate the depth to which the vessel is submerged.
1454
draftsman (or draughtsman). A person who makes drawings.
1455
drag (v.t.). To tow a line or object below the surface to determine the least DEPTH in an area or to ensure that a given
area is free from navigational dangers to a certain DEPTH. See also SWEEP.
To pull along the BOTTOM, as an anchor.
1456
drag (of theodolite). A slight movement of the graduated CIRCLE produced by the rotation of the ALIDADE.
1457
draught. See DRAFT.
1458
draughtsman. See DRAFTSMAN.
1459
drawing. The graphic representation of data on a non-volatile medium.
(U.S. terminology). An impression following the printing of a NAUTICAL CHART of either its black or its magenta
detail on matte finish transparent plastic, used in revising subsequent printings of the CHART.
1460
dredge. An apparatus for bringing up solid material from the bottom of a water area, gathering deep water organisms,
etc.
A DREDGER.
1461
dredge (v.t.). To remove solid matter from the BOTTOM of a water area.
1462
dredged area. An area of the BOTTOM of a body of water which has been deepened by dredging.
69
1463
dredger. A vessel or floating structure equipped with machinery for excavating ditches or CANALS, deepening
CHANNELS and HARBOURS, and removing solid matter from the BOTTOM of a water area. Also called a
DREDGE.
1464
dredging buoy. A BUOY marking the limit of an area where dredging is being performed.
1465
'dries'. See COVERS and UNCOVERS.
1466
drift. The SPEED of the water due to OCEAN or TIDAL CURRENTS.
A wide, slow-moving CURRENT principally caused by WINDS.
The distance a craft is moved by CURRENT and WIND.
DRIFT ANGLE or LEEWAY.
The term is also applied to any superficial deposit caused by a CURRENT of water or air.
1467
drift (v.i.). To move by action of WIND or CURRENT without control.
1468
drift angle. The difference between COURSE steered and COURSE MADE GOOD when due to action of CURRENT
and WIND.
The angle between the tangent to the turning circle and the centerline of the ship.
1469
drift bottle. An identifiable sealed bottle which is released into the SEA for use in studying CURRENTS.
1470
drift buoy. A DATA collection BUOY which is not moored to the sea bottom, but drifting freely in response to
currents, tides, and wind.
1471
drift current. See CURRENT.
1472
drift ice foot. See RAMP.
1473
drifting logship. A LOGSHIP employed for the measurement of TIDAL STREAMS and CURRENTS. It is allowed to
drift freely while its POSITIONS are fixed, during the PERIOD of OBSERVATION, by an accompanying boat, or from
STATIONS ashore.
1474
drift lead. See LEAD.
1475
drift sounding. See SOUNDING.
1476
drift station. A scientific station established on the ICE of the Arctic Ocean.
A term sometimes used in shoran operations to designate the ground station about which the aircraft flies. The
second station is then referred to as rate station.
1477
driver rod. A device employed together with a SINKER to obtain BOTTOM SAMPLES when WIRE SOUNDING. It
consists, essentially, of a galvanized iron tube the lower part of which contains a flap valve for retaining a bottom
specimen. The tube releases the SINKER when it strikes the BOTTOM. Also called driver tube.
1478
driver tube. See DRIVER ROD.
1479
drizzle. Fairly uniform PRECIPITATION composed exclusively of fine drops of water (diameter less than 0.5 mm),
very close to one another.
1480
drogue. A current measuring assembly consisting of a weighted parachute and an attached surface buoy. Also called
parachute drogue.
1481
drum. A rotating cylinder on which is set a registering card or paper for recording purposes.
Cylinder around which CABLE is wound in a winch.
1482
drum plotter. A plotter which uses a rotating drum or cylinder to move the drawing base in the direction of one
coordinate axis while the plotting head only moves along the other coordinate axis.
1483
dry bulb thermometer. See THERMOMETER.
1484
dry (or dry card) compass. See COMPASS.
1485
dry dock. See DOCK.
70
1486
drying heights. HEIGHTS above SOUNDING DATUM, of any areas (BANKS, FORESHORES, ROCKS, etc.) which
dry at LOW WATER.
1487
drying line. The line marking the transit from water to land; usually the low-water line.
1488
drying reef. A reef or part thereof which dries at low water.
1489
dry proof. An impression of a CHART pulled from the engraved PLATE onto a dry sheet of paper. This impression is
fainter than a damp-pulled copy and unsuitable for ordinary use but is free from DISTORTION.
1490
duck blinds. Nonfloating structures used for concealing waterfowl hunters. They usually consist of a wooden
framework covered with brush. They are essentially unreported to any charting authority when built. They are unlighted
and often constructed in navigable water without regard to the possible hazard they pose, especially to the small craft
operator. Many are substantial structures built on piles. Even after they are eventually reduced to ruins the pilings may
persist for years.
1491
duct. A LAYER in the OCEAN or ATMOSPHERE where REFRACTION and, probably, REFLECTION result in the
trapping and propagation within the LAYER of SOUND WAVES or ELECTROMAGNETIC WAVES.
1492
due publicity. Notification of a given action for general information through appropriate authorities within a reasonable
amount of time in a suitable manner. Used in the context of the United Nations' Law of the Sea Convention.
1493
dumb compass. See PELORUS.
1494
dumping ground. See SPOIL GROUND.
1495
dumpy level. See LEVELLING INSTRUMENT: DUMPY LEVEL.
1496
dune. A mound, RIDGE or HILL of drifted SAND on the sea coast or in a desert. See SAND DUNE and DOWN.
1497
duplex. A method in which TELECOMMUNICATION between two STATIONS can take place in both directions
simultaneously.
1498
duplexer. A switching device used to connect a TRANSMITTER and a RECEIVER to the same ANTENNA.
1499
duration of fall. See DURATION OF RISE AND FALL.
1500
duration of flood and duration of ebb. Duration of flood is the interval of time in which a tidal current is flooding, and
the duration of ebb is the interval in which it is ebbing; these intervals being reckoned from the middle of the intervening
slack waters or minimum currents. Together they cover, on an average, a period of 12.42 hours for a semidiurnal tidal
current or a period of 24.84 hours for a diurnal current. In a normal semidiurnal tidal current, the duration of flood and
duration of ebb will each be approximately equal to 6.21 hours, but the times may be modified greatly by the presence
of a non-tidal flow. In a river the duration of ebb is usually longer than the duration of flood because of the fresh water
discharge, especially during the spring months when snow and ice melt are the predominant influences.
1501
duration of rise and duration of fall. Duration of rise is the interval from low water to high water, and duration of fall
is the interval from high water to low water. Together they cover, on an average, a period of 12.42 hours for a
semidiurnal tide or a period of 24.84 hours for a diurnal tide. In a normal semidiurnal tide, the duration of rise and
duration of fall will each be approximately equal to 6.21 hours, but in shallow waters and in rivers there is a tendency
for a decrease in the duration of rise and a corresponding increase in the duration of fall.
1502
duration of tide. The time interval between LOW WATER and the following HIGH WATER or between HIGH
WATER and the following LOW WATER.
1503
dust. Any substance comminuted or pulverized, especially EARTH or other solid matter in a minute and fine state of
subdivision, so that the particles are small and light enough to be easily raised and carried in a CLOUD by the WIND.
1504
duststorm. Ensemble of particles of DUST or SAND energetically lifted to great HEIGHTS by a strong and turbulent
WIND. Also called sandstorm. Also written as two words.
1505
Dutchman's log. See LOG.
71
1506
DX90-Format. Format for supply or interchange of digital cartographic data. DX90 provides two modes: the
sequential, and the chain mode.
1507
dyke. See DIKE.
1508
dynameter. An instrument for measuring the MAGNIFYING POWER of a TELESCOPE.
1509
dynamic positioning. Manoeuvring of a vessel to keep a position relative to a seabed feature; normally underwater
acoustic position fixing systems are used for this purpose.
1510
dynamometer. An apparatus for measuring force or energy.
1511
dyne. The unit of force in the CGS SYSTEM.
72
E
1512
eagre (or eager). See BORE.
1513
earth. The PLANET which we inhabit.
The solid matter of the GLOBE in distinction from water and air. The GROUND.
1514
earth current. See CURRENT(S): TELLURIC.
1515
earth inductor. An electric instrument used to measure the INCLINATION of the EARTH's MAGNETIC FIELD.
1516
earth light. Feeble light of the dark part of the MOON's disc produced by the solar light reflected by the EARTH
including the ATMOSPHERE. Also written as one word. Also called Earthshine.
1517
earthquake. A shaking or trembling of the CRUST of the EARTH caused by underground volcanic forces or by
breaking and shifting of ROCK beneath the surface. Also written as one word.
1518
earth's crust. See CRUST.
1519
earth's magnetic field. See GEOMAGNETIC FIELD.
1520
earth's mantle. The relatively plastic region between the CRUST and core of the EARTH. Also called Asthenosphere.
1521
earthshine. See EARTH LIGHT. Also written as two words.
1522
earth tide. See TIDE.
1523
easting. The distance a craft makes good to the east. The opposite is WESTING.
In a cartesian reference system the value of one coordinate, usually expressed in metres, measured from the
CENTRAL MERIDIAN in east-west direction; used e.g. in the UTM system.
1524
ebb. The EBB STREAM. Sometimes the term 'ebb' is also used with reference to vertical tidal movement. The opposite
is FLOOD.
1525
ebb current. See EBB STREAM.
1526
ebb interval. Short for strength of ebb interval. The interval between the transit of the moon over the meridian of a
place and the time of the following strength of ebb.
1527
ebb stream. The horizontal movement of water associated with FALLING TIDE. Ebb streams generally set seaward, or
in the opposite direction to the tide progression. Also called EBB, ebb current or outgoing stream.
1528
ebb strength. Phase of the ebb tidal current at the time of maximum velocity. Also, the velocity at this time. Also called
strength of ebb.
1529
ebb tide. See TIDE: FALLING.
1530
eccentric angle. See LATITUDE: PARAMETRIC.
1531
eccentricity. The amount of deviation from a centre.
1532
eccentricity of alidade. The distance between the centre of figure of the index points of an ALIDADE and the centre of
figure of the graduated CIRCLE.
1533
eccentricity of circle. The distance between the centre of figure of a graduated CIRCLE of an instrument and its centre
of ROTATION.
1534
eccentricity of ellipse. The ratio of the distance between the centre and a focus of an ellipse to the length of its semimajor axis.
1535
eccentricity of instrument. The combination of ECCENTRICITY OF CIRCLE and ECCENTRICITY OF ALIDADE.
The effect of eccentricity of instruments on an observed DIRECTION is eliminated by having the VERNIERS or
MICROMETER MICROSCOPES, with which the CIRCLE is read, spaced at equal distances around the CIRCLE.
73
1536
eccentric reduction. In TRIANGULATION, the CORRECTION which must be applied to a DIRECTION observed by
an instrument with either the instrument or SIGNAL, or both, eccentric, to reduce the observed value to what it would
have been if there had been no ECCENTRICITY.
1537
eccentric signal. A SIGNAL which is not in the same vertical line with the STATION it represents.
1538
eccentric station. A survey point over which an instrument is centred and OBSERVATIONS are made, which is not in
the same vertical line with the STATION it represents, and to which the OBSERVATIONS will be reduced before
being combined with OBSERVATIONS at other STATIONS. Also called false station or satellite station. See
ECCENTRIC REDUCTION.
1539
echo. Reflected RADIANT ENERGY.
1540
echo(es): false. In ECHO SOUNDING, ECHOES caused by a foreign matter such as KELP or fish, or by LAYERS of
water differentiated by sudden changes of temperature or SALINITY (or both). False echoes are occasionally recorded
by ECHO SOUNDERS, and might be interpreted erroneously as the correct DEPTH. Also called side echo(es) or false
target. See PHANTOM BOTTOM.
1541
echo(es): multiple. In ECHO SOUNDING, any of the ECHOES received subsequent to the first one and due to a
multiplicity of REFLECTIONS back and forth between the BOTTOM and surface. These REFLECTIONS often
register on the DIAL of a usual indicator, or on the FATHOGRAM of a graphic recorder, at multiplies of the true
DEPTH. Such ECHOES are sometimes mistaken for the first ECHO.
1542
echo(es): side. See ECHO(ES): FALSE.
1543
echogram. A graphic record of depth measurements obtained by an ECHO SOUNDER. See FATHOGRAM.
1544
echometer (France). An ultrasonic ECHO SOUNDER with a visual depth-indicating device. The SIGNALS are
produced and received by quartz-crystal transmitting and receiving units. Its RANGE is from 6 to 660 METRES.
1545
echo ranging. The determination of distance by measuring the time interval between transmission of a radiant energy
signal, usually SOUND, and the return of its ECHO.
1546
echoscope (France). An ultrasonic ECHO SOUNDER similar to ECHOMETER. The echoscope is portable, intended
for shoal-water sounding from small boats. Its RANGE is from 1 to 60 METRES.
1547
echo sounder. An instrument for determining the DEPTH of water by measuring the time interval between the emission
of a sonic or ultrasonic SIGNAL and the return of its ECHO from the BOTTOM. Also called echo sounding instrument
(or apparatus), sonic depth finder, or ultrasonic depth finder, as appropriate. See also SUB-BOTTOM PROFILER,
SWATH(E) SOUNDING SYSTEM.
1548
echo sounding. Determination of the DEPTH of water by measuring the time interval between emission of a sonic or
ultrasonic SIGNAL and return of its ECHO from the BOTTOM. Also called acoustic sounding. See also ECHO
SOUNDER.
1549
echo sounding instrument (or apparatus). See ECHO SOUNDER.
1550
eclipse. The obscuration of a source of light by the intervention of an object.
Whole or partial obscuration of a HEAVENLY BODY by the interposition of another, or by the passing of one
luminous HEAVENLY BODY into the shadow of another.
1551
eclipse: annular. An ECLIPSE in which a thin ring of the source of light appears around the obscuring body. Annular
SOLAR ECLIPSES occur, but never annular LUNAR ECLIPSES.
1552
eclipse: lunar. An ECLIPSE of the MOON. When the MOON enters the shadow of the EARTH, it appears eclipsed to
an observer on the EARTH.
1553
eclipse: partial. An ECLIPSE in which only part of the source of light is obscured.
1554
eclipse: solar. An ECLIPSE of the SUN. When the MOON passes between the SUN and the EARTH, the SUN appears
eclipsed to an observer in the MOON's shadow.
1555
eclipse: total. An ECLIPSE in which the entire source of light is obscured.
74
1556
ecliptic. The GREAT CIRCLE formed by the intersection of the plane of the EARTH's ORBIT around the SUN (or
apparent ORBIT of the SUN around the EARTH) and the CELESTIAL SPHERE.
1557
ecliptic latitude. See LATITUDE: CELESTIAL.
1558
ecliptic system of coordinates. A set of CELESTIAL COORDINATES based on the ECLIPTIC as the PRIMARY
GREAT CIRCLE; CELESTIAL LATITUDE and CELESTIAL LONGITUDE.
1559
ecology. The science of the economy of animals and plants dealing with the relations of living organism to their
surroundings.
1560
eddy. A circular movement of water usually formed, where CURRENTS pass OBSTRUCTIONS, between two
adjacent CURRENTS flowing counter to each other, or along the edge of a PERMANENT CURRENT.
1561
eddy viscosity. The turbulent transfer of momentum by EDDIES giving rise to an internal fluid friction, in a manner
analogous to the action of molecular viscosity in LAMINAR FLOW, but taking place on a much larger scale.
4
The value of the coefficient of eddy viscosity is of the order 10 square centimetres per SECOND.
1562
edge. In TOPOGRAPHY, the CREST of a sharply pointed RIDGE.
1563
edge wave. See WAVE.
1564
eelgrass. See SEAGRASS.
1565
Ekman bottle. A REVERSING WATER BOTTLE which can be closed watertight by means of plates seated in rubber.
When at the desired DEPTH, the reversing mechanism is tripped by a MESSENGER.
1566
Ekman current meter. A widely used instrument for measuring the SPEED and direction of the CURRENT at any
DEPTH. It is designed for use from a ship or boat at anchor when the STREAM does not attain a rate of more than 3 to
3 1/2 KNOTS.
1567
Ekman spiral. Spiral, polar DIAGRAM of the extremities of the wind vectors at different HEIGHTS, representing the
variation of the WIND with HEIGHT in the FRICTION LAYER on the basis of various simplifying assumptions.
The Ekman spiral is also applied to the variation of wind-driven OCEAN CURRENTS with DEPTH below the
surface.
1568
elbow. A sudden turn in a CHANNEL, RIVER, or SHORELINE.
1569
electric log. See LOG.
1570
electric submerged log. See LOG.
1571
electromagnetic distance measurement (EDM). Any process or technique of distance measurement which depends
on a comparison of SIGNALS by electromagnetic means.
1572
electromagnetic log. See LOG.
1573
electromagnetic position fixing. Any process or technique of fixing which employs the properties of electromagnetic
waves.
1574
electromagnetic wave. See WAVE.
1575
electrometeor. Visible or audible manifestation of atmospheric electricity, either corresponding to discontinuous
electrical discharges (LIGHTNING, THUNDER) or occurring as more or less continuous PHENOMENA (SAINT
ELMO'S FIRE, POLAR AURORA).
1576
electronic chart. An integrated, interactive, navigation information system, with which the user can display the
hydrographic and positional information that is required to conduct the safe navigation of his vessel. It comprises
hydrographic and cartographic databases containing information useful for navigation.
1577
Electronic chart display and information system (ECDIS). The navigation information system which is considered
the legal equivalent of the nautical chart, displaying selected information from an electronic navigation chart (ENC)
integrated with data from positional and, optionally, other sensors.
75
1578
electronic data processing. In a COMPUTER, data processing performed largely or exclusively on electronic
equipment.
1579
electronic distance-measuring equipment (EDM). Devices that measure the phase difference between transmitted
and returned (i.e. reflected or retransmitted) ELECTROMAGNETIC WAVES, of known FREQUENCY and SPEED,
or the round-trip transit time of a pulsed SIGNAL, from which distance is computed. A wide range of such equipment is
available for surveying and navigational use. Also called distance measuring equipment (DME).
1580
electronic line of position. A LINE OF POSITION established by means of electronic equipment.
1581
electronic navigation. See NAVIGATION.
1582
electronic navigation station. See STATION.
1583
electronic navigational chart (ENC). 1. An electronic navigational chart is a subset of the electronic chart data base
held on the vessel. It contains information on features useful for navigation such as coastline, obstructions, beacons etc.
2. The digital data base that is intended to be used in conjunction with ECDIS. Standardized as to content, structure
and format the ENC may contain supplementary nautical information useful for safe navigation. The ENC is a subset of
the master data base of chart information.
1584
electronic plotting sheet. See PLOTTING SHEET.
1585
electronic telemeter. See TELEMETER.
1586
electro-optical distance measurement (EODM). Any method of electromagnetic distance measurement based on a
comparison of light signals.
1587
electrostriction. Term applied to the creation of elastic tension and changes of shape and volume of an uncharged
isolator by an electrical field.
1588
electrotape. A trade name for a precise electronic distance measuring device operating on the same principle as the
Tellurometer. Originally designated as micro-dist.
1589
elevated pole. See POLE.
1590
elevation. The vertical distance of a point or a LEVEL, on or affixed to the surface of the EARTH, measured from
MEAN SEA LEVEL. The term elevation is sometimes used synonymously with ALTITUDE which in modern use
refers particularly to the distance of points or objects above the EARTH's surface.
An area higher than its surroundings, as a HILL.
1591
elevation: angle of. See ANGLE OF ELEVATION.
1592
elevation: barometric. An ELEVATION determined with a BAROMETER.
1593
elevation of sight. Also called height of eye. The visibility distances are relevant with the elevation of the observer's
sight. When measuring a long distance by optics a line of sight should be maintained over the convex curvature of the
earth and all obstacles between the measuring points.
1594
elevation tints. See HYPSOMETRIC TINTS.
1595
ellipse. A plane curve constituting the locus of all points the sum of whose distances from two fixed points, called foci,
is constant. Also used to characterize errors in positions and measurements.
1596
ellipsoid of reference. See REFERENCE SPHEROID.
1597
ellipsoid of revolution (or rotation). A simple mathematical surface which best approximates the shape of the
EARTH. It is the surface generated by an ellipse revolving about one of its AXES. See also SPHEROID: OBLATE,
SPHEROID: PROLATE and REFERENCE SPHEROID.
1598
ellipticity of an ellipse. The ratio between the difference in length of the semi-axes of an ellipse and its semi-major
axis.
1599
ellipticity of the spheroid. See FLATTENING OF THE EARTH.
76
1600
elongation. The ANGULAR DISTANCE of a body of the SOLAR SYSTEM from the SUN. The angle at the EARTH
between lines to the SUN and another CELESTIAL BODY of the SOLAR SYSTEM. The term is usually used in
connection with INFERIOR PLANETS. The greatest elongation of such a body is its maximum ANGULAR
DISTANCE from the SUN, as observed from the EARTH.
The position of a STAR when its AZIMUTH east or west of the MERIDIAN is greatest.
1601
embankment. An artificial ELEVATION composed of EARTH, STONE, etc. to hold back water.
1602
embayment. An INDENTATION in a SHORELINE forming an open BAY.
1603
emergent nodal point. See NODAL POINT.
1604
emulsion. In PHOTOGRAPHY, a suspension of a salt of silver in gelatine or collodion, used to coat PLATES, films, or
papers.
1605
enamelled plate. In CARTOGRAPHY, enamelled working surface (normally white), on aluminium, zinc or other
dimensionally stable medium. Used to prepare colour separation originals.
1606
enclosed sea. A gulf, basin, or sea surrounded by two or more States and connected to another sea or the ocean.
1607
end lap. See OVERLAP.
1608
energy: radiant. Energy transmitted by RADIATION.
1609
engraving. The act, process or art of cutting or etching designs or letters on metal plates, wooden blocks, etc. for
printing.
Any printed impression made from an engraved surface.
1610
entrance. The SEAWARD end of a CHANNEL, HARBOUR, DOCK, etc.
1611
entrance pupil. The IMAGE of the APERTURE STOP formed by all the LENS ELEMENTS on the object side of the
APERTURE STOP.
1612
entrance window. The IMAGE of the FIELD STOP formed by all the LENS ELEMENTS on the object side of the
FIELD STOP.
1613
envelope. In electronics, a graph defining the variations in AMPLITUDE of successive OSCILLATIONS in an
amplitude-modulated wave.
1614
envelope edge. The fore part of an ENVELOPE.
1615
environment. The sum total of all external conditions which may affect an organism, community, material, or energy if
brought under the influence of these external conditions.
1616
Eotvos balance. See TORSION BALANCE.
1617
Eotvos correction. A correction applied to gravity measurements to balance the effect of the vertical force experienced
by a body moving in an east-west direction on the rotating earth.
1618
Eotvos effect. The east-west component of the movement of a ship, including the effect of marine currents, modifies the
centrifugal force of the earth's rotation. It is a vertical force experienced by a body moving in an east-west direction on
the rotating earth.
1619
epact (of the year). The AGE OF THE MOON at 00 HOUR on January 1.
1620
ephemeris. A statement presenting POSITIONS and related DATA for a CELESTIAL BODY for given EPOCHS
(dates) at uniform intervals of time. Also a publication containing such DATA for a number of CELESTIAL BODIES.
See also ALMANAC: AIR and ALMANAC: NAUTICAL.
1621
epicentre (or epicenter, epicentrum). The point of the EARTH's surface directly above the FOCUS of an
EARTHQUAKE.
1622
epipolar plane. Any plane which contains the EPIPOLES; therefore any plane containing the AIR BASE. Also called
basal plane.
77
1623
epipolar ray. The line on the plane of a PHOTOGRAPH joining the EPIPOLE and the IMAGE of an object. Also
expressed as the trace of an EPIPOLAR PLANE on a PHOTOGRAPH.
1624
epipoles. In the perspective set-up of two PHOTOGRAPHS, (two perspective projections), the points on the planes of
the PHOTOGRAPHS where they are cut by the AIR BASE.
1625
epoch. A given period of time during which a series of related acts or events takes place.
In ASTRONOMY, a particular instant for which certain DATA are given or at which an OBSERVATION is made,
and which then is usable as a REFERENCE POINT.
1626
equal altitudes. Two ALTITUDES of the same CELESTIAL BODY observed east and then west of the MERIDIAN,
when it has reached the same value. The expression also applies to the practice, essentially obsolete, of determining the
instant of local APPARENT NOON by observing equal ALTITUDES of the SUN.
1627
equal area projection.See PROJECTION.
1628
equation: condition. An equation which expresses exactly certain relationships that must exist among related
quantities, which are not independent of one another, exist a priori, and are separate from relationships demanded by
OBSERVATION.
1629
equation: correlate. An equation derived from an OBSERVATION or CONDITION EQUATION, using
undetermined multipliers, and expressing the condition that the sum of the squares of the RESIDUAL ERRORS
resulting from the application of these multipliers to the OBSERVATION or CONDITION EQUATIONS shall be a
minimum.
1630
equation: error. The probability equation which expresses the laws of the occurrence of ACCIDENTAL ERRORS.
The error equation is the basis of the method of LEAST SQUARES, used in the ADJUSTMENT of OBSERVATIONS
for determining the most probable value of a result from those OBSERVATIONS.
1631
equation: Laplace. An equation which expresses the relationships between ASTRONOMIC AZIMUTH, GEODETIC
AZIMUTH, and the ASTRONOMIC LONGITUDE and GEODETIC LONGITUDE.
1632
equation: normal. One of a set of simultaneous equations derived from OBSERVATION, CONDITION or
CORRELATE EQUATIONS. In a least-squares adjustment, values obtained from the solution of normal equations
(either directly or through the CORRELATE EQUATIONS) are applied to the OBSERVATION or CONDITION
EQUATIONS to obtain the desired CORRECTIONS.
1633
equation: observation. A CONDITION EQUATION which connects interrelated unknowns by means of an observed
function.
1634
equation: personal. See PERSONAL EQUATION.
1635
equation method. In tidal terminology, an elaborate non-harmonic method for the prediction of TIDES.
1636
equation of time. The CORRECTION to be applied to 12 hours plus UNIVERSAL TIME to obtain the Greenwich
HOUR ANGLE of the SUN, or more generally the CORRECTION to be applied to 12 hours plus LOCAL MEAN
TIME to obtain the LOCAL HOUR ANGLE of the SUN.
1637
equator. The PRIMARY GREAT CIRCLE of a sphere or SPHEROID such as the EARTH, perpendicular to the polar
AXIS.
1638
equator: astronomical. A line connecting points having 0°ASTRONOMICAL LATITUDE.
1639
equator: celestial. The GREAT CIRCLE on the CELESTIAL SPHERE whose plane is perpendicular to the AXIS of
the EARTH. Also called equinoctial.
1640
equator: geodetic. The line on the SPHEROID connecting points of 0°GEODETIC LATITUDE.
1641
equator: heat. See EQUATOR: THERMAL.
1642
equator: magnetic. That line on the surface of the EARTH connecting all points at which the magnetic DIP is zero.
Also called aclinic line.
1643
equator: terrestrial. A GREAT CIRCLE of the EARTH in the plane of the CELESTIAL EQUATOR, and equidistant
from the two POLES.
78
1644
equator: thermal. Line which circumscribes the EARTH and connects all points of highest mean annual temperature
on each MERIDIAN. Also called heat equator.
1645
equatorial calms. Zone of calm or light variable WINDS encountered, in certain regions, between the TRADE WINDS
of the two hemispheres.
1646
equatorial horizontal parallax. See PARALLAX.
1647
equatorial tide(s). See TIDE.
1648
equidistance line. See MEDIAN LINE.
1649
equilibrium. A state of balance between forces.
1650
equilibrium argument. The theoretical PHASE of a CONSTITUENT of the EQUILIBRIUM TIDE.
1651
equilibrium tide. See TIDE.
1652
equinoctial. See EQUATOR: CELESTIAL.
1653
equinoctial colure. See COLURE.
1654
equinoctial point. See EQUINOX.
1655
equinoctial spring tide(s). See TIDE.
1656
equinoctial system of coordinates. See CELESTIAL EQUATOR SYSTEM OF COORDINATES.
1657
equinoctial year. See YEAR: TROPICAL.
1658
equinox. One of the two points of intersection of the ECLIPTIC and the CELESTIAL EQUATOR, occupied by the
SUN when its DECLINATION is zero. That point occupied on or about March 21, when the SUN's DECLINATION
changes from south to north, is called vernal equinox or first point of Aries; that point occupied on or about September
23, when the DECLINATION changes from north to south, is called autumnal equinox or first point of Libra. Also
called equinoctial point.
1659
equinoxes: precession of. See PRECESSION OF THE EQUINOXES.
1660
equiphase zone. See ZONE.
1661
equipotential surface. A surface having the same potential of GRAVITY at every point.
1662
equisignal zone. See ZONE.
1663
equivalent focal length. See FOCAL LENGTH.
1664
equivalent projection. See PROJECTION: EQUAL AREA.
1665
equivalent scale. See SCALE.
1666
era. In GEOLOGY, any of the main divisions of GEOLOGICAL TIME.
1667
erect image. See IMAGE.
1668
erecting eyepiece. See EYEPIECE.
1669
erg. The unit of energy or work in the CGS SYSTEM.
1670
erosion. The general process of the wearing away of ROCKS and SOIL at the EARTH's surface by natural agencies.
1671
error. The difference between an observed or computed value of a quantity and the ideal or true value of that quantity.
1672
error: absolute. Absolute deviation (the value taken without regard to sign) from the corresponding true value.
79
1673
error: accidental. An ERROR whose occurrence depends on the law of chance only. Also called random error or
irregular error.
1674
error: clamping. A SYSTEMATIC ERROR in OBSERVATIONS made with a REPEATING THEODOLITE caused
by strains set up by the clamping devices of the instrument.
1675
error: closing. See ERROR OF CLOSURE.
1676
error: constant. A SYSTEMATIC ERROR which is the same in both magnitude and sign through a given series of
OBSERVATIONS.
1677
error: external. See ERROR: THEORETICAL.
1678
error: Gaussin. DEVIATION of a MAGNETIC COMPASS due to TRANSIENT MAGNETISM which remains in a
vessel's structure for short periods after the inducing force has been removed. This ERROR usually appears after a
vessel has been on the same HEADING for a considerable time.
1679
error: gross. The result of carelessness or a mistake; may be detected through repetition of the measurement. Also
called blunder.
1680
error: heeling. The change in the DEVIATION of a MAGNETIC COMPASS when a craft heels, due to the change in
the position of the magnetic influences of the craft relative to the EARTH's MAGNETIC FIELD and to the COMPASS.
1681
error: index. The INSTRUMENTAL ERROR which is constant and attributable to displacement of a VERNIER or
some analogous effect.
1682
error: instrumental (or instrument). A SYSTEMATIC ERROR resulting from imperfections in, or faulty
ADJUSTMENT of, instruments or devices used.
1683
error: irregular. See ERROR: ACCIDENTAL.
1684
error: mean square. The quantity whose square is equal to the sum of the squares of the individual ERRORS divided
by the number of those ERRORS.
1685
error: parallactic. An ERROR caused by personal or instrumental PARALLAX.
1686
error: periodic. An ERROR whose AMPLITUDE and direction vary systematically with time.
1687
error: personal. The result of the inability of an observer to perceive dimensional values exactly. Personal errors may
be either random or systematic in behaviour. See also PERSONAL EQUATION.
1688
error: polarization. ERROR in a RADIO BEARING or the COURSE indicated by a RADIOBEACON, due to
horizontally-polarized components of the electric field under certain transmission conditions. The terms night error or
night effect have become obsolete.
1689
error: probable. An ERROR (or deviation from the mean) of such magnitude that the likelihood of its being exceeded
in a set of OBSERVATIONS is equal to the likelihood of its not being exceeded; its value is that of the STANDARD
ERROR multiplied by 0.6745. The use of STANDARD ERROR is sometimes preferred in statistical studies.
1690
error: random. See ERROR: ACCIDENTAL.
1691
error: regular. See ERROR: SYSTEMATIC.
1692
error: residual. The difference between any value of a quantity in a series of OBSERVATIONS, corrected for known
SYSTEMATIC ERRORS, and the value of the quantity obtained from the ADJUSTMENT of that series. Sometimes
termed as residual.
1693
error: root mean square. See ERROR: STANDARD.
1694
error: sextant. The ERROR in the reading of a SEXTANT, due either to lack of proper ADJUSTMENT or to
imperfection of manufacture.
80
1695
error: standard. The square root of the arithmetic mean of squared deviations from the mean. Also called standard
deviation, when the deviations do not represent ERRORS, or root mean square error.
1696
error: station. See DEFLECTION OF THE VERTICAL.
1697
error: swirl. The additional ERROR in the reading of a MAGNETIC COMPASS during a turn, due to friction in the
compass liquid.
1698
error: systematic. An ERROR whose magnitude changes in proportion to known changes in observational conditions.
Also called regular error.
1699
error: theoretical. A SYSTEMATIC ERROR arising from natural physical conditions, beyond the control of the
observer. Also called external error.
1700
error equation. See EQUATION.
1701
error of closure. The amount by which a quantity obtained by a series of related measurements differs from the true or
fixed value of the same quantity. Also called closing error.
1702
error of closure of horizon. The amount by which the sum of a series of adjacent measured horizontal angels around a
point fails to equal exactly 360°.
1703
error of closure of triangle. The amount by which the sum of the three observed angles of a triangle fails to equal
exactly 180°plus the SPHERICAL EXCESS of the triangle. Also referred to as closure of triangle.
1704
error of collimation. The angle between the LINE OF COLLIMATION (LINE OF SIGHT) of a TELESCOPE and its
COLLIMATION AXIS; i.e., the angle by which the LINE OF SIGHT of an optical instrument differs from what it
should be. Also called collimation error.
1705
error of graduation. Inaccuracy in the GRADUATIONS of the SCALE of an instrument. Also called graduation
error.
1706
error of magnetic compass. The angle by which a compass direction differs from the true direction; the algebraic sum
of VARIATION and DEVIATION.
1707
error of run (micrometer). The difference in SECONDS of arc, between the intended value of one turn of the
MICROMETER SCREW and its actual value as determined by measuring the space between two adjacent graduation
marks of the CIRCLE with the MICROMETER. Also called run of micrometer.
1708
escarpment. A general term for a continuous scarp face.
An elongated and comparatively steep SLOPE of the SEA FLOOR, separating flat or gently sloping areas. Also
called sea scarp.
1709
establishment. The interval of time between the transit (upper or lower) of the moon and the next high water at a place.
The average establishment at the time of full or new moon is called vulgar or common establishment, or high water full
and change. Also called high water lunitidal interval, or establishment of the port. See LUNITIDAL INTERVAL.
1710
establishment of the port. See ESTABLISHMENT.
1711
estimated position (EP). See POSITION.
1712
estuary. That portion of a STREAM influenced by the TIDE of the body of water into which it flows.
A BAY, as the MOUTH of a RIVER, where the TIDE meets the river current.
1713
estimated time of arrival (ETA). The predicted time of reaching a destination or waypoint.
1714
estimated time of departure (ETD). The predicted time of leaving a place.
1715
etch (v.t.). To form an IMAGE within the surface of a printing or drawing material by the use of solvents.
1716
Eulerian current observations. A method to monitor the current at a fixed point by means of current metres.
1717
European Datum. Constituted by the International Spheroid located at the Potsdam origin.
81
1718
evaluation report. A report which summarizes pertinent facts relating to a given hydrographic survey. Included in the
report are sections which address the quality of the hydrographic survey and detailed comparisons made with prior
hydrographic surveys and the appropriate nautical chart. Specific evaluations and recommendations regarding the
adequacy of the survey to supersede prior survey data and charted information are made.
1719
evaporimeter. Instrument for measuring the amount of water evaporated into the ATMOSPHERE during a given time
interval. Also called atmometer, atmidometer.
1720
evection. A perturbation of the MOON in its ORBIT due to the attraction of the SUN. See also LUNAR
INEQUALITY.
1721
Everest spheroid. See REFERENCE SPHEROID.
1722
exercise area. An area shown on CHARTS within which naval, military or aerial exercises are carried out. Also called
military practice area.
1723
exclusive economic zone. The exclusive economic zone is an area, not exceeding 200 nautical miles from the baselines
from which the breadth of the territorial sea is measured, subject to a specific legal regime established in the United
Nations Convention on the Law of the Sea under which the coastal state has certain rights and jurisdiction.
1724
existence doubtful. Of uncertain existence. The expression is used principally on CHARTS to indicate the possible
existence of a ROCK, SHOAL, etc., the actual existence of which has not been established. Usually shown by the
abbreviation 'ED'.
1725
exit pupil. The IMAGE of APERTURE STOP formed by all the LENS ELEMENTS on the IMAGE side of the
APERTURE STOP.
1726
exit window. The IMAGE of the FIELD STOP formed by all the LENS ELEMENTS on the image side of the FIELD
STOP.
1727
ex-meridian altitude. See ALTITUDE.
1728
expansion factor. In RADIOLOCATION, factor representing the degree to which the hyperbolae belonging to a given
group of HYPERBOLIC LINES OF POSITION move apart as the distance from the BASE LINE increases.
1729
expert system. A knowledge-based computer system which utilizes artificial intelligence to do some of the inferential
computation/decision making.
1730
exploration drilling. Drilling operations aimed at the exploration of resources.
1731
exploratory survey. See SURVEY.
1732
explosive anchorage area. An area set apart for anchored ships discharging or receiving explosives.
1733
explosive fog signal. See FOG SIGNAL.
1734
exposure. In PHOTOGRAPHY, the act of exposing a light-sensitive material to a light source.
The total quantity of light received per unit area on a sensitized PLATE or film; may be expressed as the product of
the light intensity and the EXPOSURE TIME.
1735
exposure interval. The time interval between the taking of successive PHOTOGRAPHS.
1736
exposure station. See AIR STATION.
1737
exposure time. The time during which a light-sensitive material is subjected to the action of light.
1738
exterior orientation. See ORIENTATION.
1739
exterior perspective centre. See PERSPECTIVE CENTRE.
1740
external error. See ERROR: THEORETICAL.
1741
extinction coefficient. A measure of the space rate of diminution or extinction, of any transmitted light.
In OCEANOGRAPHY, the measure of ATTENUATION of downward directed light radiation in the SEA.
82
1742
extrapolation. The process of estimating the value of a quantity beyond the limits of known values by assuming that the
rate or system of change between the last few known values continues.
1743
extremely high frequency (EHF). See FREQUENCY: RADIO.
1744
extrusion. In CARTOGRAPHY, the extension of detail outside the NEAT LINE.
1745
eye base. See INTERPUPILLARY DISTANCE.
1746
eye of the storm. See TROPICAL CYCLONE.
1747
eyepiece. In an optical device, the lens group which is nearest the eye and with which the IMAGE formed by the
preceding elements is viewed.
1748
eyepiece: erecting. An EYEPIECE containing an auxiliary re-imagining system of one or two LENSES which inverts
the primary IMAGE before it reaches the EYEPIECE proper. The device is now obsolescent, the inversion being
performed by prism systems. Also called inverting eyepiece.
1749
eyepiece micrometer. See MICROMETER: OCULAR.
83
F
1750
face(s) of theodolite. Either of the two positions, 'face left' (F.L.) and 'face right' (F.R.) of the THEODOLITE, when
OBSERVATIONS are made with the VERTICAL CIRCLE on the left or on the right of the TELESCOPE respectively.
1751
facility (navigational). See AID TO NAVIGATION.
1752
facility (port). See HARBOUR WORKS.
1753
facsimile. An exact reproduction or copy.
1754
fading. Loss of strength in received SIGNALS due to temporary variations in the conditions of propagation.
1755
Fahrenheit temperature scale. A temperature scale defined by the relationship t°F = 1.8 t°C + 32; developed by
Gabriel D. Fahrenheit (1686-1736), German physicist.
1756
fair chart (British terminology). The final, carefully made plot of a HYDROGRAPHIC SURVEY. In contrast to the
FIELD BOARD (BOAT SHEET in U.S. terminology) which is a work sheet plotted during field operations from
preliminary field data, the fair chart is plotted from corrected DATA and represents the official permanent record of that
particular SURVEY. Also called fair sheet. It is called smooth sheet in U.S. terminology.
1757
fair sheet. See FAIR CHART.
1758
fair tracing (British terminology). A paper tracing of moderate size for transferring the work from the FIELD
BOARDS to the FAIR CHARTS.
1759
fairway. The main travelled part of a WATERWAY.
1760
fairway buoy. A BUOY marking a FAIRWAY, with safe water on both sides.
1761
falling tide. See TIDE.
1762
false bottom. See PHANTOM BOTTOM.
1763
false coordinates. See COORDINATES.
1764
false echo. See ECHO.
1765
false horizon. See HORIZON.
1766
false origin. See COORDINATES: FALSE.
1767
false station. See ECCENTRIC STATION.
1768
false target. See ECHO: FALSE.
1769
fan. A relatively smooth, fan-like depositional feature normally sloping away from the outer termination of a
CANYON.
1770
farad. The unit of electrical capacitance, in the SI SYSTEM.
1771
farewell buoy. The outermost BUOY marking the ENTRANCE to a CHANNEL or HARBOUR. Also called sea buoy.
Known as landfall buoy in British terminology.
1772
fast ice. SEA ICE which remains fast, generally in the position where originally formed, and which may attain a
considerable thickness. It is found along COASTS, where it is attached to the SHORE, or over SHOALS, where it may
be held in position by ISLANDS, grounded ICEBERGS or grounded polar ice.
1773
fata morgana. The name originally given to a multiple mirage phenomenon often observed over the Straits of Messina,
and supposed to be the work of the faity (in Italian: fata) Morgana; later, it was applied to any impressive multiple
MIRAGE.
84
1774
fathogram. A graphic record of depth measurements obtained by a fathometer (erroneously applied to any
ECHOGRAM).
1775
fathom. A unit of length equal to 6 FEET or 1.83 METRES.
1776
fathom curve. See FATHOM LINE, DEPTH CURVE.
1777
fathom line. A DEPTH CURVE with DEPTH expressed in FATHOMS. Also called fathom curve, isobath.
1778
fault. In GEOLOGY, a break of shear in the EARTH's CRUST with an observable displacement between the two sides
of the break, and parallel to the plane of the break.
1779
Faye anomaly. See FREE-AIR ANOMALY.
1780
feature code. An alphanumeric code (label) attached to all point, line or area data describing a cartographic feature of
particular quality.
1781
Federation of Astronomical and Geophysical Services (FAGS). Facilitates and promotes the collection of
observations, information and statistics in the field of astronomical and geophysical sciences. The International Time
Bureau is one of the services.
1782
fender. A device let down between the side of a ship or a WHARF or other ship to protect from chafing when ships are
lying alongside or to take the shock of a bump when going alongside.
1783
fetch. An area of the sea surface over which SEAS are generated by a WIND having a constant direction and SPEED.
The length of the generating area, measured in the direction of the WIND in which the SEAS are generated.
1784
fiducial axes. In PHOTOGRAMMETRY, the lines joining opposite FIDUCIAL MARKS on a PHOTOGRAPH. Also
called photograph axes.
1785
fiducial marks. In PHOTOGRAMMETRY, INDEX MARKS, usually four, which are rigidly connected with the
camera lens through the camera body and which form IMAGES on the NEGATIVE and usually define the PRINCIPAL
POINT of the PHOTOGRAPH.
Also marks, usually four in number, in any instrument, which define the axes whose intersection fixes the
PRINCIPAL POINT of a PHOTOGRAPH and fulfills the requirements of INTERIOR ORIENTATION.
In SURVEYING, an index line or point. A line or point used as a basis of reference.
1786
field board (British terminology). Wooden board, or zinc or plastic sheet, used by HYDROGRAPHERS and land
surveyors for plotting and recording the details of the SURVEY in the field. Separate boards are usually prepared for
TOPOGRAPHY and SOUNDING respectively. The former are referred to as topography boards; the latter as sounding
boards. See also BOAT SHEET, and PLANE TABLE.
1787
field chart. See CHART.
1788
field examination. A special purpose hydrographic, wire drag, or side scan sonar survey of very limited area; i.e.,
usually an investigation of one or more individual and scattered items.
1789
field inspection. In PHOTOGRAMMETRY, the process of comparing AERIAL PHOTOGRAPHS with conditions as
they exist on the GROUND, and of obtaining information to supplement or clarify that not readily discernible on the
PHOTOGRAPHS themselves.
1790
field position. See POSITION.
1791
field sheet. The hydrographer's or topographer's work sheet; it presents a graphic display of all surface and subsurface
features in the area being surveyed. See also BOAT SHEET.
1792
field stop. The physical element (such as an APERTURE STOP, DIAPHRAGM or lens periphery) of an OPTICAL
SYSTEM which limits the field of view covered by the system.
1793
field work. All activities in the field required for a hydrographic survey.
1794
figure of the earth. The defining elements of the mathematical surface which approximates the surface of the GEOID.
The figure of the earth has been proved to be approximately an OBLATE SPHEROID. See also GEOID and
SPHEROID.
85
1795
file. An entity of data for a specific task or purpose stored on a mass storage device.
1796
filter. In optics, any transparent material which, by absorption, selectively modifies the light transmitted through an
OPTICAL SYSTEM.
In ocean-wave forecasting, a set of formulas that define the particular wave frequencies and directions in the fetch
area which are of significance at the point of forecast.
1797
filtering. The process of selecting specific data from a specific source in accordance with certain rules, formulae, or
algorithms.
1798
final great circle course. See COURSE: GREAT CIRCLE.
1799
fiord (or fjord). A long narrow ARM OF THE SEA, running up between high BANKS or CLIFFS, as on the COAST
of Norway. Often has a relatively shallow SILL across its ENTRANCE.
1800
firn. Old SNOW which has become granular and dense under the action of various processes of melting and refreezing,
also including sublimation.
1801
first nodal point. See NODAL POINT.
1802
first order triangulation. See TRIANGULATION CLASSIFICATION.
1803
first point of Aries. See EQUINOX.
1804
first point of Cancer. See SOLSTICE.
1805
first point of Capricorn. See SOLSTICE.
1806
first point of Libra. See EQUINOX.
1807
first quarter. See PHASES OF THE MOON.
1808
firth. A Scottish word: an ARM OF THE SEA; an ESTUARY of a RIVER.
1809
fish aggregating device (FAD). See FISH HAVEN.
1810
fishery conservation zone. See FISHING ZONE.
1811
fish farm. An assemblage of cages, nets, rafts and floats or posts where fish, including shellfish, are artificially
cultivated.
1812
fish haven. Areas established by private interests, usually sport fishermen, to simulate natural reefs and wrecks that
attract fish. The reefs are constructed by dumping assorted junk in areas which may be of very small extent or may
stretch a considerable distance along a depth contour. Fish havens are outlined and labeled on charts. Also called fishery
reefs.
1813
fishing area. See FISHING GROUND.
1814
fishing ground. A water area in which fishing is frequently carried on. Also called fishing area or fishing zone.
1815
fishing reef. See FISH HAVEN.
1816
fishing zone. The offshore zone in which exclusive fishing rights and management are held by the coastal nation.
1817
fish lead. See LEAD.
1818
fish (or fishing) stakes. Poles or stakes placed in SHALLOW WATER to outline FISHING GROUNDS or to catch
fish.
1819
fish trap (or weir). A structure for catching fish. See also TUNNY NET.
1820
fish trap buoy. A BUOY marking the limits of a fish trap area.
1821
fish weir. See FISH TRAP.
86
1822
fix. In NAVIGATION, a relatively accurate POSITION determined without reference to any former POSITION. It may
be classed as visual, celestial, electronic, etc., depending upon the means of establishing it.
1823
fix (v.t.). In hydrographic SURVEYING, to determine, at regular intervals, the POSITION of ships or boats, while
sailing along a LINE OF SOUNDING. The usual method of fixing HYDROGRAPHIC SURVEYS within sight of
LAND is the THREE-POINT FIX METHOD.
1824
fix: circular. A useless FIX resulting from the OBSERVATIONS of two angles establishing as LOCI three coinciding
CIRCLES OF POSITION. Also called revolver, or swinger.
1825
fix: running. A POSITION determined by crossing LINES OF POSITION obtained at different TIMES and advanced
or retired to a common TIME, the expression being applied to a POSITION determined by advancing and retiring a line
over a considerable period of time.
1826
fix: split. A FIX obtained by measuring two angles to four objects whose POSITIONS are known, i.e. with no common
centre object.
1827
fix: three-point. A FIX obtained by simultaneously observing, with SEXTANTS, the two adjacent angles between
three suitably disposed objects whose POSITIONS are known, and plotting the POSITION by a STATION POINTER.
See also RESECTION and THREE-POINT PROBLEM.
1828
fixed angle plot (British terminology). Plot prepared in advance for use in normal SOUNDING in lieu of a STATION
POINTER. The arcs of equal angle subtended by selected MARKS are drawn on the SOUNDING BOARD at
convenient intervals depending on the SCALE. The observed sextant angles can then be plotted in the field by visual
inspection. See also CIRCLE SHEET, and SOUNDING: FIXED ANGLE.
1829
fixed angle sounding. See SOUNDING.
1830
fixed platform. See FIXED STATION.
1831
fixed star. A STAR. The expression is used particularly to distinguish STARS from other HEAVENLY BODIES; so
called by ancients to distinguish STARS from the wandering PLANETS.
1832
fixed station. A radiolocation station which is situated in one particular spot throughout the period of its operation. As
opposed to MOBILE STATION. Also called shore station.
In OCEANOGRAPHY, a platform from which repeated OBSERVATIONS are taken. These include coastal and
island stations, LIGHT VESSELS, WEATHER SHIPS, AUTOMATIC FLOATING STATIONS and ICE ISLANDS.
Also called fixed platform.
1833
fixing. The process of rendering a developed photographic image permanent by removing the unaffected light-sensitive
material.
1834
fixing interval. The time or distance elapsed between two subsequent fixes.
1835
fjord. See FIORD.
1836
flare stack. A tall structure used for burning-off waste oil or gas.
1837
flare triangulation. See TRIANGULATION.
1838
flat. A level tract of LAND, as the BED of a dry LAKE or an area frequently uncovered at LOW TIDE. Usually in
plural.
1839
flat-bed plotter. A plotter which uses a flat surface to mount the drawing base.
1840
flattening of the earth. The ratio of the difference between the equatorial and polar radii of the EARTH (major and
minor semi-axes of the SPHEROID) and its equatorial radius (major semi-axis). The flattening of the earth is the ellipticity of the spheroid. Also called compression.
1841
flight altitude. See ALTITUDE.
1842
flight strip. A succession of overlapping AERIAL PHOTOGRAPHS taken along a single COURSE.
1843
Flinders bar. A bar of soft unmagnetized iron placed vertically near a MAGNETIC COMPASS to counteract
DEVIATION caused by MAGNETIC INDUCTION in vertical SOFT IRON of the craft.
87
1844
float. Any buoyant object attached to nets or fishing lines: term also used for the small buoys used for current
observations.
1845
float gauge. See GAUGE.
1846
floating breakwater. A contrivance consisting of a series of square frames of timber connected by mooring chains or
CABLES attached to anchors or stone blocks in such a manner as to form a BASIN within which vessels riding to
anchor may be protected from the violence of the WAVES.
1847
floating dock. See DOCK.
1848
floating ice. Any form of ICE found floating in water.
1849
floating mark. In PHOTOGRAMMETRY, a mark seen as occupying a position in the three-dimensional space formed
by the STEREOSCOPIC FUSION of a pair of PHOTOGRAPHS and used as a reference mark in examining or measuring the STEREOSCOPIC MODEL.
1850
floating point. In computer systems the type of numeric data approximately representing real numbers. A floating point
number is composed of an exponent and a mantissa specifying the numerical value relative to the exponent. Owing to
the limited length of a computer WORD, the floating point representation may cause a loss of precision.
1851
floating triangulation. See TRIANGULATION.
1852
float-off (British terminology). The paper of a FIELD BOARD when detached from the board on completion of the
work for which the FIELD BOARD was prepared.
1853
float well. A vertical pipe or box with a relatively small opening in the bottom, used to enclose the float of a tide gauge
so the float will be little affected by nontidal motions of the water. Synonymous with stilling well.
1854
floe (or ice floe). A piece of SEA ICE other than FAST ICE. Floes over 10 km across are described as vast; those
between 1 and 10 km across as big; those between 200 and 1,000 m across as medium; those between 10 and 200 m
across as small. Floes less than 10 m across are called ICE CAKES.
1855
flood. The FLOOD STREAM. Sometimes the term 'flood' is also used with reference to vertical tidal movement. The
opposite is EBB.
An overflowing of water on LAND usually dry; inundation.
1856
flood current. See FLOOD STREAM.
1857
flood stream. The horizontal movement of water associated with the RISING TIDE. Flood streams generally set toward
the SHORE, or in the direction of the tide progression. Also called FLOOD, flood current or ingoing stream.
1858
flood tide. See TIDE: RISING.
1859
flotsam. See JETTISON.
1860
flow. The motion characteristic of a fluid.
1861
flume. An inclined CHANNEL for conveying water from a distance to be utilized for power, transportation, irrigation,
etc.
1862
fluorescence. Emission of light or other RADIANT ENERGY as a result of and only during absorption of
RADIATION from some other source. See LUMINESCENCE and PHOSPHORESCENCE.
1863
flux: luminous. Quantity, characteristic of RADIANT FLUX which expresses its capacity to produce a luminous
sensation.
1864
flux: radiant. Power emitted, transferred or received in the form of RADIATION.
1865
flux-gate magnetometer. See MAGNETOMETER.
1866
f-number. See APERTURE: RELATIVE.
1867
foam line. The front of a WAVE as it advances shoreward, after it has broken.
88
1868
focal distance. See FOCAL LENGTH.
1869
focal length. The distance from the rear NODAL POINT of a LENS to the FOCAL PLANE for an object at infinity.
The distance from the surface of a MIRROR to its FOCUS. Also called focal distance.
1870
focal length: calibrated. An adjusted value of the EQUIVALENT FOCAL LENGTH computed to distribute the effect
of lens DISTORTION over the entire field used in an AERIAL CAMERA.
1871
focal length: equivalent. The distance measured along the AXIS OF LENS from the rear NODAL POINT to the plane
of best average DEFINITION over the entire field used in an AERIAL CAMERA.
1872
focal plane. A plane parallel to the plane of a LENS or MIRROR and passing through the FOCUS. In PHOTOGRAPHY, the plane (perpendicular to the axis of the LENS) in which IMAGES of points in the object field of the LENS are
focused.
1873
focal-plane plate. A glass plate set in the CAMERA so that the surface away from the LENS coincides with the
FOCAL PLANE. Its purpose is to position the EMULSION of the film in the FOCAL PLANE when the film is physically pressed into contact with the glass plate. Also called contact glass or contact plate.
1874
focal-plane shutter. See SHUTTER.
1875
focal point. See FOCUS.
1876
focus (pl. foci). That point at which parallel RAYS of light meet after being refracted by a LENS or reflected by a
MIRROR. Also called focal point.
In SEISMOLOGY, the source of a given set of elastic WAVES. The true centre of an EARTHQUAKE, within
which the strain energy is first converted to elastic wave energy.
1877
focus (v.t.). The process of adjusting an optical instrument, PROJECTOR, CATHODE-RAY TUBE, etc., to produce a
clear and well-defined IMAGE.
1878
fog. Suspension of very small water droplets in the air, generally reducing the horizontal VISIBILITY at the EARTH's
surface to less than 1 kilometre.
1879
fog: advection. FOG which forms in the lower part of a moist AIR MASS which moves over a colder surface.
1880
fog: ice. Suspension of numerous minute ice crystals in the air, reducing the VISIBILITY at the EARTH's surface.
1881
fog: sea. ADVECTION FOG which forms over the SEA.
1882
fog: wet. FOG formed of droplets sufficiently large to deposit water on objects.
1883
fog bank. FOG, generally caused by local conditions, which extends over a small area some hundreds of METRES
wide.
1884
fog bell. A bell used as a FOG SIGNAL.
1885
fog detector light. A light used to automatically determine conditions of visibility which warrant the turning on or off
of a sound signal.
1886
fog gong. A gong used as a FOG SIGNAL.
1887
fog gun. A gun used as a FOG SIGNAL.
1888
fog horn. A HORN used as a FOG SIGNAL.
1889
fog patches. FOG in banks irregularly distributed.
1890
fog signal. A warning SIGNAL transmitted by a vessel or AID TO NAVIGATION during period of low VISIBILITY.
Also the device producing such a SIGNAL.
1891
fog signal: explosive. Detonation of an explosive used as a navigational warning during low VISIBILITY.
1892
fog signal: radio. A regularly recurring distinctive SIGNAL sent out by a RADIOBEACON during thick WEATHER.
89
1893
fog siren. A siren used as a FOG SIGNAL.
1894
fog trumpet. A trumpet used as a FOG SIGNAL.
1895
fog whistle. A whistle used as a FOG SIGNAL.
1896
following sea. A SEA in which the WAVES move in the general direction of the HEADING.
1897
following wind. WIND blowing in the general direction of a vessel's COURSE.
1898
font. Complete assortment of all the different characters of a particular size and style of type.
1899
Food and Agricultural Organization (FAO). Aims at the improvement of the standard of living, especially of the
rural population of third world countries, by increasing the production and improving the distribution of agricultural
products.
1900
foot (pl. feet). A unit of length equal to 12 INCHES, 1/6 of a FATHOM, or 30.480 centimetres.
1901
foot of the continental slope. The point of maximum change of gradient at the base of the CONTINENTAL SLOPE.
1902
footscrew. See LEVELLING SCREW.
1903
forced convection. See CONVECTION.
1904
forced wave. See WAVE.
1905
foreland. A CAPE or PROMONTORY.
1906
Forel scale. A colour scale employed as a means of determining the COLOUR OF SEA WATER.
1907
foreshore. That part of SHORE which lies between HIGH and LOW WATER MARK at ordinary TIDE.
1908
foresight. In LEVELLING, a reading on a LEVELLING ROD held on a point whose ELEVATION is to be determined.
See also BACKSIGHT.
1909
format. The general plan or arrangement of a product.
Specification of succession and type of representation of elements of information (numbers, text) on a medium. A
fixed format is equivalent to a table, while free formats use delimiters to separate individual elements or "tags" (based
on a directory) to identify elements. A set of formats or a complex format determines the structure of how information is
represented on a medium.
1910
formation sounding. See SOUNDING.
1911
form lines. Lines drawn to represent the shape of TERRAIN; unlike CONTOUR LINES, these are drawn without
regard to a true vertical DATUM or regular vertical interval.
1912
forward azimuth. See AZIMUTH: GEODETIC.
1913
forward lap. See OVERLAP.
1914
foul. 1. To entangle or become entangled; e.g. as a propeller becoming entangled in cables, nets, or seaweed.
2. To attach or come to lie on the surface of submerged objects, usually in large numbers or amounts as barnacles on
the hull of a ship.
1915
foul area. An area of numerous uncharted dangers to navigation. The area charted serves as a warning to the mariner
that all dangers are not charted individually and that navigation through the area may be hazardous.
The term "foul" should not be applied to a soft continuum with indefinite boundaries such as mud or sand; to areas
congested with marine vegetation such as kelp or grass in water; or to materials not likely to cause damage to a vessel.
1916
foul berth. A berth in which a vessel cannot swing to her anchor or moorings without fouling another vessel or striking
an obstruction.
90
1917
foul bottom. A hard, uneven, rocky or obstructed BOTTOM having poor holding qualities for anchors, or one having
ROCKS or WRECKAGE that would endanger an anchored vessel.
1918
foul ground. An area where the holding qualities for an anchor are poor, or where danger of striking or fouling the
GROUND or other OBSTRUCTIONS exists.
1919
fouling. The mass of living and non-living bodies and particles attached to or lying on the surface of a submerged manmade or introduced object; more commonly considered to be only the living or attached bodies.
1920
fractional scale. See SCALE: NATURAL.
1921
fracture zone. An extensive linear zone of unusually irregular TOPOGRAPHY of the SEA FLOOR, characterized by
large SEAMOUNTS, steep-sided or asymmetrical RIDGES, TROUGHS, or ESCARPMENTS.
1922
frazil ice. Fine spicules or plates of ICE in suspension in water.
1923
free-air anomaly. The difference between observed GRAVITY and theoretical GRAVITY which has been computed
for LATITUDE and corrected for ELEVATION of the STATION above or below the GEOID, by application of the
normal rate of change of GRAVITY for change of ELEVATION, as in free air. Also called Faye anomaly.
1924
free atmosphere. See ATMOSPHERE.
1925
free convection. See CONVECTION.
1926
free gyroscope. See GYRO: FREE.
1927
free port. A port where certain import and export duties are waived (unless goods pass into the country) to facilitate reshipment to other countries.
1928
free wave. See WAVE.
1929
freezing. See FROST.
1930
freezing point. Temperature of solidification of a liquid in given conditions.
1931
frequency. The number of VIBRATIONS or CYCLES in unit time.
1932
frequency: extremely high (EHF). See FREQUENCY: RADIO.
1933
frequency: high (HF). See FREQUENCY: RADIO.
1934
frequency: low (LF). See FREQUENCY: RADIO.
1935
frequency: medium (MF). See FREQUENCY: RADIO.
1936
frequency: natural. The lowest resonant FREQUENCY of a body or system.
1937
frequency: radio. Any FREQUENCY at which electromagnetic RADIATION of energy is useful for communication.
Radio frequencies are usually classed as very low, below 30 kilohertz; low, 30-300 kilohertz; medium, 300-3,000
kilohertz; high, 3-30 MEGAHERTZ: very high, 30-300 MEGAHERTZ; ultra high, 300-3,000 MEGAHERTZ; super
high, 3,000-30,000 MEGAHERTZ; extremely high, 30,000-300,000 MEGAHERTZ.
1938
frequency: resonant. Any FREQUENCY at which a body or system vibrates more readily.
1939
frequency: super high (SHF). See FREQUENCY: RADIO.
1940
frequency: ultra high (UHF). See FREQUENCY: RADIO.
1941
frequency: very high (VHF). See FREQUENCY: RADIO.
1942
frequency: very low (VLF). See FREQUENCY: RADIO.
1943
frequency band. See BAND OF FREQUENCY.
1944
frequency channel. See CHANNEL.
91
1945
frequency modulation. See MODULATION.
1946
frequency of soundings. See DENSITY OF SOUNDINGS.
1947
freshet. An area of comparatively fresh water at or near the MOUTH of a STREAM flowing into the SEA.
A FLOOD or overflowing of a RIVER caused by heavy RAINS or melted SNOW.
1948
friction layer. Atmospheric LAYER extending from the EARTH's surface and of depth about 600 to 800 m, within
which air motion is affected significantly by surface friction. Above this LAYER lies the 'FREE ATMOSPHERE'.
1949
fringing reef. A REEF closely attached to a SHORE, as contrasted with a BARRIER REEF which is separated from
the SHORE by a LAGOON.
1950
front. In METEOROLOGY: a) surface of separation of two AIR MASSES (frontal surface); b) line of intersection of
the surface of separation of two AIR MASSES with another surface or with the GROUND.
1951
frontal surface. See FRONT.
1952
front light. See LIGHT(S): RANGE.
1953
front nodal point. See NODAL POINT.
1954
frost (or freezing). Lowering of air temperature to a value equal to or less than the FREEZING POINT of water (0°C).
1955
frost point. The temperature to which atmospheric moisture must be cooled to reach the point of saturation with respect
to ice.
1956
frost smoke. Fog-like CLOUDS, due to the contact of cold air with relatively warm SEA WATER, which appear over
newly formed LEADS and POOLS, or leeward, of the ICE EDGE, and which may persist while SLUSH or SLUDGE
and YOUNG ICE are forming.
1957
f-stop. See APERTURE: RELATIVE.
1958
fucus. See ROCKWEED.
1959
full moon. See PHASES OF THE MOON.
1960
function key. A special key on a computer which performs a preprogrammed function.
1961
fundamental circle. See PRIMARY GREAT CIRCLE.
1962
furrow. On the sea floor, a closed, linear, narrow, shallow depression.
1963
fusion: stereoscopic. See STEREOSCOPIC FUSION.
92
G
1964
gage. See GAUGE: TIDE.
1965
gain. The ration of output voltage, current or power to input voltage, current, or power in electronic instruments.
1966
gal (derived from Galileo). The unit of ACCELERATION in the CGS SYSTEM. See MILLIGAL.
1967
gale. WIND with a SPEED between 32 and 37 KNOTS (Beaufort scale wind force 8).
1968
gale warning. See WARNING.
1969
Galton's sun signal. See HELIOSTAT.
1970
galvanometer. An instrument for detecting and determining the intensity and direction of an electric current.
1971
galvanoplasty (or galvanoplastics). The process of coating things with metal by means of electrolysis.
1972
gamma. Photographic term for negative contrast resulting from development, and not the contrast of the subject itself; a
numerical measure of CONTRAST in the development of a NEGATIVE.
A small unit of MAGNETIC FIELD INTENSITY generally used in describing the EARTH's MAGNETIC FIELD.
-5
It is defined as being equal to 10 OERSTED.
1973
gamma ray. See X-RAYS.
1974
gap. In nomenclature of undersea features, a break in a RIDGE or RISE.
Any space where survey data fail to meet minimum coverage requirements. This may be a space not covered by any
data or a space where the minimum specified OVERLAP was not obtained.
A NOTCH.
1975
gas chromatography. An analysis method used to determine dissolved oxygen and nitrogen content of SEA WATER.
1976
gas field. An area in which natural gas occurs in quantities worthy of exploitation.
1977
gat. A natural or artificial PASSAGE or CHANNEL through SHOALS or steep BANKS, or across a line of BANKS
lying between two CHANNELS.
1978
gate: hydraulic. A form of valve used to regulate the FLOW of a liquid in a pipeline, RIVER or DAM.
1979
gauge. An instrument for measuring the size or state of anything.
1980
gauge: depth. A general term for an instrument made to indicate DEPTH of water, especially one in which sea depths
are indicated by pressure of water against a spring, or by degree of compression of air in a tube.
1981
gauge: float. A TIDE GAUGE that is operated by a float in a long, vertical stationary box to which the TIDE is
admitted through an opening in the bottom. Also called box gauge.
1982
gauge: pressure. An instrument for measuring pressure.
A TIDE GAUGE operated by the change in pressure at the BOTTOM of a body of water, due to the RISE and fall of
the TIDE.
1983
gauge: rain. Instrument for measuring the depth of water from PRECIPITATION supposed distributed over a horizontal impervious surface and not subject to evaporation. Also written as one word.
1984
gauge: tide. A device for measuring the HEIGHT OF TIDE. A graduated staff in a sheltered area where visual
observations can be made; or it may consist of an elaborate recording instrument making a continuous graphic record of
tide height against time. Such an instrument is usually actuated by a float in a pipe communicating with the sea
through a small hole which filters out shorter waves.
1985
gauss. The CGS unit of MAGNETIC INDUCTION.
1986
Gaussin error. See ERROR.
93
1987
gelbstoff. Yellowish organic material suspended in sea water which causes greenish colour of the sea water in coastal
areas; usually transported into the sea by rivers.
1988
General Bathymetric Chart of the Oceans (GEBCO). A global series of small scale bathymetric charts. Edited
through international cooperation by IHO and IOC.
1989
general chart. See CHART.
1990
general notices. All information and instructions that hydrographic offices may wish to bring to the attention of
mariners but the nature of which is such that they may not properly refer to any specific nautical document.
1991
generalisation. The omission of less important detail when compiling a chart. Its purpose is to avoid overloading charts
where space is limited.
1992
geocentric coordinates. See COORDINATES.
1993
geocentric latitude. See LATITUDE.
1994
geocentric parallax. See PARALLAX: DIURNAL.
1995
geodesic. See GEODESIC LINE.
1996
geodesic line. The shortest line on a mathematically derived surface, between two points on that surface. A geodesic
line on a REFERENCE SPHEROID is called a GEODETIC LINE. Also termed a geodesic.
1997
geodesy. The science which treats of the determination of the size and figure of the EARTH (GEOID) by such direct
measurements as TRIANGULATION, LEVELLING and gravimetric OBSERVATIONS.
1998
geodesy: satellite. The discipline which employs OBSERVATIONS of an earth satellite to extract geodetic
information.
1999
geodetic azimuth. See AZIMUTH.
2000
geodetic connection. See CONNECTION.
2001
geodetic control. See CONTROL.
2002
geodetic coordinates. See COORDINATES.
2003
geodetic data. Information concerning points established by a geodetic survey, such as descriptions for recovery,
coordinate values, height above sea level, and orientation.
2004
geodetic datum. See DATUM.
2005
geodetic equator. See EQUATOR.
2006
geodetic latitude. See LATITUDE.
2007
geodetic levelling. See LEVELLING.
2008
geodetic line. See GEODESIC LINE.
2009
geodetic longitude. See LONGITUDE.
2010
geodetic meridian. See MERIDIAN.
2011
geodetic parallel. See PARALLEL.
2012
geodetic position. See POSITION.
2013
geodetic survey. See SURVEY.
2014
geographic(al) coordinates. See COORDINATES.
94
2015
geographic information system. A computer based system for handling and integrating data from a variety of sources
which is directly or indirectly spatially referenced to Earth.
2016
geographic(al) latitude. See LATITUDE.
2017
geographic(al) longitude. See LONGITUDE.
2018
geographic(al) meridian. See MERIDIAN.
2019
geographic(al) parallel. See PARALLEL.
2020
geographic(al) pole. See POLE.
2021
geographic(al) position. See POSITION.
2022
geographic(al) range. See RANGE.
2023
geoid. The FIGURE OF THE EARTH considered as a mean sea level surface extended continuously through the
CONTINENTS. The actual geoid is an EQUIPOTENTIAL SURFACE to which, at every point, the PLUMB LINE
(direction in which GRAVITY acts) is perpendicular. It is the geoid which is obtained from observed DEFLECTIONS
OF THE VERTICAL and is the surface of reference for ASTRONOMICAL OBSERVATIONS and for GEODETIC
LEVELLING. See REFERENCE SPHEROID.
2024
geologic(al) survey. See SURVEY.
2025
geologic(al) time. See TIME.
2026
geology. The science which has for its object the investigation of the EARTH's CRUST, of the STRATA which enter
into its composition with their mutual relations, and of the successive changes to which their present condition and
position are due.
2027
geology: submarine. A field of study which applies the science of GEOLOGY to the earth beneath the SEA.
2028
geomagnetic field. The MAGNETIC FIELD of the EARTH. Also called terrestrial magnetic field or earth's magnetic
field.
2029
geomagnetism. The MAGNETISM of the EARTH. Also called terrestrial magnetism.
2030
geomatics. The science and technology of spatial information management, including the acquisition, storage, analysis
and processing, display and dissemination of geo-referenced information.
2031
geometric dilution of precision. See DILUTION OF PRECISION.
2032
geometric latitude. See LATITUDE: PARAMETRIC.
2033
geometric projection. See PROJECTION: PERSPECTIVE.
2034
geomorphology. A branch of both geography and geology that deals with the form of the earth, the general
configuration of its surface, and the changes that take place in the evolution of land forms.
2035
geophysics. The study of the physical characteristics and properties of the EARTH.
2036
geosphere. The solid and liquid portions of the EARTH; the LITHOSPHERE plus the HYDROSPHERE.
2037
geostationary satellite. An earth satellite moving eastward in an equatorial, circular orbit at an altitude (approximately
35,900 kilometers) such that its period of revolution is exactly equal to (synchronous with) the rotational period of the
earth. Such a satellite will remain fixed over a point on the earth's equator. Although geostationary satellites are frequently called geosynchronous or synchronous satellites, the orbit of an eastward moving synchronous satellite must be
equatorial if the satellite is to remain fixed over a point on the equator. Otherwise, the satellite moves daily in a figureeight pattern relative to the earth. Also called fixed satellite.
2038
geostrophic wind. That horizontal wind velocity for which the Coriolis force exactly balances the horizontal pressure
force.
2039
gibbous (adj.). See PHASES OF THE MOON.
95
2040
gimbals. A device consisting of two rings pivoted at right angles to each other, for supporting anything, such as an
instrument, in such a manner that it will remain essentially horizontal when the support tilts. Also called cardanic
suspension.
2041
glacier. A mass of SNOW and ICE continuously moving from higher to lower GROUND or, if afloat, continuously
spreading. The principal forms of glaciers are: ICE SHEETS, ICE SHELVES, ICE CAPS, ICE PIEDMONTS, and
various types of mountain glaciers.
2042
glacier ice. Any ICE floating on the SEA as an ICEBERG, which originates from a land GLACIER. Also called land
ice.
2043
glacier tongue. Projecting seaward extension of GLACIER, usually afloat.
2044
glaciology. The study of SNOW and ICE on the EARTH's surface, with specific concentration on the regime of active
GLACIERS.
2045
glen. A narrow, secluded VALLEY.
2046
glitter. The spots of light reflected from a point source by the surface of the SEA.
2047
global positioning system (GPS). A satellite navigation system intended to provide highly accurate position and
velocity information in three dimensions and precise time and time interval on a global basis continuously.
2048
Global Maritime Distress and Safety System (GMDSS). The GMDSS is a global communications service based
upon automated systems, both satellite based and terrestrial, to provide distress alerting and promulgation of
MARITIME SAFETY INFORMATION for mariners.
2049
globe. The EARTH; the world.
A spherical structure on whose surface is depicted the geographical configuration of the EARTH (terrestrial globe).
2050
gnomon. Any object the shadow of which serves as an indicator, as the SHADOW PIN of a SUN COMPASS.
2051
gnomonic chart. See CHART.
2052
gnomonic projection. See PROJECTION.
2053
Gold slide. An adjustable attachment to a MERCURIAL BAROMETER for giving resultant of CORRECTIONS for
INDEX ERROR, HEIGHT of instrument above SEA LEVEL, variation in GRAVITY due to LATITUDE, temperature.
Invented by Col. E. Gold.
2054
gong buoy. See BUOY: SOUND.
2055
goniometer. An instrument for measuring angles.
A pick-up coil which eliminates the necessity of having to rotate a radio direction finder antenna to determine
direction.
2056
gorge. A narrow opening, between HILLS, usually with precipitous sides.
2057
grab. A kind of closing scoop or bucket used in dredging or for bringing up BOTTOM SAMPLES.
2058
grab sampling. A random mode of collecting samples.
2059
grad (or grade). A unit of angle measurement, equal to the angle at the centre of a circle, subtended by one fourhundredth part of its circumference.
2060
grade. Rate of SLOPE or degree of INCLINATION, as a 2% grade. See also GRADIENT and GRAD.
2061
grade correction (tape). See TAPE: GRADE CORRECTION.
2062
gradient. The change of any quantity with distance in any given direction. See PRESSURE GRADIENT, TEMPERATURE LAPSE RATE.
The amount of SLOPE, INCLINATION to the HORIZONTAL, in road, railway, etc.
2063
gradient tints. See HYPSOMETRIC TINTS.
96
2064
graduation. The placing of marks on an instrument or device to represent standard values thereon. Also the marks so
placed.
The division and subdivision of LATITUDE and LONGITUDE shown on the borders of a CHART. See also
SCALE.
2065
graduation error. See ERROR OF GRADUATION.
2066
gram(me). A CGS unit of mass equal to one one-thousandth of a KILOGRAMME.
2067
granite. Light-coloured, acidic IGNEOUS ROCK mineralogically composed primarily of QUARTZ and potassiumsodium rich feldspars in which the mineral grains are visible to the naked eye (phaneritic texture).
2068
graphic control survey. See SURVEY.
2069
graphic scale. See SCALE: BAR.
2070
graticule. The network of lines representing MERIDIANS and PARALLELS on a MAP, CHART, or PLOTTING
SHEET. See also GRID.
A SCALE at the FOCAL PLANE of an optical instrument to aid in the measurement of objects. See also RETICLE.
2071
graticule adjustment. The transportation or movement of the GRATICULE in order to change the ORIGIN of
reference.
2072
gravel. Loose detrital material ranging in size from 2 to 256 mm.
2073
gravimeter. A weighing device or instrument of sufficient sensitivity to register variations in the WEIGHT of a
constant mass when the mass is moved from place to place on the EARTH and thereby subjected to the influence of
GRAVITY at those places. Also called gravity meter.
2074
gravimetric survey. See SURVEY.
2075
graving dock. See DOCK: DRY.
2076
gravitation. In general, the mutual attraction between masses of matter (bodies).
Gravitation is the component of GRAVITY which acts towards the EARTH.
2077
gravity. That force which tends to pull bodies towards the EARTH; that is to give bodies WEIGHT. Gravity is the
resultant of two opposing forces: GRAVITATION and CENTRIFUGAL FORCE due to the ROTATION of the
EARTH.
2078
gravity: centre of. A point at which the mass of the entire body may be regarded as being concentrated.
2079
gravity: direction of. The DIRECTION indicated by a PLUMB LINE. It is perpendicular to the surface of the GEOID.
Also called direction of the force of gravity.
2080
gravity: intensity of. The magnitude with which GRAVITY acts, expressed in suitable units, usually as an
ACCELERATION, in GALS; as a force, in DYNES.
2081
gravity anomaly. The difference between the observed gravity value properly reduced to SEA LEVEL and the
theoretical GRAVITY obtained from gravity formula. See BOUGUER ANOMALY, FREE-AIR ANOMALY,
ISOSTATIC ANOMALY.
2082
gravity anomaly chart. See CHART.
2083
gravity coring. A method to obtain cores by bottom penetration solely as a result of gravity.
2084
gravity meter. See GRAVIMETER.
2085
gravity wave. See WAVE.
2086
grease ice. A later stage of freezing than frazil ice when the crystals have coagulated to form a soupy layer on the
surface. Grease ice reflects little light, giving the sea a matt appearance.
2087
great circle. See CIRCLE.
97
2088
great circle: primary. See PRIMARY GREAT CIRCLE.
2089
great circle bearing. See BEARING.
2090
great circle chart. See CHART: GNOMONIC.
2091
great circle course. See COURSE.
2092
great circle sailing. See SAILING.
2093
great circle track. See TRACK.
2094
great diurnal range. See RANGE: DIURNAL.
2095
greatest elongation. See ELONGATION.
2096
great tropic range. See RANGE.
2097
Greenwich civil time. See TIME: GREENWICH MEAN.
2098
Greenwich hour angle. See HOUR ANGLE.
2099
Greenwich mean time (GMT). See TIME.
2100
Greenwich meridian. See MERIDIAN.
2101
Greenwich time. See TIME.
2102
grid. A series of lines, usually straight and parallel, superimposed on a CHART or PLOTTING SHEET to serve as a
directional reference for NAVIGATION. See also GRATICULE.
Two sets of mutually perpendicular lines dividing a MAP, CHART, or other representation of the EARTH's surface,
into squares or rectangles to permit location of any point by a system of RECTANGULAR COORDINATES.
In electronics, an electrode with one or more openings to permit passage of electrons or ions.
2103
grid: parallactic. In PHOTOGRAMMETRY, a uniform pattern of rectangular lines drawn or engraved on some transparent material, usually glass, and placed either over the PHOTOGRAPHS of a STEREOSCOPIC PAIR or in the
OPTICAL SYSTEM of a STEREOSCOPE, in order to provide a continuous floating-mark system.
2104
grid: perspective. In PHOTOGRAMMETRY, a network of lines, drawn or superimposed on a PHOTOGRAPH, to
represent the perspective of a systematic network of lines on the GROUND or DATUM PLANE. See also GRID
METHOD.
2105
grid: Universal Transverse Mercator (UTM). A grid system in which a grid network is applied to TRANSVERSE
o
MERCATOR PROJECTIONS of zones of the EARTH's surface extending to 80 N. and S. LATITUDES.
2106
grid azimuth. See AZIMUTH.
2107
grid bearing. See BEARING.
2108
grid coordinates. See COORDINATES.
2109
grid course. See COURSE.
2110
grid declination. The angular difference in DIRECTION between GRID NORTH and TRUE NORTH. It is measured
east or west from TRUE NORTH.
2111
grid direction. See DIRECTION.
2112
gridiron. See CAREENING GRID.
2113
grid magnetic angle. See VARIATION: GRID.
2114
grid meridian. See MERIDIAN.
98
2115
grid method. In PHOTOGRAMMETRY, a method of plotting detail from OBLIQUE PHOTOGRAPHS by
superimposing a perspective of a map grid on a PHOTOGRAPH and transferring the detail by eye, that is, by using the
corresponding lines of the map grid and its perspective as placement guides. See also GRID: PERSPECTIVE.
2116
grid navigation. See NAVIGATION.
2117
grid north. See NORTH.
2118
grid ticks. Short lines indicating where selected grid lines intersect the NEAT LINE.
2119
grid variation. See VARIATION.
2120
grivation. See VARIATION: GRID.
2121
groin (or groyne). A low artificial wall-like structure of durable material extending from the LAND to seaward for a
particular purpose, such as to protect the COAST or to force a CURRENT to scour a CHANNEL. Sometimes called a
rip-rap in New England waters.
2122
gross error. See ERROR.
2123
ground. The BOTTOM of the SEA. The solid surface of the EARTH.
2124
ground (v.t. and i.). To touch BOTTOM or run aground. See STRAND.
2125
ground control. See CONTROL.
2126
ground control point. See CONTROL POINT.
2127
ground distance. The great-circle distance between two ground positions, as contrasted with SLANT DISTANCE.
Also called ground range.
2128
ground effects. Influence exerted by the GROUND on the propagation of ELECTROMAGNETIC WAVES.
2129
ground ice. See ANCHOR ICE.
2130
ground layer. Thin layer of air adjacent to the EARTH's surface and of a depth which has been variously given as 10 m
to 100 m. Also called surface boundary layer.
2131
ground log. See LOG.
2132
ground nadir. See NADIR.
2133
ground parallel. See PARALLEL.
2134
ground photograph. See PHOTOGRAPH: TERRESTRIAL.
2135
ground plane. In PHOTOGRAMMETRY, the horizontal plane passing through the GROUND NADIR of a CAMERA
STATION.
2136
ground range. See GROUND DISTANCE.
2137
ground resolution. See RESOLUTION.
2138
ground speed. In AIR NAVIGATION, the rate of motion of an aircraft along its TRACK with relation to the
GROUND. See also AIR SPEED.
2139
ground survey. See SURVEY.
2140
ground swell. A long high ocean swell; also, this SWELL as it rises to prominent HEIGHT in SHALLOW WATER,
however, usually not so high or dangerous as BLIND ROLLERS.
2141
ground truth. The information acquired by a field study to calibrate or verify geographical data acquired by remote
sensing.
99
2142
ground wave. See WAVE.
2143
group. A term distinguishing a LIGHT exhibiting two or more flashes or OCCULTATIONS from one exhibiting a
single flash or single OCCULTATION.
2144
group velocity. The VELOCITY of a wave disturbance as a whole, i.e., of an entire group of component simple
harmonic waves.
2145
growler. A piece of ICE almost awash, smaller than a BERGY BIT.
2146
guard lock. See TIDE LOCK.
2147
guidance. The exercise of directing influence over the movements of a craft or missile with particular reference to the
selection of a flight PATH.
2148
gulf. A part of the SEA extending into the LAND, usually larger than a BAY.
2149
gully. Small VALLEY cut into soft SEDIMENTS on the CONTINENTAL SHELF or CONTINENTAL SLOPE.
2150
gust. A sudden brief increase in the SPEED of the WIND.
2151
gut. A narrow PASSAGE such as a STRAIT or INLET.
A CHANNEL in otherwise less deep water, generally formed by water in motion.
2152
guyot. See TABLEMOUNT.
2153
gyre. A closed circulatory system, but larger than a WHIRLPOOL or EDDY.
2154
gyro. See GYROSCOPE.
2155
gyro: free. A two-degree-of-freedom GYRO or a GYRO the spin axis of which may be oriented in any specified
attitude. Also called free gyroscope.
2156
gyro compass. See COMPASS: GYROSCOPIC.
2157
gyro pilot. An automatic pilot controlled by GYROSCOPES.
An automatic device for steering a vessel by means of control signals from a GYROSCOPIC COMPASS.
2158
gyro repeater. An electrically operated DIAL repeating at a distance the indications of the MASTER GYRO
COMPASS.
2159
gyroscope. A rapidly rotating mass free to move about one or both AXES perpendicular to the AXIS of ROTATION
and to each other. It is characterized by GYROSCOPIC INERTIA and PRECESSION. Sometimes shortened to gyro.
2160
gyroscope: directional. A gyroscopic device used to indicate a selected horizontal DIRECTION for a limited time. It
requires periodic resetting dependent upon the gyro precession rate or change in the desired HEADING or horizontal
DIRECTION.
2161
gyroscope: free. See GYRO: FREE.
2162
gyroscopic compass. See COMPASS.
2163
gyroscopic inertia. The property of a GYROSCOPE of resisting any force which tends to change its AXIS of
ROTATION. A GYROSCOPE tends to maintain the DIRECTION of its AXIS of ROTATION in space.
2164
gyroscopic stabilization. EQUILIBRIUM in the attitude and/or COURSE of a ship or airborne vehicle maintained by
the use of GYROSCOPES. Also, the maintenance (by the use of GYROSCOPES) of a CAMERA in a desired attitude
within an airborne vehicle.
2165
gyro sextant. See SEXTANT.
100
H
2166
hachures. Short lines drawn on a CHART or MAP for representing RELIEF. These lines are drawn in the direction of
the SLOPE and intensified on the shaded side of the feature assuming the area is illuminated from the north-west.
Unlike the CONTOUR LINES. they give no indication of the actual HEIGHT of LAND above SEA LEVEL. See also
HILL SHADING.
2167
hack watch. See WATCH.
2168
hail. PRECIPITATION of small balls or pieces of ICE (HAILSTONES) with a diameter ranging from 5 to 50 mm (0.2
to 2.0 in) or sometimes more, falling either separately or agglomerated into irregular lumps.
2169
hailstone. Globule or piece of ICE, with a diameter varying between 5 and 50 mm or even more, the fall of which
constitutes HAIL. Hailstones consist almost entirely of transparent ICE, or of a series of LAYERS of transparent ICE
with a thickness of at least 1 mm, alternating with translucent LAYERS.
2170
halation. In PHOTOGRAPHY, a spreading of a photographic IMAGE beyond its proper boundaries, due especially to
REFLECTION from the side of the film or plate support opposite to that on which the EMULSION is coated. Particularly noticeable in PHOTOGRAPHS of bright objects against a darker background.
2171
half byte. 4 bits of a 8 BIT BYTE; usually used to encode the figures 0....9.
2172
half convergency. See ARC TO CHORD CORRECTION.
2173
half tide. See TIDE.
2174
half tide level. The LEVEL midway between MEAN HIGH WATER and MEAN LOW WATER. It may differ slightly
from MEAN SEA LEVEL. Also called mean tide level.
2175
halftone. In PHOTOGRAPHY or printing, a technique in which the solid IMAGE is broken up by the use of a screen
into evenly spaced dots of equal density but of varying size. This gives an illusion of continuous tone.
2176
halo (solar, lunar). Group of optical PHENOMENA, in the form of rings, arcs, pillars or bright spots, produced by the
REFRACTION or REFLECTION of light by ice crystals suspended in the ATMOSPHERE (cirriform CLOUDS, ICE
FOG, etc.).
2177
halo: large (halo of 46 ). HALO much less frequent and always less luminous than the SMALL HALO. It comprises a
o
faintly luminous ring centered on the SUN or MOON and has an apparent radius of 46 .
2178
halo: small (halo of 22 ). White, or mostly white, luminous ring of 22 radius with the luminary at its centre. The small
halo shows a faint red fringe on the inside and, in some rare cases, a violet fringe on the outside. The portion of the sky
inside the ring is conspicuously darker than the rest of the sky.
2179
halocline. A vertical GRADIENT of salinity (which is usually positive) in some LAYER of the body of water, which is
appreciably greater than the GRADIENTS above and below it.
2180
hand lead. See LEAD.
2181
hand lead sounding. See SOUNDING.
2182
hanging compass. See COMPASS.
2183
hanging traverse. See TRAVERSE: OPEN.
2184
harbour (or harbor). A natural or artificially improved body of water providing protection for vessels, and generally
ANCHORAGE and docking facilities. See also PORT.
2185
harbour: inner. The part of a HARBOUR more remote from the SEA, as contrasted with the OUTER HARBOUR.
These expressions are usually used only in a HARBOUR that is clearly divided into two parts, as by a narrow passageway or man-made structures. The inner harbour generally has additional protection and is often the principal berthing
area.
2186
harbour: island. A HARBOUR formed, or mainly protected, by ISLANDS.
o
o
o
101
2187
harbour: outer. The part of a HARBOUR towards the SEA, through which a vessel enters the INNER HARBOUR.
2188
harbour: tidal. A HARBOUR affected by the TIDES, in distinction from a HARBOUR in which the water level is
maintained by CAISSONS or gates.
2189
harbour chart. See CHART.
2190
harbour line. The line beyond which wharves and other structures cannot be extended.
2191
harbour master. A local official who has charge of mooring and berthing of vessels, collecting harbour fees, etc.
2192
harbour reach. The reach of a winding RIVER or ESTUARY which leads directly to the HARBOUR.
2193
harbour works. Permanent manmade structures built along the coast which form an integral part of the harbour system
such as jetties, moles, quays or other port facilities, coastal terminals, wharves, breakwaters, sea walls, etc.
2194
hard bottom. The sea floor not covered by unconsolidated SEDIMENT.
2195
hard iron. Iron or steel which is not readily magnetized by induction, but which retains a high percentage of the
MAGNETISM acquired. The opposite is SOFT IRON.
2196
hardware. All physical material components of a computer system as e.g. central processing unit (CPU), peripheral
devices etc.. May also include individual chips.
2197
harmonic. A sinusoidal quantity having a FREQUENCY that is an integral multiple of the FREQUENCY of a periodic
quantity to which it is related.
2198
harmonic analysis of tide. The mathematical process by which the observed TIDE at a place is analyzed by breaking it
down into a number of constituent tides of simple periodic forces, each having a fixed PERIOD. In this process the SUN
and MOON are replaced by a number of hypothetical tide-producing bodies which move in circular ORBITS around the
EARTH in the plane of the EQUATOR. See HARMONIC CONSTANTS, HARMONIC CONSTITUENT.
2199
harmonic constants. The AMPLITUDE and EPOCHS of the HARMONIC CONSTITUENT of the TIDE, or TIDAL
CURRENT at any place.
2200
harmonic constituent. One of the harmonic elements in a mathematical expression for the TIDE-PRODUCING
FORCE, and in corresponding formulae for the TIDE or TIDAL CURRENT. Each constituent represents a periodic
change or variation in the RELATIVE POSITIONS of the EARTH, SUN and MOON. Also called tidal constituent or
component.
2201
harmonic prediction. In tidal terminology, the method of predicting TIDES and TIDAL CURRENTS by combining
the HARMONIC CONSTITUENTS into a single curve. The work was usually done mechanically by a machine
designed for this purpose, called a TIDE PREDICTING MACHINE; nowadays the work is done by COMPUTERS.
2202
hatching. The drawing or engraving of fine, parallel or crossed lines to show SHADING.
2203
haven. An enclosed and protected HARBOUR.
2204
Hayford's spheroid. The SPHEROID based upon an investigation made in 1909 by Hayford, a geodesist of U.S. Coast
& Geodetic Survey, using the large TRIANGULATION NET then existing in the U.S.A., and taking into account the
inequal density of the EARTH's CRUST. The Geodetic and Geophysical Union (now the International Union of
Geodesy and Geophysics) adopted in 1924 the Hayford's spheroid (with some slight modifications) as the
INTERNATIONAL ELLIPSOID OF REFERENCE.
2205
hazard beacon. See BEACON.
2206
haze. Suspension in the ATMOSPHERE of extremely small, dry particles which are invisible to the naked eye but are
numerous enough to give the sky an appearance of OPALESCENCE.
2207
head. A precipitous CAPE, or PROMONTORY. See also HEADLAND.
That part of a RIP CURRENT that has widened out seaward of the BREAKERS.
2208
heading. The direction in which the longitudinal axis of a craft is pointed, usually expressed in DEGREES from
NORTH (TRUE, MAGNETIC or COMPASS).
102
2209
headland. A high steep PROMONTORY. Usually called HEAD when coupled with a specific name.
2210
head sea. A SEA in which the WAVES move in a direction approximately opposite to the HEADING.
2211
headwater(s). The STREAMS from the sources and upper parts of a RIVER.
2212
headway. Motion in a forward direction. Also called SEAWAY.
2213
head wind. WIND which blows in a direction opposite to that in which an object is moving, with respect to the
EARTH's surface.
2214
heat equator. See EQUATOR: THERMAL.
2215
heat lightning. Lightning flash at a distance which may be observed as a short illumination of the sky or of a CLOUD,
close to the HORIZON.
2216
heat wave. Marked warming of the air, or the invasion of very warm air, over a large area.
2217
heave. The oscillatory rise and fall of a ship due to the entire hull being lifted by the force of the sea.
2218
heave compensation. The removal of the effect of wave motion from the recorded seabed profile.
2219
heavenly body. See CELESTIAL BODY.
2220
heel. Transverse INCLINATION of a vessel due to the action of WAVES, WIND, a greater WEIGHT on one side, etc.
See also LIST.
2221
heeling error. See ERROR.
2222
heeling magnet. A permanent MAGNET placed vertically in a tube under the centre of a marine MAGNETIC COMPASS, to correct for HEELING ERROR.
2223
height. The vertical distance of a LEVEL, a point, or an object considered as a point, measured from a specified
DATUM.
The vertical dimension of an object.
2224
height finder. A stereoscopic RANGE FINDER so constructed as to indicate vertical HEIGHTS rather than SLANT
RANGE.
2225
height of cloud base. HEIGHT above the EARTH's surface, at a given point, of the base of the lowest CLOUD whose
CLOUD AMOUNT exceeds a given value. Called ceiling in U.S. terminology.
2226
height of eye correction. See DIP CORRECTION.
2227
height of tide. The vertical distance from the CHART DATUM to the level of the water at any TIME.
2228
heliocentric parallax. See PARALLAX: ANNUAL.
2229
heliograph. A device for reflecting the SUN's RAYS from one point to another for sending messages.
In METEOROLOGY, instrument which records the time interval during which solar RADIATION reaches
sufficient intensity to cast distinct shadows. Also called sunshine recorder.
2230
heliostat. An instrument composed of one or more plane MIRRORS, so mounted and arranged that a BEAM of sunlight
may be reflected by it in any desired direction and kept there by continuous adjustment. It is used in geodetic
SURVEYING for reflecting a BEAM of sunlight from a STATION towards another distant STATION, where it can be
observed with a THEODOLITE. Also called heliotrope, or Galton's sun signal.
2231
heliotrope. See HELIOSTAT.
2232
heli pad. A site on which helicopters may land and take off.
2233
helium magnetometer. See MAGNETOMETER.
2234
Helmert spheroid. See REFERENCE SPHEROID.
103
2235
hemispherical map. See MAP.
2236
henry. The unit of electrical inductance in the SI SYSTEM.
2237
hertz. A unit of FREQUENCY in the SI SYSTEM. See also CYCLE PER SECOND.
2238
hertzian waves. See WAVE(S): RADIO.
2239
high. See ANTICYCLONE.
2240
higher high water (H.H.W.). The higher of two HIGH WATERS occurring during a TIDAL DAY if the DIURNAL
INEQUALITY prevails.
2241
higher high water interval. See LUNITIDAL INTERVAL.
2242
higher low water (H.L.W.). The higher of two LOW WATERS occurring during a TIDAL DAY if DIURNAL
INEQUALITY prevails.
2243
higher low water interval. See LUNITIDAL INTERVAL.
2244
highest astronomical tide. The highest tidal level which can be predicted to occur under average meteorological
conditions and under any combination of astronomical conditions.
2245
high frequency (HF). See FREQUENCY: RADIO.
2246
highland (or highlands). High or elevated LAND; a lofty HEADLAND or CLIFF. The mountainous or elevated part of
any country; occasionally also in the names of geographical districts.
2247
high noon. See NOON: LOCAL APPARENT.
2248
high oblique photograph. See PHOTOGRAPH.
2249
high seas. The open sea beyond the exclusive economic zone, the territorial sea or the archipelagic waters of an
archipelagic state.
2250
high tide. See HIGH WATER.
2251
high water (H.W.). The highest LEVEL reached at a place by the water surface in one OSCILLATION. Also called
high tide.
2252
high water: double. A HIGH WATER consisting of two maxima of nearly the same HEIGHT separated by a relatively
small depression. See also TIDE: DOUBLE.
2253
high water: storm. The highest LEVEL to which the SEA rises during a STORM and usually marked by a line of
DEBRIS high up on the BEACH.
2254
high water full and change (H.W.F. and C.). See ESTABLISHMENT.
2255
high water inequality. See DIURNAL INEQUALITY.
2256
high water interval. See LUNITIDAL INTERVAL.
2257
high water line. See HIGH WATER MARK.
2258
high water lunitidal interval (H.W.I.). See LUNITIDAL INTERVAL.
2259
high water mark. The mark left by the TIDE at HIGH WATER. The line or LEVEL reached, especially the highest
line ever reached. Also called high water line.
A permanent MARK which indicates the maximum observed stage of TIDE.
2260
high water quadrature (H.W.Q.). The average HIGH WATER INTERVAL when the MOON is at QUADRATURE.
See LUNITIDAL INTERVAL.
2261
high water stand. See STAND OF TIDE.
104
2262
hill. A small isolated ELEVATION, smaller than a MOUNTAIN. See also KNOLL.
2263
hillock. A small HILL.
2264
hill shading. A method of indicating RELIEF on MAPS by shading normally the SLOPES facing south and east, i.e. it
is assumed that the area mapped is illuminated from the north-west. The method is often used in association with
CONTOURS.
2265
hinterland. The district behind that lying along the COAST; the back country.
2266
historic bay. Historic bays are those over which the coastal state has publicly claimed and exercised jurisdiction and
this jurisdiction has been accepted by other states. Historic bays need not match the definition of "bay" contained in the
United Nations Convention on the Law of the Sea.
2267
hoarfrost. Deposit of ICE, having a crystalline appearance, generally assuming the form of scales, needles, feathers or
fans. Hoarfrost is produced in a manner similar to DEW but at a temperature below O°C. Also written as two words.
2268
hodograph. Used in oceanography. The tidal current vector hodograph is the figure traced out by the tip of a vector
representing the current over the tidal cycle.
2269
hodometer. See ODOMETER.
2270
holding ground. An expression usually used with a modifying adjective to indicate the quality of the holding power of
the material constituting the BOTTOM of an ANCHORAGE; e.g., of good (or poor) holding ground.
2271
hole. An abrupt HOLLOW in the GROUND or ocean floor. See also PASSAGE.
2272
holiday. An unintentional unsurveyed area within a given hydrographic survey where the spacing between sounding
lines or surveys exceeds the maximum allowable limits.
2273
hollow. TROUGH or depression between CRESTS of sea-waves.
A cavity or HOLE.
2274
homing. NAVIGATION toward a point by maintaining constant some navigational COORDINATE(S), usually BEARING.
The procedure of using the direction-finding equipment of one RADIO STATION with the emission of another
RADIO STATION, where at least one of the STATIONS is mobile, and whereby the MOBILE STATION proceeds
continuously towards the other STATION.
2275
hook. A sharp bend or angle in the course or length of anything; especially a bend in a RIVER.
A projecting corner, POINT or SPIT of LAND.
2276
horizon. In general, the apparent or visible junction of the EARTH and sky, as seen from any specific position.
2277
horizon: apparent. The irregular line along which rays from the point of observation are tangent to the surface of the
EARTH. Also called visible (or local) horizon.
2278
horizon: artificial. A device for indicating the HORIZONTAL, as a bubble, GYROSCOPE, PENDULUM, or the flat
reflecting surface of a liquid.
2279
horizon: celestial. That circle of the CELESTIAL SPHERE, formed by the intersection of the CELESTIAL SPHERE
and a plane through the centre of the EARTH, and perpendicular to the zenith-nadir line. Also called rational horizon.
2280
horizon: closing the. Measuring the last of a series of horizontal angles at a STATION required to make the series
complete around the HORIZON. See also ERROR OF CLOSURE OF HORIZON.
2281
horizon: dip of the. See DIP.
2282
horizon: false. A line resembling the APPARENT HORIZON but above or below it.
2283
horizon: radio. See RADIO.
2284
horizon: rational. See HORIZON: CELESTIAL.
105
2285
horizon: sensible. That circle of the CELESTIAL SPHERE formed by the intersection of the CELESTIAL SPHERE
and a plane through any point, such as the eye of an observer, and perpendicular to the zenith-nadir line.
2286
horizon: true. In PHOTOGRAMMETRY, a horizontal plane passing through a point of vision or PERSPECTIVE
CENTRE. The APPARENT HORIZON approximates the true horizon only when the point of vision is very close to
SEA LEVEL.
2287
horizon: visible (or local). See HORIZON: APPARENT.
2288
horizon glass. That glass of a MARINE SEXTANT, attached to the frame, through which the HORIZON is observed.
That half of this glass nearer the frame is silvered to form the HORIZON MIRROR for reflecting the IMAGE of a
CELESTIAL BODY; the other half is clear.
2289
horizon line. See HORIZON TRACE.
2290
horizon mirror. The mirror part of the HORIZON GLASS. The expression is sometimes used somewhat loosely to
refer to the HORIZON GLASS.
2291
horizon photograph. In AERIAL PHOTOGRAPHY, a PHOTOGRAPH of the HORIZON, taken simultaneously with
a VERTICAL PHOTOGRAPH and used to determine the RELATIVE TILT between adjacent VERTICAL
PHOTOGRAPHS.
2292
horizon shade. One of the pivoted coloured glasses which can be swung before the HORIZON GLASS of a SEXTANT
to regulate the intensity of light.
2293
horizon system of coordinates. A set of CELESTIAL COORDINATES based on the CELESTIAL HORIZON as the
PRIMARY GREAT CIRCLE; usually ALTITUDE and AZIMUTH or AZIMUTH ANGLE.
2294
horizontal (adj). Parallel to the plane of the HORIZON; perpendicular to the DIRECTION OF GRAVITY.
2295
horizontal axis. See AXIS.
2296
horizontal circle. See CIRCLE.
2297
horizontal control. See CONTROL.
2298
horizontal control datum. The position on the SPHEROID OF REFERENCE assigned to the HORIZONTAL
CONTROL (TRIANGULATION and TRAVERSE) of an area and defined by (1) the POSITION (LATITUDE and
LONGITUDE) of one selected STATION in the area, and (2) the AZIMUTH from the selected STATION to an
adjoining STATION. See also DATUM: GEODETIC.
2299
horizontal coplane. See COPLANE: BASAL.
2300
horizontal dilution of precision (HDOP). See DILUTION OF PRECISION.
2301
horizontal force instrument. See VIBRATING NEEDLE.
2302
horizontal intensity of the earth's magnetic field. The strength of the horizontal component of the EARTH'S
MAGNETIC FIELD.
2303
horizontal parallax. See PARALLAX.
2304
horizontal photograph. See PHOTOGRAPH.
2305
horizontal plane. See PLANE.
2306
horizon trace. In PHOTOGRAMMETRY, an imaginary line, in the plane of a PHOTOGRAPH, which represents the
IMAGE of the TRUE HORIZON; it corresponds to the intersection of the plane of a PHOTOGRAPH and the
horizontal plane containing the internal PERSPECTIVE CENTRE or rear NODAL POINT of the LENS. Also called
horizon line.
2307
horn. FOG SIGNAL using compressed air or electricity to vibrate a diaphragm. Horns exist in a variety of types which
differ greatly in their SOUND and power. Further to the recent action taken by the HYDROGRAPHER of the U.K.
such terms as NAUTOPHONE, TYPHON and others are gradually being embraced by the general term 'Horn'.
106
2308
horn buoy. See BUOY: SOUND.
2309
hour. A 24th part of a DAY.
2310
hour angle. ANGULAR DISTANCE west of a CELESTIAL MERIDIAN, the arc of the CELESTIAL EQUATOR, or
the angle at the CELESTIAL POLE, between the UPPER BRANCH of a CELESTIAL MERIDIAN and the HOUR
o
CIRCLE of a CELESTIAL BODY or the VERNAL EQUINOX, measured westward through 24 HOURS (360 ). It is
usually further designated as local, Greenwich, or sidereal, as the origin of measurement is the LOCAL or
GREENWICH MERIDIAN, or the HOUR CIRCLE of the VERNAL EQUINOX.
2311
hour circle. A GREAT CIRCLE on the CELESTIAL SPHERE passing through the CELESTIAL POLES. Also called
declination circle, circle of declination, or circle of right ascension.
2312
hulk. Usually refers to an unrigged hull of a wrecked or condemned ship.
2313
humidity. Atmospheric water vapour content, expressed in any of several measures, such as relative humidity.
2314
humidity of the air. Water vapour content of the air.
2315
hummock. A natural ELEVATION of the EARTH's surface resembling a HILLOCK, but smaller and lower.
In ice terminology, a mound of ICE raised by pressure. May be fresh or weathered.
2316
hummocked ice. SEA ICE piled haphazardly one piece over another, and which may be weathered.
2317
hummocking. Pressure process by which LEVEL ICE becomes broken up into HUMMOCKS.
2318
Hunter short base apparatus. A BASE APPARATUS designed for measuring short BASES by the subtended
method. It consists of a jointed STEEL TAPE made up of four sections suspended in CATENARY between regularly
spaced supports. The Hunter short base apparatus may be used over rough GROUND which is unsuitable for ground
TAPING.
2319
hunting. Fluctuation about a midpoint due to INSTABILITY, as OSCILLATIONS of the needle of an instrument about
the zero point, or alternate LEAD and LAG of a synchronous motor with respect to the alternating current.
2320
hurricane. Term, derived from a Caribbean word, first applied to TROPICAL CYCLONES of the Caribbean Sea.
WIND with a speed equal to or greater than 58 KNOTS. (Beaufort scale wind force 12.)
2321
hurricane warning. See WARNING.
2322
hydrograph. Used in oceanography. The tidal current vector hydrograph is the figure traced out by the tip of a vector
representing the current over the tidal cycle.
2323
hydrographer. A person who studies and practices the science of HYDROGRAPHY; the term is often applied to the
person in charge of a hydrographic department or office of a country.
2324
hydrographic airborne laser sounder. A system for measuring the depth of water by sending a LASER pulse from an
aircraft and recording the time difference between the sea surface and the bottom reflection.
2325
hydrographic chart. See CHART: NAUTICAL.
2326
hydrographic circle. See CIRCLE.
2327
hydrographic data acquisition. All on-site measurements to collect hydrographic data.
2328
hydrographic data processing system. A system for verification, selection, and calculation of hydrographic survey
data.
2329
hydrographic datum. See DATUM: CHART.
2330
hydrographic sextant. See SEXTANT: SOUNDING.
2331
hydrographic signal. See SIGNAL.
2332
hydrographic survey. See SURVEY.
107
2333
hydrographic survey examination. Review of a hydrographic survey that is directed toward evaluating compliance
with, and the adequacy of, standards, rather than a careful examination of the data and their quality. The survey is
carefully examined for adequacy with respect to data acquisition and conformance with applicable standards and project
instructions. In addition, the overall condition of the records and the Descriptive Report are examined. The digital data
representing the survey is plotted and subjected to a cursory examination (spot check) to ensure that digital data
standards are being adhered to. The examination of the survey data is limited only to that necessary to evaluate the
acquisition and processing procedures.
2334
hydrographic survey sheet. An inclusive term used to designate both BOAT SHEETS and SMOOTH SHEETS. Also
called survey sheet.
2335
hydrography. That branch of applied science which deals with the measurement and description of the physical
features of the navigable portion of the EARTH's surface and adjoining coastal areas, with special reference to their use
for the purpose of NAVIGATION.
2336
hydrologic front. A relatively narrow transition zone separating two water masses in the ocean.
2337
hydrologic series. Simultaneous observations carried out to obtain oceanographic data at specified levels.
2338
hydrology. The scientific study of the waters of the EARTH, especially with relation to the effects of
PRECIPITATION and evaporation upon the occurrence and character of water in STREAMS, LAKES, and on or
below the land surfaces.
2339
hydrometeor. METEOR consisting of an ensemble of liquid or solid water particles falling through or suspended in the
ATMOSPHERE, blown by the WIND from the EARTH'S surface or deposited on objects on the ground or in the free
air.
2340
hydrometer. An instrument for determining the SPECIFIC GRAVITY of liquids.
2341
hydrophone. An electroacoustic TRANSDUCER that responds to water-borne SOUND WAVES and delivers essentially equivalent electric WAVES. See also PRESSURE HYDROPHONE.
2342
hydrophone streamer. A chain of separate receivers for seismic sound sources towed by a ship. The streamer contains
many individual hydrophone elements and is divided electronically into a number of discrete sections or channels.
2343
hydrophotometer. An instrument used to measure the EXTINCTION COEFFICIENT of transmission of light in water.
It consists of a constant light source placed at a specific distance from a photocell. When placed in water, the electrical
OUTPUT of the photocell is proportional to the amount of light striking the cell which, in turn, depends upon the
transparency of the water. The instrument is calibrated to read 100 percent light transmission in air.
2344
hydroplastic corer. See CORER.
2345
hydrosphere. The waters of the EARTH's surface collectively.
The 'water sphere' in comparison and contrast with LITHOSPHERE and ATMOSPHERE.
2346
hydrostatic instability. See INSTABILITY: STATIC.
2347
hydrostatic levelling. The transfer of level between two points by the use of a pipe filled with water laid on the sea bed
with vertical sections at each end.
2348
hydrostatic pressure. See PRESSURE.
2349
hydrostatic stability. See STABILITY: STATIC.
2350
hygrograph. HYGROMETER which includes an arrangement for the time recording of atmosphere humidity.
2351
hygrometer. An instrument for measuring the HUMIDITY OF THE AIR. See also PSYCHROMETER.
2352
hygrothermograph. Instrument resulting from the combination of a THERMOGRAPH and a HYGROGRAPH and
furnishing, on the same DIAGRAM, simultaneous time recording of atmospheric temperature and humidity. Also called
thermohygrograph.
108
2353
hyperbola. An open curve with two parts, all points of which have a constant difference in distance from two fixed
points called foci.
2354
hyperbolic line of position. A LINE OF POSITION in the shape of a hyperbola, determined by measuring the
difference in distance to two fixed points.
2355
hyperbolic navigation. See NAVIGATION.
2356
hyperbolic number(s). Numerical figures characterizing the hyperbolae of a pattern or LATTICE in a HYPERBOLIC
SYSTEM of RADIOLOCATION.
2357
hyperbolic system. Radiolocation system supplying HYPERBOLIC LINES OF POSITION.
2358
hypsograph. A circular instrument of the slide-rule type used to compute ELEVATIONS from vertical angles and
horizontal distances.
2359
hypsographic (or hypsometric) curve. A curve used to indicate the proportion of the area of the surface at various
ELEVATIONS above or DEPTHS below a given DATUM.
2360
hypsometer. A device for measuring HEIGHTS of land surfaces by the boiling point of water.
2361
hypsometric curve. See HYPSOGRAPHIC CURVE.
2362
hypsometric tints. A succession of shades or colour graduations used to depict ranges of ELEVATIONS. Also called
gradient tints or elevation tints.
2363
hypsometry. The determination of ELEVATIONS above SEA LEVEL. Generally applied to the determination of
ELEVATIONS through the measurement of air pressure by observing the boiling point of a liquid.
2364
hysteresis. Retardation or LAG in the effect of changing forces, as in ship's MAGNETISM induced by the EARTH's
MAGNETIC FIELD.
109
I
2365
ice. The solid form of water.
2366
iceberg. A large mass of floating or stranded ICE broken away from a GLACIER or from an ICE SHELF. Often of
considerable HEIGHT (in any case more than 5 m above the LEVEL of the SEA).
2367
ice blink. A typical whitish glare on low CLOUDS above an accumulation of distant ICE. It is especially glowing when
observed on the HORIZON.
2368
icebound (adj.). Said of a HARBOUR, INLET, etc. when NAVIGATION by ships is prevented due to ICE, except
possibly with the assistance of an icebreaker.
Of a ship, surrounded so closely by ICE as to be incapable of proceeding.
2369
ice cake. A FLOE smaller than 10 m across. If less than 2 m, it is termed BRASH ICE or small ice cake.
2370
ice cap. See ICE SHEET.
2371
ice cluster. A concentration of SEA ICE covering hundreds of square kilometres, which is found in the same region
every summer.
2372
ice concentration. In SEA ICE reporting, the ratio of the areal extent of ICE present to the total areal extent of ICE and
water. Concentration is usually reported in tenths. Also called ice cover.
2373
ice cover. See ICE CONCENTRATION.
2374
ice edge. The BOUNDARY at any given time between the open sea and SEA ICE of any kind, whether drifting or fast.
2375
ice field. Area of PACK ICE consisting of any size FLOES, which is greater than 10 km across.
2376
ice floe. See FLOE.
2377
ice fog. See FOG.
2378
icefoot. A narrow strip of ICE attached to the COAST, unmoved by TIDES and remaining after the FAST ICE has
broken free.
2379
ice free. Water surface completely free of ICE.
2380
ice front. The vertical CLIFF forming the seaward face of an ICE SHELF. See ICE WALL.
2381
ice island. A form of tabular BERG found in the Arctic Ocean, with a thickness of 30 to 50 m and from a few thousand
square metres to 500 sq. km in area. Ice islands are characterized by a regularly undulating surface, which gives them a
ribbed appearance from the air.
2382
ice limit. The average position of the ICE EDGE in any given month or period based on OBSERVATIONS over a
number of years.
2383
ice piedmont. ICE covering a coastal strip of low-lying LAND backed by MOUNTAINS. The surface of an ice
piedmont slopes gently seawards and may be anything from 50 m to 50 km wide, fringing long stretches of
COASTLINE with ice cliffs. Ice piedmonts frequently merge into ICE SHELVES.
2384
ice rind. A thin, elastic, shining crust of ICE, formed by the freezing of SLUDGE on a quiet sea surface. Thickness less
than 5 cm.
2385
ice rise. A mass of ICE resting on ROCK and surrounded either by an ICE SHELF or partly by an ICE SHELF and
partly by SEA. No ROCK is exposed and there may be none above SEA LEVEL. Ice rises often have a dome-shaped
surface. The largest known is about 100 km across.
2386
ice sheet. A continuous mass of ICE and SNOW of considerable thickness and large area. Ice sheets may be resting on
ROCK (see INLAND ICE SHEET) or floating (see ICE SHELF). Ice sheets of less than 40,000 sq. km resting on
ROCK are called ice caps.
110
2387
ice shelf. A floating ICE SHEET of considerable thickness. Ice shelves are usually of great horizontal extent and have a
level or gently undulating surface. They are nourished by local snow accumulation and often also by the seaward
extension of land glaciers. Limited areas may be aground. The initial stage is called BAY ICE until the surface is more
than about 2 m above SEA LEVEL. The seaward edge is termed an ICE FRONT.
2388
ice storm. Intense formation of ICE on objects by the freezing, on impact, of drops of RAIN or DRIZZLE.
2389
ice wall. An ice cliff forming the seaward margin of an INLAND ICE SHEET, ICE PIEDMONT or ICE RISE. The
rock basement may be at or below SEA LEVEL. See ICE FRONT.
2390
identification beacon. See BEACON.
2391
igneous rock. ROCK formed by solidification of molten material or MAGMA.
2392
illuminated contours. An application of ILLUMINATED RELIEF in which CONTOURS appear lighter on illuminated SLOPES and darker on the shadow SLOPES.
2393
illuminated relief. The representation of RELIEF with the appearance of lighting from one or more directions, giving a
three-dimensional impression. Also called shaded relief.
2394
illumination (at a point of a surface). Quotient of the LUMINOUS FLUX incident on an infinitesimal element of the
surface containing the point under consideration, by the area of that element.
2395
image. The optical counterpart of an object.
2396
image: erect. An IMAGE that appears upright or in the same relative position as the object.
2397
image: inverted. An IMAGE that appears upside down in relation to the object.
2398
image: real. An IMAGE actually produced and capable of being shown on a surface, as in a CAMERA.
2399
image: virtual. An IMAGE that cannot be shown on a surface but is visible, as in a MIRROR.
2400
image point. In PHOTOGRAMMETRY, the IMAGE on a PHOTOGRAPH corresponding to a definite object on the
GROUND.
2401
imagery. Techniques to obtain, process or interpret images created by different types of radiation, e.g. light, infrared, xrays.
2402
impedance. The total opposition offered to an alternating current. It may consist of any combination of resistance,
inductive reactance, or capacitive reactance.
2403
impersonal micrometer. See MICROMETER: TRANSIT.
2404
impulse. See PULSE.
2405
inch. A unit of length equal to 1/12 of a FOOT or 2.54 cm.
2406
incidence: angle of. See ANGLE OF INCIDENCE.
2407
incident nodal point. See NODAL POINT.
2408
incineration areas (at sea). An offshore area officially designated as suitable for the burning of chemical waste by
specially equipped ships.
2409
inclination. The angle which a line or surface makes with the VERTICAL, horizontal or with another line or surface.
2410
inclination: magnetic. See DIP.
2411
inclination of the horizontal axis. The vertical angle between the HORIZONTAL AXIS of a surveying or astronomical instrument and the plane of the HORIZON.
111
2412
inclinometer. An instrument for measuring the INCLINATION to the horizontal of the longitudinal axis of an aircraft.
See DIP CIRCLE, WIRE ANGLE INDICATOR.
2413
indelta. Inland area where a RIVER subdivides (now in common use, especially in Australia).
2414
indentation. A recess in a COASTLINE.
2415
index arm. A slender bar carrying an index; particularly that bar which pivots at the centre of curvature of the arc of a
MARINE SEXTANT and carries the index and the VERNIER or MICROMETER. Also called index bar.
2416
index bar. See INDEX ARM.
2417
index chart. See CHART.
2418
index contours. Certain CONTOUR LINES (usually every fifth) accentuated by use of a line heavier than the
intervening ones.
2419
index correction. That CORRECTION due to INDEX ERROR.
2420
index error. See ERROR.
2421
index glass. See INDEX MIRROR.
2422
index mark. In PHOTOGRAMMETRY, a real mark (such as a cross or dot) lying in the plane or the object space of a
PHOTOGRAPH and used singly as a reference mark in certain types of monocular instruments, or as one of a pair to
form a FLOATING MARK (as in certain types of STEREOSCOPES).
2423
index map. See MAP.
2424
index mirror. The MIRROR attached to the INDEX ARM of a MARINE SEXTANT. Also called index glass.
2425
index of refraction. See REFRACTION: INDEX OF.
2426
index shade. On a SEXTANT, one of the pivoting coloured glasses which can be swung before the INDEX MIRROR
for reducing the glare of the SUN.
2427
Indian spring low water. An arbitrary TIDAL DATUM approximating the LEVEL of the mean of the LOWER LOW
WATER at SPRING TIDES. It was first used in waters surrounding India. Also called Indian tide plane.
2428
Indian tide plane. See INDIAN SPRING LOW WATER.
2429
indicator. That part of electronic equipment in which the DATA obtained by the RECEIVER is presented for visual
OBSERVATION. This is usually in the form of a SCOPE or DIAL.
2430
indirect levelling. See LEVELLING.
2431
indirect wave. See WAVE.
2432
induced magnetism. See MAGNETISM.
2433
inequality. A systematic departure from the mean value of a quantity. See ANNUAL INEQUALITY, DIURNAL INEQUALITY, LUNAR INEQUALITY, PARALLAX INEQUALITY, PHASE INEQUALITY.
2434
inertia: gyroscopic. See GYROSCOPIC INERTIA.
2435
inertial navigation. See NAVIGATION.
2436
inferior conjunction. See CONJUNCTION.
2437
inferior mirage. See MIRAGE.
2438
inferior planet (s). See PLANET (S): INFERIOR.
2439
inferior transit. See MERIDIAN TRANSIT.
112
2440
infrared (adj.). Having a FREQUENCY immediately beyond the red end of the visible SPECTRUM said of RAYS of
longer WAVE LENGTH than visible light, but shorter than RADIO WAVES.
2441
infrasonic (adj.). Having a FREQUENCY below the audible RANGE.
2442
ingoing stream. See FLOOD STREAM.
2443
initial great circle course. See COURSE: GREAT CIRCLE.
2444
initial great circle direction. INITIAL GREAT CIRCLE COURSE.
2445
initial meridian. See MERIDIAN.
2446
initial point. The ORIGIN of a system in the rectangular system of SURVEYS of which a PRINCIPAL MERIDIAN
and a BASE LINE constitute the axes for a given area. Also called fundamental point.
2447
inland ice sheet. An ICE SHEET of considerable thickness and more than about 50,000 sq. km in area, resting on
ROCK. Inland ice sheets near SEA LEVEL may merge into ICE SHELVES.
2448
inlet. A narrow opening by which the water penetrates into the LAND.
2449
inner harbour. See under HARBOUR.
2450
inner neat line. See NEAT LINE.
2451
innocent passage. Navigation through certain sea areas of a coastal State without being prejudicial to the peace, good
order or security of that State. See also TRANSIT PASSAGE.
2452
inogen light. Leading mark based on the interference effect of 3 separately placed rasterboards. An arrow pointing in
the direction of the line is displayed when not sailing along the leading line.
2453
input. What is put in, as electric current or other power put into a machine.
DATA to be transferred from an external storage medium, such as punched cards, into the internal STORAGE of a
COMPUTER.
2454
input impedance. The complex opposition to alternating current between the input terminals of any device.
2455
inset. In CARTOGRAPHY: a) a small area outside the NEAT LINES of a MAP or CHART included within the NEAT
LINES or borders to avoid publishing a separate graphic of the small area alone; b) a representation of a small area on a
larger SCALE (e.g., town-plan inset), or of a large area at a smaller SCALE (e.g., orientation inset); c) any information,
not normally appearing within the geographic limits of a MAP, which has been enclosed by border lines and included
within the map neat lines. Insets are always placed in areas where important features will not be obscured.
2456
inshore (adj. and adv.). Near or towards the SHORE.
2457
inshore traffic zone. A routeing measure comprising a designated area between the landward boundary of a traffic
separation scheme and the adjacent coast, to be used in accordance with the provisions of the International Regulations
for Preventing Collisions at Sea.
2458
insolation. Amount of direct solar RADIATION incident per unit horizontal area at a given level. Downward-directed
solar RADIATION (global RADIATION).
2459
instability. Property of the state of rest or continuous movement of a system such that any disturbance introduced into
this state grows. In METEOROLOGY, the term is often used as a synonym of STATIC INSTABILITY.
2460
instability: static. State of hydrostatic equilibrium of the ATMOSPHERE in which a particle of air moved from its
initial level undergoes a hydrostatic force which tends to remove it further from this level. Also called hydrostatic
instability.
2461
installation: offshore. Manmade structure usually built for the exploration or exploitation of marine resources, marine
scientific research, tide observations, etc.
2462
instrumental (or instrument) correction. That CORRECTION due to INSTRUMENTAL ERROR.
113
2463
instrumental (or instrument) error. See ERROR.
2464
instrumental (or instrument) parallax. See PARALLAX.
2465
insular. Of or pertaining to an island or islands.
2466
insular shelf. A zone around an island that extends from the low water line to a depth at which there is usually a marked
increase of slope towards oceanic depths.
2467
insulated (or insulating) water bottle. See WATER BOTTLE.
2468
intake. The place where water is taken into a channel or pipe from a RIVER or other body of water, to drive a mill, or
supply a CANAL, waterworks, etc.
2469
intended track. See TRACK.
2470
intensity: luminous (in a direction). Quotient of the LUMINOUS FLUX emitted by a source, or by an element of a
source in an infinitesimal cone containing the given direction, by the solid angle of that cone.
2471
intensity: magnetic. See MAGNETIC FIELD INTENSITY.
2472
intensity: sound. At a point, the average rate of sound energy transmitted in a specified direction through a unit area
normal to this direction at the point considered. The square of the SOUND PRESSURE.
2473
intensity of gravity. See GRAVITY.
2474
intensity of magnetization. See MAGNETIZATION.
2475
intercardinal point. Any of the four directions midway between the CARDINAL POINTS: north-east, north-west,
south-east, south-west.
2476
intercept. The name given in MARCQ ST. HILAIRE METHOD to the difference between the calculated ALTITUDE
and the TRUE ALTITUDE of a CELESTIAL BODY. Also called altitude difference.
2477
intercept method. See MARCQ ST. HILAIRE METHOD.
2478
interface. A surface, usually plane, forming the BOUNDARY between adjacent solids, spaces or immiscible liquids.
In data processing it describes all information (signals, data) and the specifications ("protocol") required for
exchanging data between two units of a system. Interfaces exist between hardware and software units but also between
computer and human user.
2479
interference. Extraneous SIGNALS, NOISES, etc., that hinder proper reception of the desired SIGNAL in electronic
equipment. See WAVE INTERFERENCE.
2480
Intergovernmental Oceanographic Commission (IOC). Established within UNESCO to promote the scientific
investigation of the oceans through the concerted action of Member States.
2481
interior orientation. See ORIENTATION.
2482
interior perspective centre. See PERSPECTIVE CENTRE.
2483
interlines (of sounding). Those SOUNDING LINES running between the normally spaced lines usually when the
BOTTOM is known or suspected to be irregular or if more detailed information about the sea bottom relief is required.
2484
internal waters. Waters on the landward side of the baseline of the territorial sea and landlocked waters within the
state.
2485
internal wave. See WAVE.
2486
International Association for the Physical Sciences of the Ocean (IAPSO). Promotes the study of scientific
problems relating to the ocean and interactions at its boundaries.
2487
International Association of Geodesy (IAG). One association of IUGG.
114
2488
International Association of Geomagnetism and Aeronomy (IAGA). Promotes international coordination of efforts
to further the sciences of geomagnetism and aeronomy.
2489
International Association for Hydraulic Research (IAHR). Stimulates and promotes hydraulic research, both basic
and applied, in all its aspects.
2490
International Association of Lighthouse Authorities (IALA). Association of authorities responsible for the provision
or maintenance of lighthouses and other aids to marine navigation.
2491
International Association of Meteorology and Atmospheric Physics (IAMAP). Promotes meteorological research
and investigation including all aspects of atmospheric physics, particularly in those fields which require international
cooperation.
2492
International Association of Scientific Hydrology (IASH). Promotes and develops the study of hydrology; initiates,
facilitates and coordinates research on such hydrological problems requiring international cooperation.
2493
International Association of Seismology and Physics of the Earth's Interior (IASPEI). Develops the study of
seismology and physics of the earth's interior in the economic, social and scientific aspects.
2494
International Association of Theoretical and Applied Limnology (IAL). Furthers the progress of theoretical and
applied limnology by holding congresses, by publishing the proceedings of the congresses, and by providing a sound
foundation of methods and techniques of limnological investigations.
2495
International Association of Volcanology and Chemistry of the Earth's Interior (IAV). Promotes research in all
matters relating to volcanic activity; coordinates research in mineralogy, chemistry and physical chemistry for the
benefit of volcanologists.
2496
International Atomic Time. See ATOMIC TIME: INTERNATIONAL.
2497
International Bureau of Weights and Measures (IBWM). Establishment of international standards and of
measurement scales of physical sizes; determination of fundamental physical constants.
2498
International Cartographic Association (ICA). Advances the study of cartographic problems; instigates cartographic
research involving cooperation between nations.
2499
International (INT) Chart. A nautical chart with limits and scale in conformity with an internationally agreed scheme
of such charts; carries the INT number of that sheet; conforms to the Chart Specifications of the IHO.
2500
International Commission for the Scientific Exploration of the Mediterranean Sea (ICSEM). Serves as liaison for
research in Mediterranean laboratories; promotes international activities on behalf of countries bordering the
Mediterranean.
2501
International Council for the Exploration of the Sea (ICES). Promotes research and investigations for the study of
the sea, particularly programs related to living resources.
2502
International Council of Scientific Unions (ICSU). Coordinates and facilitates activities of International Scientific
Unions in the field of exact and natural sciences; maintains relations with the specialized and related agencies of the
UN.
2503
International Cooperative Investigations of the Tropical Atlantic (ICITA). An international expedition coordinated
by the IOC.
2504
international date line. See DATE LINE.
2505
International Ellipsoid of Reference. A reference ellipsoid having the following approximate dimensions: semimajor
axis 6378388.0 METRES; semiminor axis 6356911.9 METRES; and the flattening or ellipticity 1/297. See also
HAYFORD'S SPHEROID and FLATTENING OF THE EARTH.
2506
International Federation of Surveyors (FIG). Brings together the leading national associations to exchange views of
general interest to the profession and organizes the liaison between the various affiliated associations.
2507
International Geological Congress (IGC). Congresses held by IUGS.
2508
International Geographical Union (IGU). Founded in 1922 to promote the study of geographical problems, IGU
initiates and coordinates research and provides for scientific discussion and publication.
115
2509
International Geophysical Year (IGY). By international agreement, a period during which greatly increased
OBSERVATION of world-wide geophysical PHENOMENA is undertaken through the cooperation effort of
participating nations.
2510
International Hydrographic Bureau (IHB). Founded in 1921 in the Principality of Monaco, to establish a close and
permanent association among the hydrographic offices of its Member States; since 1970 the headquarters of the
INTERNATIONAL HYDROGRAPHIC ORGANIZATION.
2511
International Hydrographic Organization (IHO). Coordinates the activities of national hydrographic offices;
promotes standards and provides advice to developing countries in the fields of hydrographic surveying and production
of nautical charts and publications.
2512
International Ice Patrol (IIP). Activities of the International Ice Patrol include collecting and analyzing data
concerning iceberg detection and movement. The Patrol's mission is to provide the latest information on iceberg
positions and computer prediction of the extent of the iceberg danger zone to North Atlantic Mariners. Areas of study
include iceberg detection, drift and deterioration, surface object drift, and currents in the Grand Banks Region.
2513
International Indian Ocean Expedition (IIOE or IOE). An international expedition between 1959 and 1965 under
the general coordination of the IOC.
2514
International Map of the World (IMW). The Map of the World on the SCALE of 1/1 000 000 which was planned
under the auspices of the International Geographical Union and carried out by very many of the countries of the world.
2515
International Maritime Organization (IMO). Formerly called IMCO, the IMO is the specialized agency of the
UNITED NATIONS responsible for maritime safety and efficiency of navigation.
2516
International nautical mile. A unit of length equal to 1,852 METRES. This value was approved by the International
Hydrographic Conference of 1929 and has been adopted by nearly all maritime states.
2517
International Scientific Radio Union (ISRU). Promotes and organizes international cooperative research in radio
science.
2518
International Telecommunications Union (ITU). Maintains and extends international cooperation for the improvement and rational use of telecommunications.
2519
International Union of Geodesy and Geophysics (IUGG). Promotes the study of all problems relating to the
configuration and physics of the earth, its oceans and atmosphere; comprises a number of international associations.
2520
International Union of Geological Sciences (IUGS). Contributes to the advancement of investigations relating to the
study of the Earth.
2521
International Union of Pure and Applied Physics (IUPAP). Creates and encourages international cooperation in
physics; secures international agreement on symbols, units, nomenclature, and standards.
2522
International waters. A nonlegal term that refers to those waters subject to the high seas freedom of navigation and
overflight, i.e., contiguous zone, EEZ, and high seas.
2523
interocular distance. See INTERPUPILLARY DISTANCE.
2524
interpolation. The process of determining intermediate values between given values in accordance with some known or
assumed rate or system of variation.
2525
interpupillary distance. The distance between centres of the eye pupils of an individual. Also called eye base, and used
interchangeable with interocular distance.
2526
interrogator. A radar transmitter which sends out a PULSE that triggers a TRANSPONDER. An interrogator is usually
combined in a single unit with a RESPONSOR, which receives the reply from a TRANSPONDER and produces an
OUTPUT suitable for feeding to a display system, the combined unit being called an interrogator-responsor.
Short for interrogator-responsor. Also called challenger.
2527
interrogator-responsor. See INTERROGATOR and RESPONSOR.
116
2528
intersected point. See STATION: INTERSECTION.
2529
intersection. In SURVEYING, the procedure of determining the horizontal POSITION of an unoccupied point
(INTERSECTION STATION) by direction observations from two or more known POSITIONS.
In PHOTOGRAMMETRY, the procedure of determining the horizontal POSITION of a point by intersecting lines
of direction obtained photogrammetrically. The lines of direction may be obtained directly from VERTICAL
PHOTOGRAPHS or by graphic or mathematical rectification of tilted PHOTOGRAPHS.
2530
intersection station. See STATION.
2531
intertidal zone. The zone generally considered to be between MEAN HIGH WATER and MEAN LOW WATER
levels.
2532
intertropical convergence zone. The zone which separates the trade winds.
2533
intervalometer. A timing device for automatically operating the SHUTTER of a CAMERA at selected intervals.
2534
invar. An alloy of nickel and steel which has a low coefficient of expansion.
2535
invar tape. See TAPE.
2536
invar wire. See WIRE.
2537
inverse Mercator projection. See PROJECTION.
2538
inversion layer. Atmospheric LAYER, horizontal or approximately so, in which the temperature increases with
increasing HEIGHT. See TEMPERATURE INVERSION.
2539
inverted compass. See COMPASS: HANGING.
2540
inverted image. See IMAGE.
2541
inverting eyepiece. See EYEPIECE: ERECTING.
2542
ionosphere. That part of the ATMOSPHERE, extending from about 70 to 500 km, in which ions and free electrons
exist in sufficient quantities to reflect ELECTROMAGNETIC WAVES.
2543
ionospheric disturbance. A sudden outburst of ultraviolet light on the sun, known as a Solar Flare, which produces
abnormally high ionization in the region of the D-layer. The result is a sudden increase in radio wave absorption, with
particular severity in the upper medium and lower high frequencies. It has negligible effects on the heights of the
reflecting/refracting layers and, consequently, upon critical frequencies, but enormous transmission may occur.
2544
ionospheric storm. Violent changes in the state of the IONOSPHERE.
2545
ionospheric wave. See WAVE: SKY.
2546
ironbound (adj.). Said of a rugged, rocky COAST which affords no ANCHORAGE.
2547
irradiance (at a point of a surface). Quotient of the FLUX of RADIATION incident on an infinitesimal element of
surface containing the point under consideration, by the area of that element.
2548
irradiation (at a point of a surface). Product of an IRRADIANCE and its duration.
2549
irregular error. See ERROR: ACCIDENTAL.
2550
island. A piece of LAND completely surrounded by water.
2551
island harbour. See under HARBOUR.
2552
island shelf. See CONTINENTAL SHELF.
2553
island slope. See CONTINENTAL SLOPE.
117
2554
isle. An ISLAND. Now more usually applied to an ISLAND of smaller size, except in established appellation, as the
'British Isles'.
2555
islet. A small ISLAND.
2556
isobar. Line joining points of equal pressure on a given surface (level surface, vertical cross section, etc.).
2557
isobath. See DEPTH CURVE, FATHOM LINE.
2558
isobathytherm. A line or surface showing the DEPTHS in OCEANS or LAKES at which points have the same
temperature. Isobathytherms are usually drawn to show cross sections of the water mass.
2559
isobront. Line joining, on a CHART, places on the EARTH's surface where, on a given day, the first clap of
THUNDER has been heard simultaneously.
In CLIMATOLOGY, line drawn on a CHART through places which have the same average number of days on
which THUNDER is heard in a given period.
2560
isocentre. The unique point common to the plane of a PHOTOGRAPH, its PRINCIPAL PLANE, and the plane of an
assumed truly VERTICAL PHOTOGRAPH taken from the same CAMERA STATION and having an equal
PRINCIPAL DISTANCE.
The point of intersection on a PHOTOGRAPH of the true PRINCIPAL LINE and the ISOMETRIC PARALLEL.
The point on a PHOTOGRAPH intersected by the bisector of the angle between the PLUMB LINE and the photograph perpendicular. The isocentre is significant because it is the centre of radiation for DISPLACEMENTS of
IMAGES caused by TILT.
2561
isoclinal (or isoclinic) (adj.). Of or pertaining to equal MAGNETIC DIP.
2562
isoclinal (n.). See ISOCLINAL LINE.
2563
isoclinal (or isoclinic) line. A line connecting points of equal MAGNETIC DIP. Also called isoclinal.
2564
isodynamic (adj.). Of or pertaining to equality of force.
2565
isodynamic line. A line connecting points of equal MAGNETIC INTENSITY, either the total or any component.
2566
isogon. Line which is the locus of points at which the DIRECTION OF WIND is the same.
2567
isogonal (or isogonic) (adj.). Having equal angles.
2568
isogonal (or isogonic) (n.). See ISOGONIC LINE.
2569
isogonic line. A line connecting points of equal magnetic VARIATION. Also called isogonal (or isogonic).
2570
isogram. That line on a CHART or DIAGRAM connecting points having equal values of same PHENOMENON.
2571
isogriv. A line connecting points of equal GRID VARIATION.
2572
isohaline (or isohalsine). A line connecting points of equal SALINITY in the OCEAN.
2573
isohalsine. See ISOHALINE.
2574
isolated danger mark. A navigation mark used alone to indicate a danger, e.g. a reef or shoal.
2575
isoline. A line representing the intersection of the plane of a VERTICAL PHOTOGRAPH with the plane of an
overlapping OBLIQUE PHOTOGRAPH. If the VERTICAL PHOTOGRAPH were tilt-free, the isoline would be the
ISOMETRIC PARALLEL of the OBLIQUE PHOTOGRAPH.
2576
isomagnetic (adj.). Of or pertaining to lines connecting points of equality in some MAGNETIC ELEMENT.
2577
isomagnetic (n.). See ISOMAGNETIC LINE.
2578
isomagnetic line. A line connecting points of equality in some MAGNETIC ELEMENT.
2579
isometric (adj.). Of or pertaining to equal measure.
118
2580
isometric latitude. See LATITUDE.
2581
isometric parallel. See PARALLEL.
2582
isopleth. An ISOGRAM of equal or constant value of a given quantity, with respect to either time or space.
2583
isopor. See ISOPORIC LINE.
2584
isoporic line. A line connecting points of equal annual rate of change of a MAGNETIC ELEMENT. Also called isopor.
2585
isopycnic (adj.). Of or pertaining to equal density.
2586
isopycnic (n.). See ISOPYCNIC LINE.
2587
isopycnic line. A line connecting points of equal density. Also called isopycnic.
2588
isoradial. A RADIAL from the ISOCENTRE.
2589
isostasy. A condition of approximate EQUILIBRIUM in the outer part of the EARTH, such that the gravitational effect
of masses extending above the surface of the GEOID in continental areas is approximately counterbalanced by a
deficiency of density in the material beneath those masses while the effect of deficiency of density in the ocean waters is
counterbalanced by an excess of density in the material under the OCEANS.
2590
isostatic anomaly. The difference between an observed value of GRAVITY and a theoretical value at the point of
OBSERVATION which has been corrected for ELEVATION of the STATION above the GEOID and for the effect of
TOPOGRAPHY over the whole EARTH, and for its isostatic compensation.
2591
isotherm. In METEOROLOGY, the line which is the locus of points which have the same value of air temperature.
2592
isothermal (or isothermic) (adj.). Of or relating to equal temperature.
2593
isotope. Two or more nuclides having the same atomic number, hence constituting the same element, but differing in
mass number.
2594
isotropic (or isotropus) (adj.). Having the same physical properties in all directions.
2595
isthmus. A narrow strip of LAND connecting two larger bodies of LAND.
119
J
2596
jack-up rig. A rig which provides a stable drilling structure in shallow waters by extending supporting legs onto the
seabed. The legs are retracted when the rig is under tow.
2597
jellyfish. Any of various free-swimming COELENTERATES having a disc- or bell-shaped body of jellylike consistency. Many have long tentacles with nematocysts (stinging cells). Some are capable of producing glowing ball
LUMINESCENCE.
Any jellylike free-floating organism. The term 'jellyfish' often is applied to the ctenophores and may be applied to
certain tunicates. Also called medusa.
2598
jetsam. See JETTISON.
2599
jettison. The throwing overboard of objects, especially to lighten a craft in distress. Jettisoned objects that float are
termed flotsam; those that sink, jetsam; and heavy articles that are buoyed for future recovery, lagan. See DERELICT.
2600
jetty. In U.S. terminology, a structure, such as a WHARF or PIER, so located as to influence CURRENT or protect the
ENTRANCE to a HARBOUR or RIVER.
In British terminology, a PIER, usually of solid construction, intended as a berthing place for vessels. See DOCK,
LANDING, WHARF.
2601
joule. The unit of work or energy in the SI SYSTEM.
2602
joystick. In computer systems, a pointing device operated by pressing a stick in a desired direction.
2603
Julian day. The number of each day, as reckoned consecutively since the beginning of the present Julian period on
January 1, 4713 BC. The Julian day begins at noon, 12 hours later than the corresponding civil day.
2604
junction. Place of meeting or joining, as that of a TRIBUTARY with a main RIVER, or of two CHANNELS in a
WATERWAY.
In LEVELLING, the place where two or more LINES OF LEVELS are connected together.
In HYDROGRAPHIC SURVEY, the joining of two adjacent survey sheets. See OVERLAP.
2605
junction buoy. A BUOY marking the inner end of a MIDDLE GROUND.
Usually called a MIDDLE GROUND BUOY in British terminology, without regard to direction of travel.
120
K
2606
Kalman filter. In electronics, a mathematical-statistical method for predicting a time-variable signal in the presence of
disturbances. The method exploits the fact that certain characteristic parameters of the process vary slowly with time, so
that a best estimate of the signal can be obtained as a function of time.
2607
katabatic wind. An offshore wind produced by cold air draining from high ground by convection. The cold air replaces
the lighter warm air which is rising over the sea.
2608
kay. See CAY.
2609
kedging. Moving a vessel by laying out an anchor and then hauling the vessel up to the anchor.
2610
keg buoy. A BUOY consisting of a keg to which is attached a small pole with a flag, used by fishermen to mark the
position of a trawl line. See DAN BUOY.
2611
kelp. One of an order of usually large blade-shaped or vinelike brown ALGAE.
2612
Kelvin temperature scale. Thermodynamic scale of temperature (T K) defined by assigning to the triple point of pure
o
water, considered as a fundamental fixed point, the temperature of 273.16 K. Also called absolute temperature scale.
2613
Kelvin wave. A long ocean wave whose amplitude decreases from right to left along the wave crest when viewed in the
direction of travel in the northern hemisphere and from left to right in the southern hemisphere. The component of
gravity acting down the slope is exactly balanced by the deflecting force of the earth's rotation, the CORIOLIS FORCE.
2614
key. See CAY.
2615
kilogram(me). The unit of mass in the SI system.
2616
kite. A mechanical contrivance towed beneath the surface to warn of arrival in water of a certain DEPTH. See
SUBMARINE SENTRY.
A contrivance for holding the inner end of an OROPESA SWEEP to the required DEPTH.
2617
kite otter. A multi-plane device which can be used either as a KITE or as an OTTER depending on the way it is slung.
See OROPESA SWEEP.
2618
klaxon. A small power FOG SIGNAL sometimes operated by hand.
2619
knoll. A relatively small isolated ELEVATION of a rounded shape.
An ELEVATION rising less than 1,000 METRES from the SEA FLOOR and of limited extent across the SUMMIT.
Also called HILL.
2620
knot. A division of the LOG LINE, by which the ship's SPEED is measured.
A nautical unit of SPEED. One knot is one NAUTICAL MILE per HOUR. The name is derived from the knots in
the LOG LINE.
2621
kymatology. The science of WAVES and wave motion.
o
121
L
2622
labour (or labor) (v.i.). To pitch and roll heavily under conditions which subject the ship to unusually heavy stresses
caused by confused or turbulent seas or unstable stowage or cargo.
2623
lag. The delay between change of condition and the indication of the change on an instrument.
Delay in human reaction.
The amount one cyclic motion is behind another, expressed in DEGREES. The opposite is LEAD.
2624
lagging of the tide(s). The periodic retardation in the time of occurrence of high and low water due to changes in the
relative positions of the moon and the sun.
2625
lagan. See JETTISON.
2626
lagging of the tide(s). The retardation in the TIME of occurrence of HIGH and LOW WATER due to changes in the
relative positions of the MOON and the SUN. The opposite effect is called PRIMING OF THE TIDE(S). See also
DAILY RETARDATION.
2627
lagoon. An enclosed area of salt or brackish water separated from the OPEN SEA by some more or less effective, but
not complete, obstacle such as low sand bank. The name most commonly used for the area of water enclosed by a
BARRIER REEF or ATOLL.
2628
Lagrangian current observations. The method for observing ocean currents by tracking the movement of drifting
floats, buoys, tracers etc. The rate and direction of movement of a particular sample of water is measured. This is the
opposite to EULARIAN CURRENT OBSERVATIONS where the movement of water past a fixed point is measured by
a current meter.
2629
lake. A large body of water entirely surrounded by LAND.
2630
lake breeze. See SEA BREEZE.
2631
lake ice. ICE formed in LAKES.
2632
Lambert conformal conic projection. See PROJECTION.
2633
laminar flow. FLOW in which the fluid moves smoothly along STREAMLINES which are arranged in parallel
LAYERS or sheets; opposite of TURBULENT FLOW. Also called streamline flow.
2634
lamp: signal. A compact, portable battery-operated electric lamp used as a TARGET for OBSERVATIONS or
SURVEYS of high PRECISION. The parabolical reflector is mounted in a special case so as to facilitate pointing and
adjusting.
2635
land. The solid portion of the EARTH's surface, as opposed to SEA, water.
A part of the EARTH's surface marked off by natural or political BOUNDARIES.
2636
land breeze. WIND of coastal regions blowing at night from the LAND towards a large water surface as a result of
nocturnal cooling of the land surface.
2637
landfall. The first sighting of LAND when approached from seaward. By extension, the term is sometimes used to refer
to the first contact with LAND by any means, as by RADAR.
2638
landfall buoy. See FAREWELL BUOY.
2639
land ice. See GLACIER ICE.
2640
landing. A place where boats receive or discharge passengers, freight, etc.
2641
landing area. In aeronautical terminology, the part of the movement area intended for the landing or take-off run of
aircraft.
2642
landlocked (adj.). Almost or quite enclosed by LAND. Said of an area of water, as a BAY, HARBOUR, etc., entirely
protected from the SEA.
122
2643
landmark. Any MONUMENT or fixed object used to mark a BOUNDARY on the GROUND.
Any prominent object on LAND which can be used in determining a location or a DIRECTION. See also MARK.
2644
land mile. See STATUTE MILE.
2645
land navigation. See NAVIGATION.
2646
landslide (or landslip). The sliding down of a mass of land on a MOUNTAIN or cliff-side; land which has so fallen.
2647
land survey. See SURVEY: CADASTRAL.
2648
land territory. Continental or insular land masses that are above water at high tide.
2649
lane. An established route as an air lane or shipping lane.
In an electronic radiolocation lattice, the zone between two lines on which measured values, expressed in terms of
the system's electronic unit (WAVE LENGTH or MICROSECOND), are whole numbers and are one unit apart. See
LATTICE.
A LEAD.
2650
Laplace azimuth. See AZIMUTH.
2651
Laplace equation. See EQUATION.
2652
Laplace station. See STATION.
2653
lappened ice. See ANCHOR ICE.
2654
large correction (British terminology). A new printing of a CHART corrected from important information which is too
comprehensive to promulgate by Admiralty NOTICES TO MARINERS or to insert conveniently by hand on existing
copies of the CHART. When large corrections are made, the CHART is not revised throughout but all copies in
circulation are cancelled.
2655
large halo. See HALO.
2656
Large Automatic Navigation Buoy (lanby). A large buoy designed to take the place of a lightship where construction
of an offshore light station is not feasible. See also BUOY: SUPER.
2657
large scale. See SCALE.
2658
large scale survey. See SURVEY.
2659
LASH. See LIGHTER ABOARD SHIP.
2660
laser. Light amplification by stimulated emission of RADIATION. A device that produces an intense BEAM of
monochromatic, spatially coherent light.
2661
last quarter. See PHASES OF THE MOON.
2662
lateral system. A buoyage system generally used for well defined CHANNELS; buoyage marks indicate the
POSITION of dangers in relation to the route to be followed by mariners in their vicinity.
2663
latitude. ANGULAR DISTANCE from a PRIMARY GREAT CIRCLE or plane. One of the COORDINATES used to
describe a POSITION, the other being LONGITUDE.
2664
latitude: astronomical. ANGULAR DISTANCE between the DIRECTION OF GRAVITY and the plane of the
EQUATOR.
Astronomical latitude is the LATITUDE which results directly from OBSERVATIONS on CELESTIAL BODIES,
uncorrected for DEFLECTION OF THE VERTICAL.
2665
latitude: celestial. ANGULAR DISTANCE north or south of the ECLIPTIC; the arc of a CIRCLE OF LATITUDE
between the ECLIPTIC and a point on the CELESTIAL SPHERE, measured northward or southward from the
ECLIPTIC through 90°, and labelled N or S to indicate the direction of measurement. Also called ecliptic latitude.
123
2666
latitude: geocentric. The angle at the centre of the EARTH between the plane of the EQUATOR and a line to a point
on the surface of the EARTH.
2667
latitude: geodetic. The angle which the NORMAL at a point on the SPHEROID makes with the plane of the
GEODETIC EQUATOR.
2668
latitude: geographic(al). A general term, applying alike to ASTRONOMICAL and GEODETIC LATITUDES.
2669
latitude: geometric. See LATITUDE: PARAMETRIC.
2670
latitude: isometric. An auxiliary LATITUDE used in the conformal mapping of the SPHEROID on a sphere.
2671
latitude: magnetic. The angle whose tangent is one half the tangent of the magnetic inclination or DIP.
2672
latitude: parametric. The angle at the centre of a sphere which is tangent to the SPHEROID along the GEODETIC
EQUATOR, between the plane of the EQUATOR and the radius to the point intersected on the sphere by a straight line
perpendicular to the plane of the EQUATOR and passing through the point on the SPHEROID whose parametric
latitude is defined. Parametric latitude is an auxiliary LATITUDE used in problems of GEODESY and
CARTOGRAPHY. Also called reduced latitude, geometric latitude or eccentric angle.
2673
latitude: reduced. See LATITUDE: PARAMETRIC.
2674
latitude: terrestrial. ANGULAR DISTANCE from the EQUATOR, measured northward or southward through 90°
and labelled N or S to indicate the direction of measurement.
2675
latitude factor. The change in LATITUDE along a CELESTIAL LINE OF POSITION per 1' change in LONGITUDE.
2676
latitude line. A LINE OF POSITION extending in a generally east-west direction.
2677
latitude scale. See SCALE.
2678
lattice. A pattern formed by two or more families of intersecting lines, such as HYPERBOLIC LINES OF POSITION
or parts of circles, drawn on CHARTS, PLOTTING SHEETS or SOUNDING BOARDS.
2679
launch. Large open or half decked boat.
2680
lava. The fluid or semi-fluid matter flowing from a volcano.
The substance that results from the cooling of the molten ROCK. Part of the ocean bed is composed of lava.
2681
layer. A single thickness, coat, fold or STRATUM.
2682
layer depth. In OCEANOGRAPHY, the thickness of the MIXED LAYER; or the DEPTH to the top of the THERMOCLINE.
2683
layer depth prediction. Predetermining the DEPTH to the top of the THERMOCLINE over a given ocean area.
2684
layering. A method of emphasizing on a CHART differences in HEIGHT or DEPTH by use of varying tints. Also
referred to as layer tinting.
2685
layer of no motion. A LAYER, assumed to be at rest at some DEPTH in the OCEAN.
2686
layer tinting. See LAYERING.
2687
lead (lèd). A heavy, soft, malleable, bluish-grey metallic chemical element. Anything made of this metal, such as a
WEIGHT for sounding DEPTHS of water.
2688
lead (led). A navigable PASSAGE through ICE.
The amount one cyclic motion is ahead of another, expressed in DEGREES.
2689
lead: deep sea. A heavy SOUNDING LEAD the WEIGHT of which may be varied from about 15 to over 50 kilos
depending on the DEPTHS to be sounded. Also called dipsey lead.
2690
lead: drift. SOUNDING LEAD dropped to BOTTOM, to indicate movement of a vessel.
124
2691
lead: fish. A fish-shaped SOUNDING LEAD which reduces to a minimum the INCLINATION of the wire when
trailed, making unnecessary its removal from the water between SOUNDINGS.
2692
lead: hand. A light SOUNDING LEAD (3 to 5 kilos) having usually a line of not more than 40 to 50 METRES.
2693
lead: sounding. A LEAD attached to a line used for measuring the DEPTH of water. Also called plummet.
2694
leader cable. See CABLE.
2695
leading light(s). See LIGHT.
2696
leading line (British terminology). A line passing through two or more clearly defined charted objects, and along which
a vessel can approach safely.
2697
leading marks. (British terminology). AIDS TO NAVIGATION or other indicators so located as to indicate the path to
be followed. Leading marks identify a LEADING LINE when they are in TRANSIT. See also RANGE.
2698
lead line. A line, graduated with attached MARKS and fastened to a SOUNDING LEAD, used for determining the
DEPTH of water when making SOUNDINGS by hand. Generally used in DEPTHS of less than 45 METRES (25 FATHOMS). Lead lines are braided or left-laid. Also called sounding line.
2699
lead line correction. A CORRECTION to be applied to the DEPTHS taken with a rope LEAD LINE to take into account the shrinking and stretching. This difficulty has been overcome by inserting a wire heart in the rope.
2700
leadsman. A person using a SOUNDING LEAD to determine DEPTH of water.
2701
league. A varying measure of distance, usually about three MILES.
2702
leaper. See LIPPER.
2703
leap year. See YEAR: CIVIL.
2704
least count. The finest reading that can be made directly (without estimation) from a VERNIER or MICROMETER.
2705
least depth. The shoalest sounding value obtained on a feature.
2706
least squares. A method of adjusting OBSERVATIONS in which the sum of the squares of all the deviations or
residuals derived in fitting the OBSERVATIONS to a mathematical model, is made a minimum. Least squares have also
been designated as minimum squares.
2707
ledge. A shelf-like projection, on the side of a ROCK or MOUNTAIN.
A rocky formation continuous with and fringing the SHORE.
2708
lee. That side towards which the WIND blows; the sheltered side.
2709
lee shore. SHORE that is to leeward of a vessel. See WEATHER SHORE.
2710
lee tide. See TIDE: LEEWARD.
2711
leeward (adj. and adv.). Toward the LEE, or in the general direction toward which the WIND is blowing. The opposite
is WINDWARD.
2712
leeward tidal current. See TIDE: LEEWARD.
2713
leeward tide. See TIDE.
2714
leeway. The leeward motion of a vessel due to WIND. It may be expressed as distance, SPEED, or angular difference
between COURSE steered and COURSE through the water.
DRIFT ANGLE. Also called drift.
2715
leeway angle. The angle between true heading and track of a vessel caused by wind action.
2716
left bank. Of a RIVER, the BANK of the left-hand side as one proceeds downstream.
2717
left-right indicator. An instrument indicating the orthogonal distance of a position from a pre-defined track.
125
2718
leg. Each straight section of a TRAVERSE.
One part of a craft's TRACK consisting of a single COURSE line.
2719
legend. A description, explanation, table of SYMBOLS, and other information, printed on a MAP or CHART to
provide a better understanding and interpretation of it. The TITLE of a MAP or CHART formerly was considered part
of the legend, but this usage is obsolete.
2720
length correction (tape). See TAPE: LENGTH CORRECTION.
2721
lens. A plane, convex, or concave combination of glass or transparent material surfaces adapted for changing the
direction of LIGHT RAYS to enlarge or reduce the apparent size of objects.
See ACHROMATIC LENS, APOCHROMATIC LENS, ANALLACTIC LENS, OBJECTIVE LENS, EYEPIECE,
LENS ELEMENT, LENS SYSTEM, MAGNIFYING GLASS.
2722
lens axis. See AXIS OF LENS.
2723
lens distortion. See DISTORTION.
2724
lens element. One LENS of a complex LENS SYSTEM.
2725
lens system. The combination of two or more LENSES placed in series on the same PRINCIPAL AXIS.
2726
levee. An EMBANKMENT to prevent the overflow of a RIVER.
A landing place, PIER, QUAY.
A depositional EMBANKMENT bordering a CANYON, VALLEY or deep-sea channel.
2727
level. A horizontal plane or line; especially, such a plane taken as a basis for the measurement of ELEVATION. See
SEA LEVEL, MEAN SEA LEVEL, HALF TIDE LEVEL, STILL WATER LEVEL.
A level tract of land; a stretch of country approximately horizontal and unbroken by ELEVATIONS.
In SURVEYING and LEVELLING, either a SPIRIT LEVEL or a LEVELLING INSTRUMENT.
2728
level (v.t.). To make perfectly horizontal by means of a LEVEL.
2729
level: bull's eye. See LEVEL: SPIRIT.
2730
level: circular. See LEVEL: SPIRIT.
2731
level: dumpy. See LEVELLING INSTRUMENT: DUMPY LEVEL.
2732
level: plate. A SPIRIT LEVEL attached to the plate of a surveying instrument for the purpose of levelling the graduated
CIRCLE or, indirectly, making the VERTICAL AXIS truly vertical.
2733
level: self aligning.See LEVELLING INSTRUMENT: SELF ALIGNING LEVEL.
2734
level: spirit. A small closed vessel of glass (vial), having the inside surface of its upper part curved in form; the vessel is
nearly filled with a fluid of low viscosity (alcohol or ether), enough free space being left for the formation of a bubble of
air and gas, which will always assume a position at the top of the vessel. There are two types of spirit levels used in
SURVEYING: one has the curved surface spherical in form, producing a bubble of circular outline; and is properly
called a circular level (also universal level or bull's eye level). The other and much more generally used type has a
vessel in the form of circular tube, the longitudinal axis of which is also circular in form. It is the type usually referred to
when the term 'spirit level' is used. The spirit level is also called spirit bubble or sensitive bubble.
2735
level: striding. A SPIRIT LEVEL so mounted that it can be placed above and parallel with the HORIZONTAL AXIS
of a surveying or astronomical instrument, and so supported that it can be used to measure the INCLINATION OF THE
HORIZONTAL AXIS to the plane of the HORIZON. Generally, its mounting has supports in the form of inverted eyes
which rest directly upon the pivots on which the TELESCOPE of the instrument rotates.
2736
level: tilting. See LEVELLING INSTRUMENT: TILTING LEVEL.
2737
level: universal. See LEVEL: SPIRIT.
2738
level: Y. See LEVELLING INSTRUMENT: Y LEVEL.
126
2739
level axis. See AXIS OF SPIRIT LEVEL.
2740
level ice. SEA ICE with a flat surface which has never been hummocked.
2741
levelling (or leveling). The operation of determining differences of ELEVATION between points on the surface of the
EARTH; the determination of the ELEVATION of points relative to some arbitrary or natural LEVEL SURFACE
called a DATUM. Also called differential levelling.
2742
levelling: barometric. A method of determining differences of ELEVATION from differences of ATMOSPHERIC
PRESSURE observed with a BAROMETER.
2743
levelling: direct. The determination of differences of ELEVATION by a continuous series of short horizontal lines.
Vertical distances from these lines to adjacent ground marks are determined by direct OBSERVATIONS on graduated
rods with a LEVELLING INSTRUMENT equipped with a SPIRIT LEVEL.
2744
levelling: geodetic. SPIRIT LEVELLING of a high order of ACCURACY, usually extended over large areas, to furnish
accurate VERTICAL CONTROL as a basis for the CONTROL in the vertical dimension for all surveying and mapping
operations.
2745
levelling: indirect. The determination of differences of ELEVATION from (a) vertical angles and horizontal distances,
as in TRIGONOMETRIC LEVELLING; (b) comparative ELEVATIONS derived from values of ATMOSPHERIC
PRESSURE determined with a BAROMETER, as in BAROMETRIC LEVELLING; and (c) ELEVATIONS derived
from values of the boiling point of water determined with a HYPSOMETER, as in THERMOMETRIC LEVELLING.
2746
levelling: reciprocal. TRIGONOMETRIC LEVELLING wherein vertical angles have been observed at both ends of
the line to eliminate ERRORS.
2747
levelling: spirit. The determination of ELEVATIONS of points with respect to each other or with respect to a common
DATUM, by use of a LEVELLING ROD and an instrument using a SPIRIT LEVEL to establish a horizontal LINE OF
SIGHT.
2748
levelling: thermometric. The determination of ELEVATIONS above SEA LEVEL from observed values of the boiling
point of water. See HYPSOMETER.
2749
levelling: trigonometric. The determination of differences of ELEVATIONS by means of observed vertical angles,
combined with lengths of lines.
2750
levelling: water. A method of obtaining relative ELEVATIONS by observing HEIGHTS with respect to the surface of
a body of still water, such as a LAKE. The relative ELEVATIONS of objects along its SHORES are obtained by taking
the differences of their HEIGHTS with respect to the surface of the water.
2751
levelling instrument. An instrument designed for the accurate measurement of height differences by the process of
LEVELLING. Its essential parts are a TELESCOPE and a SPIRIT LEVEL. Also called a LEVEL.
2752
levelling instrument: dumpy level. A LEVELLING INSTRUMENT which has its TELESCOPE permanently
attached to the levelling base, either rigidly or by a hinge that can be manipulated by a MICROMETER SCREW.
2753
levelling instrument: self-aligning level. A LEVEL in which a sensitive prism element inside the TELESCOPE acts
on the principle of the PENDULUM and ensures that the LINE OF SIGHT is horizontal, even if the axis of the
TELESCOPE is several MINUTES out of the HORIZONTAL.
2754
levelling instrument: tilting level. A LEVELLING INSTRUMENT in which the final LEVELLING of the instrument
is obtained by small controlled amounts of rotation of the TELESCOPE about a HORIZONTAL AXIS.
2755
levelling instrument: Y level. A LEVELLING INSTRUMENT having the TELESCOPE, with attached SPIRIT
LEVEL, supported in Y's. The TELESCOPE can be rotated about its longitudinal axis in the Y's and it can be lifted and
reversed, end for end.
2756
levelling plate. A plate designed to support the LEVELLING ROD as an aid to ACCURACY in LEVELLING.
2757
levelling rod. A straight rod or bar, designed for use in measuring a vertical distance between a point on the ground and
the LINE OF COLLIMATION of a LEVELLING INSTRUMENT which has been adjusted to horizontal position. Also
called levelling staff.
127
2758
levelling screw. One of the three screws of surveying and astronomic instruments used for levelling same. Also called
footscrew.
2759
levelling staff. See LEVELLING ROD.
2760
level net. Lines of SPIRIT LEVELLING connected together to form a system of loops and circuits extending over an
area. Also called survey net.
2761
level surface. A surface which, at every point, is perpendicular to the DIRECTION OF GRAVITY. A level surface is
an EQUIPOTENTIAL SURFACE. The GEOID or, in general, any surface parallel to it, is a level surface. If changes in
ELEVATION due to TIDES, WINDS, etc. are neglected, the surface of the SEA is a level surface. A level surface is not
a plane surface, but it is sometimes so regarded in SURVEYS of limited areas.
2762
librations of moon. Motions of the MOON due to which certain margins round the MOON's LIMB occasionally pass
out of view while a corresponding margin on the other side comes into view. The librations enable 59 per cent of the
MOON's surface to be seen at one time or another.
2763
lidar. An instrument that measures distance to a reflecting object by emitting timed pulses of light and measuring the
time between emission and reception of reflected pulses. The measured time interval is converted to distance.
2764
life buoy. See BUOY.
2765
life saving station. A place where equipment for saving life at SEA is maintained. Also called Coast Guard station.
2766
light. A luminous or lighted AID TO NAVIGATION.
For internationally agreed abbreviations of light characteristics see the International Chart Specifications.
2767
light: aerial obstruction. LIGHT marking an obstacle which constitutes a danger to AIR NAVIGATION.
2768
light: aeromarine. A marine-type LIGHT in which a proportion of the BEAM is deflected to an angle of 10°-15°
above the HORIZON for the use of aircraft.
2769
light: aeronautical ground. Any LIGHT specially provided as an AID TO NAVIGATION, other than a LIGHT displayed on an aircraft.
2770
light: alternating. A signal LIGHT that shows, in any given direction, two or more colours in a regularly repeated
sequence with a regular periodicity.
2771
light(s): boundary. LIGHTS marking the BOUNDARY of a LANDING AREA.
2772
light: catoptric. A LIGHT concentrated into a narrow BEAM by means of one or more REFLECTORS (as opposed to
DIOPTRIC).
2773
light: composite group-flashing. A flashing light in which a sequence of groups of one or more flashes, which are
specified in number, is regularly repeated, and the groups comprise different numbers of flashes.
2774
light: composite group-occulting. An occulting light in which a sequence of groups of one or more eclipses, which are
specified in number, is regularly repeated, and the groups comprise different numbers of eclipses.
2775
light: continuous ultra quick. A light showing 160 or more, usually 240 to 300, flashes per minute.
2776
light: continuous very quick. A light showing 80 to 159, usually either 100 or 120, flashes per minute.
2777
light: dioptric. A LIGHT concentrated into a parallel BEAM by means of refracting LENSES and prisms (as opposed
to CATOPTRIC).
2778
light: direction (or directional). A LIGHT illuminating a sector of very narrow angle and intended to mark a
DIRECTION to be followed.
2779
light: equal-interval. A LIGHT with all durations of light and darkness equal. The term 'equal-interval light' has been
replaced by isophase light in many countries.
2780
light: fixed. A signal light that shows continuously, in any given direction, with constant luminous intensity and colour.
128
2781
light: fixed and flashing. A rhythmic light in which a fixed light is combined with a flashing light of higher luminous
intensity.
2782
light: fixed and group-flashing. A FIXED LIGHT varied at regular intervals by a GROUP of two or more flashes of
greater brilliance. This CHARACTER is being gradually suppressed.
2783
light: flashing. A rhythmic LIGHT in which the total duration of light in a PERIOD is clearly shorter than the total
duration of darkness and all the appearances of light are of equal duration.
2784
light: front. See LIGHT(S): RANGE.
2785
light: group-flashing. A flashing LIGHT in which a group of two or more flashes, which are specified in number, is
regularly repeated.
2786
light: group-occulting. An occulting LIGHT in which a group of two or more eclipses, which are specified in number,
is regularly repeated.
2787
light: group quick. A light in which flashes are combined in groups including the same number of quick flashes
(repetition rate : 50-79 per minute) and in which groups are repeated at regular intervals.
2788
light: group very quick. A light in which very quick flashes are combined in groups including the same number of
flashes (repetition rate : 80-159 per minute) and in which groups are repeated at regular intervals.
2789
light: intermittent. See LIGHT: RHYTHMIC.
2790
light: interrupted quick-flashing. A quick LIGHT in which the sequence of flashes is interrupted by regularly
repeated ECLIPSES of constant and long duration.
2791
light: interrupted ultra quick. A light in which the ultra quick flashes (160 or more per minute) are interrupted at
regular intervals by eclipses of long duration.
2792
light: interrupted very quick. A light in which the very rapid alterations of light and darkness are interrupted at
regular intervals by eclipses of long duration.
2793
light: isophase. See LIGHT: EQUAL-INTERVAL.
2794
light(s): leading. Two or more LIGHTS associated so as to form a LEADING LINE to be followed.
2795
light: linear. A luminous SIGNAL having perceptible length, as contrasted with a POINT LIGHT.
2796
light: long-flashing. A FLASHING LIGHT in which a single flash of not less than two SECONDS duration is regularly repeated.
2797
light: marine. A LIGHT intended primarily for MARINE NAVIGATION.
2798
light: Morse code. A rhythmic LIGHT in which appearances of light of two clearly different durations are grouped to
represent a character or characters in the Morse code.
2799
light: obstruction. LIGHT indicating the presence of an OBSTRUCTION.
2800
light: occasional. A LIGHT not regularly exhibited.
2801
light: occulting. A rhythmic LIGHT in which the total duration of light in a PERIOD is clearly longer than the total
duration of darkness and all the eclipses are of equal duration.
2802
light: point. A luminous SIGNAL appearing without perceptible length, as contrasted with a LINEAR LIGHT.
2803
light: quick-flashing. A LIGHT exhibiting without interruption very rapid regular alternations of light and darkness.
2804
light(s): range. Two or more LIGHTS in the same horizontal DIRECTION, particularly those LIGHTS so placed as
NAVIGATIONAL AIDS to mark any line of importance to vessels, as a CHANNEL. The one nearest the observer is
the front light and the one farthest from the observer is the rear light. See LIGHT(S): LEADING.
2805
light: rear. See LIGHT(S): RANGE.
129
2806
light: revolving. See LIGHT: ROTATING.
2807
light: rhythmic. A signal LIGHT that shows intermittently, in any given direction, with a regular periodicity. Also
referred to as intermittent light.
2808
light: rotating (or revolving). A LIGHT which has one or more BEAMS which rotate.
2809
light(s): runway. LIGHTS marking a RUNWAY.
2810
light: sector (or sectored). A LIGHT presenting different appearances (in particular, different colours) over various
parts of the HORIZON of interest to maritime NAVIGATION.
2811
light: short-flashing. A FLASHING LIGHT having individual flashes of less than two seconds duration.
2812
light(s): tidal. LIGHTS shown at the ENTRANCE of a HARBOUR to indicate TIDE and TIDAL CURRENT
conditions within the HARBOUR.
2813
light: undulating. A continuously luminous LIGHT which alternatively increases and decreases in brightness in cyclic
sequence.
2814
light: unwatched. A navigational LIGHT, usually automatic in operation, without any permanently-stationed personnel
to superintend it.
2815
light(s): vertical. Two or more LIGHTS disposed vertically to give a different CHARACTER or appearance.
2816
light (or lighted) beacon. See BEACON.
2817
light beam. A group of PENCILS of light, as those originating at the many points of an illuminated surface. A BEAM
of parallel LIGHT RAYS is a special case in which each PENCIL is of such small cross-section that it may be regarded
as a RAY.
2818
light (or lighted) buoy. See BUOY.
2819
light characteristics. See CHARACTERISTICS OF LIGHT.
2820
lighted sound buoy. See BUOY.
2821
light float. A boat-like structure used instead of a light buoy in waters where strong streams or currents are experienced,
or when a greater elevation than that of a light buoy is necessary.
2822
lighthouse. A distinctive structure on or off a COAST exhibiting a major LIGHT designed to serve as an AID TO
NAVIGATION.
2823
light list. See LIST OF LIGHTS.
2824
lightning. Luminous manifestations accompanying a sudden electrical discharge which takes place from or inside a
CLOUD or, less often, from high structures on the GROUND or from MOUNTAINS.
2825
light pencil. A bundle of LIGHT RAYS originating at, or directed to, a single point.
2826
light ray. The geometrical concept of a single element of light propagated in a straight line and of infinitesimal crosssection; used in analytically tracing the path of light through an OPTICAL SYSTEM.
2827
light sector. A sector in which a navigational LIGHT is visible. See ARC OF VISIBILITY.
2828
lightship. A distinctively marked vessel anchored or moored at a charted point, to serve as an AID TO NAVIGATION.
By night it displays a characteristic LIGHT(S), and is usually equipped with other devices, such as a FOG SIGNAL,
SUBMARINE SOUND SIGNAL, and RADIOBEACON, to assist NAVIGATION. Also called light vessel.
2829
light vessel. See LIGHTSHIP.
2830
light-year. A unit of length equal to the distance light travels in one YEAR. This unit is used as a measure of stellar
distance.
130
2831
Lighter Aboard Ship (LASH). A cargo carrying system using specially built ships and lighters. Cargoes are loaded
into LASH lighters which are towed to a LASH ship where they are embarked. At their destination the LASH lighters
are disembarked and towed away to their unloading berths. Special berths or anchorages are sometimes designated for
LASH ships.
2832
limb. The graduated curved part of an instrument for measuring angles, as that part of a MARINE SEXTANT carrying
the altitude scale, or arc.
The circular outer edge of a CELESTIAL BODY. The half with the greatest ALTITUDE is called the upper limb
and the half with the least ALTITUDE, the lower limb.
2833
limestone. A ROCK which consists chiefly of calcium carbonate.
2834
limnology. The scientific study of the biological, chemical, geographical, and physical features of fresh waters,
especially of LAKES and PONDS.
2835
linear light. See LIGHT.
2836
linear parallax. See PARALLAX: ABSOLUTE STEREOSCOPIC.
2837
linear scale. See SCALE: BAR.
2838
linear speed. See SPEED.
2839
line of apsides. The line connecting the two orbital points (called apsides) that are nearest and farthest from the centre
of attraction, as the PERIGEE and the APOGEE in the case of an ORBIT about the EARTH, and the PERIHELION and
the APHELION in the case of an ORBIT about the SUN.
2840
line of collimation. See COLLIMATION.
2841
line of constant scale. Any line on a PHOTOGRAPH which is parallel to the TRUE HORIZON or to the ISOMETRIC
PARALLEL.
2842
line of delimitation. A line drawn on a map or chart depicting the separation of any type of maritime jurisdiction.
2843
line of equidistance. See MEDIAN LINE.
2844
line of flow. The vector line showing the DIRECTION OF CURRENT at a given TIME. Also called STREAMLINE.
2845
line of force. A line indicating the direction in which a force acts, as in a MAGNETIC FIELD. See MAGNETIC
LINES OF FORCE.
2846
line of levels. A continuous series of measured differences of ELEVATION.
2847
line of nodes. The straight line connecting the two points of intersection of the ORBIT of a PLANET, PLANETOID, or
COMET and the ECLIPTIC, or the line of intersection of the planes of the ORBITS of a SATELLITE and its primary.
See NODE.
2848
line of position. A line indicating a series of possible POSITIONS of a craft, determined by OBSERVATION or
measurement. Also called position line. See CELESTIAL LINE OF POSITION, CIRCLE OF POSITION, COURSE
LINE, ELECTRONIC LINE OF POSITION, FIX, HYPERBOLIC LINE OF POSITION, LATITUDE LINE,
LEADING LINE, LONGITUDE LINE, RETIRED LINE OF POSITION, SONIC LINE OF POSITION, SPEED LINE,
SUMNER LINE, SURFACE OF POSITION, VISUAL LINE OF POSITION.
2849
line of sight. The straight line between two points. This line is in the direction of a GREAT CIRCLE, but does not
follow the curvature of the EARTH. See also COLLIMATION: LINE OF.
2850
line of sounding. A series of SOUNDINGS along a predetermined line, and at stated intervals, when SURVEYING.
Also referred to as sounding line. See CHECK LINES, CROSS LINES, CROSS-SECTION LINES, INTER LINE,
SPLIT LINE, STARRED LINES, TRACK LINE OF SOUNDING, SYSTEMS OF SOUNDING LINES.
2851
line spacing. Distance between sounding lines. Spacing usually depends on the type of survey, the instruments used,
and the demanded accuracy.
2852
line squall. SQUALL which occurs along a SQUALL LINE.
131
2853
lipper. Slight ruffling or roughness on a water surface.
Light spray from small WAVES. Also called leaper.
2854
liquid compass. See COMPASS.
2855
list. INCLINATION to one side, as of a vessel until she has found EQUILIBRIUM in an inclined position. Listing is a
static condition, as distinguished from heeling which is dynamic. See HEEL.
2856
list of lights. A publication tabulating navigational LIGHTS, with their locations, CANDLE POWERS, CHARACTERISTICS, etc. to assist in their identification, and details of any accompanying FOG SIGNAL. A list of lights may
contain other information useful to a navigator. Also called light list.
2857
list of radio signals. A publication tabulating and combining particulars of: coast radio stations, port radio stations,
RADIO DIRECTION FINDING STATIONS, RADIOBEACONS, etc., as well as other information on radio services
useful to a navigator.
2858
lithification. The process of induration, cementation, petrification, consolidation, and crystallization which convert
MAGMA and newly deposited SEDIMENTS into ROCK.
2859
lithographic image. An ink-receptive image on the lithographic press plate, either photographic or direct hand or
transfer image. The design or drawing on stone or metal plate.
2860
lithographic transfer. A PROOF of design or type matter pulled with special transfer ink on transfer paper from a
LITHOGRAPHIC IMAGE or a relief image. Such PROOFS are used to transfer an IMAGE to the PLATE or stone.
2861
lithography. The art or process of printing from a flat stone or metal PLATE by a method based on the repulsion
between grease and water. The original lithographic material was Bavarian LIMESTONE; but zinc and aluminium are
now used.
2862
lithology. The scientific study of ROCKS. Literally, the science of STONES.
2863
lithosphere. The solid, rocky part of the EARTH; EARTH's CRUST distinguished from ATMOSPHERE,
HYDROSPHERE.
2864
litre (or liter). The basic unit of capacity in the METRIC SYSTEM. It is equal to one cubic decimetre.
2865
littoral (adj.). Of or pertaining to a SHORE, especially of the SEA.
2866
littoral (n.). A coastal region.
INTERTIDAL ZONE.
2867
local apparent noon. See NOON.
2868
local apparent time. See TIME.
2869
local attraction. LOCAL MAGNETIC DISTURBANCE.
Also deflection of the PLUMB LINE due to a MOUNTAIN or other irregularity in EARTH's CRUST.
2870
local frequency oscillator. An oscillator used to derive an intermediate frequency by beating with the signal carrying
frequency in Superheterodyne reception.
2871
local horizon. See HORIZON: APPARENT.
2872
local hour angle. See HOUR ANGLE.
2873
localizer. A radio facility which provides SIGNALS for lateral GUIDANCE of aircraft with respect to a RUNWAY
centre line.
2874
local magnetic disturbance. An ANOMALY of the MAGNETIC FIELD of the EARTH, extending over a relatively
small area, due to local magnetic influences. Also called local attraction or magnetic anomaly.
2875
local mean time. See TIME.
2876
local meridian. See MERIDIAN.
132
2877
local sidereal time. See TIME.
2878
local time. See TIME.
2879
local transit. See TRANSIT.
2880
loch. The Scottish term for (1) a LAKE, and (2) a FIORD.
2881
lock. A WET DOCK in a WATERWAY, permitting a ship to pass from one level to another. See TIDE LOCK.
2882
lock gate(s). Pair of massive hinged doors at each end of a LOCK.
2883
locking. In ELECTRONIC NAVIGATION, a term describing the condition of two TRANSMITTERS when their
SIGNALS maintain a stable phase relationship. One STATION is then said to be locked to the other.
2884
locus (pl. loci). All possible positions of a point or curve satisfying stated conditions.
2885
log. An instrument for measuring the SPEED or distance or both travelled by a vessel.
2886
log (v.t.). Said of a ship moving at a specified SPEED according to the indications given by the LOG.
2887
log: chip. A LOG consisting essentially of a weighted wooden quadrant attached to a bridle in such a manner that it will
float in a vertical position, and a LOG LINE, SPEED being measured by casting the quadrant overboard and counting
the KNOTS in the line paid out in unit time.
2888
log: Dutchman's. A buoyant object thrown overboard to determine the SPEED of a vessel by timing its passage
between two marks, of known distance apart, on the vessel.
2889
log: electric. A graphic recording of the various electrical properties of a SEDIMENT or ROCK through which a hole
has been drilled.
2890
log: electric submerged. An electrically-operated LOG installed inside the hull of the vessel with a tube extending
through the hull into the water.
2891
log: electromagnetic. A LOG consisting of a pulsating MAGNET mounted on a probe pointing downwards with two
contacts on the sides of the probe. The movement of the water through the MAGNETIC FIELD is reflected by the
contacts and the ripple of voltage thus induced can be converted to measure the SPEED of the craft.
2892
log: ground. A device for determining the COURSE and SPEED made good over the GROUND in SHALLOW
WATER, consisting of a LEAD attached to a line. The LEAD is thrown overboard and allowed to rest on the
BOTTOM. The COURSE being made good is indicated by the direction the line tends and the SPEED by the amount of
line paid out in unit time.
2893
log: patent. Former name for a towed LOG.
Any mechanical LOG, particularly a TAFFRAIL LOG.
2894
log: taffrail. A LOG consisting essentially of a rotator towed through the water by a braided LOG LINE attached to a
distance registering device usually secured at the TAFFRAIL, the railing at the stern. Also called PATENT LOG.
2895
logarithmic scale. See SCALE.
2896
log book. Book in which events connected with the ship are entered. Also written as one word.
2897
log boom. Heavy logs chained or lashed together and moored or anchored so as to enclose and contain rafted logs. See
also BOOM.
2898
log chip. The wooden quadrant forming part of a CHIP LOG. Also called log ship.
2899
log factor. The ratio represented by the true distance divided by the LOG distance.
2900
log factor scale. See SCALE.
2901
logging. 1. Gauging ship's speed with a log.
2. Record events.
133
2902
log line. A graduated line used to measure the SPEED of a vessel through the water or to measure the SPEED of a
CURRENT from a vessel at anchor. The line secured to a LOG. See CURRENT POLE.
2903
log ship. See LOG CHIP. Also written as one word.
2904
long baseline acoustic system. An underwater position fixing system which consists of an array of seabed transponders
with baselines of several kilometres.
2905
longitude. ANGULAR DISTANCE, along a PRIMARY GREAT CIRCLE, from the adopted REFERENCE POINT.
One of COORDINATES used to describe a POSITION the other being LATITUDE.
2906
longitude: astronomical. The angle between the plane of the CELESTIAL MERIDIAN and the plane of an INITIAL
MERIDIAN, arbitrarily chosen. Astronomical longitude is the LONGITUDE which results directly from OBSERVATIONS on CELESTIAL BODIES, uncorrected for DEFLECTION OF THE VERTICAL.
2907
longitude: celestial. ANGULAR DISTANCE east of the VERNAL EQUINOX, along the ECLIPTIC; the arc of the
ECLIPTIC or the angle at the ecliptic pole between the CIRCLE OF LATITUDE of the VERNAL EQUINOX and the
CIRCLE OF LATITUDE of a point on the CELESTIAL SPHERE, measured eastward from the CIRCLE OF
LATITUDE of the VERNAL EQUINOX, through 360°.
2908
longitude: geodetic. The angle between the plane of the GEODETIC MERIDIAN and the plane of an INITIAL
MERIDIAN, arbitrarily chosen.
2909
longitude: geographic(al). A general term, applying alike to ASTRONOMICAL and GEODETIC LONGITUDE.
2910
longitude: terrestrial. The intercepted arc of EQUATOR, or the angle at the POLE, between the MERIDIAN of a
point on the EARTH, and the PRIME MERIDIAN, measured eastward or westward from the PRIME MERIDIAN
through 180°and labelled E or W to indicate the direction of measurement.
2911
longitude factor. The change in LONGITUDE along a CELESTIAL LINE OF POSITION per 1' change in
LATITUDE.
2912
longitude line. A LINE OF POSITION extending in a generally north-south direction.
2913
longitude signal. See SIGNAL.
2914
longitudinal wave. See WAVE.
2915
long range navigation. See NAVIGATION.
2916
longshore current. A current paralleling the shore largely within the surf zone. It is caused by the excess water brought
to the zone by the small net mass transport of wind waves. Longshore currents feed into rip currents.
2917
lookout station. A distinctive structure or place on SHORE from which personnel keep watch upon events at SEA or
along the COAST.
2918
lookout tower. Any tower surmounted by a small house in which a watch is habitually kept, as distinguished from an
OBSERVATION TOWER in which no watch is kept.
2919
loom. The glow of a light which is below the HORIZON, caused by REFLECTION by solid particles in the air.
Vague first appearance of LAND at SEA.
2920
looming. An apparent ELEVATION of distant terrestrial objects by abnormal ATMOSPHERIC REFRACTION.
Because of looming, objects below the HORIZON are sometimes visible. The opposite is SINKING.
The appearance indistinctly of an object during a period of low VISIBILITY.
2921
loop. In OCEANOGRAPHY, that part of a STANDING WAVE where the vertical motion is greatest and the horizontal
VELOCITIES are least. Loops (sometimes called antinodes) are associated with CLAPOTIS and with SEICHE action
resultant from resonant wave reflecting in a HARBOUR or BAY.
2922
loop antenna. A DIRECTIONAL ANTENNA consisting essentially of one or more complete turns of wire.
2923
'lost' station. See STATION: UNRECOVERABLE.
2924
lough. Irish equivalent of the Scottish LOCH.
134
2925
louver shutter. See SHUTTER.
2926
love wave (or Q-wave). See WAVE.
2927
low. See DEPRESSION.
2928
lower branch. That half of a MERIDIAN or CELESTIAL MERIDIAN from POLE to POLE which passes through the
ANTIPODE or NADIR of a place.
2929
lower culmination. See MERIDIAN TRANSIT.
2930
lower high water (L.H.W.). The lower of two HIGH WATERS occurring during a TIDAL DAY if the DIURNAL
INEQUALITY prevails.
2931
lower high water interval. See LUNITIDAL INTERVAL.
2932
lower limb. See LIMB.
2933
lower low water (L.L.W.). The lower of two LOW WATERS occurring during a TIDAL DAY if the DIURNAL
INEQUALITY prevails.
2934
lower low water interval. See LUNITIDAL INTERVAL.
2935
lower transit. See MERIDIAN TRANSIT.
2936
lowest astronomical tide. The lowest tide level which can be predicted to occur under average meteorological
conditions and under any combination of astronomical conditions.
2937
lowest low water. An arbitrary LEVEL conforming to the lowest TIDE observed at a place, or somewhat lower.
2938
low frequency (LF). See FREQUENCY: RADIO.
2939
lowland. Low and relatively level LAND at a lower ELEVATION than adjoining districts.
2940
low oblique photograph. See PHOTOGRAPH.
2941
low tide. See LOW WATER.
2942
low-tide elevation. A naturally formed area of land which is surrounded by and above water at low tide, but submerged
at high tide.
2943
low velocity layer. Any LAYER in which the VELOCITY of compressional wave propagation is lower than in the
adjacent LAYERS. Such a LAYER can act as an efficient channel for the propagation of elastic WAVES for great
distances.
2944
low water (L.W.). The lowest LEVEL reached at a place by the water surface in one OSCILLATION. Also called low
tide.
2945
low water: double. A LOW WATER consisting of two minima separated by a relatively small elevation. See TIDE:
DOUBLE.
2946
low water full and change (L.W.F. and C.). The average interval of time between the TRANSIT (upper or lower) of
the full or new MOON and the next LOW WATER.
2947
low water inequality. See DIURNAL INEQUALITY.
2948
low water interval. See LUNITIDAL INTERVAL.
2949
low water line. See LOW WATER MARK.
2950
low water lunitidal interval (L.W.I.). Low water interval. See LUNITIDAL INTERVAL.
2951
low water mark. The intersection of the plane of LOW WATER with the SHORE. The line along a COAST, or
BEACH, to which the SEA recedes at LOW WATER. Also called low water line.
135
2952
low water quadrature (L.W.Q.). The average low water interval when the MOON is at QUADRATURE.
2953
low water stand. See STAND OF TIDE.
2954
loxodrome. A curve, on the surface of a sphere, intersecting all GREAT CIRCLES of the sphere at a constant oblique
angle, theoretically never reaching the POLE while closely approaching it. See RHUMB LINE.
2955
loxodromic curve. A LOXODROME. A RHUMB LINE.
2956
lubber (or lubber's) line. A REFERENCE LINE on any direction-indicating instrument, marking the reading which
coincides with the HEADING.
2957
lull. A momentary decrease in the SPEED of the WIND.
2958
lumen. The unit of LUMINOUS FLUX in the SI SYSTEM.
2959
luminance (at a point of surface, in a direction). Quotient of the LUMINOUS INTENSITY, in a given direction, of an
infinitesimal element of the surface containing the point under consideration, by the orthogonally projected area of the
element on a plane perpendicular to the given direction.
2960
luminescence. Any emission of light at temperatures below that required for incandescence. See
BIOLUMINESCENCE, FLUORESCENCE, PHOSPHORESCENCE.
2961
luminous flux. See FLUX.
2962
luminous intensity. See INTENSITY.
2963
luminous range. See RANGE.
2964
luminous signal. See SIGNAL.
2965
lunar day. See DAY.
2966
lunar distance. The angle, at an observer on the EARTH, between the MOON and another CELESTIAL BODY. This
was the basis of a method formerly used to determine LONGITUDE at SEA.
2967
lunar eclipse. See ECLIPSE.
2968
lunar inequality. Variation in the MOON's motion in its ORBIT, due to attraction by other bodies of the SOLAR
SYSTEM. See EVECTION, PERTURBATION.
A minute fluctuation of a MAGNETIC NEEDLE from its mean position, caused by the MOON.
2969
lunar month. See MONTH: SYNODICAL.
2970
lunar rainbow. See MOONBOW.
2971
lunar tide. See under TIDE.
2972
lunation. See MONTH: SYNODICAL.
2973
lunicurrent interval. The interval between the moon's transit (upper or lower) over the local or Greenwich meridian
and a specified phase of the tidal current following the transit. Examples are strength of flood interval and strength of
ebb interval, which may be abbreviated to flood interval and ebb interval, respectively. The interval is described as local
or Greenwich according to whether the reference is to the moon's transit over the local or Greenwich meridian. When
not otherwise specified, the reference is assumed to be local.
2974
lunitidal interval. The interval of time between the TRANSIT (upper or lower) of the MOON over the LOCAL or
GREENWICH MERIDIAN and the next HIGH WATER or LOW WATER at a place. The interval is assumed to be
local unless otherwise specified. The average of all high water intervals is called mean high water lunitidal interval,
high water interval, or corrected establishment. The average of all low water intervals is called mean low water
lunitidal interval, or low water interval. The expressions higher high water interval, lower high water interval, higher
low water interval, and lower low water interval are used when there is considerable DIURNAL INEQUALITY. See
ESTABLISHMENT.
2975
lurch. A sudden ROLL to one side. See LIST.
136
2976
lux. Unit of ILLUMINATION in the SI SYSTEM.
2977
L-Z graph. A graph used to determine 'in situ' DEPTHS of oceanographic OBSERVATIONS by the wire depths minus
THERMOMETRIC DEPTH method.
137
M
2978
madrepore. A branching or stag-horn CORAL, also any perforated stone coral.
2979
magenta (adj.). A mixture of red and blue in equal parts.
2980
magma. The molten material in a state of fusion under the CRUST of the EARTH from which IGNEOUS ROCKS are
formed.
2981
magnet. A body which produces a MAGNETIC FIELD around itself. It has the property of attracting certain materials
capable of being magnetized. See HEELING MAGNET.
2982
magnetic annual change. The amount of SECULAR CHANGE in the EARTH'S MAGNETIC FIELD which occurs in
one YEAR. Also referred to as annual change.
2983
magnetic annual variation. The small systematic TEMPORAL VARIATION in the EARTH'S MAGNETIC FIELD
which occurs after the trend for SECULAR CHANGE has been removed from the average monthly values. Also
referred to as annual variation.
2984
magnetic anomaly. See LOCAL MAGNETIC DISTURBANCE.
2985
magnetic azimuth. See AZIMUTH.
2986
magnetic bearing. See BEARING.
2987
magnetic chart. See CHART.
2988
magnetic compass. See COMPASS.
2989
magnetic compensation. See COMPENSATION OF MAGNETIC COMPASS.
2990
magnetic compensator. See COMPENSATOR.
2991
magnetic course. See COURSE.
2992
magnetic daily (or diurnal) variation. OSCILLATIONS of the EARTH'S MAGNETIC FIELD which have a
periodicity of about a day and that depend to a close approximation only on LOCAL TIME and GEOGRAPHIC
LATITUDE.
2993
magnetic declination. See VARIATION.
2994
magnetic deviation. See DEVIATION.
2995
magnetic dip. See DIP.
2996
magnetic element. VARIATION, DIP, or MAGNETIC INTENSITY.
2997
magnetic equator. See EQUATOR.
2998
magnetic field. The space in which a magnetic influence exists.
2999
magnetic field intensity. The magnetic force exerted on a UNIT MAGNETIC POLE placed at any specified point of
space. It is a vector quantity. Its direction is taken as the direction toward which a north MAGNETIC POLE would tend
to move under the influence of the field. Also called magnetic intensity, magnetic field strength.
3000
magnetic field strength. See MAGNETIC FIELD INTENSITY.
3001
magnetic inclination. See DIP.
3002
magnetic induction. The act or process by which material becomes magnetized when placed in a MAGNETIC FIELD.
3003
magnetic intensity. See MAGNETIC FIELD INTENSITY.
138
3004
magnetic latitude. See LATITUDE.
3005
magnetic lines of force. Closed lines indicating by their direction the direction of magnetic influence.
3006
magnetic meridian. See MERIDIAN.
3007
magnetic moment. The quantity obtained by multiplying the distance between two MAGNETIC POLES by the
average strength of the poles.
3008
magnetic needle. A small, slender magnetized bar which tends to align itself with MAGNETIC LINES OF FORCE.
3009
magnetic north. See NORTH.
3010
magnetic observation(s). See OBSERVATION.
3011
magnetic observatory. A place where buildings are equipped for observing temporal changes in the EARTH'S
MAGNETIC FIELD.
3012
magnetic permeability. The property of a magnetizable substance that determines the degree in which it modifies the
magnetic flux in the region occupied by it.
3013
magnetic pole. Either of the two places on the surface of the EARTH where the magnetic DIP is 90°, that in the
northern hemisphere being designated north magnetic pole, and that in the southern hemisphere being designated south
magnetic pole. The magnetic poles are not fixed and do not coincide with the GEOGRAPHICAL POLES.
Either of those two points of a MAGNET where the magnetic force is greatest.
3014
magnetic range. See RANGE.
3015
magnetic retentivity. The ability to retain MAGNETISM after removal of the magnetizing force. Also called
remanence.
3016
magnetic secular change. The temporal variation in the value of a MAGNETIC ELEMENT which occurs over a
period of years.
3017
magnetic station. See STATION.
3018
magnetic storm. A disturbance in the EARTH'S MAGNETIC FIELD, associated with abnormal solar activity, and
capable of seriously affecting both radio and wire transmission.
3019
magnetic survey. See SURVEY.
3020
magnetic temporal variation. Any change in the EARTH'S MAGNETIC FIELD which is a function of time. Also
referred to as temporal variation.
3021
magnetic variation. See VARIATION.
3022
magnetism. The ability to attract magnetic material, notably iron and steel.
3023
magnetism: induced. MAGNETISM acquired by a piece of magnetic material while it is in a MAGNETIC FIELD.
3024
magnetism: permanent. MAGNETISM which is retained for long periods without appreciable reduction, unless the
MAGNET is subjected to a demagnetizing force. Because of the slow dissipation of such MAGNETISM, it is sometimes called subpermanent magnetism.
3025
magnetism: residual. MAGNETISM which remains after removal of the magnetizing force.
3026
magnetism: subpermanent. See MAGNETISM: PERMANENT.
3027
magnetism: temporary. MAGNETISM of craft which changes in amount with every change of HEADING. Also
called transient magnetism.
3028
magnetism: terrestrial. See GEOMAGNETISM.
3029
magnetism: transient. See MAGNETISM: TEMPORARY.
139
3030
magnetization. The degree to which a body is magnetized. The MAGNETIC MOMENT per unit volume. Also called
intensity of magnetization.
3031
magnetize (v.t.). To produce magnetic properties. The opposite is DEMAGNETIZE.
3032
magnetogram. An analogue time record of the temporal variations in a MAGNETIC ELEMENT measured at a
MAGNETIC OBSERVATORY.
3033
magnetograph. A MAGNETIC OBSERVATORY instrument consisting of one or more (usually 3) VARIOMETERS,
one for each MAGNETIC ELEMENT recorded, and a recorder.
3034
magnetometer. An instrument for measuring the intensity and/or the direction of the EARTH'S MAGNETIC FIELD.
3035
magnetometer: cesium. An OPTICAL PUMPING MAGNETOMETER which employs a cesium absorption cell.
3036
magnetometer: flux-gate. An instrument which uses a wire wound saturable core inductor to measure the EARTH'S
MAGNETIC FIELD.
3037
magnetometer: helium. An OPTICAL PUMPING MAGNETOMETER which employs a helium absorption cell.
3038
magnetometer: nuclear precession. A MAGNETOMETER that utilizes the precessional characteristics of hydrogen
nuclei when in an ambient MAGNETIC FIELD. Also known as proton precession magnetometer.
3039
magnetometer: optical pumping. A highly sensitive MAGNETOMETER which employs a metastable helium or
alkali metal absorption cell whose ATOMS absorb maximum energy from an infrared BEAM when a frequency
modulation oscillator is tuned to its resonant FREQUENCY. The resonant FREQUENCY is proportional to the strength
of the EARTH'S MAGNETIC FIELD.
3040
magnetometer: proton precession. See MAGNETOMETER: NUCLEAR PRECESSION.
3041
magnetometer: quartz horizontal. A MAGNETOMETER in which the torque exerted on a suspended MAGNET by
the EARTH's horizontal MAGNETIC FIELD is balanced against the torque exerted by the quartz suspension fibre when
o
twisted through 360 .
3042
magnetometer: rubidium vapour. An OPTICAL PUMPING MAGNETOMETER which employs a rubidium vapour
absorption cell.
3043
magnetometer: transit. An instrument used primarily for observing the declination of the EARTH'S MAGNETIC
FIELD.
3044
magnetometer: unifilar. A MAGNETOMETER, designed for use on SHORE, employed to measure the horizontal
intensity of the EARTH's MAGNETISM; it can also be used to determine VARIATION.
3045
magnetometer: vector airbone. A FLUX-GATE MAGNETOMETER which measures the intensity and direction of
the EARTH'S MAGNETIC FIELD from an aircraft.
3046
magnetometer survey. See SURVEY.
3047
magnetometric zero balance. A MAGNETIC OBSERVATORY instrument used for accurate measurement of the
vertical component of the EARTH'S MAGNETIC FIELD.
3048
magnetostriction. The PHENOMENON wherein ferromagnetic material experience an elastic strain when subjected to
an external MAGNETIC FIELD. Also, the converse PHENOMENON in which mechanical stresses cause a change in
the MAGNETIC INDUCTION of a ferromagnetic material.
3049
magnetostriction transducer. See TRANSDUCER.
3050
magnetron. An electron tube for converting direct-current energy into radio-frequency energy by means of a
MAGNETIC FIELD.
3051
magnification. The apparent enlargement of anything. In optics, the term relates to the properties of LENSES and
LENS SYSTEMS to produce an IMAGE which differs in dimension from the related object.
140
3052
magnifying glass. A LENS or combination of LENSES that increases the apparent size of an object seen through it.
3053
magnifying power. The ratio of the apparent length of a linear dimension as seen through an optical instrument to that
seen by the unaided eye. Sometimes shortened to power.
3054
magnitude. The importance, quality or size of something.
In ASTRONOMY, relative brightness of a CELESTIAL BODY. According to the accepted classification, a STAR
of the 1st magnitude is a hundred times as bright as a STAR of the 6th magnitude (the faintest STAR that can be seen
with the unaided eye) and the distribution of magnitudes is logarithmic in terms of brightness. Thus each reduction in
magnitude means an increase of brightness of about 2 1/2.
3055
mainland. The principal LAND or largest part of a CONTINENT, as distinguished from a relatively small ISLAND or
PENINSULA.
3056
main scheme station. See STATION.
3057
maintained depth. The depth at which a channel is kept by human influence, usually by dredging.
3058
maintenance. All procedures and activities required to keep equipment operational.
3059
major planet. See PLANET.
3060
make the land. To sight and approach or reach LAND from seaward.
3061
make way. To progress through the water.
3062
making way. Progressing through the water.
3063
manoeuvre. Planned and controlled movement of a vehicle.
3064
mangrove. One of several genera of tropical trees or shrubs which produce many prop roots and grow along low-lying
COASTS into SHALLOW WATER.
3065
manometer. An instrument for measuring pressure of gases and vapours.
3066
mantle. The relatively plastic region between the CRUST and CORE of the EARTH. Also called asthenosphere.
3067
manuscript map. See MAP.
3068
map. A representation (usually on a flat medium) of all or a portion of the EARTH or other CELESTIAL BODY,
showing the relative size and position of features to some given SCALE or PROJECTION; also, a representation of all
or part of the CELESTIAL SPHERE. A map may emphasize, generalize, or omit the representation of certain features
to satisfy specific requirements. Maps are frequently categorized and referred to according to the type of information
which they are primarily designed to convey, to distinguish them from maps of other types.
3069
map (v.t.). To prepare a MAP or engage in a mapping operation.
3070
map: anaglyphic. A MAP specially printed in two complementary colours in such a way that, when viewed through a
twin EYEPIECE of the same colours, a three-dimensional impression of RELIEF is seen.
3071
map: base. A MAP showing certain fundamental information, used as a base upon which additional data of specialized
nature are compiled. Also, a MAP containing all the information from which MAPS showing specialized information
can be prepared; a source map.
3072
map: cadastral. A MAP showing the BOUNDARIES of subdivision of LAND, usually with the BEARINGS and
lengths thereof and the area of individual tracts, for purposes of describing and recording ownership. A cadastral map
may also show culture, drainage, and other features relating to the value and use of LAND. See also PLAT.
3073
map: contour. A TOPOGRAPHIC MAP which portrays RELIEF by means of CONTOURS.
3074
map: hemispherical. A MAP of one half of the EARTH's surface, bounded by the EQUATOR, or by MERIDIANS.
3075
map: index. In AERIAL PHOTOGRAPHY, a MAP showing the location and numbers of FLIGHT STRIPS and
PHOTOGRAPHS.
141
3076
map: manuscript. The original drawing of a MAP as compiled or constructed from various DATA, such as GROUND
SURVEYS, PHOTOGRAPHS, etc.
3077
map: planimetric. A MAP which presents only the horizontal positions for the features represented; distinguished from
a TOPOGRAPHIC MAP by the omission of RELIEF in measurable form.
3078
map: reconnaissance. The plotted result of a RECONNAISSANCE SURVEY.
3079
map: relief. A MAP emphasizing RELIEF or relative ELEVATIONS. See RELIEF MODEL.
3080
map: sketch. A MAP drawn freehand and greatly simplified which, although preserving the essential space
relationships, does not truly preserve SCALE or ORIENTATION.
3081
map: special purpose. Any MAP designed primarily to meet specific requirements.
3082
map: substitute. A hasty reproduction of wide-coverage AERIAL PHOTOGRAPHS, PHOTOMAPS, or MOSAICS,
or of provisional MAPS, or any document used in place of a MAP, when the precise requirements of a MAP cannot be
met.
3083
map: thematic. A MAP designed to demonstrate particular features or concepts. In conventional use, this term excludes
TOPOGRAPHIC MAPS.
3084
map: topographic. A MAP which represents the horizontal and vertical positions of the features represented;
distinguished from a PLANIMETRIC MAP by the addition of RELIEF in measurable form. A topographic map uses
CONTOURS or comparable SYMBOLS to show MOUNTAINS, VALLEYS and PLAINS.
3085
map nadir. See NADIR.
3086
map parallel. See AXIS OF HOMOLOGY.
3087
map projection. See PROJECTION.
3088
map scale. See SCALE.
3089
Marcq St. Hilaire method. The establishing of a LINE OF POSITION from the OBSERVATION of the ALTITUDE
of a CELESTIAL BODY, and the calculation of its ALTITUDE and AZIMUTH by the use of an ASSUMED
POSITION. First introduced by Commandant Marcq St. Hilaire of the French Navy. See INTERCEPT, SUB-POINT.
Also referred to as Saint Hilaire method or intercept method.
3090
maregraph plongeur. An instrument for measuring changes in SEA LEVEL by automatically recording changes in
pressure at sea bottom. Two BOURDON TUBES are open to pressure and a mechanism records the resultant movements of their free ends.
3091
margin. In CARTOGRAPHY, that area of a MAP or CHART lying outside the border. 'Margin' is preferred to the term
'surround'.
3092
marginal information (or data). The notations printed in the MARGINS or borders of MOSAICS, PLANS, or MAPS.
3093
marigram. See TIDE CURVE.
3094
marigraph. A recording TIDE GAUGE.
3095
marina. A harbour facility for small boats, yachts, etc., where supplies, repairs, and various services are available.
3096
marine. An adjective meaning relating to navigation or shipping; relating to or connected with the sea; used, or adopted
for use at sea. Sometimes called maritime, but maritime is more frequently applied to that which borders on the sea.
3097
marine barometer. See BAROMETER.
3098
marine biology. See BIOLOGY.
3099
marine borer. Any marine invertebrate that excavates tunnels, holes, or depressions in one or more of a variety of
materials by abrasive, chewing, or chemical action.
142
3100
marine chart. See CHART: NAUTICAL.
3101
marine farm. See FISH FARM.
3102
marine light. See LIGHT.
3103
marine navigation. See NAVIGATION.
3104
marine nature reserve (U.S. marine sanctuary). An officially designated area in which there may be restrictions on
entry, fishing, anchoring, and other activities in order to protect the marine environment.
3105
marine railway. A track, cradle, and winding mechanism for hauling vessels out of the water so that the hull can be
exposed as in a dry dock. This is also called a patent slip in British terminology.
3106
marine sextant. See SEXTANT.
3107
marine stabilizer. See STABILIZER.
3108
maritime. Bordering on, concerned with, or related to the sea.
3109
maritime boundary delimitation. The process of establishing LINE(S) OF DELIMITATION at sea.
3110
maritime meteorology. Branch of the METEOROLOGY which is concerned with the interaction between the SEA
and ATMOSPHERE.
3111
Maritime Safety Information (MSI). Navigational and meteorological warnings, meteorological forecasts, distress alerts and other urgent safety related messages broadcast to ships.
3112
mark. One of the bits of leather, cloth, etc. indicating a specified length of a LEAD LINE.
A charted conspicuous object, structure, or LIGHT serving as an indicator for guidance or warning of a craft; a
BEACON.
A definite object ,such as an imprinted metal disk, used to designate a survey point and sometimes refers to the entire
survey monument. Mark is used with a qualifying term such as station, reference, azimuth, or bench. See also BENCH
MARK and REFERENCE MARK.
3113
mark: geodetic. See MARK.
3114
mark boat. A temporary SOUNDING MARK consisting of a whaler moored head and stern, with a SIGNAL on board.
3115
marker. That which marks something.
A MARKER BEACON. See also RADIOBEACON.
3116
marker beacon. A RADIOBEACON which radiates a SIGNAL to define an area, as an AID TO NAVIGATION.
Usually called marker radiobeacon or marker.
3117
marker buoy. A temporary BUOY used in SURVEYING to mark a location of particular interest such as a SHOAL or
REEF. See also STATION BUOY.
3118
marker radiobeacon. See MARKER BEACON.
3119
marks and deeps. The divisions used in marking a hand LEAD LINE.
3120
marl. A crumbling, earthy DEPOSIT, particularly one of CLAY mixed with SAND, lime, decomposed SHELLS, etc.
Sometimes a LAYER of marl becomes quite compact. Part of the ocean bed is composed of marl.
3121
Marsden chart. A system introduced by Marsden early in the nineteenth century for showing the distribution of
meteorological DATA on a CHART especially over the OCEANS. A Mercator map projection is used; the world
o
o
between 90 N and 80 S being divided into Marsden 'squares' each of 10 degrees latitude by 10 degrees longitude.
These squares are systematically numbered to indicate position. Each square may be divided into quarter squares, or into
100 one-degree subsquares numbered from 00 to 99 to give the position to the nearest degree.
3122
marsh. A tract of low-lying LAND flooded at times and generally swampy.
143
3123
massif. A large mountain-mass; the central mass of a MOUNTAIN; a compact and more or less independent portion of
a RANGE.
3124
mass transport. In OCEANOGRAPHY, the voluminous transfer of water from one region to another.
3125
master. An instrument which controls another similar instrument called a REPEATER.
A MASTER STATION.
3126
master compass. See COMPASS.
3127
master gyro compass. See COMPASS.
3128
master station. The governing station of two or more synchronized transmitting stations. Often shortened to MASTER.
See SLAVE STATION.
3129
masthead. The top of a mast.
3130
masthead angle. The vertical angle subtended by a ship's mast.
3131
mathematical model. A mathematical representation, usually of a process, device, or concept, which permits
mathematical manipulation of variables as a means to determine how the process, device, or concept would behave in
various situations as e.g. the application of a specific simulation.
3132
Matthews table. An echo sounding correction table.
3133
matrix. In OCEANOGRAPHY, ROCK or SEDIMENT in which larger grains are imbedded in a mass of smaller grains.
In printing, a metal plate, usually of copper, for moulding the face of a type.
In graphic arts, a mold in which type characters are cast in line-casting machines and foundry type.
3134
matte. Conglomerate of SAND, MUD and SEAWEED forming a SHOAL or REEF.
3135
maximum thermometer. See THERMOMETER.
3136
meander (Often in plural). A winding, convolution or winding COURSE, as of a STREAM.
A deviation of the flow pattern of a CURRENT.
3137
mean diurnal high water inequality. See DIURNAL INEQUALITY.
3138
mean diurnal low water inequality. See DIURNAL INEQUALITY.
3139
mean draft. See DRAFT.
3140
mean higher high water (M.H.H.W.). The average HEIGHT or HIGHER HIGH WATERS at a place over a 19-year
period.
3141
mean high water (M.H.W.). The average HEIGHT of all HIGH WATERS at a place over a 19-year period.
3142
mean high water lunitidal interval (M.H.W.I.). See LUNITIDAL INTERVAL.
3143
mean high water neaps (M.H.W.N.). The average HEIGHT of the HIGH WATERS of NEAP TIDES. Also called
neap high water.
3144
mean high water springs (M.H.W.S.). The average HEIGHT of the HIGH WATERS of SPRING TIDES. Also called
spring high water.
3145
mean lower low water (M.L.L.W.). The average HEIGHT of the LOWER LOW WATERS at a place over a 19-year
period.
3146
mean lower low water springs (M.L.L.W.S.). The average HEIGHT of lower low water springs at a place.
3147
mean low water (M.L.W.). The average HEIGHT of all LOW WATERS at a place over a 19-year period.
3148
mean low water lunitidal interval (M.L.W.I.). See LUNITIDAL INTERVAL.
144
3149
mean low water neaps (M.L.W.N.). The average HEIGHT of the LOW WATERS of NEAP TIDES. Also called neap
low water.
3150
mean low water springs (M.L.W.S.). The average HEIGHT of the LOW WATERS of SPRING TIDES. This LEVEL
is used as a TIDAL DATUM in some areas. Also called spring low water.
3151
mean neap range. See NEAP RANGE.
3152
mean neap rise. The HEIGHT of MEAN HIGH WATERS NEAPS above the CHART DATUM. Also called neap
rise.
3153
mean noon. See NOON.
3154
mean range (of tide). The difference in the HEIGHT between MEAN HIGH WATER and MEAN LOW WATER.
3155
mean rise (of tide). The HEIGHT of MEAN HIGH WATER above the CHART DATUM.
3156
mean sea level. The average HEIGHT of the surface of the SEA at a TIDE STATION for all stages of the TIDE over a
19-year period, usually determined from hourly height readings measured from a fixed predetermined reference level
(CHART DATUM).
3157
mean solar day. See DAY: SOLAR.
3158
mean solar time. See TIME.
3159
mean sounding velocity. Mean values for VELOCITY OF SOUND through the vertical water column of specific
DEPTHS based on different VELOCITIES OF SOUND in different sections of the column. These values yield more
nearly correct DEPTHS when sonic DEPTH FINDERS are used. The VELOCITY OF SOUND at any specific DEPTH
may differ considerably from the mean.
3160
mean sphere depth. The uniform DEPTH to which the water would cover the EARTH if the solid surface were smoothed off and were parallel to the surface of the GEOID. The accepted figure for this DEPTH is 2,440 METRES. The
mean DEPTH of the SEA is 3,800 METRES.
3161
mean spring range. See SPRING RANGE.
3162
mean spring rise. The HEIGHT of MEAN HIGH WATER SPRINGS above the CHART DATUM. Also called spring
rise.
3163
mean square error. See ERROR.
3164
mean sun. See SUN.
3165
mean tide level. See HALF TIDE LEVEL.
3166
mean time. See TIME: MEAN SOLAR.
3167
mean water level. The average surface level of a body of water.
3168
measured distance. A COURSE at SEA, whose ends are indicated by RANGES ashore, and whose length has been
accurately measured for determining the SPEED of vessels.
3169
measured mile. A MEASURED DISTANCE of one NAUTICAL MILE.
3170
measurement. The (detailed) dimensions of a physical quantity.
3171
median line. A line every point of which is equidistant from the nearest points on the baselines of two or more states
between which it lies.
3172
median valley. The axial DEPRESSION of the mid-oceanic RIDGE system. See RIFT.
3173
medimarimeter. An apparatus for recording the MEAN SEA LEVEL.
3174
medium frequency (MF). See FREQUENCY: RADIO.
145
3175
medusa. See COELENTERATE and JELLYFISH.
3176
megacycle. One million CYCLES; one thousand KILOCYCLES. The term is often used incorrectly as the equivalent of
one million CYCLES PER SECOND.
3177
megahertz. One million HERTZ; one thousand KILOHERTZ. The term is used as the equivalent of one million
CYCLES PER SECOND.
3178
melting point. Temperature of change from the solid to the liquid phase of a substance. It is a function of pressure.
3179
menu. A list of commands and/or options. The user selects the desired command by moving the CURSOR to the
respective position on the menu or by entering an appropriate code at the command entry line of the DISPLAY.
3180
Mercator: transverse. See PROJECTION: TRANSVERSE MERCATOR.
3181
Mercator chart. See CHART.
3182
Mercator projection. See PROJECTION.
3183
Mercator sailing. See SAILING.
3184
mercurial (or mercury) barometer. See BAROMETER.
3185
meridian. A north-south reference line, particularly a GREAT CIRCLE through the GEOGRAPHICAL POLES of the
EARTH, from which LONGITUDES (or DEPARTURES) and AZIMUTHS are reckoned; or a plane normal to the
GEOID or SPHEROID defining such a line. The term usually refers to the UPPER BRANCH.
3186
meridian: astronomical. A line on the surface of the EARTH connecting points having the same ASTRONOMICAL
LONGITUDE. Because the DEFLECTION OF THE VERTICAL is not the same at all points, an astronomical
meridian is an irregular line, not lying in a single plane. Also called terrestrial meridian.
3187
meridian: celestial. A GREAT CIRCLE of the CELESTIAL SPHERE through the CELESTIAL POLES and the
ZENITH. The expression usually refers to the UPPER BRANCH.
3188
meridian: central. See MERIDIAN: INITIAL.
3189
meridian: compass. A line through the north-south points of a MAGNETIC COMPASS. The compass card axis lies in
the compass meridian.
3190
meridian: geodetic. A line on a SPHEROID which has the same GEODETIC LONGITUDE at every point.
3191
meridian: geographic(al). A general term, applying alike to an ASTRONOMICAL or a GEODETIC MERIDIAN.
3192
meridian: Greenwich. The ASTRONOMICAL MERIDIAN through the centre of the TRANSIT instrument of the
observatory of Greenwich, England, serving as the reference for GREENWICH TIME, in contrast with LOCAL
MERIDIAN.
3193
meridian: grid. One of the GRID lines extending in a grid north-south direction.
3194
meridian: initial. A MERIDIAN through the ORIGIN of a system of GRID COORDINATES and used as y-AXIS of
the system. Also called central meridian.
3195
meridian: local. The MERIDIAN through any particular place or observer, serving as the reference for LOCAL TIME,
in contrast with GREENWICH MERIDIAN.
3196
meridian: magnetic. A line of horizontal magnetic force of the EARTH. The vertical plane in which a freely
suspended, symmetrically magnetized NEEDLE, influenced by no transient, artificial, magnetic disturbance, will come
to rest.
3197
meridian: photograph. In PHOTOGRAMMETRY, the IMAGE on a PHOTOGRAPH of any horizontal line in the
object space which is parallel to the PRINCIPAL PLANE. Since all such lines meet at infinity, the IMAGE of the
meeting point is at the intersection of the PRINCIPAL LINE and the HORIZON TRACE, and all photograph meridians
pass through that point.
146
o
3198
meridian: prime. The MERIDIAN of LONGITUDE 0 , used as the origin for measurement of LONGITUDE. The
MERIDIAN of Greenwich, England, is almost universally used for this purpose.
3199
meridian: principal (U.S. terminology). A true north-south line (a MERIDIAN) extending both north and south of the
INITIAL POINT in the rectangular system of SURVEYS. Together with the BASE LINE they constitute the axes of a
system and the INITIAL POINT the ORIGIN of that system. See PRINCIPAL LINE.
3200
meridian: standard. The MERIDIAN used for reckoning STANDARD TIME.
A MERIDIAN of a map projection, along which the SCALE is as stated.
3201
meridian: terrestrial. See MERIDIAN: ASTRONOMICAL.
3202
meridian: true. A MERIDIAN. The expression is used to distinguish the GREAT CIRCLE through the
GEOGRAPHICAL POLES from MAGNETIC MERIDIAN, COMPASS MERIDIAN, or GRID MERIDIAN.
3203
meridian: zone. The MERIDIAN used for reckoning ZONE TIME.
3204
meridian altitude. See ALTITUDE.
3205
meridian angle. ANGULAR DISTANCE east or west of the local CELESTIAL MERIDIAN; the arc of the
CELESTIAL EQUATOR, or the angle at the CELESTIAL POLE, between the UPPER BRANCH of the local
CELESTIAL MERIDIAN and the HOUR CIRCLE of a CELESTIAL BODY, measured eastward or westward from the
o
local CELESTIAL MERIDIAN through 180 , and labelled E or W to indicate the direction of measurement. See HOUR
ANGLE.
3206
meridian-arc method. A method of determining the dimensions of the ELLIPSOID by measuring (by TRIANGULATION) the linear distances between three points on a MERIDIAN and the ANGULAR DISTANCES between them
from observed differences in their ASTRONOMICAL LATITUDES.
3207
meridian distance. In ASTRONOMY, the HOUR ANGLE of a CELESTIAL BODY when close to but not exactly on
the ASTRONOMICAL MERIDIAN.
In PLANE SURVEYING, the perpendicular distance in a horizontal plane of a point from a MERIDIAN of
reference.
3208
meridian distance: double. The algebraic sum of the perpendicular distances from the two ends of any line of a
TRAVERSE to the initial, or reference, meridian.
3209
meridian passage. See MERIDIAN TRANSIT.
3210
meridian sailing. See SAILING.
3211
meridian telescope. See TELESCOPE.
3212
meridian transit. The apparent passage of a CELESTIAL BODY across a CELESTIAL MERIDIAN. Upper or
superior transit is the passage across the UPPER BRANCH of the CELESTIAL MERIDIAN. Lower or inferior transit
is the passage across the LOWER BRANCH. The lower transit may take place either above the HORIZON as is the
case of CIRCUMPOLAR CELESTIAL BODIES, or across that branch of the MERIDIAN lying below the observer's
HORIZON. Also called TRANSIT, meridian passage, CULMINATION.
3213
meridional difference. The difference between the MERIDIONAL PARTS of any two given PARALLELS.
3214
meridional distance. The difference of LATITUDE between two points on a map PROJECTION's GRATICULE converted to suitable linear units.
3215
meridional orthographic projection. See PROJECTION.
3216
meridional parts. The length of the arc of a MERIDIAN between the EQUATOR and a given PARALLEL on a
MERCATOR CHART, expressed in units of 1 MINUTE of LONGITUDE at the EQUATOR.
3217
meridional plane. Any plane containing the polar AXIS of the EARTH.
3218
meroplankton. Chiefly the floating development stages (eggs and larvae) of the BENTHOS and NEKTON.
3219
mesa. A high TABLELAND (S.W. and W. United States).
147
3220
messenger. In oceanographic terminology, a cylindrical metal WEIGHT, usually hinged and with a latch so that it can
be fastened around a wire, and sent down to actuate WATER BOTTLES and CURRENT METERS after they have
been lowered to the desired DEPTH.
3221
metacentre (or metacenter). That point in a floating body at which a vertical line drawn through its CENTRE OF
BUOYANCY when it is upright meets the vertical line drawn through its CENTRE OF BUOYANCY when it is tipped.
CENTRE OF GRAVITY of the unsubmerged part of a floating body; for stable EQUILIBRIUM the metacentre must be
above the CENTRE OF GRAVITY.
3222
meteor. PHENOMENON other than a CLOUD, observed in the ATMOSPHERE or on the surface of the EARTH,
which consists of a precipitation, a suspension or a deposit of aqueous or non-aqueous liquid or solid particles, or a
PHENOMENON of the nature of an optical or electrical manifestation.
3223
meteoric dust. Atmospheric dust originating from METEORS.
3224
meteorite. A METEOR that reaches the surface of the EARTH as a solid particle.
3225
meteorological element. Atmospheric variable or PHENOMENON which characterize the state of the WEATHER at a
specific place at a given time: air temperature, ATMOSPHERIC PRESSURE, WIND, HUMIDITY,
THUNDERSTORM, FOG, PRECIPITATION, etc.
3226
meteorological observations. See OBSERVATION.
3227
meteorological optical range table. A table from the International Visibility Code which gives the code number of
meteorological visibility and the meteorological visibility for several weather conditions such as thin fog (Code No. 4meteorological visibility 1/2-1 nautical mile); clear (Code No. 7-meteorological visibility 5 1/2-11 nautical miles).
3228
meteorological tide. See TIDE.
3229
meteorological visibility. See VISIBILITY.
3230
meteorology. Science of the ATMOSPHERE.
3231
meter. (1) A person who measures.
(2) An instrument or apparatus for measuring.
(3) A device for measuring a specified thing as in THERMOMETER or BAROMETER.
See also METRE.
3232
meter wheel. A special block used to measure payed out sampling line at OCEANOGRAPHIC STATIONS.
3233
method of squares. See SQUARES: METHOD OF.
3234
metonic cycle. A PERIOD of 19 YEARS, after which the various PHASES OF THE MOON fall on approximately the
same DAYS of the YEAR as in the previous CYCLE.
3235
metre (or meter). The basic unit of length in the SI SYSTEM.
3236
metric system. A system of weights and measures, based upon the metre.
3237
metrology. The science of weights and measures.
3238
micrometer. An auxiliary device to provide measurement of very small angles or dimensions, by an instrument such as
a TELESCOPE. See MICROMETER: FILAR, MICROMETER: TRANSIT.
3239
micrometer: filar. A device attached to a TELESCOPE or microscope, consisting of a wire thread (filament)
connected with a screw in such manner that as the screw is turned, the wire moves through a continuous succession of
parallel positions, all in the FOCAL PLANE of the instrument. Any small angle may be measured by noting the number
of turns and fractions of a turn of the screw which are made in moving the wire from one bisection to another, and
multiplying this by the value of one turn. See MICROMETER: OCULAR, MICROMETER MICROSCOPE, and
MICROMETER COMB.
3240
micrometer: impersonal. See MICROMETER: TRANSIT.
148
3241
micrometer: ocular. A FILAR MICROMETER so placed that its wire moves in the principal FOCAL PLANE of a
TELESCOPE. Also called an eyepiece micrometer.
3242
micrometer: run of. See ERROR OF RUN.
3243
micrometer: transit. A form of registering MICROMETER with its movable wire placed in the FOCAL PLANE of an
astronomic TRANSIT and at right angles to the direction of motion of the IMAGE of a STAR which is observed at or
near CULMINATION. The transit micrometer is also termed an impersonal micrometer, because it almost completely
eliminates the effect of the PERSONAL EQUATION on time observations made with it.
3244
micrometer comb. A notched SCALE placed at right angles to the movable wire of a MICROMETER and so designed
that one turn of the MICROMETER SCREW will move the micrometer wire across one notch of the comb; the central
notch of the comb in conjunction with the zero of the micrometer head furnishes a fiducial point from which all
micrometer readings are reckoned. The comb is used for keeping count of whole turns of the MICROMETER SCREW,
parts of turns being read on the graduated micrometer head.
3245
micrometer drum. A graduated drum by which the motion of a traveling wire in a microscope can be measured.
3246
micrometer microscope. A FILAR MICROMETER so placed that its wire moves in the FOCAL PLANE of a microscope.
3247
micrometer screw. A finely-threaded screw of definite PITCH, with a head graduated to show how much the screw has
been moved in or out; used in MICROMETERS.
3248
micron. One millionth of a METRE; one thousandth of a millimetre.
3249
microphone. An electroacoustic device containing a TRANSDUCER which is actuated by SOUND WAVES and delivers essentially equivalent electric WAVES.
3250
microprocessor. Component of a data processing device made up of microcircuits integrated on a single chip.
3251
microsecond. One millionth of a SECOND.
3252
microseisms. More or less persistent feeble earth tremours caused by natural sources such as atmospheric pressure
systems or waves.
3253
microwave. A very short RADIO WAVE, usually 30 cm to 0.3 mm.
3254
microwave distance measurement. Any method of ELECTROMAGNETIC DISTANCE MEASUREMENT based on
a comparison of radio microwave signals.
3255
mid-channel buoy. A BUOY for marking the middle of a CHANNEL.
3256
middle ground. A shallow area in otherwise deeper water with CHANNELS on both sides of it.
3257
middle ground buoy. A BUOY marking a SHOAL with CHANNELS on both sides. See BIFURCATION BUOY,
JUNCTION BUOY.
3258
middle latitude. Half the arithmetical sum of the LATITUDES of two places on the same side of the EQUATOR.
3259
middle latitude sailing. See SAILING.
3260
mid-extreme tide. See TIDE.
3261
midnight. Twelve HOURS from NOON, or the instant the time reference crosses the LOWER BRANCH of the reference CELESTIAL MERIDIAN.
3262
mil. 1. 1/6400 of the circumference of a circle. Approximately 1/1000 radian.
2. 1/1000 of an inch.
3263
mile. A unit of distance. See INTERNATIONAL NAUTICAL MILE, SEA MILE, STATUTE MILE.
3264
military practice area. See EXERCISE AREA.
149
3265
Milky Way. A broad, faintly luminous band seen across the sky at night, consisting of innumerable STARS and
nebulae, so distant as to be indistinguishable without a TELESCOPE.
3266
millibar. A unit of pressure equal to 1/1,000 of a BAR. The millibar is much used in METEOROLOGY.
3267
milligal. A unit of ACCELERATION equal to 1/1,000 of a GAL, or 1/1,000 centimetre per SECOND, per SECOND.
This unit is used in gravity measurement, being approximately one-millionth of the average GRAVITY at the EARTH's
surface.
3268
mineral development platform. See PLATFORM: MINERAL DEVELOPMENT.
3269
minimum squares. See LEAST SQUARES.
3270
minimum thermometer. See THERMOMETER.
3271
minor control. See CONTROL: PHOTOGRAMMETRIC.
3272
minor control plot. See RADIAL TRIANGULATION.
3273
minor planet. An ASTEROID.
3274
minus soundings. See SOUNDING.
3275
minute. The sixtieth part of an HOUR; sixty SECONDS.
The sixtieth part of a DEGREE of arc; sixty SECONDS.
3276
mirage. Optical PHENOMENON consisting essentially of steady or wavering, single or multiple, upright or inverted,
vertically enlarged or reduced, IMAGES of distant objects.
3277
mirage: inferior. Particular case of MIRAGE, occurring over stretches of water, land, SHORES, roads, etc. strongly
heated by INSOLATION, and in which the virtual IMAGE is found below the actual object. The case in which objects
situated on or slightly above the normal HORIZON become invisible is popularly termed SINKING.
3278
mirage: superior. Special case of MIRAGE, observable over snow-fields, cold SEAS, etc., in which the virtual
IMAGE is above the actual object. The case in which objects below and beyond the normal HORIZON become visible
is popularly termed LOOMING.
3279
mire. A piece of wet swampy GROUND.
3280
mirror. Any surface which produces IMAGES by REFLECTION of LIGHT RAYS.
3281
mist. Suspension in the air of microscopic water droplets or wet hygroscopic particles, reducing the VISIBILITY at the
EARTH's surface.
3282
mixed current. See CURRENT.
3283
mixed layer. In OCEANOGRAPHY, the surface layer of virtually isothermal water, which frequently exists above the
THERMOCLINE. The thickness of the layer is dependent on the temperature gradient.
3284
mixed seas. The state of the sea resulting from the interaction of wind, waves, and swell.
3285
mixed tide. See TIDE.
3286
moat (or sea moat). An annular depression that may not be continuous, located at the base of many SEAMOUNTS or
ISLANDS.
3287
mobile rig. See RIG.
3288
mobile station. A radiolocation station intended to be used at unspecified points. As opposed to FIXED STATION.
3289
mock moons. Name given sometimes to PARASELENAE, PARANTISELENAE and ANTISELENAE when they are
bright.
3290
mock suns. Name often given to PARHELIA, PARANTHELIA and ANTHELIA when they are particularly bright.
150
3291
mock-up. A model of something to be used for testing or study
3292
modulated wave. See WAVE.
3293
modulating wave. See WAVE.
3294
modulation. VARIATION of some characteristic of a WAVE, called the CARRIER WAVE, in accordance with
instantaneous values of another WAVE, called the MODULATING WAVE. Variation of AMPLITUDE is amplitude
modulation, variation of FREQUENCY is frequency modulation, and variation of PHASE is phase modulation. See
MODULATION: PULSE and MODULATION: SPACE.
3295
modulation: amplitude. The process of changing the amplitude of a carrier wave in accordance with the variations of a
modulating wave.
3296
modulation: frequency. Angle modulation of a sine-wave carrier in which the instantaneous frequency of the
modulated wave differs from the carrier frequency by an amount proportional to the instantaneous value of the
modulating wave.
3297
modulation: pulse. The process of forming very short bursts of a CARRIER WAVE, separated by relatively long
periods during which no CARRIER WAVE is transmitted.
3298
modulation: sideband. A particular kind of amplitude modulation in which one of the two frequency bands on both
sides of the carrier (and possibly the carrier itself) is suppressed, allowing a considerable reduction of the spectral width
of the signal.
3299
modulation: space. The combining of SIGNALS in space to form a SIGNAL of desired characteristics.
3300
moire. Undesirable patterns occurring when REPRODUCTIONS are made from halftone PROOFS or steel
ENGRAVINGS, caused by conflict between the RULING of the HALFTONE screen and the dots or lines of the
original; a similar pattern occurring in multicolour halftone reproductions and usually due either to incorrect screen
angles or misregister of the colour impressions during printing.
3301
moiré effect. The effect created by transmitting light through two separate, overlapping families of parallel lines. See
also INOGEN LIGHT.
3302
mole. A massive structure of masonry or large stones serving as a PIER or BREAKWATER, or both.
Unit of quantity of matter in the SI system.
3303
moment. The tendency or degree of tendency to produce motion about an AXIS. Numerically it is the quantity obtained
by multiplying the force, SPEED, or mass, by the distance from the point of application or CENTRE OF GRAVITY to
the AXIS. See MAGNETIC MOMENT.
3304
moment of inertia. The quantity obtained by multiplying the mass of each small part of a body by the square of its
distance from an AXIS, and adding all the results.
3305
momentum. Quantity of motion. That property of a particle which is given by the product of its mass with its
VELOCITY.
3306
monitoring. Checking of the operation and performance of an electronic system through reception of its SIGNALS.
3307
monochromatic (adj.). Of, or having one colour. Of, or producing light of one WAVE LENGTH.
3308
monsoon. WIND of the general circulation of the ATMOSPHERE, typified by the seasonal persistence of a given wind
direction and by a pronounced change in this direction from one season to another. The term is generally confined to
those cases in which the primary cause is the differential heating (changing in nature from summer to winter) of a
CONTINENT relative to a neighbouring OCEAN.
3309
montage. A series of related pieces of copy appearing as one to tell a complete story.
3310
month. A measure of TIME based on the motion of the MOON in its ORBIT.
3311
month: anomalistic. The interval of time between two successive passages of the MOON in its ORBIT through
PERIGEE. The length of the anomalistic month is 27.55455 mean SOLAR DAYS.
151
3312
month: dracontic. See MONTH: NODICAL.
3313
month: lunar. See MONTH: SYNODICAL.
3314
month: nodical. The interval of time between two successive passages of the MOON through the same NODE of its
ORBIT. The length of the nodical month averages 27.21222 mean SOLAR DAYS. Also called dracontic month.
3315
month: sidereal. The interval of time between two successive passages of the MOON past as FIXED STAR. The
length of the sidereal month averages 27.321661 mean SOLAR DAYS.
3316
month: synodical. The interval of time between two successive CONJUNCTIONS or OPPOSITIONS of the MOON.
The length of the synodical month is 29.5305888 mean SOLAR DAYS. Also called lunation or lunar month.
3317
month: tropical. The average period of REVOLUTION of the MOON about the EARTH with respect to the VERNAL
EQUINOX. The length of the tropical month averages 27.321582 mean SOLAR DAYS.
3318
monument (U.S. terminology). In SURVEYING, a structure used or erected to mark the POSITION of a STATION;
permanence is implied.
3319
moon. The SATELLITE of the EARTH. See LIBRATIONS OF MOON and PHASES OF THE MOON.
3320
moonbow. RAINBOW whose formation is the same as that of the ordinary RAINBOW, but whose light comes from
the MOON and not from the SUN. Also called lunar rainbow.
3321
moor (v.t.). To secure a boat or other floating thing to a fixed object or the seabottom.
3322
mooring. A place where a vessel may be secured.
(Usually in pl.) The equipment used to secure a vessel.
The process of securing a vessel or oceanographic instruments other than anchoring with a single anchor.
3323
mooring buoy. See BUOY.
3324
morse code light. See LIGHT.
3325
mosaic. In PHOTOGRAMMETRY, as assembly of AERIAL PHOTOGRAPHS whose edges usually have been torn, or
cut, and matched to form a continuous photographic representation of a portion of the EARTH's surface.
3326
mosaic: controlled. A MOSAIC oriented and scaled to horizontal GROUND CONTROL; usually assembled from
rectified PHOTOGRAPHS. See also ORTHOPHOTOMOSAIC, UNCONTROLLED MOSAIC.
3327
most probable value. That value of a quantity which is mathematically determined from a series of observations and is
more probably free of the effects of blunders and errors than any other value that might stem from the same series of
observations.
3328
mother vessel. The lead vessel when surveying with several vessels.
3329
mount. A large HILL or MOUNTAIN, usually a detached, characteristically conical mass of earth. The term 'mount' is
always used instead of MOUNTAIN when it precedes a proper name.
3330
mountain. A natural ELEVATION of the EARTH's surface rising more or less abruptly from the surrounding LEVEL,
and attaining an ALTITUDE which, relatively to adjacent ELEVATIONS, is impressive or notable.
3331
mountains. On the sea floor, a well-delineated subdivision of a large and complex positive feature. See CORDILLERA.
3332
mountain chain. A complexity of several MOUNTAIN RANGES.
3333
mountain range. A line of MOUNTAINS. Also referred to as range of mountains.
3334
mouse. In computer systems, a pointing device operated by moving on a flat surface. See also CURSOR, JOYSTICK.
3335
mouth. The place of discharge of a STREAM into the OCEAN or ENTRANCE to a BAY from the OCEAN.
152
3336
mud. Pelagic or terrigenous detrital material consisting mostly of silt and clay-sized particles (less than 0.06 millimetre)
but often containing varying amount of SAND and/or organic materials. It is a general term applied to any sticky finegrained SEDIMENT whose exact size classification has not been determined.
3337
mud: red. A reddish-brown terrigenous deep-sea MUD which accumulates on the SEA FLOOR in the neighbourhood
of deserts and off the MOUTHS of great RIVERS; contains calcium carbonate up to 25 per cent.
3338
mud snapper. See SNAPPER.
3339
multi-beam echo sounder. Wide swath echo sounder for use in seabed mapping and surveying using the multi-beam
principle. Depths are measured directly below and transverse to the ship's track. The width of the swath is a function of
the number of beams and their aperture.
3340
multiple echo(es). See ECHO.
3341
multiple lens camera. See CAMERA.
3342
multiple lens photograph. See PHOTOGRAPH.
3343
multiple sea sampler. An instrument which comprises six WATER BOTTLES arranged so that they trip and take
WATER SAMPLES at different selected DEPTHS from a vessel under way.
3344
multiple tide staff. See TIDE STAFF.
3345
multiplex. In PHOTOGRAMMETRY, an instrument for making a TOPOGRAPHIC MAP from AERIAL
PHOTOGRAPHS. A three-dimensional optical model of the TERRAIN to be mapped is produced, in miniature, by
direct optical PROJECTION from a pair of overlapping PHOTOGRAPHS. This instrument uses the ANAGLYPH
principle.
3346
multispectral imagery. Images obtained simultaneously in a number of discrete bands in the electromagnetic spectrum.
3347
multispectral scanner. A remote-sensing device which is capable of recording data in the ultraviolet and visible
portions of the electromagnetic spectrum, as well as the infrared.
153
N
3348
nadir. That point on the CELESTIAL SPHERE directly beneath the observer, and directly opposite to the ZENITH.
3349
nadir: ground. The point on the GROUND vertically beneath the PERSPECTIVE CENTRE of the camera lens.
3350
nadir: map. The map position for the GROUND NADIR.
3351
nadir: photograph. In PHOTOGRAMMETRY, the point at which a vertical line through the PERSPECTIVE
CENTRE of the camera lens pierces the plane of the PHOTOGRAPH. Also called nadir point, or plumb point.
3352
nadir point. See NADIR: PHOTOGRAPH.
3353
nadir radial. See RADIAL.
3354
name. The label of a numerical value used particularly to refer to the N (north) or S (south) label of LATITUDE and
DECLINATION. When LATITUDE and DECLINATION are both N or both S, they are said to be of the same name,
but if one is N and the other S, they are said to be of contrary name.
3355
nanosecond. A thousand millionth of a SECOND.
3356
Nansen bottle. A device used by oceanographers to obtain subsurface samples of SEA WATER. The bottle is lowered
by wire; its valves are open at both ends. It is then closed 'in situ' by allowing a weight (called a MESSENGER) to slide
down the wire and strike the reversing mechanism. This causes the bottle to turn upside down, closing the valves and
reversing the REVERSING THERMOMETERS which are mounted in a special thermometer case on it. If, as is usually
done, a series of bottles is lowered, then the reversal of each bottle releases another MESSENGER to actuate the bottle
beneath it.
3357
Napier's (or Napier) diagram. A DIAGRAM on which compass deviation is plotted for various HEADINGS, and the
points connected by a smooth curve, permitting a ready conversion of deviations from compass to magnetic
HEADINGS, or vice versa.
3358
narrow-beam echo sounder. A sounder with a transducer of small aperture (typically 2° to 5°) required for high
resolution mapping.
3359
narrows. A NAVIGABLE narrow part of a BAY, STRAIT, RIVER, etc.
3360
natural frequency. See FREQUENCY.
3361
natural scale. See SCALE.
3362
natural year. See YEAR: TROPICAL.
3363
nature of the bottom. See BOTTOM: NATURE OF.
3364
nautical (adj.). Of or pertaining to ships, NAVIGATION (chiefly marine) or seamen. In contrast, navigational refers to
NAVIGATION only.
3365
nautical almanac. See ALMANAC.
3366
nautical astronomy. See ASTRONOMY.
3367
nautical chart. See CHART.
3368
nautical mile. A unit of length used principally in NAVIGATION. See INTERNATIONAL NAUTICAL MILE.
3369
nautical plan. A large scale nautical chart or a large scale inset of a nautical chart.
3370
nautical twilight. See TWILIGHT.
3371
nautophone. A HORN having a diaphragm oscillated by electricity.
3372
NAVAREA. The short title of an area in the WORLD-WIDE NAVIGATIONAL WARNING SERVICE.
154
3373
navigability. Of a vessel: capability of being controlled and steered.
Of a water area: capability of being navigated.
3374
navigable (adj.). Affording passage to a craft; capable of being navigated.
3375
navigable area surveys (NAS). Navigable Area Surveys are basic hydrographic surveys with restricted area coverage.
The coverage is reduced by omitting requirements for:
1. Development of the 0-foot depth curve and foul, nearshore areas not considered navigable;
2. Complete field edit of the survey area. Navigable Area Surveys may also be restricted to the main navigable
channel or corridor.
3376
navigable semicircle. See DANGEROUS SEMICIRCLE.
3377
navigable waters. Waters usable, with or without improvements, as routes for commerce in the customary means of
travel on water.
3378
navigation. The process of directing the movement of a craft from one point to another.
3379
navigation: acoustic. See NAVIGATION: SONIC.
3380
navigation: aerial. See NAVIGATION: AIR.
3381
navigation: air. The NAVIGATION of aircraft. Occasionally called aerial navigation or navigation. See
NAVIGATION: SURFACE.
3382
navigation: astro. See NAVIGATION: CELESTIAL.
3383
navigation: celestial. NAVIGATION with the aid of CELESTIAL BODIES. Also called astro-navigation.
3384
navigation: coastwise. NAVIGATION in the vicinity of a COAST, in contrast with OFFSHORE NAVIGATION.
3385
navigation: Doppler. NAVIGATION using equipment employing Doppler shift measurement techniques with respect
to transmitted and reflected SIGNALS to automatically compute DRIFT ANGLE and GROUND SPEED. DRIFT
ANGLE and GROUND SPEED are used in DEAD RECKONING performed either manually or, as in many
installations, by dead reckoning COMPUTERS. In either case, craft HEADING is a necessary INPUT.
3386
navigation: electronic. NAVIGATION by means of electronic equipment. The expression 'electronic navigation' is
more inclusive than radio navigation, since it includes navigation involving any electronic device or instrument.
3387
navigation: grid. NAVIGATION by the use of GRID DIRECTIONS.
3388
navigation: hyperbolic. NAVIGATION by the use of HYPERBOLIC LINES OF POSITION.
3389
navigation: inertial. DEAD RECKONING performed automatically by a device which gives a continuous indication
of POSITION by double integration of ACCELERATION since leaving a starting point.
3390
navigation: land. NAVIGATION of vehicles across LAND or ICE. The expression is generally used in connection
with the crossing of a region devoid of roads or LANDMARKS, so that methods similar to those employed in AIR or
MARINE NAVIGATION must be employed.
3391
navigation: long range. NAVIGATION requiring only aids usable at long RANGE, relatively few of which could
provide world coverage. The opposite is SHORT RANGE NAVIGATION.
3392
navigation: marine. NAVIGATION of water craft.
3393
navigation: offshore. NAVIGATION at distance from a COAST, in contrast with COASTWISE NAVIGATION.
3394
navigation: radio. See NAVIGATION: ELECTRONIC.
3395
navigation: short range. NAVIGATION employing only aids usable at short RANGES. The opposite is LONG
RANGE NAVIGATION.
3396
navigation: sonic. NAVIGATION by means of SOUND WAVES whether or not they are within the audible RANGE.
Also called acoustic navigation.
155
3397
navigation: submarine. NAVIGATION of a submarine, whether submerged or surfaced.
3398
navigation: surface. NAVIGATION of a craft on the surface of the EARTH. The expression is used particularly with
reference to NAVIGATION of vessels on the surface of water. See NAVIGATION: LAND and NAVIGATION:
UNDERWATER.
3399
navigation: underwater. The NAVIGATION of a submerged vessel. Occasionally called SUBMARINE
NAVIGATION.
3400
navigational(adj.). See NAUTICAL.
3401
navigational aid (U.S. terminology). An instrument, device, CHART, method, etc., intended to assist in the
NAVIGATION of a craft. An AID TO NAVIGATION is a navigational aid but the latter expression should not be
confused with the former which refers only to devices external to a craft.
3402
navigational astronomy. See ASTRONOMY: NAUTICAL.
3403
navigational drafts. See DRAFT.
3404
navigational observation. Observations necessary to fix the position of a vessel.
3405
navigational parameters. All data characterising the position and motion of a vessel in a system of coordinates.
3406
navigational planet(s). See PLANET(S): NAVIGATIONAL.
3407
navigational (or navigation) satellite. An artificial earth-orbiting SATELLITE designed for navigational purposes.
3408
navigational stars. Selected bright STARS whose POSITIONS are precisely tabulated in NAUTICAL ALMANACS
for navigational purposes.
3409
navigational triangle. See ASTRONOMICAL TRIANGLE.
3410
navigational warning. A broadcast message containing urgent information relevant to safe navigation.
3411
navstar global positioning system. A satellite navigation system.
3412
NAVTEX. Narrow-band
INFORMATION.
3413
neaped. See BENEAPED.
3414
neap high water. See MEAN HIGH WATER NEAPS.
3415
neap low water. See MEAN LOW WATER NEAPS.
3416
neap range. The mean semidiurnal RANGE OF TIDE when NEAP TIDES are occurring; the mean difference in
HEIGHT between neap high water and neap low water. Sometimes called mean neap range.
3417
neap rise. See MEAN NEAP RISE.
3418
neap tide(s). See TIDE.
3419
nearshore. Close to the SHORE.
3420
neat line. Line, usually grid or graticule, bounding the detail of a MAP. Also referred to as inner neat line to
differentiate from border drawn outside of neat line. Also written as one word.
3421
nebula (pl. nebulae). An aggregation of matter outside the SOLAR SYSTEM, large enough to occupy a perceptible
area but which has not been resolved into individual STARS.
3422
neck. In OCEANOGRAPHY, the narrow band of water flowing swiftly seaward through the SURF. See CURRENT:
RIP.
In geography, a narrow piece of LAND with water on each side; an ISTHMUS.
3423
needle. Short for MAGNETIC NEEDLE.
direct-printing
telegraphy
156
system
for
transmission
of
MARITIME
SAFETY
3424
negative. A photographic IMAGE on film, PLATE, or paper, in which the subject tones to which the EMULSION is
sensitive are reversed or complementary.
3425
negative altitude. See ANGLE OF DEPRESSION.
3426
negative engraving. A chart reproduction process in which the compilation manuscript, or other data, is photographed
onto a plastic or glass negative. The art of creating FACSIMILE images on a reproduction media by utilizing hand
engraving techniques.
3427
negative gradient. In OCEANOGRAPHY, a LAYER of water where temperature decreases with DEPTH.
3428
nekton. Those animals of the PELAGIC DIVISION that are active swimmers, such as most of the adult squids, fishes,
and marine mammals.
3429
neritic province. See PELAGIC DIVISION.
3430
network. In SURVEYING, a pattern or configuration of STATIONS called geodetic network.
In geography, a complex system of RIVERS, CANALS, etc.
In RADIO, a CHAIN of transmitting RADIO STATIONS owned and operated as a unit.
3431
new chart. See CHART.
3432
new edition (of chart). In British terminology, a new printing of an existing CHART embodying the latest information
received in the Hydrographic Department. The CHART is entirely revised throughout and modernized in style, all
copies of the CHART in circulation being cancelled. When a new edition is published the LARGE and SMALL
CORRECTIONS dates are removed (these corrections being embodied in the new edition).
In U.S. terminology, a new printing of an existing CHART embodying corrections that have become so extensive or
of such importance to NAVIGATION as to render all previous printings obsolete.
3433
new ice. A general term which includes FRAZIL ICE, SLUSH, SLUDGE, PANCAKE ICE and ICE RIND.
3434
new moon. See PHASES OF THE MOON.
3435
new print (of chart). In U.S. terminology, a new issue of a CHART embodying only minor corrections. Such
corrections are applied to the NEGATIVES and a new printing plate made. New prints do not render previous printings
of the current edition obsolete.
3436
new print date (of chart). In U.S. terminology, the date when a NEW PRINT of a CHART is issued which embodies
changes or corrections of a relatively minor character. The new print date is added to the right of the edition date in the
lower left-hand corner of the CHART.
3437
new survey. See RESURVEY.
3438
newton. The unit of force in the SI SYSTEM.
3439
niggerhead. Large blocks of CORAL torn loose from the outer face of a REEF and tossed on to the REEF FLAT by
STORM WAVES or TSUNAMIS. The blocks are blackened by a crust of lichens after detachment from the REEF.
3440
night effect (or error). See ERROR: POLARIZATION.
3441
nimbostratus. See CLOUD GENERA.
3442
nipped (adj. and adv.). Said of a ship which is BESET when ICE forcibly presses against it. See BESET, ICEBOUND.
3443
nipping. The closing of ICE around a ship so that the ship is BESET and subjected to pressure from the ICE.
3444
no-bottom sounding(s). See SOUNDING.
3445
no-check position. See STATION: INTERSECTION.
3446
noctiluca. A genus of usually pale pink luminescent dinoflagellates large enough to be seen by the unaided eye. This
particular organism is responsible for much of the sheet-type LUMINESCENCE noted in coastal waters of various parts
of the world OCEAN.
157
3447
nocturnal arc. See ARC: ASTRONOMICAL.
3448
nodal point. In optics, one of the two points on the OPTICAL AXIS of a LENS (or a system of LENSES) such that a
RAY emergent from the second point is parallel to the RAY incident at the first. The first nodal point is referred to as
the front nodal point or incident nodal point, and the second nodal point as the rear nodal point or emergent nodal
point.
An AMPHIDROMIC POINT.
In ASTRONOMY, a NODE.
3449
nodal point: emergent. See NODAL POINT.
3450
nodal point: front. See NODAL POINT.
3451
nodal point: incident. See NODAL POINT.
3452
nodal point: rear. See NODAL POINT.
3453
node. A point that is the start or end point of a line segment.
In ASTRONOMY, one of the two points of intersection of the ORBIT of a PLANET, PLANETOID, or COMET
with the ECLIPTIC, or of the ORBIT of a SATELLITE with the plane of the orbit of its primary. That point at which
the body crosses to the north side of the reference plane is called the ascending node; the other, the descending node.
The line connecting the nodes is called LINE OF NODES. Also called NODAL POINT. See REGRESSION OF THE
NODES.
In OCEANOGRAPHY, that part of a STANDING WAVE where the vertical motion is least and the horizontal
VELOCITIES are greatest. See PARTIAL NODE.
In optics, a NODAL POINT.
3454
nodical month. See MONTH.
3455
nodules. In OCEANOGRAPHY, concretionary lumps of manganese, cobalt, iron, and nickel found widely scattered on
the ocean floor. ROCKS of various sizes and shapes often are encrusted with these metals.
3456
noise. Any undesired SOUND. By extension, noise is any unwanted disturbance within a useful FREQUENCY BAND,
such as undesired electric WAVES in a transmission channel or device.
3457
nominal range. See RANGE.
3458
nomogram (or nomograph). A DIAGRAM showing, to SCALE, the relationship between several variables in such
manner that the value of one which corresponds to known values of the others can be determined graphically. See
CONVERSION SCALE, CONVERSION TABLE.
3459
nonharmonic constants. Tidal or tidal current constants such as LUNITIDAL INTERVALS, ranges, and inequalities,
which can be derived directly from OBSERVATION without regard to the HARMONIC CONSTITUENTS.
3460
nonharmonic method. In TIDE PREDICTION, an approximate method based on the principle that 'the TIDE follows
the MOON'. It makes use of the close relationship that exists between the TIME of TIDE at most places and the
MOON's MERIDIAN TRANSIT.
3461
nontidal current. See CURRENT.
3462
noon. The instant at which a time reference is over the UPPER BRANCH of the reference MERIDIAN.
3463
noon: apparent. Twelve o'clock APPARENT TIME.
3464
noon: local apparent. Twelve o'clock LOCAL APPARENT TIME. Sometimes called high noon.
3465
noon: mean. Twelve o'clock MEAN TIME.
3466
normal. In general, a straight line perpendicular to a surface or to another line.
In GEODESY, a straight line perpendicular to the surface of the SPHEROID.
3467
normal equation. See EQUATION.
158
3468
normal water. A standard SEA WATER preparation, the CHLORINITY of which lies between 19.30 and 19.50 per
mille (0/00) and has been determined to within ± 0.001 per mille. Normal water is used as a convenient comparison
standard for chlorinity measurements of sea water samples by TITRATION. It is prepared by the Hydrographical
Laboratories, Copenhagen, Denmark. Also called standard sea water.
3469
north: compass. The direction north as indicated by a MAGNETIC COMPASS.
3470
north: grid. An arbitrary REFERENCE DIRECTION used with GRID NAVIGATION.
The northerly or zero direction indicated by the grid datum of directional reference.
3471
north: magnetic. The direction indicated by the north seeking POLE of a freely suspended MAGNETIC NEEDLE
influenced only by the EARTH's MAGNETIC FIELD.
3472
north: true. The DIRECTION of the north GEOGRAPHIC POLE.
3473
north celestial pole. See POLE: CELESTIAL.
3474
north geographical pole. See POLE: GEOGRAPHICAL.
3475
northing. The distance a craft makes good to the north. The opposite is SOUTHING.
In a cartesian reference system the value of one coordinate, usually expressed in metres, measured from the origin in
north-south direction; used e.g. in the UTM system.
3476
north magnetic pole. See MAGNETIC POLE.
3477
notch (or gap). A narrow passage between two ELEVATIONS, as MOUNTAINS; a deep close PASS; a DEFILE.
3478
Notice to Mariners. A periodical or casual notice issued by hydrographic offices, or other competent authorities,
regarding changes in AIDS TO NAVIGATION, dangers to NAVIGATION, important new SOUNDINGS, and, in
general, all such information as affects NAUTICAL CHARTS, SAILING DIRECTIONS, LIGHT LISTS and other
nautical publications.
3479
nuclear precession magnetometer. See MAGNETOMETER.
3480
numerical scale. See SCALE: NATURAL.
3481
nunatak. An isolated hill or mountain peak of rock projecting above an INLAND ICE SHEET.
3482
nun buoy. A BUOY the above water part of which is in the shape of a cone or a truncated cone.
3483
nutation. Irregularities in the precessional motion of the EQUINOXES because of varying positions of the MOON,
and, to a lesser extent, of other CELESTIAL BODIES, with respect to the ECLIPTIC. Because of nutation the
EARTH's AXIS nods like a top, describing an irregular circle about the mean pole in a period of about 19 years.
3484
Nyquist frequency. The highest frequency that may be uniquely resolved in a time series from a given sampling
interval. The Nyquist frequency is equal to twice the sampling interval. Analyzing frequencies for which the Nyquist
criterion is not met leads to ALIASING.
159
O
3485
object-glass. See OBJECTIVE LENS.
3486
objective. See OBJECTIVE LENS.
3487
objective lens. In TELESCOPES and microscopes,the optical component which receives light from the object and
forms the first or primary IMAGE. In a CAMERA, the IMAGE formed by the objective lens is the final IMAGE. In a
TELESCOPE or microscope used visually, the IMAGE formed by the objective lens is magnified by the EYEPIECE.
Also called objective or object-glass.
3488
oblate spheroid. See SPHEROID.
3489
oblique photograph. See PHOTOGRAPH.
3490
oblique plotting instrument. An instrument (usually monocular) for plotting from OBLIQUE PHOTOGRAPHS.
3491
obliquity of the ecliptic. The acute angle between the plane of the ECLIPTIC and the plane of the CELESTIAL
EQUATOR, about 23°27'.
3492
obscured(adj.). Said of the arc of a LIGHT SECTOR designated by its limiting BEARINGS in which the LIGHT is not
visible from seaward.
3493
observation. The act or practice of noting and recording facts and events as for some scientific study. The measure of a
quantity whose value is desired. The DATA so noted and recorded.
A single measure, at a single setting of an apparatus.
3494
observation(s): astronomical. OBSERVATIONS of CELESTIAL BODIES, with appropriate instruments.
In NAVIGATION, the measurement of ALTITUDE and AZIMUTH of CELESTIAL BODIES.
3495
observation(s): magnetic. Measurement of any of the MAGNETIC ELEMENTS.
3496
observation(s): meteorological. Evaluation or measurement of one or more meteorological elements.
3497
observation(s): tidal. A series of measurements taken in order to provide the information required for the
REDUCTION OF SOUNDINGS, and the DATA for TIDAL PREDICTION and investigation.
3498
observation equation. See EQUATION.
3499
observation spot (or pillar). A position ashore determined from celestial observations.
3500
observation tower. A tower from which one's surroundings can be observed, but at which a watch is not habitually
maintained, as at a LOOKOUT TOWER. Such towers are temporarily erected for observations in geodetic networks.
3501
observed altitude. See ALTITUDE.
3502
observed tide. Those data from tide observing equipment such as tide gauges, staffs, etc. "Actual tides" is an expression
often used in referring to "observed tides".
3503
obstruction. In MARINE NAVIGATION, anything that hinders or prevents movement, particularly anything that
endangers or prevents passage of a vessel. The term is usually used to refer to an isolated danger to NAVIGATION,
such as a SUNKEN ROCK or PINNACLE.
3504
obstruction buoy. A BUOY marking an OBSTRUCTION.
3505
obstruction light. See LIGHT.
3506
occasional light. See LIGHT.
3507
occluded front. See OCCLUSION.
160
3508
occlusion. Process of progressive decrease of area of warm sector at the EARTH's surface, and its ultimate
disappearance, by the junction of the cold AIR MASSES which initially precede the WARM FRONT and follow the
COLD FRONT.
FRONT between these two cold AIR MASSES, after their junction (also termed occluded front).
3509
occultation. The concealment or extinguishment of the light of an AID TO NAVIGATION during the dark periods of
its CYCLE.
In ASTRONOMY, the concealment of a CELESTIAL BODY by another which crosses the line of view. Thus, the
MOON occults a STAR when it passes between the observer and the STAR.
3510
occupy (v.t.). In SURVEYING, to observe with a surveying instrument at a STATION; also to set a surveying
instrument over a point for the purpose of making OBSERVATIONS.
In OCEANOGRAPHY, to stop a ship at a selected location, an OCEANOGRAPHIC STATION, for the purpose of
gathering oceanographic observations.
3511
ocean. The vast body of water on the surface of the GLOBE, which surrounds the LAND; the main or great SEA.
One of the main areas into which this body of water is divided geographically.
3512
ocean acoustic tomography. A method to determine the ocean structure based on precise measurements of transit time
of acoustic waves between a net of transmitters and receivers.
3513
ocean current. See CURRENT.
3514
ocean eddy. A moving or stationary local rotating formation where water predominantly moves along circular paths.
3515
ocean remote sensing. A kind of remote sensing especially for conducting investigations and surveys of the ocean and
the sea.
3516
oceanic circulation. A unique interrelated system of major ocean currents within a large area; usually a closed circular
pattern such as in the North Atlantic, Mediterranean, etc.
3517
oceanic plateau. A comparatively flat topped elevation of the sea-bed which rises steeply from the ocean floor on all
sides, and is of considerable extent across the summit.
3518
oceanic province. See PELAGIC DIVISION.
3519
oceanic ridge. A long elevation of the ocean floor with either irregular or smooth topography and steep sides, often
separating ocean basins.
3520
oceanographic cast. See CAST.
3521
oceanographic features. Physical qualities characterising the state of environment in water bodies of the World's
Oceans. These features include temperature and salinity, electric conductivity, density, hydrostatic pressure,
transparency, the range and character of tidal and other water level oscillations, the speed and direction of currents, the
characteristics of waves and ice, etc.
3522
oceanographic slide rule. A specially designed SLIDE RULE used for calculating the CORRECTION of thermal
expansion of a deep sea REVERSING THERMOMETER.
3523
oceanographic section. A successive series of oceanographic stations carried out in a specified direction.
3524
oceanographic station. See STATION.
3525
oceanographic survey. See SURVEY.
3526
oceanography. The study of the SEA, embracing and integrating all knowledge pertaining to the SEA's physical
boundaries, the chemistry and physics of SEA WATER, MARINE BIOLOGY, and SUBMARINE GEOLOGY.
In strict usage oceanography is the description of the marine environment, whereas oceanology is the study of the
OCEANS and related sciences.
3527
oceanology. See OCEANOGRAPHY.
161
3528
ocean station. As defined by the International Civil Aviation Organization, a specifically located area of ocean surface,
roughly square and 200 NAUTICAL MILES on a side. An ocean station vessel on patrol is said to be 'on station' when
it is within the perimeter of the area.
3529
ocean station vessel (OSV). Ship assigned to operate at the location of an OCEAN WEATHER STATION. Also called
weather ship.
3530
ocean water. Water having the physical-chemical characteristics of the OPEN SEA, where continental influences are at
a minimum.
3531
ocean weather station. STATION aboard a suitably equipped and staffed ship which tries to maintain a fixed maritime
location and which observes and reports for international exchange the OBSERVATIONS of specified elements.
3532
octant. A double-reflecting instrument for measuring angles. It is similar to a SEXTANT but has an arc of only 45°.
3533
ocular micrometer. See MICROMETER.
3534
odograph. A mechanical instrument containing a distance-measuring element which is moved or turned by an amount
proportional to the actual distance travelled; a compass element which provides a fixed-reference direction, and an
integrator which provides for the resolution of the direction of motion into components and for the summation or
integration of the distance components.
Also an instrument for recording the distance travelled by a vehicle or pedestrian.
3535
odometer (or hodometer). An instrument for measuring the distance travelled by a craft. See also SPEEDOMETER.
3536
oersted. The CGS unit of MAGNETIC FIELD INTENSITY in the SI system.
3537
offing. That part of the visible SEA a considerable distance from the SHORE, or that part just beyond the limits of the
area in which a pilot is needed.
3538
offset. In SURVEYING, a short line perpendicular to a surveyed line, measured to a line or point for which DATA are
desired, thus locating the second line or point with reference to the first or surveyed line. An offset is also a jog in a
SURVEY or other line, the line having approximately the same direction both before and after passing the jog. Offsets
are measured from a surveyed line or lines to the edges of an irregular-shaped body of water, or to any irregular line
which it is desired to locate.
3539
offset lithography. A method of printing in which an image is transferred from a printing PLATE on to a rubbersurfaced blanket and thence on the paper. The image on the plate is a RIGHT READING IMAGE.
3540
offshore(adj. and adv.). Away from the SHORE.
3541
offshore(n.). The comparatively flat zone of variable width which extends from the outer margin of the rather steeply
sloping shoreface to the edge of the CONTINENTAL SHELF.
3542
offshore navigation. See NAVIGATION.
3543
offshore wind. WIND blowing from the LAND toward the SEA. See LAND BREEZE.
3544
off soundings. Said of a vessel navigating beyond the 100-FATHOM LINE. In earlier times, said of a vessel in water
deeper than could be sounded with the HAND LEAD.
3545
ohm. The unit of electrical resistance in the SI system.
3546
oil field. An area in which oil occurs in quantities worthy of exploitation.
3547
old ice. Any SEA ICE more than 1 year old.
3548
omnibearing. The MAGNETIC BEARING of an OMNIRANGE.
3549
omnidirectional antenna. See ANTENNA.
3550
omnidirectional beacon. See OMNIRANGE.
162
3551
omnidirectional range. See OMNIRANGE.
3552
omnirange. A radio AID TO NAVIGATION providing direct indication of the MAGNETIC BEARING
(OMNIBEARING) of that STATION from any direction. Also called omnidirectional range or omnidirectional
beacon.
3553
one-way traffic lane. See TRAFFIC LANE.
3554
onshore wind. WIND blowing from SEA toward the LAND. See SEA BREEZE.
3555
on soundings. Said of a vessel navigating within the 100-FATHOM LINE. In earlier times, said of a vessel in water
sufficiently shallow for sounding by HAND LEAD.
3556
on the beam. Bearing approximately 090°relative (on the starboard beam) or 270°relative (on the port beam). The
expression is often used loosely for broad on the beam, or bearing exactly 090°or 270°relative. Also called abeam. See
also BROAD ON THE BEAM.
3557
on the bow. Bearing approximately 045° relative (on the starboard bow) or 315° relative (on the port bow). The
expression is often used loosely for broad on the bow, or bearing exactly 045°or 315°relative. See also BROAD ON
THE BOW.
3558
on the quarter. Bearing approximately 135°relative (on the starboard quarter) or 225°relative (on the port quarter).
The expression is often used loosely for broad on the quarter, or bearing exactly 135°or 225°relative. See also BROAD
ON THE QUARTER.
3559
ooze. A soft MUD or SLIME.
A fine-grained pelagic SEDIMENT containing undissolved SAND- or silt-sized, calcareous or siliceous skeletal
remains of small marine organisms in proportion of 30 percent or more, the remainder being amorphous clay-sized
material.
3560
opacity (optical). The ratio of the incident to the transmitted (or reflected) light. It varies with the use of scattered or
specular light.
3561
opalescence. Whitish colour of the ATMOSPHERE and a slight change of the apparent colour of objects with respect
to normal (for example, bluish colour of an object normally black or dark) produced by the SCATTERING of light by
small particles held in suspension in the ATMOSPHERE.
3562
open coast. A COAST that is not sheltered from the SEA.
3563
open end traverse. See TRAVERSE: OPEN.
3564
opening. A break in a COASTLINE or a PASSAGE through a REEF, between SHOALS, etc.
Any break in SEA ICE which reveals the water.
3565
open pack ice. FLOES seldom in contact with many LEADS and POOLS. ICE CONCENTRATION 4/10th to 9/10th.
3566
open port. A PORT which is not ICEBOUND during winter.
3567
open roadstead. A ROADSTEAD with relatively little protection from the SEA.
3568
open sea. That part of the OCEAN not enclosed by HEADLANDS, within narrow STRAITS, etc. See HIGH SEA.
3569
open sound. A BAY similar to a LAGOON but with large OPENINGS between the protecting ISLANDS.
3570
open traverse. See TRAVERSE.
3571
open water. A relatively large area of free navigable water in an ice-encumbered SEA.
In U.S. terminology, an area of SEA with less than one-tenth ICE CONCENTRATION.
3572
operating system. System which controls and monitors the execution of programs in the COMPUTER.
3573
operative sheet. See FIELD BOARD.
163
3574
opisometer. A recording device designed to measure by revolutions of a small wheel, continuous linear distances on a
MAP. Used in measuring the length of SHORELINE by closely following all the INDENTATIONS and sinuosities of
the SHORE.
3575
opposite coasts. The geographical relationship of the coasts of two States facing each other.
3576
opposition. The situation of two periodic quantities differing by half a CYCLE.
In ASTRONOMY, the situation of two CELESTIAL BODIES having either CELESTIAL LONGITUDES or
sidereal HOUR ANGLES differing by 180°. The term is usually used only in relation to the position of a SUPERIOR
PLANET or the MOON with reference to the SUN.
3577
optical axis. See AXIS OF LENS.
3578
optical centre. The point of intersection of lines which represent within the LENS those RAYS whose emergent
directions are parallel to their respective incident directions. This point lies on the optical axis.
3579
optical flat. A surface, usually of glass, ground and polished plane within a fraction of a WAVE LENGTH of light. An
optical element or glass blank with an optical flat is used to test the flatness of other surfaces.
3580
optical parallax. See PARALLAX: INSTRUMENTAL.
3581
optical path. The path followed by a RAY of light through an OPTICAL SYSTEM.
3582
optical pumping magnetometer. See MAGNETOMETER.
3583
optical square. A small hand instrument used to set off a right angle.
3584
optical system. A series of LENSES, APERTURES, prisms, MIRRORS, etc., so arranged as to perform a definite
optical function.
3585
orange peel sampler. A bottom sediment sampling device capable of obtaining as much as 1/2 cubic foot of sample
from the ocean floor. Named for its likeness to an orange that has its peel quartered.
3586
orbit. The path of a body or particle under the influence of a gravitational or other force. For instance, the orbit of a
CELESTIAL BODY is its path relative to another body around which it revolves.
In water waves, the path of a water particle affected by the wave motion.
3587
ordinate. See COORDINATES: PLANE RECTANGULAR.
3588
Organization for Economic Cooperation and Development (OECD). Member States promote economic growth,
employment, and improved standards of living for a sound and harmonious development of world economy.
3589
orientation. The act of establishing the correct relationship in direction with reference to the POINTS of the
COMPASS. The state of being in correct relationship in direction with reference to the POINTS of the COMPASS. A
MAP is in orientation when the map SYMBOLS are parallel with their corresponding ground features. A PHOTOGRAPH is in orientation when it correctly presents the perspective view of the ground or when IMAGES on the
PHOTOGRAPH appear in the same direction from the point of observation as do the corresponding map symbols. See
ORIENTATION OF PLANE TABLE, ORIENTATION OF SURVEYING INSTRUMENT, ORIENTATION:
PHOTOGRAMMETRIC.
3590
orientation: absolute. In PHOTOGRAMMETRY, the scaling, levelling, and ORIENTATION to GROUND
CONTROL (in a photogrammetric instrument) of a relatively oriented stereoscopic model or group of models.
3591
orientation: basal. In PHOTOGRAMMETRY, the establishment of the POSITION of both ends of an AIR BASE with
respect to a ground system of COORDINATES. In all, six elements are required. These are essentially the threedimensional COORDINATES of each end of the BASE.
3592
orientation: exterior. In PHOTOGRAMMETRY, the determining (analytically or in a photogrammetric instrument) of
the POSITION of the CAMERA STATION and the attitude of the taking CAMERA at the instant of EXPOSURE. In
stereoscopic instrument practice, exterior orientation is divided into two parts, RELATIVE and ABSOLUTE ORIENTATION. Also called outer orientation.
3593
orientation: inner. See ORIENTATION: INTERIOR.
164
3594
orientation: interior. In PHOTOGRAMMETRY, the determining (analytically or in a photogrammetric instrument) of
the interior perspective of the PHOTOGRAPH as it was at the instant of EXPOSURE. Elements of interior orientation
are the CALIBRATED FOCAL LENGTH, location of the calibrated PRINCIPAL POINT, and the calibrated LENS
DISTORTION. Also called inner orientation.
3595
orientation: outer. See ORIENTATION: EXTERIOR.
3596
orientation: photogrammetric. The recreation of natural terrain features at a miniature SCALE by the optical
projection of overlapping PHOTOGRAPHS. The model is formed when all corresponding LIGHT RAYS from the two
PROJECTORS intersect in space. See also ORIENTATION: ABSOLUTE, ORIENTATION: BASAL,
ORIENTATION: EXTERIOR, ORIENTATION: INTERIOR.
3597
orientation: relative. In PHOTOGRAMMETRY, the determining (analytically or in a photogrammetric instrument) of
the POSITION and attitude of one of a pair of overlapping PHOTOGRAPHS with respect to the other PHOTOGRAPH.
3598
orientation of plane table. Placing the PLANE TABLE in such a position that every line drawn on the SURVEY
SHEET from the point which represents the POSITION of the table on the ground to any other point on the sheet, is
parallel to the corresponding line in nature.
3599
orientation of surveying instrument. Placing the instrument in such position that the HORIZONTAL CIRCLE reads
0°when the LINE OF COLLIMATION is parallel to the direction it had at an earlier (initial) position of the instrument,
or to a standard line of reference. If the line of reference is a MERIDIAN, the CIRCLE will show AZIMUTHS referred
to that MERIDIAN.
3600
origin. In SURVEYING, the reference position from which angles or distances are reckoned. See also
COORDINATES: ORIGIN OF.
3601
origin: false. See COORDINATES: FALSE.
3602
original. See REPRODUCTION.
3603
original chart. See CHART.
3604
origin of coordinates. See COORDINATES: ORIGIN OF.
3605
orography. The branch of physical geography which deals with the formation and features of MOUNTAINS; the
description of MOUNTAINS.
3606
oropesa sweep. Towed wire used for sweeping sea bottom when surveying SHOALS or WRECKS. It consists of a wire
running from the stern of the vessel and held out on the water by an OTTER which also pulls down against a towed
FLOAT. The amount of wire between FLOAT and OTTER determines the DEPTH of the outer end of the sweep. The
inner end of the sweep is held to the required DEPTH and in line with the stern of the vessel by a KITE.
3607
orthochromatic(adj.). Said of photographic surfaces sensitive to ultra-violet, blue, yellow, green and orange RAYS.
Insensitive to red RAYS.
3608
orthodrome. Any line on a CHART representing a GREAT CIRCLE TRACK between two points.
3609
orthogonal(adj.). At right angles; rectangularly meeting, crossing, or lying at right angles.
3610
orthographic projection. See PROJECTION.
3611
orthometric correction. The CORRECTION to ELEVATIONS which takes into account the spheroidal shape of the
EARTH and brings the ELEVATIONS to their true HEIGHT above MEAN SEA LEVEL.
3612
orthomorphic(adj.). Preserving the correct shape; of a PROJECTION which gives no local DISTORTION. See
PROJECTION: CONFORMAL.
3613
orthomorphic projection. See PROJECTION: CONFORMAL.
3614
orthophotograph. A photographic copy, prepared from a perspective PHOTOGRAPH, in which the
DISPLACEMENTS of IMAGES due to TILT and RELIEF have been removed.
165
3615
orthophotomap. A PHOTOMAP made from an assembly of ORTHOPHOTOGRAPHS. It may incorporate special
cartographic treatment, photographic edge enhancement, colour separation, or a combination of these.
3616
orthophotomosaic. An assembly of ORTHOPHOTOGRAPHS forming a uniform-scale mosaic.
3617
orthophotoscope. A photomechanical device, used in conjunction with a double-projection anaglyphic instrument, for
producing ORTHOPHOTOGRAPHS.
3618
oscillation. The variation, usually with time, of the magnitude of a quantity with respect to a specified reference when
the magnitude is alternately greater and smaller than the reference.
Half an oscillatory CYCLE, consisting of a fluctuation or VIBRATION in one direction; half a VIBRATION.
3619
oscillator. A device for producing OSCILLATIONS, especially one of the non-rotating type, as the sound generator of a
sonic DEPTH FINDER or a radio frequency generator. A submarine oscillator is a large, electrically-operated
diaphragm horn which produces a SOUND for transmission through water.
3620
oscillatory wave. See WAVE.
3621
oscillograph. A device for recording or indicating OSCILLATIONS or changes in an electric current.
3622
oscilloscope. A type of OSCILLOGRAPH that visually records an electrical WAVE on a fluorescent SCREEN, as of a
CATHODE-RAY TUBE.
3623
otter. Plane surface towed forward of its middle length so that it will incline and dive. Used in fishing, minesweeping or
SURVEYING. See KITE, KITE OTTER, and OROPESA SWEEP.
3624
outcrop. Naturally protruding, or erosionally exposed or uncovered part of a ROCK, most of which is covered by
overlying material.
3625
outer harbour. See HARBOUR.
3626
outer limit. The extent to which a coastal State claims or may claim a specific jurisdiction in accordance with the
provisions of International Law.
3627
outfall diffuser. A structure on an outfall through which liquids are discharged. The structure will usually project above
the level of the outfall and can be an obstruction to navigation.
3628
outflow. The FLOW of water from the RIVER or its ESTUARY to the SEA.
Total volume for any given period of time.
3629
outgoing stream. See EBB STREAM.
3630
output. The amount of power or energy produced by a machine.
3631
overfalls. Short, breaking WAVES occurring when a strong CURRENT passes over a SHOAL or other submarine
OBSTRUCTION or meets a contrary CURRENT or WIND. See RIPS.
3632
overlap. In CARTOGRAPHY and SURVEYING, the amount by which one CHART or SURVEY SHEET extends also
over an adjoining CHART or sheet.
The amount by which different sets of survey data, obtained with the same system, cover the same area; customarily
expressed as a percentage.
3633
overlapping pair. In PHOTOGRAMMETRY, two PHOTOGRAPHS taken at different exposure stations in such a
manner that a portion of one PHOTOGRAPH shows the same terrain as shown on a portion of the other
PHOTOGRAPH. This term covers the general case and does not imply that the PHOTOGRAPHS were taken for
stereoscopic examination. See also STEREOSCOPIC PAIR.
3634
overlay. In mapping, a record on a transparent medium to be superimposed on another record.
3635
overlay tracing. A plotting on TRACING CLOTH at the SCALE of the smooth sheet used in conjunction with the
smooth sheet. See FAIR CHART.
166
3636
overprint. In CARTOGRAPHY, an additional PLATE, generally in a distinctive colour, printed down on a MAP or
CHART which is already complete in itself. Overprints may be used to reproduce specialized information (e.g., to add
aeronautical information to a TOPOGRAPHIC MAP) or to incorporate revision data without the amendment of existing
PLATES.
3637
overtide. A shallow water harmonic tide constituent with a SPEED that is a multiple of the SPEED of one of the basic
constituents of the TIDE-PRODUCING FORCE. See HARMONIC CONSTITUENT, and SHALLOW WATER
CONSTITUENT.
3638
ozalid print. See PRINT: OZALID.
167
P
3639
pack ice. Term used in a wide sense to include any area of SEA ICE, other than FAST ICE, no matter what form it
takes or how it is disposed. Pack ice may be described as VERY OPEN PACK ICE (1/10ths-3/10ths), OPEN PACK
ICE (4/10ths-6/10ths), CLOSE PACK ICE (7/10ths-9/10ths), VERY CLOSE PACK ICE (almost 10/10th with little if
any water visible).
3640
pair of compasses. See COMPASS.
3641
paleomagnetism. Remanent MAGNETISM produced by the EARTH's field when a material was initially formed.
3642
Pan American Institute of Geography and History (PAIGH). Develops, coordinates, and disseminates geographical,
cartographic, historical, geophysical and related scientific studies.
3643
pancake ice. Pieces of NEW ICE, usually approximately circular, about 30 cm to 3 m across, and with raised rims, due
to the pieces striking against each other as the result of WIND and SWELL.
3644
panchromatic (adj.). Sensitive to light of all colours, as a film or plate emulsion.
3645
panel. In cartography the completed assembly of pieces of film positives onto a grid or projection which is used as a
base for compilation.
In photogrammetry an element of a target used for control station identification on aerial photography.
3646
pantograph. An instrument for copying a CHART, drawing, etc., to any desired SCALE within the limits of the
instrument.
3647
paper. For printing hydrographic charts, heavyweight, single layer paper is used. Such paper is generally made wholly
or partly from rags and simulates hand-made paper. It is strong, moisture resistant and manufactured to withstand
surface erasure.
3648
parabola. An open curve all points of which are equidistant from a fixed point, called the focus, and a straight line.
3649
parachute drogue. See DROGUE.
3650
parallactic angle. That angle of the ASTRONOMICAL TRIANGLE at the CELESTIAL BODY; the angle between a
body's HOUR CIRCLE and its VERTICAL CIRCLE. Also called position angle.
In PHOTOGRAMMETRY, the angle subtended by the eye of the observer at the object viewed. Also called angle of
convergence or angular parallax.
3651
parallactic error. See ERROR.
3652
parallactic grid. See GRID.
3653
parallax. An apparent displacement of the position of a body with respect to a reference point or system, caused by a
shift in the point of observation.
3654
parallax: absolute stereoscopic. In PHOTOGRAMMETRY, considering a pair of AERIAL PHOTOGRAPHS of
equal PRINCIPAL DISTANCE, the algebraic difference of the distances of the two IMAGES from their respective
PHOTOGRAPH NADIRS, measured in a horizontal plane and parallel to the AIR BASE. Also called horizontal parallax, linear parallax, or x-parallax.
3655
parallax: angular. See PARALLACTIC ANGLE.
3656
parallax: annual. The angle subtended at a CELESTIAL BODY by the radius of EARTH's ORBIT. Also called heliocentric parallax, or stellar parallax.
3657
parallax: diurnal. The difference in the apparent direction or position of a CELESTIAL BODY as observed from the
centre of the EARTH and a point on its surface. This varies with the body's ALTITUDE and distance from the EARTH.
Also called geocentric parallax.
3658
parallax: equatorial horizontal. HORIZONTAL PARALLAX as observed at the EQUATOR, as it attains its
maximum value.
168
3659
parallax: geocentric. See PARALLAX: DIURNAL.
3660
parallax: heliocentric. See PARALLAX: ANNUAL.
3661
parallax: horizontal. In ASTRONOMY, the GEOCENTRIC PARALLAX of a body on the observer's HORIZON.
In PHOTOGRAMMETRY, PARALLAX: ABSOLUTE STEREOSCOPIC.
3662
parallax: instrumental (or instrument). That change which may result from the position in which an observer stands
with respect to the FIDUCIAL MARKS on an instrument (personal parallax); or by the imperfect ADJUSTMENT of
the optics of the instrument (optical parallax).
3663
parallax: linear. See PARALLAX: ABSOLUTE STEREOSCOPIC.
3664
parallax: optical. See PARALLAX: INSTRUMENTAL.
3665
parallax: personal. See PARALLAX: INSTRUMENTAL.
3666
parallax: solar. The EQUATORIAL HORIZONTAL PARALLAX of the SUN.
3667
parallax: vertical. See PARALLAX: Y-.
3668
parallax: X-. See PARALLAX: ABSOLUTE STEREOSCOPIC.
3669
parallax: Y-. In PHOTOGRAMMETRY, the difference between the perpendicular distances of the two IMAGES of a
point on a pair of photographs from the vertical plane containing the AIR BASE. The existence of y-parallax is an
indication of TILT in either or both PHOTOGRAPHS and/or a difference in flight heights, and interferes with stereoscopic examination of the pair. Also called vertical parallax or want of correspondence.
3670
parallax bar. See STEREOMETER.
3671
parallax correction. A CORRECTION due to PARALLAX, particularly that SEXTANT ALTITUDE correction due
to the difference between the apparent direction from a point on the surface of the EARTH to a CELESTIAL BODY
and the apparent direction from the centre of the EARTH to the same body.
3672
parallax difference. In PHOTOGRAMMETRY, the difference in the ABSOLUTE STEREOSCOPIC PARALLAXES
of two points imaged on a pair of PHOTOGRAPHS. Customarily used in determination of the difference in
ELEVATIONS of objects.
3673
parallax in altitude. GEOCENTRIC PARALLAX of a body at any ALTITUDE. The expression is used to distinguish
the PARALLAX at the given ALTITUDE from the HORIZONTAL PARALLAX when the body is in the HORIZON.
3674
parallax inequality. The variation in the RANGE OF TIDE or in the SPEED of TIDAL CURRENTS due to the
continual change in the distance of the MOON from the EARTH.
3675
parallel. A circle (or approximation of a circle) on the surface of the EARTH, parallel to the EQUATOR and
connecting points of equal LATITUDE. Also called parallel of latitude.
3676
parallel: astronomical. A line on the surface of the EARTH which has the same ASTRONOMICAL LATITUDE at
every point. Because the DEFLECTION OF THE VERTICAL is not the same at all points on the EARTH, an
astronomical parallel is an irregular line, not lying in a single plane.
3677
parallel: celestial. See PARALLEL OF DECLINATION.
3678
parallel: geodetic. A line on the SPHEROID which has the same GEODETIC LATITUDE at every point. A geodetic
parallel, other than the EQUATOR, is not a GEODETIC LINE. In form, it is a SMALL CIRCLE whose plane is
parallel with the plane of the GEODETIC EQUATOR.
3679
parallel: geographic(al). A line on the EARTH having the same LATITUDE at every point. The term is applicable
alike to an ASTRONOMICAL PARALLEL or to a GEODETIC PARALLEL.
3680
parallel: ground. In PHOTOGRAMMETRY, the intersection of the plane of the PHOTOGRAPH with the plane of
reference of the GROUND. See also AXIS OF HOMOLOGY.
169
3681
parallel: isometric. In PHOTOGRAMMETRY, the intersecting line between the plane of a PHOTOGRAPH and a
horizontal plane having an equal perpendicular distance from the same PERSPECTIVE CENTRE.
3682
parallel: photograph. In PHOTOGRAMMETRY, the IMAGE on a PHOTOGRAPH of any horizontal line in the
object space which is perpendicular to the PRINCIPAL PLANE. All photograph parallels are perpendicular to the
PRINCIPAL LINE. The photograph parallel passing through the PRINCIPAL POINT is the principal parallel and that
passing through the ISOCENTRE is the ISOMETRIC PARALLEL.
3683
parallel: principal. See PARALLEL: PHOTOGRAPH.
3684
parallel: standard. A PARALLEL of latitude which is used as a control in the computation of a map PROJECTION.
For a tangent cone, this is the PARALLEL of tangency. For a secant cone, the two PARALLELS of intersection are the
standards.
3685
parallel motion protractor. See PROTRACTOR.
3686
parallel of altitude. See ALMUCANTAR.
3687
parallel of declination. A circle of the CELESTIAL SPHERE parallel to the CELESTIAL EQUATOR. Also called
celestial parallel.
3688
parallel of latitude. See PARALLEL.
3689
parallel plate. An optical disk with optically flat, parallel surfaces; used especially in optical MICROMETERS.
3690
parallel rulers (or rule). An instrument for transferring a line parallel to itself.
3691
parallel sailing. See SAILING.
3692
parallel sounding. A system of surveying in which the MOTHER VESSEL takes soundings while following a given
course; at the same time an array of satellite boats takes soundings along parallel courses at a fixed distance from the
MOTHER VESSEL. The satellite boats determine their position relative to the MOTHER VESSEL.
The term is also employed when a single vessel takes multiple lines of soundings with transducers arranged at
regular intervals on outriggers.
3693
parameter. A quantity which remains constant within the limits of a given case or situation.
3694
parametric. Characterizing a quantity which is influenced by the behaviour of one or more parameters .
3695
parametric latitude. See LATITUDE.
3696
paranthelion. PHOTOMETEOR of the HALO family, consisting of white, round, luminous spots, having a diameter
slightly greater than that of the SUN, which appears at 120°from it in the case of ordinary paranthelia, and at 90°in the
case of extraordinary paranthelia. The HEIGHT of the spots above the HORIZON is that of the SUN.
3697
parantiselena. PHOTOMETEOR of the HALO family, analogous to the PARANTHELION, the luminary being the
MOON.
3698
paraselene. Optical phenomenon of the HALO family, similar to but less brilliant than the PARHELION, the luminary
being the MOON.
3699
paraselenic circle. PHOTOMETEOR of the HALO family, analogous to the PARHELIC CIRCLE, the luminary being
the MOON.
3700
parhelia associated with the 22°halo. PHOTOMETEOR of the HALO family, consisting of two luminous iridescent
spots which appear on the PARHELIC CIRCLE close to the SMALL HALO.
3701
parhelia associated with the 46°halo. PHOTOMETEOR of the HALO family consisting of two luminous, iridescent
spots which appear on the PARHELIC CIRCLE close to the LARGE HALO.
3702
parhelic circle. PHOTOMETEOR of the HALO family, consisting of a white, horizontal circle, situated at the same
angular height as the SUN.
3703
partial eclipse. See ECLIPSE.
170
3704
partial node. The point, line, or surface, in a STANDING WAVE system where some characteristic of the wave field
has a minimum AMPLITUDE differing from zero.
3705
partial tide. See TIDE.
3706
particle velocity. In ocean wave studies, the instantaneous VELOCITY of a water particle undergoing orbital motion.
At the CREST, its direction is the same as the direction of progress of the WAVE, and at the TROUGH it is in the
opposite direction.
3707
particular scale. See SCALE.
3708
pascal. The unit of pressure in the SI SYSTEM.
3709
pass. A break in a MOUNTAIN RANGE, permitting easier passage from one side of the range to the other; also called
a COL.
A navigable CHANNEL leading to a HARBOUR or RIVER. Sometimes called PASSAGE.
A narrow connecting CHANNEL between two bodies of water.
3710
passage. A narrow navigable CHANNEL, especially one through REEFS or ISLANDS. Sometimes called a PASS, or
in New England waters a HOLE.
3711
passage: meridian. See MERIDIAN TRANSIT.
3712
passive system. A system which records energy emitted or reflected but does not produce or transmit energy of its own.
3713
passometer. A pocket-size instrument which registers the number of steps taken by the pedestrian carrying it. See
PEDOMETER.
3714
pass point. In PHOTOGRAMMETRY, a point whose horizontal and/or vertical position is determined from PHOTOGRAPHS by photogrammetrical methods and which is intended for use (as in the manner of a SUPPLEMENTAL
CONTROL POINT) in the ORIENTATION of other PHOTOGRAPHS.
3715
patch. In ice terminology, a collection of PACK ICE, less than 10 km across.
3716
patent log. See LOG.
3717
path. A line of movement; course taken, as the path of a METEOR.
A line connecting a series of points in space and constituting a proposed or travelled route.
3718
pattern. See LATTICE.
3719
P-code. The Precise (or Protected) GPS code; a very long (about 1014 bit) sequence of pseudo-random binary biphase
modulations on the GPS carrier at a chip rate of 10.23 Mhz which does not repeat itself for about 267 days. Each oneweek segment of the P-code is unique to one GPS satellite and is reset each week. See also C/A CODE.
3720
peak. A prominent elevation either pointed or of very limited extent across the SUMMIT. Also called pike.
3721
pebble. A small STONE worn smooth and rounded by the action of water, SAND, ICE, etc. ranging in diameter
between 4 and 64 millimetres.
3722
pecked line. In CARTOGRAPHY, a SYMBOL consisting of a line broken at regular intervals.
3723
pedometer. A pocket-size instrument which registers in linear units the distance traversed by the pedestrian carrying it.
See PASSOMETER.
3724
pelagic-abyssal sediments. Deep sea SEDIMENTS that are free of terrestrial material except for a small proportion of
very fine CLAY.
3725
pelagic division. In the classification of the marine environment and its inhabitants, a primary division of the SEA
which includes the whole mass of water. The division is made up of the neritic province which includes that water
shallower than 200 METRES, and the oceanic province which includes that water deeper than 200 METRES. The other
primary division of the SEA is the BENTHIC DIVISION.
171
3726
pelorus. A COMPASS CARD in the form of a metal plate mounted in GIMBALS to maintain a horizontal position and
fitted with SIGHT-VANES for observing BEARINGS where direct use of the COMPASS for this purpose is
impracticable. Also called dumb compass or bearing plate. See also ALIDADE.
3727
pencil. In optics, a set of RAYS coming to or spreading out from a point. See LIGHT PENCIL.
3728
pencil beam. A BEAM in which the RADIANT ENERGY is concentrated in an approximately conical or cylindrical
portion of space of relatively small diameter. This type beam is used for many revolving navigational LIGHTS.
3729
pendulum. A body so suspended from a fixed point as to swing freely to and from under the combined forces of
GRAVITY and MOMENTUM.
A vertical bar so supported from below by a stiff spring as to vibrate to and for under the combined action of
GRAVITY and the restoring force of the spring.
3730
pendulum: working. A PENDULUM which is used (swung) in a determination of the INTENSITY OF GRAVITY.
3731
pendulum sextant. See SEXTANT.
3732
peninsula. A piece of LAND that is almost an ISLAND, being nearly surrounded by water; by extension any piece of
LAND projecting into the SEA, so that the greater part of its BOUNDARY is COASTLINE.
3733
peninsula: submarine. An elevated portion of the SUBMARINE RELIEF resembling a PENINSULA. The opposite is
SAC.
3734
perch. A staff placed on top of a BUOY, ROCK, or SHOAL as a MARK for navigators. A ball or cage is sometimes
placed at the top of the perch, as an identifying MARK.
A unit of length equal to 5.5 YARDS or 16.5 FEET. Also called ROD, POLE.
3735
percolation. The process by which water is forced by wave action through the interstices of the bottom sediment and
has a tendency to reduce WAVE HEIGHTS.
3736
perigean range (of tide). The average of all monthly TIDE RANGES occurring at the TIME of PERIGEE. It is larger
than the MEAN RANGE, where the TYPE OF TIDE is either semidiurnal or mixed, and is of no practical significance
where the TYPE OF TIDE is diurnal.
3737
perigean tides. See TIDE.
3738
perigee. That orbital point nearest the EARTH when the EARTH is the centre of attraction, as opposed to APOGEE.
3739
perihelion. That orbital point nearest the SUN, when the SUN is the centre of attraction, as opposed to APHELION.
3740
period. The interval needed to complete a CYCLE.
Any specified duration of time.
3741
period (of a navigational light). The TIME taken to exhibit one complete sequence of intervals of light and darkness.
3742
periodic current. See CURRENT.
3743
periodic error. See ERROR.
3744
periodic wave(s). See WAVE.
3745
peripheral equipment. In computer systems, any unit of equipment, distinct from the central unit, which may provide
the system with outside communication.
3746
permafrost. A LAYER of SOIL or BEDROCK at a variable depth beneath the surface of the EARTH in which the
temperature has been below freezing continuously from a few to several thousands of years. Permafrost exists where the
summer heating fails to descend to the base of the LAYER of frozen ground.
3747
permanent current. See CURRENT.
172
3748
Permanent International Association of Navigation Congresses (PIANC). Fosters progress of inland and maritime
waterways, of ports and of coastal areas by research and information exchange.
3749
permanent magnetism. See MAGNETISM.
3750
permeability: magnetic. See MAGNETIC PERMEABILITY.
3751
personal correction. The CORRECTION due to PERSONAL ERROR.
3752
personal equation. The time interval between the sensory perception of a PHENOMENON and the motor reaction
thereto. Personal equation may be either positive or negative, as an observer may anticipate the occurrence of an event,
or wait until he actually sees it occur before making a record. This is a SYSTEMATIC ERROR, treated as of the
constant type. It is a PERSONAL ERROR, for which the term personal equation is reserved. It is of special significance
in OBSERVATIONS of TIME, made to determine CHRONOMETER CORRECTION.
3753
personal error. See ERROR.
3754
personal parallax. See PARALLAX: INSTRUMENTAL.
3755
perspective centre. The point of origin or termination of bundles of PERSPECTIVE RAYS. The two such points
usually associated with a survey photograph are the interior perspective centre and the exterior perspective centre. In a
perfect lens-camera system, PERSPECTIVE RAYS from the interior perspective centre to the photographic IMAGES
enclose the same angles as the corresponding RAYS from the exterior perspective centre to the objects photographed.
In a LENS having DISTORTION this is true only for a particular zone of the PHOTOGRAPH. In a perfectly adjusted
lens-camera system the exterior and interior perspective centres correspond, respectively, to the front and rear NODAL
POINTS of the camera lens.
3756
perspective grid. See GRID.
3757
perspective plane. Any plane containing the PERSPECTIVE CENTRE. The intersection of a perspective plane and the
GROUND will always appear as a straight line on an AERIAL PHOTOGRAPH.
3758
perspective projection. See PROJECTION.
3759
perspective ray. A line joining a PERSPECTIVE CENTRE and a point object.
3760
perturbation. Disturbance in the orbital PATH of a CELESTIAL BODY, natural or artificial, due to attraction of
another body. See LUNAR INEQUALITY.
3761
Ph. A SCALE used for expressing the acidity or ALKALINITY of solutions.
3762
phantom bottom. A false BOTTOM indicated by an ECHO SOUNDER, some distance above the actual BOTTOM.
Such an indication, quite common in the deeper parts of the OCEAN,is due to large quantities of small organisms. Also
called deep scattering layer (DSL) or false bottom.
3763
phase. The visible aspect of an object.
The amount by which a CYCLE has progressed from a specified origin.
In ASTRONOMY, any of the stages of variation in the illumination of the MOON or a PLANET. See PHASE(S)
OF THE MOON.
In physics, the state of aggregation of a substance, for example, solid (ICE), liquid (water), or gas (vapour).
3764
phase angle. The phase difference of two periodically recurring PHENOMENA of the same FREQUENCY, expressed
in angular measure.
The angle at a CELESTIAL BODY between the SUN and EARTH.
3765
phase inequality. Variations in the TIDES or TIDAL CURRENTS associated with changes in the PHASE OF
THE MOON.
3766
phase lag. Angular retardation of the maximum of a constituent of the observed TIDE behind the corresponding
maximum of the same constituent of the hypothetical EQUILIBRIUM TIDE. Also called tidal epoch.
3767
phase modulation. See MODULATION.
3768
phase of a navigational light. Each element of the sequence of intervals of light and darkness (e.g. a flash, an
ECLIPSE).
173
3769
phase(s) of the moon. The various appearances of the MOON during different parts of the SYNODICAL MONTH.
The CYCLE begins with new moon or change of the MOON at CONJUNCTION. The visible part of the waxing moon
increases in size during the first half of the CYCLE until full moon appears at OPPOSITION, after which the visible
part of the waning moon decreases for the remainder of the CYCLE. First quarter occurs when the waxing moon is at
east QUADRATURE, last quarter when the waning moon is at west QUADRATURE. From last quarter to new and
from new to first quarter the MOON is crescent; from first quarter to full and from full to last quarter it is gibbous.
3770
phase velocity. VELOCITY, measured over a short time period, at which a particular WAVE CREST is propagated a
medium.
3771
phenomenon (pl. phenomena). Any fact, circumstance, or experience that is apparent to the senses and that can be
scientifically described or appraised; as, an ECLIPSE is a PHENOMENON of ASTRONOMY.
3772
phonometer. An instrument for measuring the intensity or FREQUENCY of SOUNDS.
3773
phosphorescence. The production of light without sensible heat.
Emission of electromagnetic RADIATION by a substance as a result of previous absorption of RADIATION of
shorter WAVE LENGTH. In contrast to FLUORESCENCE, the emission may continue for a considerable time after
cessation of the existing IRRADIATION.
3774
phot. The unit of ILLUMINATION in the CGS system.
3775
photic (adj.). Of SEA WATER, that is penetrated or influenced by sunlight.
3776
photoalidade. A photogrammetric instrument having a telescopic ALIDADE, a plateholder, and a hinged ruling arm
mounted on a tripod frame. It is used for plotting lines of direction and measuring vertical angles to selected features
appearing on OBLIQUE and TERRESTRIAL PHOTOGRAPHS.
3777
photo base. The length of the AIR BASE as represented on a PHOTOGRAPH.
3778
photocompose (v.t.). To combine distinct parts of chart original by photographic processes.
3779
photocontrol point. See CONTROL POINT.
3780
photodelineation. The DELINEATION of features on a PHOTOGRAPH. See also COMPILATION.
3781
photoelectric pilot. A device for automatic steering in conjunction with the MAGNETIC COMPASS. Its pinnacle unit,
or directive element, consists of a high-grade MAGNETIC COMPASS of special construction, a simple light system,
and a photoelectric cell, so arranged that the slightest deviation of the vessel from its COURSE is detected and relayed
to the steering engine unit.
3782
photoengraving. A process by which PHOTOGRAPHS are reproduced on printing plates especially one in which the
REPRODUCTION is in relief: opposed to PHOTOGRAVURE. A PLATE so made. A PRINT from such a PLATE.
3783
photogoniometer. An instrument for measuring angles from the true PERSPECTIVE CENTRE to points on a PHOTOGRAPH.
3784
photogram. A survey photograph. Either of a pair of stereoscopic PHOTOGRAPHS.
3785
photogrammetric camera. See CAMERA.
3786
photogrammetric control. See CONTROL.
3787
photogrammetric extension. See PHOTOTRIANGULATION.
3788
photogrammetric survey. See SURVEY.
3789
photogrammetry. The science or art of obtaining reliable measurements from PHOTOGRAPHS.
3790
photogrammetry: aerial. PHOTOGRAMMETRY utilizing AERIAL PHOTOGRAPHS.
3791
photogrammetry: analytical (or analytic). PHOTOGRAMMETRY in which solutions are obtained by mathematical
means.
174
3792
photogrammetry: terrestrial. PHOTOGRAMMETRY utilizing TERRESTRIAL PHOTOGRAPHS.
3793
photograph. A general term for a positive or negative picture made with a CAMERA on sensitized material, or
PRINTS from such a camera original.
3794
photograph: aerial. Any PHOTOGRAPH taken from the air. Sometimes called air photograph.
3795
photograph: composite. In AERIAL PHOTOGRAPHY, a PHOTOGRAPH made by assembling the separate
PHOTOGRAPHS, made by the several LENSES of a MULTIPLE LENS CAMERA in simultaneous EXPOSURE, into
the equivalent of a PHOTOGRAPH taken with a single wide-angle lens.
3796
photograph: ground. See PHOTOGRAPH: TERRESTRIAL.
3797
photograph: high oblique. An OBLIQUE PHOTOGRAPH in which the APPARENT HORIZON is included within
the field of view.
3798
photograph: horizontal. PHOTOGRAPH taken with the camera axis horizontal.
3799
photograph: low oblique. An OBLIQUE PHOTOGRAPH in which the APPARENT HORIZON is not included
within the field of view.
3800
photograph: multiple lens. A PHOTOGRAPH made with a MULTIPLE LENS CAMERA.
3801
photograph: oblique. A PHOTOGRAPH taken with the camera axis intentionally directed between the HORIZONTAL and the VERTICAL.
3802
photograph: terrestrial. A PHOTOGRAPH taken by a CAMERA located on the ground. Sometimes called ground
photograph.
3803
photograph: vertical. An AERIAL PHOTOGRAPH made with the camera axis vertical (or as nearly vertical as practicable in an aircraft).
3804
photograph axes. See FIDUCIAL AXES.
3805
photograph centre. The centre of a PHOTOGRAPH as indicated by the IMAGES of the FIDUCIAL MARK or
MARKS of the CAMERA. In a perfectly adjusted CAMERA the photograph centre and the PRINCIPAL POINT are
identical.
3806
photograph coordinates. See COORDINATES.
3807
photograph meridian. See MERIDIAN.
3808
photograph nadir. See NADIR.
3809
photograph parallel. See PARALLEL.
3810
photograph perpendicular. The perpendicular from the interior perspective centre to the plane of the photograph.
3811
photographic interpretation. The examination of photographic IMAGES for the purpose of identifying objects and
deducing their significance.
3812
photography. The art or process of producing IMAGES on sensitized material through the action of light.
3813
photography: aerial. The art, science, or process of taking AERIAL PHOTOGRAPHS.
3814
photogravure. A photoengraving process by which PHOTOGRAPHS or textual matters are reproduced on intaglio
printing plate or rolls from which they may be transferred to paper.
3815
photohead plotter. A device used to plot information by exposure of a photographic film.
3816
photoindex. A MOSAIC made by assembling individual PHOTOGRAPHS, with accompanying designations, into their
proper relative positions and copying the assembly photographically at a reduced SCALE.
3817
photolithograph. A lithograph produced by PHOTOLITHOGRAPHY. See LITHOGRAPHY.
175
3818
photolithography. That branch of lithographic printing in which PHOTOGRAPHY is employed for production of the
IMAGE on the final printing surface. The original printing surface, lithographic stone, has been almost completely
displaced by thin and flexible sheets of metal (zinc, aluminium, stainless steel, bimetallic PLATES, polymetallic
PLATES).
3819
photomap. A photomosaic of a specified land area, which also contains marginal information, descriptive DATA, and a
reference grid and/or projection. See also MOSAIC.
3820
photometeor. Optical phenomenon of the ATMOSPHERE.
3821
photometer. An instrument used in measuring the intensity of light, especially in determining the relative intensity of
different lights.
3822
photosphere. The visible surface of the SUN and direct source of almost all its RADIATION. It is a gaseous LAYER
some 400 km thick, below which the SUN becomes opaque.
3823
photosynthesis. The formation of carbohydrates in living plants from water and carbon dioxide, by the action of
sunlight on the CHLOROPHYLL.
3824
phototheodolite. A ground-survey instrument combining a THEODOLITE and a SURVEYING CAMERA in which
the relationship between the camera axis and the LINE OF COLLIMATION of the THEODOLITE can be measured.
3825
phototopography. The science of SURVEYING in which the detail is plotted entirely from PHOTOGRAPHS taken at
suitable ground stations.
3826
phototriangulation. The process for the extension of HORIZONTAL and/or VERTICAL CONTROL whereby the
measurements of angles and/or distances on overlapping PHOTOGRAPHS are related into a spatial solution using the
perspective principles of the PHOTOGRAPHS. Generally, this process involves using AERIAL PHOTOGRAPHS, and
is called aerotriangulation, aerial triangulation, or photogrammetric extension.
3827
photozincography. The use of a zinc plate in PHOTOENGRAVING.
3828
pictomap. A map supplement on which the photographic imagery of a standard photomosaic has been converted into
interpretable colours and symbols by means of tonal masking techniques.
3829
picture control point. See CONTROL POINT.
3830
picture plane. A plane upon which a system of lines or RAYS from an object to form an IMAGE or picture can be
projected. In perspective drawing, the system of RAYS is understood to converge to a single point. In PHOTOGRAMMETRY, the PHOTOGRAPH is the picture plane.
3831
piedmont (adj.). Situated or formed at the base of MOUNTAINS.
3832
pie graph. Circular SYMBOL divided into sectors to indicate proportions of a total value.
3833
pier. A long, narrow structure extending into the water to afford a berthing place for vessels, to serve as a promenade,
etc. See also JETTY.
3834
pierhead. The outer end of a PIER. Also called wharfhead.
3835
piezoelectric effect. The PHENOMENON, exhibited by certain crystals, in which mechanical compression produces a
potential difference between opposite crystal faces, or, an applied electric field produces corresponding changes in
dimensions.
3836
piezoelectricity. The property exhibited by some asymmetrical crystalline materials which when subjected to strain in
suitable directions develop electric POLARIZATION proportional to the strain. Inverse piezoelectricity is the effect in
which mechanical strain is produced in certain asymmetrical crystalline materials when subjected to an external electric
field; the strain is proportional to the electric field.
3837
piggot gun. A coring instrument for obtaining deep-sea BOTTOM SAMPLES. This instrument uses an explosive
charge to drive a metal bit into the BOTTOM at the instant the sharp end of the bit strikes the BOTTOM.
3838
pigmentation. A colouring of tissue by deposition of PIGMENTS.
176
3839
pigments. A colouring matter used as paint or dye or a natural colouring matter of a tissue.
3840
pile. A long heavy timber or section of steel, wood, concrete, etc., forced into the earth to serve as a support, as for a
PIER, or to resist lateral pressure.
3841
piling. A group of piles set in a row.
3842
pillar buoy. A BUOY composed of a tall central structure on a broad flat base.
3843
pilot. 1. A person who directs the movements of a vessel through pilot waters, usually a person who has demonstrated
extensive knowledge of channels, aids to navigation, dangers to navigation, etc., in a particular area and is licensed for
that area.
2. A book of sailing directions.
3844
pilot chart. See CHART.
3845
pilot station. The office or headquarters of pilots; the place where the services of a pilot may be obtained.
3846
pilot waters. Areas in which the services of a marine pilot are available. Waters in which NAVIGATION is by piloting.
More usually called pilotage waters in British terminology.
3847
pilotage waters. See PILOT WATERS.
3848
ping. An acoustic pulse signal projected by an underwater TRANSDUCER.
3849
pinger. A battery powered acoustic device equipped with a TRANSDUCER that transmits SOUND WAVES. When
the pinger is attached to a wire and lowered into the water, the direct and bottom reflected sound can be monitored with
a listening device. The difference between the arrival time of the DIRECT and REFLECTED WAVES is used to
compute the distance of the pinger from the ocean bottom.
3850
pingo. Small conical hills having a large central core of ice formed from the encroachment of permafrost and the
resulting hydrostatic pressure.
3851
pingo-like features (PLF). Small conical undersea features having the geomorphological appearance of pingos.
3852
pinnacle. Any high tower or spire-shaped pillar of rock or coral, alone or cresting a SUMMIT. It may extend above the
surface of the water. It may or may not be a hazard to SURFACE NAVIGATION.
3853
pinnacled iceberg. An iceberg weathered in such manner as to produce spires or pinnacles. Also called pyramidal
iceberg, irregular iceberg.
3854
pinpoint (v.t. and i.). To establish (POSITION) with great ACCURACY.
3855
pip. See BLIP.
3856
pipe. A hollow metal tube, of varying diameters and lengths, imbedded in the bottom in a manner similar to a pile. Pipes
are often used as privately maintained aids to navigation and in the determination of beach or bottom sand migration
(deposition or erosion).
3857
pipeline. A string of interconnected pipes used for the transport of matter, nowadays mainly oil or gas .
3858
pitch. The oscillations of a ship about the transverse axis, due to the bow and stern being raised or lowered on passing
through successive crests and troughs of waves. Also called pitching.
The distance along the axis of a screw or other helix between consecutive threads or ribs.
The distance a propeller would advance longitudinally, in one revolution if there were no slip.
3859
pitching. See PITCH.
3860
pivot. A spindle or pin by which a movable part of an instrument is supported so as to be free to turn. The pivot of a
COMPASS is usually a fixed point on which the NEEDLE hangs by a single jewelled cap.
3861
pivot point. After a ship has assumed its DRIFT ANGLE in a turn, the point on the centerline between the bow and the
CENTRE OF GRAVITY at which the resultant of the velocities of rotation and transaction is directed along the
centerline. To an observer on board, the ship appears to rotate about this point.
177
3862
pixel. Contraction for "picture element". The smallest element resolvable by electronic raster devices such as
SCANNER, DISPLAY, and PLOTTER. See REMOTE SENSING.
3863
plain. Any LAND with a flat or very slightly undulating surface.
A flat, gently sloping or nearly level region of the SEA FLOOR, for example, ABYSSAL PLAIN.
3864
plan. An orthographic drawing on a horizontal plane, as of an instrument, a horizontal section, or a layout.
A large scale map or chart of a small area.
3865
plane: horizontal. A plane perpendicular to the DIRECTION OF GRAVITY; any plane tangent to the GEOID or
parallel to such a plane.
In SURVEYING, a plane perpendicular to the PLUMB LINE within which or on which angles and distances are
observed.
3866
plane: vertical. Any plane passing through a point on the EARTH and containing the ZENITH and NADIR of that
point.
In SURVEYING, a plane at right angles to a HORIZONTAL PLANE and within which angles and distances are
observed.
3867
plane coordinates. See COORDINATES: PLANE RECTANGULAR.
3868
plane rectangular coordinates. See COORDINATES.
3869
plane sailing. See SAILING.
3870
plane surveying. See SURVEYING.
3871
planet. A CELESTIAL BODY of the SOLAR SYSTEM, shining by reflected light and revolving around the SUN.
3872
planet(s): inferior. The PLANETS with ORBITS smaller than that of the EARTH: Mercury and Venus.
3873
planet(s): major. The four largest PLANETS (Jupiter, Saturn, Uranus and Neptune).
3874
planet(s): minor. See ASTEROID.
3875
planet(s): navigational. The four PLANETS commonly used for celestial observations: Venus, Mars, Jupiter, and
Saturn.
3876
planet(s): superior. The PLANETS with ORBITS larger than that of the EARTH: Mars, Jupiter, Saturn, Uranus,
Neptune, and Pluto.
3877
plane table. A field device for plotting the lines of a SURVEY directly from the OBSERVATIONS. It consists
essentially of a drawing board mounted on a TRIPOD, with a ruler on which a TELESCOPE or other sighting device is
mounted. See ALIDADE. Also written as one word.
3878
plane table traverse. See TRAVERSE.
3879
planetary (adj.). Of a PLANET or the PLANETS. Like a PLANET. Terrestrial.
3880
planetoid. See ASTEROID.
3881
planform. The outline or shape of a body of water as determined by the STILL WATER LEVEL.
3882
planimeter. A mechanical integrator for measuring the area of a plane surface.
3883
planimetric map. See MAP.
3884
planimetry. The measurement of plane surfaces.
The plan details of a MAP.
3885
planisphere. A MAP or CHART that is the PROJECTION of all or part of a sphere on a plane.
A representation, on a plane, of the CELESTIAL SPHERE, especially one on a polar PROJECTION, with means
provided for making certain measurements such as ALTITUDE and AZIMUTH. See STAR FINDER.
3886
plankton. The passively drifting or weakly swimming organisms in marine and fresh waters.
178
3887
plan position indicator (PPI). A cathode-ray SCOPE on which SIGNALS appear in correct relation to each other, so
that the scope face presents a maplike representation of the area about the transmitter, the direction of a TARGET being
represented by the direction of its ECHO from a centre and range by its distance from that centre.
3888
planning chart. A chart designed for use in planning voyages or flight operations or investigating areas of marine or
aviation activities.
3889
plat (U.S. terminology). A diagram drawn to SCALE showing land boundaries and subdivisions, and identification of
the several units shown thereon, and including one or more certificates indicating due approval. A plat differs from a
MAP in that it does not necessarily show additional cultural, drainage and relief features. See also MAP:
CADASTRAL.
3890
plate. A thin, metal, plastic, or paper sheet, that carries the printing image and whose surface is treated to make only the
image areas ink-receptive.
3891
plateau. A flat or nearly flat area of considerable extent, dropping off abruptly on one or more sides; a TABLELAND.
3892
plate level. See LEVEL.
3893
platform. In geographical literature, a natural or artificial TERRACE; a flat elevated piece of GROUND; a
TABLELAND, a PLATEAU.
In oceanographic terminology, any man-made structure (aircraft, ship, BUOY, or tower) from or on which
oceanographic instruments are suspended or installed.
Structures which are erected on or over the seabed and subsoil for the purpose of exploring for, developing,
removing and transporting resources therefrom.
3894
platform: mineral development. A PLATFORM used in the exploitation of minerals.
3895
platform: offshore. A permanent offshore structure, either fixed or floating, used in the production of oil or natural gas.
3896
platform: piled. A platform with a steel jacket fixed by piles to the seabed.
3897
platform jacket. The section of a platform from base to deck level, on which deck modules are fitted.
3898
plot (v.t.). To draw lines and points to represent certain conditions graphically, as the various lines and points on a
CHART or PLOTTING SHEET, representing the progress of a craft, a graphical solution of a problem, etc.
3899
plotter. An instrument used for plotting straight lines and measuring angles on a CHART or PLOTTING SHEET. See
PROTRACTOR.
In data processing it stands for
a) Vector plotter : An electromechanical device for automatically drawing curves. The curves are generated by a
sequence of linear incremental pieces ("vectors") depending on the resolution provided by the device. For cartographic
purposes, high precision FLAT-BED PLOTTERS (drawing tables) are used.
b) Raster or electrostatic plotter : A sophisticated electronic device for producing pictures by means of raster
techniques. The picture is generated by lines of PIXELS drawn sequentially, typically with a resolution of 200-400
pixels per inch. Raster plotters can produce complete pictures in short time irrespective of the complexity of the
picture's contents.
3900
plotting. See PLOT.
3901
plotting board. A stiff transparent polar coordinate plotting sheet for tracking other vessels and aircraft and solving
problems involving RELATIVE MOVEMENT.
3902
plotting sheet. A blank CHART, usually on the MERCATOR PROJECTION, showing only the GRATICULE and a
COMPASS ROSE, so that the plotting sheet can be used for any LONGITUDE.
In hydrographic SURVEYING, a working sheet on which the main STATIONS of the SURVEY are plotted. It
forms the framework of the SURVEY and provides the basis for accurately locating and plotting all the detail of the
SURVEY. See also LATTICE.
3903
plotting sheet: electronic. A CHART showing time difference or phase difference curves of a circular or a hyperbolic
navigational system. These LATTICE lines are used to accurately position the DATA collected during HYDROGRAPHIC or OCEANOGRAPHIC SURVEYS.
179
3904
plumb bob. A conical device, usually of brass and suspended by a cord, by means of which a point can be projected
vertically into space over relative short distances. Also referred to as plummet.
3905
plumb line. The LINE OF FORCE in the geopotential field.
The continuous curve to which the direction of the normal GRAVITY is everywhere tangential.
3906
plumb line: deflection of. See DEFLECTION OF THE VERTICAL.
3907
plumb point. See NADIR: PHOTOGRAPH.
3908
plummet. A SOUNDING LEAD. A PLUMB BOB.
3909
plunging breaker. See BREAKER.
3910
pluviograph. RAIN GAUGE which includes an arrangement for the time recording of the depth of water from
PRECIPITATION.
3911
pocket compass. See COMPASS.
3912
Poincaré wave. A long period gravity wave. The superposition of incident and reflected plane waves (Sverdrup Waves)
such that the composite wave fronts are perpendicular to the coast with a set of nodal lines normal to the wave fronts.
The term is used in tidal analysis to study ocean tides and tides in open seas and gulfs.
3913
point. One thirty-second of a circle, or 11 1/4 DEGREES. Also called COMPASS POINT when used in reference to
COMPASS directions.
The extreme end of a CAPE; or the outer end of any land area protruding into the water, usually less prominent than
a CAPE.
In digital cartography, the 0-dimensional geometric primitive of an object that specifies location.
3914
pointing line. See COLLIMATION: LINE OF.
3915
point of Aries. See EQUINOX.
3916
point of arrival. See ARRIVAL: POINT OF.
3917
point of destination. See DESTINATION: POINT OF.
3918
point of origin. See COORDINATES: ORIGIN OF.
3919
point of symmetry. The point in the FOCAL PLANE of a CAMERA about which all lens DISTORTIONS are
symmetrical. If the LENS were perfectly mounted, the point of symmetry would coincide with the PRINCIPAL POINT.
3920
polar aurora. See AURORA.
3921
polar axis. See AXIS.
3922
polar bearing. See BEARING.
3923
polar chart. See CHART.
3924
polar circle. Either the ARCTIC CIRCLE (north polar circle) or the ANTARCTIC CIRCLE (south polar circle).
3925
polar coordinates. See COORDINATES.
3926
polar distance. ANGULAR DISTANCE from a CELESTIAL POLE; the arc of an HOUR CIRCLE between a
CELESTIAL POLE, usually the ELEVATED POLE, and a point on the CELESTIAL SPHERE, measured from the
CELESTIAL POLE through 180°. When the DECLINATION and LATITUDE are of the same name,
CODECLINATION is the same as polar distance measured from the ELEVATED POLE.
3927
polar front. Quasi-permanent FRONT of great extent, of middle latitudes, which separates relatively cold polar air and
relatively warm tropical air, and on which WAVES are produced.
3928
polar ice. SEA ICE that is more than one year old (in contrast to WINTER ICE). The WMO code defines polar ice as
any SEA ICE more than one year old and more than 3 metres thick.
180
3929
Polaris correction. A CORRECTION to be applied to the OBSERVED ALTITUDE of Polaris to obtain the
LATITUDE.
3930
polarization. A condition of RADIANT ENERGY in which the VIBRATIONS take place in a regular manner, as in a
straight line, circle or ellipse, in a plane perpendicular to the path of travel.
3931
polarization error. See ERROR.
3932
polar orthographic projection. See PROJECTION.
3933
polder. LAND reclaimed from the SEA or other body of water by the construction of an EMBANKMENT to restrain
the water. See DIKE.
3934
pole. Either of the two points of intersection of the surface of a sphere or SPHEROID and its AXIS.
The origin of a system of POLAR COORDINATES.
Either of the two MAGNETIC POLES of a MAGNET.
A long slender rod, as of timer or metal. Such a rod used for SOUNDING is called SOUNDING POLE.
3935
pole: celestial. Either of the two points of intersection of the CELESTIAL SPHERE and the extended AXIS of the
EARTH, labelled N or S to indicate either the north celestial pole or the south celestial pole.
3936
pole: depressed. The CELESTIAL POLE below the HORIZON, of opposite NAME to the LATITUDE.
3937
pole: elevated. The CELESTIAL POLE above the HORIZON, agreeing in NAME with the LATITUDE.
3938
pole: geographic(al). Either of the two points of intersection of the surface of the EARTH with its AXIS, labelled N or
S to indicate either the north geographical pole or the south geographical pole.
3939
pole: magnetic. See MAGNETIC POLE.
3940
pole: terrestrial. One of the POLES of the EARTH. See POLE.
3941
pollution. The direct or indirect alteration of the physical, chemical, thermal, biological or radioactive properties of any
part of the environment in such a way as to create a hazard or potential hazard to the health, safety or welfare of any
living species.
3942
polyconic projection. See PROJECTION.
3943
polygon. A non-selfintersecting, closed chain defining the boundary of an area.
3944
polynia. A water area enclosed in ICE, generally fast; this water area remains constant and usually has an oblong shape;
sometimes limited to one side by the COAST.
Any enclosed sea water area in PACK ICE other than a LEAD, not large enough to be called OPEN WATER. If a
polynia is found in the same region every year, for example, off the MOUTHS of big RIVERS, it is called a recurring
polynia. A temporary small clearing in PACK ICE which consists of small ICE FLOES and BRASH ICE in continuous
local movement is called an unstable polynia; an opening which is flanked by large FLOES and therefore appears to be
relatively stable is called a stable polynia. When frozen over, a polynia becomes an ice skylight from the point of view
of the submariner.
3945
polyvinyl corer. See CORER: HYDROPLASTIC.
3946
pond. A small body of still water of artificial formation, its BED being either hollowed out of the SOIL or formed by
embanking and damming up a natural HOLLOW.
3947
pontoon. Floating structure, usually rectangular in shape which serves as landing, pierhead or bridge support.
3948
pool. A small body of still or standing water, permanent or temporary; chiefly one of natural formation.
A deep or still place in a RIVER or STREAM.
In ice terminology, any enclosed relatively small area in PACK ICE, drift ICE, other than a LEAD. See POLYNIA.
3949
porosity. The ratio of the aggregate volume of pore space in a ROCK or SEDIMENT to its total volume, usually
expressed as a percentage.
181
3950
port. A place provided with terminal and transfer facilities for loading and discharging cargo or passengers, usually
located in a HARBOUR.
The left side of a craft, facing forward. The opposite is STARBOARD.
3951
port authority. The entity responsible for administration and maintenance of harbour facilities.
3952
port handbook. A handbook for a specific port.
3953
position. DATA which define the location of a point with respect to a reference system. The COORDINATES which
define such a location. The place occupied by a point on the surface of the EARTH, or in space.
3954
position: adjusted. An adjusted value of the coordinate position of a point on the EARTH.
3955
position: apparent. In ASTRONOMY, the POSITION of a CELESTIAL BODY reduced to the centre of the EARTH.
It differs from the position in which the object is observed as to the effects of REFRACTION, DIURNAL ABERRATION, and DIURNAL PARALLAX.
3956
position: assumed. A point at which a craft is assumed to be located, particularly one used as preliminary to
establishing certain navigational DATA, as that point of the surface of the EARTH for which the computed ALTITUDE
is determined in the solution of a celestial OBSERVATION.
3957
position: astronomical. A point on the EARTH whose COORDINATES have been determined as a result of OBSERVATION of CELESTIAL BODIES. The expression is usually used in connection with POSITIONS on LAND
determined with great ACCURACY for SURVEY purposes.
A point on the EARTH, defined in terms of ASTRONOMICAL LATITUDE and LONGITUDE.
3958
position: dead reckoning. The POSITION of a craft determined by DEAD RECKONING, or by advancing a previous
POSITION for COURSES and distances.
3959
position: detached. In HYDROGRAPHIC SURVEY, an expression indicating a POSITION taken, to locate ROCKS,
floating AIDS TO NAVIGATION, least DEPTHS on SHOALS or other dangers or features of importance.
3960
position: estimated. The most probable POSITION of a craft determined from incomplete DATA or DATA of
questionable ACCURACY. Such a POSITION might be determined by applying a correction to the DEAD
RECKONING POSITION.
3961
position: field. A POSITION computed while field work is in progress to determine the acceptability of the
OBSERVATIONS or to provide a preliminary POSITION for other purposes.
3962
position: geodetic. A point on the EARTH, the COORDINATES of which have been determined by
TRIANGULATION from an initial STATION whose location has been established as a result of ASTRONOMICAL
OBSERVATIONS. The COORDINATES of such a POSITION depend upon the REFERENCE SPHEROID used.
3963
position: geographic(al). The POSITION of a point on the surface of the EARTH expressed in terms of LATITUDE
and LONGITUDE, either ASTRONOMICAL or GEODETIC.
A SUB-POINT.
3964
position: relative. A point defined with reference to another POSITION, either fixed or moving.
3965
position angle. See PARALLACTIC ANGLE.
3966
position angles. The two sextant angles observed on a SURVEY SHIP for determining its POSITION.
3967
position approximate. Of inexact POSITION. The expression is used principally on CHARTS to indicate that the
POSITION of a WRECK, SHOAL, etc., has not been accurately determined or does not remain fixed. Usually shown by
the abbreviation 'PA'.
3968
position circle. See CIRCLE OF POSITION.
3969
position dilution of precision (PDOP). See DILUTION OF PRECISION.
3970
position doubtful. Of uncertain POSITION. The expression is used principally on CHARTS to indicate that a
WRECK, SHOAL, etc., has been reported in various POSITIONS and not definitely determined in any. Usually shown
by the abbreviation 'PD'.
182
3971
positioning. The process of determination of a position.
3972
position line. See LINE OF POSITION.
3973
positive. In PHOTOGRAPHY, an IMAGE of the original object which corresponds to the same in the scheme of light
and shade.
3974
positive altitude. See ANGLE OF ELEVATION.
3975
positive gradient. In OCEANOGRAPHY, a positive rate of change with DEPTH.
3976
post. A small BEACON, more substantial than a PERCH, used for marking CHANNELS. See also PILE.
3977
potable water intake (PWI). A structure designed for the intake of drinking water. The intake is usually elevated
above the bottom, supported and protected by a debris-screening structure (CRIB), a separately charted feature.
3978
potential density. In OCEANOGRAPHY, the DENSITY that a parcel of water would have if raised adiabatically to the
surface, that is, if determined from the parcel's 'in situ' SALINITY and POTENTIAL TEMPERATURE.
3979
potential temperature. In OCEANOGRAPHY, the temperature that a WATER SAMPLE would attain if raised adiabatically to the sea surface. For the deepest points of the OCEAN, which are just over 10 000 METRES, the adiabatic
cooling would be less than 1.5°C.
3980
pound. A unit of mass, equal to 0.45359237 KILOGRAMS.
3981
power. See MAGNIFYING POWER.
3982
precautionary area. A routeing measure comprising an area within defined limits where ships must navigate with
particular caution and within which the direction of traffic flow may be recommended.
3983
precession. Change in the direction of the AXIS of ROTATION of a spinning body, as a GYROSCOPE, when acted
upon by a torque. The direction of motion of the AXIS is such that it causes the direction of spin of the GYROSCOPE
to tend to coincide with that of the impressed torque.
3984
precession of the equinoxes. The conical motion of the EARTH's AXIS about the vertical to the plane of the
ECLIPTIC, caused by the attractive force of the SUN, MOON, and other PLANETS on the equatorial protuberance of
the EARTH.
3985
precipitation. PHENOMENON made up of an aggregate of aqueous particles, liquid or solid, crystallized or
amorphous, which fall from a CLOUD or group of CLOUDS and reach the ground.
3986
precipitation intensity. Amount of PRECIPITATION collected in unit time interval. See RAINFALL AMOUNT.
3987
precision. The degree of refinement of a value not to be confused with ACCURACY, which is the degree of
conformance with the correct value.
3988
precision ephemeris. The ephemeris which describe the orbit of a navigational satellite precisely. They are of higher
precision than the broadcast ephemeris but not available in real time.
3989
predicted tide(s). See TIDE.
3990
preferred channel mark. A distinctive lateral mark used to indicate both the point at which a channel divides and the
channel that has been designated as preferred channel.
3991
preferred datum. A geodetic datum selected as a base for consolidation of local independent datums within a
geographical area. Also called major datum.
3992
preliminary survey. See SURVEY: RECONNAISSANCE.
3993
press proof. A lithographed impression taken from among the first copies run on the press and used for cheking
purposes. Also called press pull.
3994
pressure: atmospheric. Pressure (force per unit area) exerted by the ATMOSPHERE, on any surface, by virtue of its
WEIGHT: it is numerically equal to the WEIGHT of a vertical column of air above the surface of unit base area,
extending to the outer limit of the ATMOSPHERE.
183
3995
pressure: barometric. ATMOSPHERIC PRESSURE as indicated by a BAROMETER.
3996
pressure: hydrostatic. The pressure at a given DEPTH due to the WEIGHT of the water column above that DEPTH.
3997
pressure: sound. The instantaneous pressure at a point in a medium in the presence of a SOUND WAVE, minus the
static pressure at that point.
3998
pressure-altitude. An ATMOSPHERIC PRESSURE expressed in terms of ALTITUDE which corresponds to that
pressure in the STANDARD ATMOSPHERE.
3999
pressure gauge. See GAUGE.
4000
pressure gradient. Vector, perpendicular to the isobaric line or surface, directed towards low pressure and of intensity
equal to the rate of variation of the pressure with distance. Also called barometric gradient.
4001
pressure hydrophone. A HYDROPHONE in which the electric OUTPUT substantially corresponds to the
instantaneous SOUND PRESSURE of the impressed SOUND WAVE.
4002
pressure ice. A general term for FLOATING ICE which has been squeezed together and in places forced upwards,
when it can also be described as RAFTED ICE, HUMMOCKED ICE, PRESSURE RIDGE, TENTED ICE.
4003
pressure plate. In PHOTOGRAPHY, a flat plate (usually of metal but frequently of glass or other substance) which, by
means of mechanical force, presses film into contact with the focal-plane plate of a CAMERA.
4004
pressure ridge. A ridge or wall of HUMMOCKED ICE where one FLOE has been pressed against another.
4005
pressure wave. A short-period oscillation of pressure such as that associated with the propagation of SOUND through
the ATMOSPHERE; a type of LONGITUDINAL WAVE.
4006
Price-Gurley current meter. A battery powered electromechanical CURRENT METER which measures current speed
only.
4007
pricker. A pointed tool used instead of a pencil for laying off finer and more accurate lines on a PLOTTING SHEET.
4008
primary circle. See PRIMARY GREAT CIRCLE.
4009
primary great circle. A GREAT CIRCLE used as the origin of measurement of a COORDINATE; particularly such a
circle 90°from the POLES of a system of SPHERICAL COORDINATES, as the EQUATOR. Also called primary circle, fundamental circle.
4010
primary radar. See RADAR.
4011
primary tide. See TIDE.
4012
primary tide station. See STATION: TIDE.
4013
prime meridian. See MERIDIAN.
4014
prime vertical. See PRIME VERTICAL CIRCLE.
4015
prime vertical circle. The VERTICAL CIRCLE through the east and west points of the HORIZON. Often shortened to
prime vertical.
4016
priming of the tide(s). The acceleration in the TIMES of occurrence of HIGH and LOW WATER due to changes in the
relative positions of the MOON and the SUN. The opposite effect is called LAGGING OF THE TIDES.
4017
principal axis. See AXIS OF LENS.
4018
principal distance. The perpendicular distance from the internal PERSPECTIVE CENTRE to the plane of a particular
finished NEGATIVE or PRINT. This distance is equal to the CALIBRATED FOCAL LENGTH corrected for both the
enlargement or reduction ratio of the film or paper shrinkage or expansion and maintains the same perspective angles at
the internal PERSPECTIVE CENTRE to points on the finished NEGATIVE or PRINT, as existing in the taking
CAMERA at the moment of EXPOSURE.
184
4019
principal line. In PHOTOGRAMMETRY, the trace of the PRINCIPAL PLANE upon the PHOTOGRAPH, (e.g., the
line through the PRINCIPAL POINT and the PHOTOGRAPH NADIR).
4020
principal meridian. See MERIDIAN.
4021
principal parallel. See PARALLEL: PHOTOGRAPH.
4022
principal plane. In PHOTOGRAMMETRY, the vertical plane through the internal PERSPECTIVE CENTRE
containing the photograph perpendicular of a tilted PHOTOGRAPH.
4023
principal point. In PHOTOGRAMMETRY, the foot of the perpendicular from the interior PERSPECTIVE CENTRE
to the plane of the PHOTOGRAPH (i.e. the foot of the photograph perpendicular).
4024
principal scale. See SCALE.
4025
principal vertical circle. The VERTICAL CIRCLE through the north and south points of the HORIZON, coinciding
with the CELESTIAL MERIDIAN.
4026
print. In PHOTOGRAPHY, a copy made from a transparency by photographic means.
4027
print: blue. A nonreproducible blue image or outline usually printed photographically on paper.
4028
print: contact. A photographic PRINT made from either a NEGATIVE or a POSITIVE in contact with a sensitized
material.
4029
print: ozalid. A photographic contact print developed by a dry diazo process. The process produces a POSITIVE from
a positive IMAGE or a NEGATIVE from a negative IMAGE.
4030
print: ratio. A PRINT in which the SCALE has been changed from that of the NEGATIVE or transparency by
projection printing.
4031
printing plates. Any one-piece printing surface of any size, strength, or surface preparation, bearing an image made
manually, mechanically or photographically, specifically for the purpose of printing such an image onto some other
material.
4032
prismatic astrolabe. See ASTROLABE.
4033
probability. The likelihood of an event measured by the ratio of the favourable cases to the whole number of cases
possible.
4034
probable error. See ERROR.
4035
probe. Any device inserted in an environment for the purpose of obtaining information about the environment.
4036
processor. See MICROPROCESSOR.
4037
production platform. A term used to indicate a permanent offshore structure equipped to control the flow of oil or gas.
For charting purposes, the use of the term is extended to include all permanent platforms associated with oil or gas
production, e.g., field terminal, drilling and accommodation platforms, and "booster" platforms located at intervals
along some pipelines. It does not include entirely submarine structures. See also PLATFORM.
4038
profile. A graph or curve showing elevation or distribution of some property vs. distance along a line. The vertical
SCALE may be greatly exaggerated with respect to the horizontal SCALE. An example of a profile is the graphic record
made by a recording ECHO SOUNDER operating while a vessel is underway.
A vertical section of the surface of the GROUND, or of underlying STRATA, or both, along any fixed line.
4039
profiling: continuous seismic. Determination of the subsoil strata and geological structure by use of sound sources
which emit acoustic pulses to penetrate the seabed. Travel time between emission of pulses and reception is usually
measured in a towed streamer.
4040
program (or programme). The complete sequence of COMPUTER instructions and routines necessary to solve a data
processing problem.
4041
programming language. A language used to prepare computer programs, for example Fortran, Pascal and many
others.
185
4042
progressive wave. See WAVE.
4043
progress sketch. A MAP or sketch showing work accomplished. In TRIANGULATION and TRAVERSE, each point
established is shown on the progress sketch as well as lines observed over and BASES measured. In a levelling survey,
the progress sketch shows the route followed and the towns passed through, but not necessarily the locations of the
BENCH MARKS.
4044
prohibited area. An area shown on CHARTS within which NAVIGATION and/or anchoring is prohibited.
In aviation terminology, a specified area within the land areas of a state or territorial waters adjacent thereto over
which the flight of aircraft is prohibited.
4045
projection. The representation of a figure on a surface, either plane or curved, according to a definite plan. In a
PERSPECTIVE PROJECTION this is done by means of projecting lines emanating from a single point, which may be
infinity.
In CARTOGRAPHY, any systematic arrangement of MERIDIANS and PARALLELS portraying the curved surface
of the sphere or SPHEROID upon a plane. Also called map projection or chart projection.
In PHOTOGRAPHY, the reduction or enlargement of a POSITIVE or NEGATIVE, by projecting the IMAGE
through a LENS.
4046
projection: azimuthal (or zenithal). A PROJECTION on which the AZIMUTHS or DIRECTIONS of all lines
radiating from a central point or POLE are the same as the AZIMUTHS or DIRECTIONS of the corresponding lines on
the sphere.
4047
projection: azimuthal equidistant. An AZIMUTHAL PROJECTION on which straight lines radiating from the centre
or pole of projection represent GREAT CIRCLES in their TRUE AZIMUTHS from the centre, and lengths along these
lines are of exact SCALE. This PROJECTION is neither EQUAL AREA nor CONFORMAL.
4048
projection: azimuthal orthomorphic. See PROJECTION: STEREOGRAPHIC.
4049
projection: Cassini. A conventional PROJECTION constructed by computing the lengths of arcs along a selected
GEOGRAPHIC MERIDIAN and along a GREAT CIRCLE perpendicular to that MERIDIAN, and plotting these as
RECTANGULAR COORDINATES on a plane.
4050
projection: conformal. A PROJECTION in which all angles around any point are correctly represented. In such a
PROJECTION the SCALE is the same in all DIRECTIONS about any point. Very small shapes are correctly represented, resulting in an orthomorphic projection. Hence, the terms of 'conformal' and 'orthomorphic' are used
synonymously since neither characteristic can exist independently of the other.
4051
projection: conic (or conical). A PROJECTION produced by projecting the GEOGRAPHIC MERIDIANS and
PARALLELS onto a cone which is tangent to (or intersects) the surface of a sphere, and then developing the cone into a
plane.
4052
projection: cylindrical. A PROJECTION produced by projecting the GEOGRAPHICAL MERIDIANS and
PARALLELS onto a cylinder which is tangent to (or intersects) the surface of a sphere, and then developing the
cylinder into a plane.
4053
projection: equal area. A PROJECTION having a constant area scale. Such a PROJECTION is not conformal and is
not used for NAVIGATION. Also called equivalent projection.
4054
projection: equivalent. See PROJECTION: EQUAL AREA.
4055
projection: geometric. See PROJECTION: PERSPECTIVE.
4056
projection: gnomonic. A PERSPECTIVE PROJECTION on a plane tangent to the surface of a sphere having the point
of projection at the centre of the sphere. The PROJECTION is neither CONFORMAL nor EQUAL AREA. It is the only
PROJECTION on which GREAT CIRCLES on the sphere are represented as straight lines. For this reason this
PROJECTION is used principally for CHARTS for GREAT CIRCLE SAILING.
4057
projection: inverse Mercator. The name given to the TRANSVERSE MERCATOR PROJECTION when the latter is
extended right over both POLES. It is used for air charts of polar areas.
186
4058
projection: Lambert conformal conic. A CONFORMAL PROJECTION of the conical type, on which all
GEOGRAPHIC MERIDIANS are represented by straight lines which meet in a common point outside the limits of the
MAP, and the GEOGRAPHIC PARALLELS are represented by a series of arcs of circles having this common point for
a centre. MERIDIANS and PARALLELS intersect at right angles, and angles on the EARTH are correctly represented
on the PROJECTION. This PROJECTION may have one or two STANDARD PARALLELS along which the SCALE
is held exact.
4059
projection: Mercator. A CONFORMAL PROJECTION of the cylindrical type. The EQUATOR is represented by a
straight line true to SCALE; the GEOGRAPHIC MERIDIANS are represented by parallel straight lines perpendicular
to the line representing the EQUATOR; they are spaced according to their distance apart at the EQUATOR. The
GEOGRAPHIC PARALLELS are represented by a second system of straight lines perpendicular to the family of lines
representing the MERIDIANS, and therefore parallel with the EQUATOR. CONFORMALITY is achieved by
mathematical analysis, the spacing of the PARALLELS being increased with the increasing distance from the
EQUATOR to conform with the expanding SCALE along the PARALLELS resulting from the MERIDIANS being
represented by parallel lines. Since RHUMB LINES appear as straight lines and DIRECTIONS can be measured
directly, this PROJECTION is widely used in NAVIGATION.
4060
projection: meridional orthographic. An ORTHOGRAPHIC PROJECTION having the plane of the projection
parallel to the plane of some selected MERIDIAN; in this PROJECTION, the GEOGRAPHIC PARALLELS and the
CENTRAL MERIDIAN are straight lines, the outer MERIDIAN is a full circle, and the other MERIDIANS are arcs of
ellipses.
4061
projection: orthographic. A perspective azimuthal PROJECTION in which the projecting lines, emanating from a
point at infinity, are perpendicular to a tangent plane. This PROJECTION is used chiefly in NAUTICAL
ASTRONOMY for interconverting COORDINATES of the CELESTIAL EQUATOR and HORIZON systems.
4062
projection: orthomorphic. See PROJECTION: CONFORMAL.
4063
projection: perspective. The representation of a figure on a surface, either plane or curved, by means of projecting
lines emanating from a single point, which may be infinity. Also called geometric projection.
4064
projection: polar orthographic. An ORTHOGRAPHIC PROJECTION having the plane of the projection
perpendicular to the AXIS of ROTATION of the EARTH (parallel with the plane of the EQUATOR); in this
PROJECTION, the GEOGRAPHIC MERIDIANS are straight lines.
4065
projection: polyconic. A PROJECTION having the central GEOGRAPHIC MERIDIAN represented by a straight line,
along which the spacing for lines representing the GEOGRAPHIC PARALLELS is proportional to the distances apart
of the PARALLELS; the PARALLELS are represented by arcs of circles which are not concentric, but whose centres
lie on the line representing the CENTRAL MERIDIAN, and whose radii are determined by the lengths of the elements
of cones which are tangent along the PARALLELS. All MERIDIANS except the central one are curved. This
PROJECTION is neither CONFORMAL nor EQUAL AREA but it has been widely used for MAPS of small areas
because of the ease with which it can be constructed.
4066
projection: skewed. Any standard PROJECTION used in MAP or CHART construction, which does not conform to a
general north-south format with relation to the NEAT LINES of the MAP or CHART.
4067
projection: stereographic. A PERSPECTIVE PROJECTION having the point of PROJECTION at the opposite end of
the diameter of the sphere from the point of tangency of the plane of projection. It is conformal and is the only
AZIMUTHAL PROJECTION having that quality. When the centre of the PROJECTION is located at a POLE of the
sphere, it is called a stereographic polar projection; when on the EQUATOR, a stereographic meridional projection;
and when on some other selected PARALLEL of LATITUDE, a stereographic horizon projection. Also called
azimuthal orthomorphic projection.
4068
projection: stereographic horizontal. See PROJECTION: STEREOGRAPHIC.
4069
projection: stereographic meridional. See PROJECTION: STEREOGRAPHIC.
4070
projection: stereographic polar. See PROJECTION: STEREOGRAPHIC.
4071
projection: transverse cylindrical orthomorphic. See PROJECTION: TRANSVERSE MERCATOR.
187
4072
projection: transverse Mercator. A PROJECTION of the cylindrical type, being in principle equivalent to the regular
MERCATOR PROJECTION turned (transversed) 90° in AZIMUTH. In this PROJECTION, the CENTRAL
MERIDIAN is represented by a straight line, corresponding to the line which represents the EQUATOR on the regular
MERCATOR PROJECTION. Neither the GEOGRAPHICAL MERIDIANS, except the CENTRAL MERIDIAN, nor
the GEODETIC PARALLELS, except the EQUATOR (if shown), are represented by straight lines. It is a
CONFORMAL PROJECTION. Also called transverse cylindrical orthomorphic projection.
4073
projection: Universal Transverse Mercator. See GRID: UNIVERSAL TRANSVERSE MERCATOR (UTM).
4074
projection: zenithal. See PROJECTION: AZIMUTHAL.
4075
projector. An optical instrument which throws the IMAGE of a NEGATIVE or PRINT upon a SCREEN or other
viewing surface, usually at a larger scale.
An underwater acoustic TRANSMITTER. See UNDERWATER SOUND PROJECTOR.
4076
projector: reflecting. In PHOTOGRAMMETRY, an instrument by means of which the IMAGE of an AERIAL
PHOTOGRAPH can be projected onto a MAP. By varying the position of the projector lens, the scale of the projected
IMAGE can be varied, and, by tilting the table top, compensation can be made for any tilt in the PHOTOGRAPH.
4077
prolate spheroid. See SPHEROID.
4078
prominent object. Objects which are easily identifiable, but do not justify being classed as conspicuous.
4079
promontory. A high point of LAND extending into a body of water. A CAPE.
4080
proof. In CARTOGRAPHY, an advanced copy of a MAP produced to check the design, register and/or to enable
ERRORS to be detected and corrected before final printing.
4081
proof plotting. An advanced copy of a map or chart produced by a PLOTTER to check the design and registration, and
to detect and correct errors before final printing.
4082
propagated error. An error which occurs in one operation and contaminates subsequent operations.
4083
properties of sea water. See SEA WATER, SALINITY.
4084
proportional dividers. An instrument consisting in its simple form of two legs pointed at both ends and provided with
an adjustable PIVOT, so that for any given pivot setting, the distance between one set of pointed ends always bears the
same ratio to the distance between the other set. A change in the PIVOT changes the ratio. The dividers are used in
transferring measurements between CHARTS or other drawings which are not at the same SCALE.
4085
protected reversing thermometer. See THERMOMETER.
4086
proton precession magnetometer. See MAGNETOMETER: NUCLEAR PRECESSION.
4087
protractor. An instrument for measuring angles on a surface; an angular SCALE. In its most usual form it consists of a
circle or part of one (usually a semicircle) graduated in DEGREES. See PROTRACTOR: THREE ARM and
COMPASS ROSE.
4088
protractor: Cust. Square or rectangular sheet of transparent xylonite engraved with a circle graduated in DEGREES
and half DEGREES. Observed angles are drawn, in general, on the under side. See PROTRACTOR: THREE ARM.
4089
protractor: parallel motion. An instrument consisting essentially of a PROTRACTOR and one or more arms attached
to a parallel motion device, so that the movement of the arms is everywhere parallel. The protractor can be rotated and
set at any position so that it can be oriented to a CHART. Also called universal drafting machine.
4090
protractor: three arm. An instrument consisting essentially of a circle graduated in DEGREES, to which is attached
one fixed arm and two arms pivoted at the centre and provided with clamps so that they can be set at any angle to the
fixed arm, within the limits of the instrument. It is used for finding a ship's POSITION, when the angles between three
fixed and known points are measured.
In British terminology, a perspex (or transparent plastic) device used when the MARKS are too close for the use of a
STATION POINTER. This instrument has replaced the CUST PROTRACTOR.
188
4091
province. In OCEANOGRAPHY and in a morphological sense, a region composed of a group of similar physiographic
features whose characteristics are markedly in contrast with surrounding areas (rarely used in marine
CARTOGRAPHY).
4092
psephyte. A coarse fragmental ROCK (conglomerate) or DEPOSIT composed of rounded PEBBLES.
4093
psychrometer. Instrument used to measure the humidity of the ATMOSPHERE. It comprises two identical THERMOMETERS, the bulb of one of which is dry, while that of the other is wet and covered by a film of pure water or ICE.
4094
pseudorange. The time shift required to align (correlate) a replica of the GPS code generated in the receiver with the
received GPS code, scaled into distance by the speed of light. This time shift is the difference between the time of signal
reception (measured in the receiver time frame) and the time of emission (measured in the satellite time frame).
4095
puddle. An accumulation on the ICE of melt water, mainly due to melting SNOW, but in the more advanced stages also
to the melting of ICE. Initial stage consists of patches of melted SNOW.
4096
pull. An impression from an individual printing PLATE.
4097
pulsar. A rotating neutron star emitting electromagnetic radiation in regular pulses related to its rotational period.
4098
pulse (or impulse). A variation of quantity whose value is normally constant (often zero), the variation being
characterized by a rise and a decay. A common example is a very short burst of electromagnetic energy. See WAVE:
CONTINUOUS.
4099
pulse length. The time interval during which the amplitude of a pulse is at or greater than a specified value, usually
stated in terms of a fraction or percentage of the maximum value.
4100
pulse modulation. See MODULATION.
4101
pulse radio altimeter. See ALTIMETER: RADIO.
4102
pulse repetition rate. The rate at which recurrent PULSES are transmitted, usually expressed in PULSES per
SECOND.
4103
pumice. An excessively cellular, glassy LAVA. It is very light and can float on water until it becomes waterlogged and
sinks.
4104
punch register system. System involving the use of prepunched holes in the flat and plate and a set of plastic pins or
buttons which are used in registering succeeding flats, positioning the image on the plate, and positioning the plate on
the press. See also REGISTRATION.
4105
punched (or punch) card equipment. A system whose principal feature is that numbers are recorded on cards by
means of holes punched in successive columns of a card, the row of the card indicating the digit.
4106
pycnocline. A vertical positive density GRADIENT in some LAYER of a body of water, which is appreciably greater
than GRADIENTS above and below it.
189
Q
4107
Q-factor. The pressure coefficient of the unprotected THERMOMETER expressed in °C.
4108
QTG station. A RADIO STATION which is prepared to provide QTG service, that is to say, to transmit upon request
from a ship, a radiosignal, the BEARING of which can be taken by that ship.
4109
quadrant. A double-reflecting instrument for measuring angles. It is similar to a SEXTANT, but has an arc of 90°.
Also a surveying or astronomical instrument composed of a graduated arc about 90°in length, equipped with a sighting
device.
4110
quadrantal correctors. Masses of SOFT IRON placed near a MAGNETIC COMPASS to correct for QUADRANTAL
DEVIATION. Spherical quadrantal correctors are called quadrantal spheres.
4111
quadrantal deviation. See DEVIATION.
4112
quadrantal sphere. See QUADRANTAL CORRECTORS.
4113
quadrature. An ELONGATION of 90°usually specified as east or west in accordance with the direction of the body
from the SUN. The MOON is at quadrature at first and last quarters. See PHASES OF THE MOON.
The situation of two periodic quantities differing by a quarter of a CYCLE.
4114
quadripod. A four-legged stand for TRIANGULATION, SIGNALS, etc.
4115
quality control. All procedures which ensure that the product meets certain standards and specifications.
4116
quality of the bottom. See BOTTOM: NATURE OF.
4117
quarantine anchorage. An area where a vessel anchors when satisfying quarantine regulations.
4118
quarantine buoy. A BUOY marking the location of a QUARANTINE ANCHORAGE.
4119
quarter-diurnal tide(s). See TIDE.
4120
quartering sea. WAVES moving in a direction approximately 45°from a vessel's HEADING, striking the vessel on the
quarter.
4121
quarter point. The fourth of the distance from one POINT of the COMPASS to another, equivalent to about two
DEGREES and forty-nine MINUTES.
4122
quartz. Crystalline silica. In its most common form it is colourless and transparent, but it takes a large variety of forms
of varying degrees of opaqueness and colour. It is the most common solid mineral. Part of the ocean bed is composed of
quartz.
4123
quartz clock. See CLOCK: CRYSTAL.
4124
quartz horizontal magnetometer. See MAGNETOMETER.
4125
quay. A WHARF approximately parallel to the SHORELINE and accommodating ships on one side only, the other side
being attached to the SHORE. It is usually of solid construction, as contrasted with the open pile construction usually
used for PIERS.
4126
quayage. A comprehensive term embracing all the structures in a PORT alongside which vessels can lie.
4127
quenching. The great reduction in underwater sound transmission or reception resulting from absorption and
SCATTERING of sound energy by air bubbles entrapped around the sonar dome. See ATTENUATION.
4128
quicksand. A loose mixture of SAND and water that yields to the pressure of heavy objects. Such objects are difficult
to extract once they begin sinking.
4129
quintant. A double-reflecting instrument for measuring angles. It is similar to a SEXTANT, but has an arc of 72°.
4130
Q-wave. See WAVE: LOVE.
190
R
4131
race. Swiftly flowing water in a narrow CHANNEL or RIVER; also the CHANNEL itself which may be artificial as in
a mill-race. Also a swift rush of water through a narrow CHANNEL in TIDAL WATERS and caused by the tidal
movement of the waters. See TIDE RACE.
4132
Racon. A RADAR BEACON which returns a coded SIGNAL which provides identification of the beacon as well as
RANGE and BEARING. The RANGE and BEARING are indicated by the location of the first character received on
the radar PPI scope. The name 'racon' is derived from the words radar beacon.
4133
radar. A method, system or technique of using beamed, reflected, and timed RADIO WAVES for detecting, locating,
or tracking objects, and for measuring ALTITUDES. The electronic equipment or apparatus used to generate, transmit,
receive, and usually, to display radio scanning or locating waves; a radar set. The name 'radar' is derived from the words
radio detecting and ranging.
4134
radar: primary. RADAR which transmits a SIGNAL and receives the incident energy reflected from an object to
detect the object in contrast to secondary radar which receives PULSES from a TRANSPONDER triggered by
PULSES transmitted from the RADAR.
4135
radar: secondary. See RADAR: PRIMARY.
4136
radar altimeter. See ALTIMETER: RADIO.
4137
radar beacon. A TRANSPONDER BEACON transmitting a coded SIGNAL on radar frequency, permitting an interrogating craft to determine the BEARING and RANGE of the TRANSPONDER. Also called RACON. See RAMARK.
4138
radar bearing. See BEARING.
4139
radar buoy. See BUOY.
4140
radar chain. An arrangement of radar sets in a chain usually used for vessel traffic control.
4141
radar chart. See CHART.
4142
radar conspicuous object. An object which returns a strong radar echo.
4143
radar dome. A dome shaped structure used to protect the antenna of a radar installation.
4144
radar surveillance station. A radar station established for traffic surveillance.
4145
radargrammetry. The process of obtaining reliable measurements in bi- and three-dimensional image processing by
means of RADAR.
4146
radar guided tracks. Recommended TRACKS along which ships can be guided by coastal radar stations in the event
of bad VISIBILITY.
4147
radar reflector. A device capable of or intended for reflecting radar signals.
4148
radar-responder. See RADAR BEACON.
4149
radarsonde. Equipment used for determining high-level WINDS, by means of RADAR aimed at a TARGET carried by
a free balloon.
4150
radar target. An object which reflects a sufficient amount of a radar signal to produce an echo signal on the radar
screen.
4151
radar view. A depiction (photographic reproduction or drawing) of appearance of LANDMARKS on the PPI scope of
a radar set at a particular geographic location, intended to facilitate the identification of the COAST. This can aid the
navigator to identify or match his own radar image of these same LANDMARKS.
191
4152
radial. A straight line extending outward from a centre.
In PHOTOGRAMMETRY, a line or direction from the RADIAL CENTRE to any point on a PHOTOGRAPH. The
RADIAL CENTRE is assumed to be the PRINCIPAL POINT, unless otherwise designated (e.g., NADIR RADIAL).
See also ISORADIAL.
4153
radial: nadir. A RADIAL from the nadir point. See NADIR: PHOTOGRAPH.
4154
radial centre. In PHOTOGRAMMETRY, the selected point on a PHOTOGRAPH from which RADIALS (directions)
to various IMAGE POINTS are drawn or measured (i.e., the origin of RADIALS). The radial centre is either the
PRINCIPAL POINT, the nadir point, the ISOCENTRE, or a SUBSTITUTE CENTRE.
4155
radial distortion. See under DISTORTION.
4156
radial plot. See RADIAL TRIANGULATION.
4157
radial triangulation. The aerotriangulation procedure, either graphical or analytical, in which directions from the
RADIAL CENTRE, or approximate RADIAL CENTRE, of each overlapping PHOTOGRAPH are used for horizontalcontrol extension by the successive INTERSECTION and RESECTION of these direction lines. A radial triangulation
also is correctly called a radial plot or a minor-control plot. If made by analytical methods, it is called an analytical
radial triangulation. A radial triangulation is assumed to be graphical unless prefixed by the word analytical.
4158
radian. The unit of plane angles in the SI SYSTEM.
4159
radiant energy. See ENERGY.
4160
radiant flux. See FLUX.
4161
radiation. Emission or transfer of energy in the form of ELECTROMAGNETIC WAVES or particles.
The energy itself is also termed RADIANT ENERGY.
4162
radiation fog. A major type of FOG, produced over a land area when radiational cooling reduces the air temperature to
or below its DEW POINT.
4163
radio. Communication by ELECTROMAGNETIC WAVES, without a connecting wire.
A RADIO RECEIVER.
Sometimes called wireless particularly in British terminology.
4164
radio aids. An aid to navigation transmitting information by radio waves.
4165
radio acoustic ranging. Determining distance by a combination of RADIO and SOUND, the RADIO being used to
determine the instant of transmission or reception of the SOUND, and distance being determined by the TIME of transit
of SOUND, usually in water. Also called radio acoustic sound ranging. See DISTANCE FINDING STATION, ECHO
RANGING, SONOBUOY.
4166
radio acoustic sound ranging. See RADIO ACOUSTIC RANGING.
4167
radio altimeter. See ALTIMETER.
4168
radiobeacon. A RADIO TRANSMITTER which emits a distinctive or characteristic SIGNAL used for the determination of BEARINGS, COURSES or location. One intended to mark a specific location is called MARKER
BEACON.
4169
radiobeacon buoy. See BUOY.
4170
radio bearing. See BEARING.
4171
radiocommunications. Any TELECOMMUNICATION by means of RADIO WAVES.
4172
radio compass. See RADIO DIRECTION FINDER.
4173
radio direction finder. Radio receiving equipment which determines the direction of arrival of a SIGNAL by
measuring the ORIENTATION of the WAVE FRONT or of the magnetic or electric vector. Radio direction finders may
be either manual or automatic. Also called direction finder. Formerly called radio compass.
192
4174
radio direction finding (or finder) station. A RADIO STATION intended to determine only the direction of other
stations by means of transmission from the latter.
4175
radio fog signal. See FOG SIGNAL.
4176
radio frequency. See FREQUENCY.
4177
radio horizon. The line at which direct RAYS from a transmitting ANTENNA become tangent to the EARTH's
surface. Its distance from the transmitting ANTENNA is greater than that of the visible HORIZON, and increases with
decreasing FREQUENCY.
4178
radiolocation. Determination of POSITION or of a LINE OF POSITION by means of radio equipment. See
NAVIGATION: ELECTRONIC.
4179
radio mast. A tower, pole, or other structure for elevating an ANTENNA.
4180
radiometer. An instrument for measuring the intensity of RADIANT ENERGY.
4181
radio navigation. See NAVIGATION: ELECTRONIC.
4182
radio navigational warning. A radio-transmitted message affecting the safe NAVIGATION of vessels or aircraft.
4183
radio range. A radio facility the emissions of which are intended to provide a definite course guidance.
4184
radio range station. A radio navigation land station in the aeronautical radio navigation service providing radio
EQUISIGNAL ZONES. In certain instances a radio range station may be placed aboard a ship.
4185
radio receiver. Equipment for receiving radio signals and converting them into usable form.
4186
radio signals: list of. See LIST OF RADIO SIGNALS.
4187
radiosonde. Instrument carried through the ATMOSPHERE, equipped with devices permitting one or several meteorological elements (pressure, temperature, humidity, etc.) to be determined, and provided with a RADIO
TRANSMITTER for sending this information.
4188
radio sonobuoy. See SONOBUOY.
4189
radio spectrum. The RANGE of electromagnetic RADIATIONS useful for communication by RADIO (approximately
10 kilohertz to 300,000 MEGAHERTZ).
4190
radio stars. Sources of RADIO WAVES existing in the universe. The position of many of the radio stars have been
plotted but their SIGNALS are generally very weak.
4191
radio station. A place equipped to transmit RADIO WAVES. Such a station may be either stationary or mobile, and
may also be provided with a RADIO RECEIVER. In British terminology, also called w/t station.
4192
radiotheodolite. Electronic THEODOLITE designed to give the direction in space of a RADIO TRANSMITTER
carried by a free balloon.
4193
radio time signal. A TIME SIGNAL sent by RADIO.
4194
radio transmitter. Equipment for generating radio signals.
4195
radio wave(s). See WAVE.
4196
radius: cruising. See CRUISING RADIUS.
4197
radius of visibility. See under VISIBILITY.
4198
radius vector. A straight line connecting a fixed REFERENCE POINT or centre with a second point, which may be
moving. In ASTRONOMY, the expression is usually used to refer to the straight line connecting a CELESTIAL BODY
with another which revolves around it, as a radius vector of the EARTH and MOON. See COORDINATES: PLANE
POLAR and COORDINATES: POLAR.
193
4199
radome. A dome, usually of glass reinforced plastic, housing a radar aerial. These domes are often prominent. The term
is also used for domes or pods housing similar equipment in ships or on aircraft.
4200
rafted ice. Type of PRESSURE ICE formed by one FLOE overriding another.
4201
rafting. Pressure process whereby one piece of ICE overrides another. Most common in NEW and YOUNG ICE.
4202
rain. PRECIPITATION of liquid water particles in the form of drops of more than 0.5 mm diameter or of smaller widely scattered drops.
4203
rainbow. Groups of concentric arcs with colours ranging from violet to red, produced on a "screen" of water drops (raindrops, droplets of DRIZZLE or FOG) in the ATMOSPHERE by LIGHT from the SUN or MOON.
4204
rainfall amount. Thickness of the layer of water which accumulates on a horizontal surface, as the result of one or
more falls of PRECIPITATION, in the absence of infiltration or evaporation, and if any part of the precipitation falling
as SNOW or ICE were melted. Also called amount of precipitation.
4205
rain gauge. See GAUGE.
4206
raise the land (v.t.). To sight LAND by approaching to the point where it appears above the HORIZON.
4207
ram. The underwater projection of ICE from an ICE FRONT, ICE WALL, ICEBERG, or FLOE.
4208
Ramark. A radar marker beacon which continuously transmits a SIGNAL appearing as a radial line on the PPI, the line
indicating the DIRECTION of the BEACON. Ramarks are intended primarily for marine use. The name 'ramark' is
derived from the words radar marker.
4209
ramp. A sloping structure that can either be used, as a landing place, at variable water levels, for small vessels, landing
ships, or a ferry boat, or for hauling a cradle carrying a vessel.
An accumulation of SNOW that forms an inclined plane between land or land ice elements and SEA ICE or ICE
SHELF. Also called drift ice foot.
4210
random error. See ERROR: ACCIDENTAL.
4211
range. Two or more objects in line. Such objects are said to be in range. An observer having them in range is said to be
on the range. See also TRANSIT.
Distance in a single direction or along a GREAT CIRCLE.
The extreme distance at which an object or LIGHT can be seen, or a SIGNAL detected or used.
The distance a craft can travel without refuelling, usually called CRUISING RADIUS.
The difference in extreme values of a variable quantity.
4212
range: cruising. See CRUISING RADIUS.
4213
range: diurnal. The difference in HEIGHT between MEAN HIGHER HIGH WATER and MEAN LOWER LOW
WATER. Also called great diurnal range.
4214
range: geographic(al). The greatest distance at which a LIGHT can be seen as a function of the curvature of the
EARTH and the HEIGHTS of the light source and the observer.
4215
range: great tropic. The difference in HEIGHT between TROPIC HIGHER HIGH WATER and TROPIC LOWER
LOW WATER.
4216
range: luminous. The greatest distance at which a LIGHT can be seen merely as a function of its LUMINOUS INTENSITY, the METEOROLOGICAL VISIBILITY, and the sensitivity of the observer's eye.
4217
range: magnetic. A RANGE oriented in a given magnetic direction and used to assist in determination of the deviation
of a MAGNETIC COMPASS. See DEVIATION: MAGNETIC.
4218
range: nominal. The LUMINOUS RANGE of a LIGHT in a homogenous ATMOSPHERE in which the
METEOROLOGICAL VISIBILITY is 10 SEA MILES.
4219
range: small diurnal. The difference in HEIGHT between mean LOWER HIGH WATER and mean HIGHER LOW
WATER.
194
4220
range: small tropic. The difference in HEIGHT between TROPIC LOWER HIGH WATER and TROPIC HIGHER
LOW WATER.
4221
range finder. An optical instrument for measuring the distance to an object.
4222
range height indicator. A SCOPE which simultaneously indicates RANGE and HEIGHT of a RADAR TARGET.
4223
range light(s). See LIGHT.
4224
range of mountains. See MOUNTAIN RANGE.
4225
range of tide. The difference in HEIGHT between consecutive HIGH and LOW TIDES at a place. Also called tidal (or
tide) range.
4226
range of visibility. The extreme distance at which an object or LIGHT can be seen. See RANGE: GEOGRAPHICAL,
and RANGE: LUMINOUS.
4227
range rod. A simple SURVEYOR's rod, fitted with a sharp-pointed steel shoe. It is usually painted red and white
alternately, and used to line up points of a SURVEY.
4228
rapid(s). Portions of a STREAM with accelerated CURRENT where it descends rapidly but without a break in the
SLOPE of the BED sufficient to form a waterfall. Usually used in the plural.
4229
raster data presentation. Method of digitally representing data of an image by a matrix-like scheme of PIXELs.
4230
rate. In ELECTRONIC NAVIGATION, the designation of PULSE REPETITION RATE for a pair of transmitting stations, their SIGNALS, and the resulting LINES OF POSITION.
4231
rate station. See DRIFT STATION.
4232
rational horizon. See HORIZON: CELESTIAL.
4233
ratio of ranges. The ratio of the HEIGHT OF TIDE at the SUBORDINATE STATION to the HEIGHT OF TIDE at
the REFERENCE STATION.
4234
ratio of rise. The ratio of the HEIGHT OF TIDE at two places.
4235
ratio print. See PRINT.
4236
ravine. In general, any steep-sided VALLEY.
4237
ray. A BEAM of RADIANT ENERGY of infinitesimal cross-section, such as a LIGHT RAY.
4238
Rayleigh criterion. Used in tidal analysis. Only those harmonic constituents which are separated by at least a complete
period from their neighbouring constituents over the length of data available should be included in the harmonic analysis
of a given time series.
4239
reach. A straight section of a RIVER, especially a navigable RIVER between two bends. See also SEA REACH.
An ARM OF THE SEA extending into the LAND.
4240
real image. See IMAGE.
4241
rear light. See LIGHT(S): RANGE.
4242
rear nodal point. See NODAL POINT.
4243
receiver. One who or that which receives anything, particularly a RADIO RECEIVER.
4244
recession of a shoreline. Landward movement of the SHORELINE. Also called retrogression of a beach.
4245
reciprocal bearing. See BEARING.
4246
reciprocal levelling. See LEVELLING.
4247
reckoning. In NAVIGATION, computation by which the POSITION of a ship is found. See DEAD RECKONING.
195
4248
recommended course. See TRACK: RECOMMENDED.
4249
recommended route. See ROUTE: RECOMMENDED.
4250
recommended track. See TRACK: RECOMMENDED.
4251
reconnaissance. In SURVEYING, a general examination or SURVEY of the main features, or certain specific features,
of a region, usually as a preliminary to a more detailed SURVEY.
An examination of an area to gain specific information, as the weather conditions, extent and nature of ICE, etc.
4252
reconnaissance map. See MAP.
4253
reconnaissance survey. See SURVEY.
4254
recorder. The man on a survey party who records the observational DATA.
A recording instrument.
The part of an instrument or machine that records.
4255
recording anemometer. See ANEMOGRAPH.
4256
recording barometer. See BAROMETER.
4257
recoverable station. See STATION.
4258
recovery of station. In SURVEYING, the identifying and checking of an original STATION. This is considered as
recovered when its MARK (MONUMENT) is identified as authentic and proved to be occupying its original site.
4259
rectangular coordinates. See COORDINATES.
4260
rectification. The process of projecting a tilted or OBLIQUE PHOTOGRAPH onto an horizontal reference plane, the
angular relationship between the PHOTOGRAPH and the plane being determined by ground methods.
4261
rectified altitude. See ALTITUDE: APPARENT.
4262
rectilinear current. See CURRENT: REVERSING.
4263
rectilinear stream. See CURRENT: REVERSING.
4264
rectoblique plotter. A mechanical device intended for RECTIFICATION of individual RAYS on tilted or OBLIQUE
PHOTOGRAPHS.
4265
recurrence rate. See REPETITION RATE.
4266
red mud. See MUD.
4267
red sector. A sector of the CIRCLE OF VISIBILITY of a navigational LIGHT in which a red light is exhibited. Such
sectors are designated by their limiting BEARINGS, as observed at some point other than the LIGHT. Red sectors are
often located so that they warn of danger to vessels.
4268
red tide. A red or reddish-brown discoloration of surface waters, most frequently in coastal regions, caused by
concentration of certain microscopic organisms, particularly dinoflagellates. Toxins produced by the dinoflagellates can
cause mass kills of fishes and other marine animals.
4269
reduced latitude. See LATITUDE: PARAMETRIC.
4270
reduction. The process of substituting for an observed value one derived therefrom.
4271
reduction of soundings. The CORRECTION of the observed DEPTHS, for the HEIGHT OF TIDE above or below the
plane of reference at the TIME of SOUNDING. Usually the term reduction of soundings does not cover CORRECTIONS other than those due to TIDE. See CORRECTION OF SOUNDINGS, LEAD LINE CORRECTION and TIDE
REDUCER.
4272
reduction of tides. The processing of observed tidal data to obtain mean values of TIDAL CONSTANTS.
196
4273
reduction to centre. The amount which must be applied to a DIRECTION observed at an ECCENTRIC STATION, or
to an ECCENTRIC SIGNAL, to reduce such DIRECTION to what it would be if there were no such ECCENTRICITY.
4274
reduction to sea level. A reduction applied to a measured horizontal length on the EARTH's surface to reduce it to the
surface of the SEA LEVEL DATUM.
4275
reduction to the meridian. The process of applying a CORRECTION to an ALTITUDE observed when a body is near
the CELESTIAL MERIDIAN of the observer, to find the ALTITUDE at MERIDIAN TRANSIT. See ALTITUDE: EXMERIDIAN.
4276
reed horn. A HORN that produces SOUND by means of a steel reed vibrated by air under pressure.
4277
reef. A mass of rock or coral which either reaches close to the sea surface or is exposed at low tide, posing a hazard to
NAVIGATION.
4278
reef flat. A flat expanse of dead reef rock which is partly or entirely dry at LOW TIDE.
4279
reference direction. A DIRECTION used as a basis for comparison of other DIRECTIONS.
4280
reference ellipsoid. See REFERENCE SPHEROID.
4281
reference level. See DATUM: CHART and DATUM: VERTICAL CONTROL.
4282
reference line. Any line which can serve as a reference or base for the measurement of other quantities. Also called
datum line.
4283
reference mark. In SURVEYING, a supplementary MARK of permanent character close to a STATION or to a BASE
TERMINAL, to which it is related by an accurately measured distance and DIRECTION, and/or a difference in
ELEVATION.
4284
reference object. A well-defined object selected as a starting point in the DIRECTION METHOD OF
OBSERVATION.
4285
reference plane. See DATUM: CHART, and DATUM: VERTICAL CONTROL.
4286
reference point. Any point which can serve as a reference or base for the measurement of other quantities. Also called
datum point.
4287
reference spheroid (or ellipsoid). A theoretical figure whose dimensions closely approach the dimensions of the
GEOID. The exact dimensions are determined by various considerations of the section of the EARTH's surface
considered. The SPHEROIDS of Bessel, Clarke, Delambre, Everest, Hayford, Helbert and others have been adopted as
reference spheroids in geodetic work by different countries. Also called spheroid of reference, or ellipsoid of reference.
See also SPHEROID: OBLATE.
4288
reference station. See STATION.
4289
reference tape. A BASE TAPE employed solely for use as a STANDARD of comparison. Also called standard tape.
4290
reflectance. The ratio of light given off by an object to the amount of light striking the object, expressed as percentage.
4291
reflected wave. See WAVE.
4292
reflecting projector. See PROJECTOR.
4293
reflecting telescope. See TELESCOPE.
4294
reflection. The process whereby a surface of discontinuity turns back a portion of the incident RADIATION into the
medium through which the RADIATION approached. See SURFACE REFLECTION.
4295
reflection: angle of. See ANGLE OF REFLECTION.
4296
reflectivity. The ratio of the RADIANT ENERGY reflected by a surface to that incident upon it.
197
4297
reflector. A device capable of or intended for reflecting particles or RADIANT ENERGY. See RADAR REFLECTOR.
4298
refracted wave. See WAVE.
4299
refracting telescope. See TELESCOPE.
4300
refraction. The process in which the direction of energy propagation is changed as the result of a change in density
within the propagating medium, or as the energy passes through the INTERFACE representing a density discontinuity
between two media.
4301
refraction: angle. See ANGLE OF REFRACTION.
4302
refraction: astronomical. The apparent displacement of an object that results from LIGHT RAYS from a source
outside the ATMOSPHERE being bent in passing the ATMOSPHERE. This results in all objects appearing to be higher
above the HORIZON than they actually are.
4303
refraction: atmospheric. Refraction resulting when a ray of radiant energy passes obliquely through the atmosphere. It
may be called astronomical refraction if the ray enters the atmosphere from outer space, or terrestrial refraction if it
emanates from a point on or near the surface of the EARTH.
4304
refraction: coastal. A small change in the direction of travel of a RADIO WAVE when it crosses a SHORELINE
obliquely due to a difference in conducting and reflecting properties between land and water, and thus velocity.
4305
refraction: coefficient of. The ratio of the ANGLE OF REFRACTION at the point of observation to the angle at the
centre of the EARTH subtended by the arc connecting the point of observation and the observed point.
4306
refraction: index of. The ratio of the sine of the ANGLE OF INCIDENCE to the sine of the ANGLE OF
REFRACTION.
4307
refraction correction. A CORRECTION due to REFRACTION, particularly such a CORRECTION to a SEXTANT
ALTITUDE,due to ATMOSPHERIC REFRACTION.
4308
refraction of light. The bending of LIGHT RAYS in passing from one transparent medium into another which has a
different INDEX OF REFRACTION.
4309
refraction of water waves. The process by which the direction of a WAVE moving in SHALLOW WATER at an
angle to the contours is changed. That part of the WAVE advancing in shallower water moves more slowly than the
other part still advancing in deeper water, causing the WAVE CREST to bend toward alignment with the underwater
contours. Also called wave refraction.
The bending of WAVE CRESTS by CURRENTS.
4310
refuge. A place of safety for a vessel in danger.
4311
regime. In CLIMATOLOGY, term used to characterize the seasonal distribution of one or more elements at a given
place.
4312
registration. Correct positioning of one component of a composite map image in relation to the other components.
Achieved, for example, by punching sets of holes, having a fixed horizontal relationship to each other, in each
component sheet and then attaching the components together using specially designed fasteners. See also PUNCH
REGISTER SYSTEM.
4313
region A,B. Within the IALA Maritime Buoyage System there are two international buoyage regions, designated as
Region A and Region B, where lateral marks differ only in the colours of port and starboard hand marks.
4314
regression of the nodes. Precessional motion of a set of NODES. The expression is used principally with respect to the
MOON, the NODES of which make a complete westerly REVOLUTION in approximately 18.6 years.
4315
regular error. See ERROR: SYSTEMATIC.
4316
relative accuracy. See ACCURACY: RELATIVE.
4317
relative aperture. See APERTURE: RELATIVE.
4318
relative bearing. See BEARING.
198
4319
relative humidity. The ratio of the actual vapor pressure to the vapor pressure corresponding to saturation at the
prevailing temperature.
4320
relative motion. Motion of one object or body relative to another. The expression is usually used in connection with
problems involving motion of one craft, torpedo, or missile relative to another, the direction of such motion being called
direction of relative movement, and the SPEED of such motion being called speed of relative movement or relative
speed. Usually called apparent motion when applied to the change of position of a CELESTIAL BODY as observed
from the EARTH. Also called relative movement.
4321
relative orientation. See ORIENTATION.
4322
relative position. See POSITION.
4323
relative speed. See RELATIVE MOVEMENT.
4324
relative tilt. See TILT.
4325
relative wind. For a moving object, WIND VECTOR relative to this object. Also called apparent wind. See
TRUE WIND.
4326
release. A device for holding or releasing a mechanism, particularly the device by which the TANGENT SCREW of a
SEXTANT or surveying instrument is held in place or disengaged from the LIMB, or CIRCLE respectively. In
oceanography acoustic releases are used to sever deployed instruments from their anchoring.
4327
relief. The ELEVATIONS or the inequalities, collectively, of a land surface; represented on a MAP or CHART by
CONTOURS, HYPSOMETRIC TINTS, SHADING, SPOT ELEVATIONS, HACHURES, etc.
4328
relief: submarine. Inequalities of the ocean bed, or their representation on a CHART.
4329
relief displacement. DISPLACEMENT of IMAGES radially inward or outward with respect to the PHOTOGRAPH
NADIR, according as the ground objects are, respectively, below or above the ELEVATION of the GROUND NADIR.
4330
relief map. See MAP.
4331
relief model. A scaled representation in three dimensions of a section of the CRUST of the EARTH, or of another
HEAVENLY BODY. A relief model primarily designed to display features on the surface of the EARTH is sometimes
known as a topographic model.
4332
remanence. See MAGNETIC RETENTIVITY.
4333
remote sensing. The measurement or acquisition of information of some property of an object or phenomenon by a
recording device that is not in physical or infinite contact with the object or phenomenon under study. Sometimes
restricted to the practice of data collection in the wavelengths from ultraviolet to radio regions.
4334
remotely operated vehicle (ROV). An unmanned submersible craft which can be used either for observation purposes
or to perform hydrographic surveys, or for working purposes. Also called "remotely controlled vehicle (RCV)".
4335
repeatability. See REPEATABLE ACCURACY.
4336
repeatable accuracy. In a navigation system, the measure of the accuracy with which the system permits the user to
return to a position as defined only in terms of the coordinates peculiar to that system. For example, the distance
specified for the repeatable accuracy of the system such as LORAN-C is the distance between two LORAN-C positions
established using the same stations and time-difference readings at different times. The correlation between the
geographical coordinates and the system coordinates may or may not be known.
4337
repeater. A device for repeating at a distance the indications of an instrument or device. See COMPASS REPEATER,
GYRO REPEATER, STEERING REPEATER.
4338
repeating instrument. See THEODOLITE: REPEATING.
4339
repeating theodolite. See THEODOLITE.
199
4340
repetition method of observation. A method of observing horizontal angles by which the OBSERVATIONS of each
angle are completed separately. See THEODOLITE: REPEATING.
4341
repetition rate. The rate at which recurrent SIGNALS are transmitted. Also called recurrence rate.
4342
reported danger. An object dangerous to NAVIGATION which is shown on a CHART but the existence of which has
not been confirmed. Sometimes called VIGIA.
4343
representative fraction. See SCALE: NATURAL.
4344
reprint (of a chart) (U.S. terminology). An issue of a CHART the supply of which is approaching exhaustion. The
reprint is an exact duplicate of the current issue with no changes in printing or publication data.
4345
reproducible. An original drawing, photographic POSITIVE or NEGATIVE on stable base material to be used in the
process of REPRODUCTION.
4346
reproduction. In CARTOGRAPHY, the processes involved in printing copies from an original drawing. The principal
processes are PHOTOGRAPHY, LITHOGRAPHY (or ENGRAVING), and printing.
A printed copy of an original drawing, made by any of the processes of reproduction.
4347
repromat. Reproduction material, generally in the form of positive or negative copies on film or glass for each colour
plate, from which a map or chart may be reproduced without redrafting.
4348
reseau. A NETWORK.
In PHOTOGRAPHY, a glass plate on which is etched a NETWORK of fine lines. Sometimes used as a focal-plane
plate to provide a means of calibrating film DISTORTION.
4349
resection. The graphical or analytical determination of a POSITION as the intersection of at least three lines of known
relative direction to corresponding points of known POSITION.
In PHOTOGRAMMETRY, the determination of the position and/or attitude of a CAMERA, or the PHOTOGRAPH
taken with that CAMERA, with respect to the exterior coordinate system.
4350
resection station. See STATION.
4351
reservoir. A place where anything is collected and stored, generally in large quantity; especially a POND, LAKE or
BASIN, either natural or artificial, for the storage, regulation and control of water.
4352
residual. See ERROR: RESIDUAL.
4353
residual deviation. See DEVIATION.
4354
residual error. See ERROR.
4355
residual magnetism. See MAGNETISM.
4356
resolution. The separation by an optical system of parts of an object or of two or more objects close together. The
degree of ability to make such a separation, called RESOLVING POWER, is expressed as the minimum distance
between two objects that can be separated.
The degree of ability of a radar set to indicate separately the echoes of two targets in range and bearing.
4357
resolving power. A mathematical expression of DEFINITION in a RADAR or OPTICAL SYSTEM, usually stated as
the maximum number of lines per millimetre that can be seen as separate lines in the IMAGE.
4358
resonance. Re-enforcement or prolongation of any wave motion, such as SOUND, RADIO WAVES, etc., resulting
when the NATURAL FREQUENCY of the body or system in VIBRATION is equal to that of an impressed
VIBRATION.
In TIDES, the water movement resulting from the natural PERIOD of OSCILLATION of a body of water which
approximates the PERIOD of one of the TIDE-PRODUCING FORCES.
4359
resonant frequency. See FREQUENCY.
4360
resource exploration. The search for economic deposits of minerals, ore, gas, oil or coal.
4361
responder. A transmitter, fitted to a submersible or on the seabed, which can be triggered by a hardwired external
control signal to transmit an interrogation signal which is received by a TRANSDUCER or HYDROPHONE.
200
4362
responder beacon. See TRANSPONDER BEACON.
4363
response. For a device or system, the motion or other OUTPUT resulting from an excitation or stimulus under special
conditions.
4364
responsor. A RADIO RECEIVER which receives a reply from a TRANSPONDER and produces an OUTPUT suitable
for feeding to a display system. A responsor is usually combined in a single unit with an INTERROGATOR which
sends out the PULSE that triggers a TRANSPONDER, the combined unit being called an interrogator-responsor.
4365
restitution. The process of determining the true planimetric position of objects whose images appear on photographs.
Restitution corrects for distortion resulting from both tilt and relief displacement.
4366
restricted area. A specified area designated by appropriate authority and shown on CHARTS, within which
NAVIGATION is restricted in accordance with certain specified conditions.
4367
resurvey. A retracing on the GROUND of the lines of an earlier SURVEY, in which all points of the earlier SURVEY
that are recovered are held fixed and used as a control. If too few points of the earlier SURVEY are recovered to satisfy
the control requirements of the resurvey, a new survey may be made. A resurvey is related directly to an original
SURVEY although several resurveys may interpose between them.
4368
retardation. In ELECTRONIC NAVIGATION, the amount of delay in TIME or PHASE ANGLE introduced by the
resistivity of the GROUND over which the SIGNAL is passing.
In tide terminology, DAILY RETARDATION.
4369
retentivity: magnetic. See MAGNETIC RETENTIVITY.
4370
reticle (or reticule). A system of wires, hairs, threads, etched lines, or the like, placed normal to the AXIS of a
TELESCOPE at its principal FOCUS, by means of which the TELESCOPE is sighted on a STAR, SIGNAL, or
TARGET, or by means of which appropriate readings are made on some SCALE, such as a LEVELLING or STADIA
ROD. See also CROSS WIRES, GRATICULE, DIAPHRAGM.
In PHOTOGRAMMETRY, a mark such as a cross or system of lines lying in the image plane of a viewing
apparatus and used singly as a reference mark in certain types of monocular instruments or as one of a pair to form a
FLOATING MARK as in certain types of STEREOSCOPES.
4371
reticle ring. The ring across which the system of wires, hairs, threads, or the like of a RETICLE are streched; or the
ring which supports the glass DIAPHRAGM when the RETICLE is a system of lines etched on glass.
4372
retired line of position. A LINE OF POSITION which has been moved backward along the COURSE line to
correspond with a TIME previous to that at which the line was established. Called a transferred position line in British
terminology.
4373
retrogression of a beach. See RECESSION OF A SHORELINE.
4374
reverberation. Continuation of RADIANT ENERGY, particularly SOUND by multiple REFLECTION.
SOUND scattered towards the source, principally from the ocean surface (surface reverberation) or BOTTOM
(bottom reverberation), and from small scattering sources in the medium such as bubbles of air and suspended solid
matter (volume reverberation).
4375
reverse azimuth. See AZIMUTH: BACK.
4376
reversing current. See CURRENT.
4377
reversing thermometer. See THERMOMETER.
4378
reversing water bottle. See WATER BOTTLE.
4379
revetment. Facing of stone or other material, either permanent or temporary, placed along the edge of a stream to
stabilize the bank and to protect it from the erosive action of the stream.
4380
revolution. Motion of a CELESTIAL BODY in its ORBIT; circular motion about an AXIS usually external to the
body. The terms revolution and ROTATION are often used interchangeably but, with reference to the motions of a
CELESTIAL BODY, revolution refers to the motion in an ORBIT or about an AXIS external to the body, while
ROTATION refers to motion about an AXIS within the body. Thus, the EARTH revolves about the SUN annually and
rotates about its AXIS daily.
201
4381
revolver. See FIX: CIRCULAR.
4382
revolving light. See LIGHT: ROTATING.
4383
rho-teta system. Positioning system measuring the distance (rho) and direction (teta) from an existing control station to
a mobile or another point.
4384
rhumb. See RHUMB LINE.
4385
rhumb line. A line on the surface of the EARTH making the same oblique angle with all MERIDIANS; a
LOXODROME spiralling toward the POLES in a constant true direction. PARALLELS and MERIDIANS, which also
maintain constant true directions, may be considered special cases of the rhumb line. A rhumb line is a straight line on a
MERCATOR PROJECTION. Sometimes shortened to rhumb.
4386
rhumb line sailing. See SAILING.
4387
ria. A long narrow INLET, with DEPTH gradually diminishing inward; a CREEK. Any broad RIVER opening into the
OCEAN.
4388
ridge. a) A long, narrow ELEVATION with steep sides.
b) A long, narrow ELEVATION often separating ocean basins.
c) The major oceanic mountain systems of global extent.
d) Region of the ATMOSPHERE in which pressure is high relative to the surrounding region at the same level. It is
represented on a WEATHER CHART by a system of nearly parallel ISOBARS or CONTOURS, of approximately Ushape, which are concave towards an ANTICYCLONE.
See OCEANIC RIDGE? TROUGH? WEDGE and PRESSURE RIDGE.
4389
rift. A cleft, fissure or chasm in the EARTH. See MEDIAN VALLEY.
4390
rift valley. See MEDIAN VALLEY.
4391
rig. A temporary, mobile structure, either fixed or floating, used in the exploration stages of oil and gas fields.
4392
right ascension. ANGULAR DISTANCE east of the vernal EQUINOX; the arc of the CELESTIAL EQUATOR, or the
angle at the CELESTIAL POLE, between the HOUR CIRCLE of the vernal EQUINOX and the HOUR CIRCLE of a
point on the CELESTIAL SPHERE, measured eastward from the HOUR CIRCLE of the vernal EQUINOX through 24
hours.
4393
right bank. Of a RIVER, the BANK on the right-hand side as one proceeds downstream.
4394
right reading image. An IMAGE which may be read or observed normally whether in NEGATIVE or
POSITIVE form.
4395
rill mark. A small groove, furrow or CHANNEL made in MUD or SAND on a BEACH by tiny STREAMS following
an outflowing TIDE.
4396
rip current. See CURRENT.
4397
ripple. The ruffling of the surface of water, hence a little curling WAVE or UNDULATION.
A WAVE controlled to a significant degree by both surface tension and GRAVITY.
4398
ripple mark. Undulating surface features of various shapes produced in unconsolidated sediments by wave or current
action.
4399
rip-rap. See GROIN.
4400
rips. A turbulent agitation of water generally caused by the interaction of CURRENTS and WIND; in nearshore
regions, rips may also be caused by CURRENTS flowing swiftly over an irregular BOTTOM.
4401
rise. A long, broad ELEVATION that rises gently and generally smoothly from the SEA FLOOR.
4402
rise (v.i.). Of a CELESTIAL BODY, to cross the visible HORIZON while ascending. The opposite is SET.
4403
rise of tide. The HEIGHT of HIGH WATER above DATUM. Also called tidal rise.
202
4404
rising tide. See TIDE.
4405
river. A relatively large natural STREAM of water.
4406
river discharge. The rate of FLOW of water past a point in a STREAM, expressed as volume per unit time (usually
cubic feet per second).
4407
river harbour. A harbour which lies on the banks of a river.
4408
river mouth. The exit or point of discharge of a river into the sea, a lake, or another river.
4409
river roadstead. A ROADSTEAD which lies in a river.
4410
rivulet. A small RIVER.
4411
road(s). See ROADSTEAD.
4412
roadstead. An area near the SHORE, where vessels can anchor in safety; usually a shallow INDENTATION in the
COAST. Also called road or roads. See OPEN ROADSTEAD.
4413
roaring forties. An expression often used to denote that belt in the OCEANS, between 40 and 50 south LATITUDE,
where strong westerly WINDS prevail.
4414
Roberts radio current meter. An electro-mechanical CURRENT METER which measures current speed and
direction. This METER can be suspended below an anchored BUOY or ship which is equipped with a RADIO
TRANSMITTER that transmits the current measurements to a ship or shore based monitor station.
4415
rock. Any formation of natural origin that constitutes an integral part of the LITHOSPHERE. The natural occurring
material that forms the firm, hard, and solid masses of the ocean floor.
An isolated rocky formation or a single large STONE, usually one constituting a danger to NAVIGATION. See
ROCK AWASH, SUNKEN ROCKS, PINNACLE and ROCK WHICH COVERS AND UNCOVERS.
4416
rock awash. A ROCK awash at CHART DATUM.
4417
rock borer. A member of any of several families of bivalves that live in cavities they bore in soft ROCK, concrete and
other material.
4418
rocket. In hydrography or navigation, a pyrotechnic projectile used for signalling, or for life-saving purposes.
4419
rocket sounding. Determination of one or more upper-air meteorological elements by means of rocket-borne
instruments.
4420
rocket station. A LIFE SAVING STATION equipped with line-carrying rocket apparatus.
4421
rock flour. Finely ground rock particles, chiefly silt size, resulting from glacial ABRASION. A component of marine
DEPOSITS off glacial stream mouths.
4422
rockweed. One of a group of marine plants, principally of an order (Fucales) of the brown ALGAE, mostly multibranched and leathery, which grow attached to ROCKS in the INTERTIDAL ZONE by means of an organ called a
holdfast. Also called wrack or fucus.
4423
rock which covers and uncovers. A ROCK of small area (PINNACLE) that COVERS AND UNCOVERS at various
states of the TIDE.
4424
rocky area. An area with a rocky BOTTOM.
4425
rod. A unit of length equal to 5.5 YARDS or 16.5 FEET. Also called PERCH or POLE.
A STADIA or LEVELLING ROD. See also SOUNDING POLE.
4426
rod: levelling. See LEVELLING ROD.
4427
rod: range. See RANGE ROD.
4428
rod: sounding. See SOUNDING POLE.
o
203
o
4429
rodded points. Points where the ROD was actually held, as opposed to points sketched in between.
4430
rodman. A person using a surveying ROD.
4431
Roentgen rays. See X-RAYS.
4432
roll (or rolling). The oscillation of a ship about the longitudinal axis.
In PHOTOGRAMMETRY, a rotation of a CAMERA or a photograph-coordinate system about either the
photograph x axis or the exterior x axis.
4433
roller. An indefinite term, sometimes considered to denote one of a series of long-crested, large WAVES which roll in
upon a COAST, as after a STORM.
Large BREAKERS on exposed COASTS formed by SWELL coming from a great distance.
See COMBER.
4434
rollers: blind. See BLIND ROLLERS.
4435
roof prism. A type of prism in which the IMAGE is reverted by a roof, that is, two surfaces inclined at 90 to
each other.
4436
root mean square error. See ERROR: STANDARD.
4437
rose. Name given to a COMPASS CARD, or other DIAGRAM, having radiating lines.
4438
Rossby wave(s). Ignoring friction or depth changes; if a parcel of water with no initial relative vorticity (i.e. no rotation)
is moved northward, as f (the Coriolis parameter) increases the parcel will gain negative relative vorticity and will
circulate clockwise. The Coriolis force will be greater on the poleward side of the parcel than on the equatorward side
and hence the parcel will be subjected to a net southward restoring force. This force will push the parcel south of the
latitude of zero relative vorticity overshoots and the circulation becomes counterclockwise. Due to the Coriolis variation
the parcel will now experience a northward restoring force. Thus the variation of f provides a restoring force (in the
horizontal plane) allowing oscillation to occur just as the effect of gravity does (vertically) for surface or internal waves.
In reality Rossby waves are complicated by depth variations and frictional effects.
4439
rotary current. See CURRENT.
4440
rotary stream. See CURRENT: ROTARY.
4441
rotating light. See LIGHT.
4442
rotating loop radiobeacon. See ROTATING RADIOBEACON STATION.
4443
rotating prism. See DOVE PRISM.
4444
rotating radiobeacon station. A special type of RADIOBEACON station emitting a BEAM of WAVES to which a
uniform turning movement is given, the BEARING of the station being determined by means of an ordinary listening
RECEIVER and a STOP WATCH. Also referred to as rotating loop radiobeacon.
4445
rotation. Turning of a body about an AXIS within the body, as the daily rotation of the EARTH. See REVOLUTION.
4446
rotten ice. SEA ICE which has become honeycombed in the course of melting, and which is in an advanced state of
disintegration.
4447
roundabout. A TRAFFIC SEPARATION SCHEME in which traffic moves in a counter-clockwise direction around a
specified point or zone.
4448
route: recommended. A route of undefined width, for the convenience of ships in transit, which is often marked by
centreline buoys.
4449
route (or routeing) chart. See CHART.
4450
routeing. A complex of measures concerning routes followed by ships and aiming at reducing the risk of casualties
(TRAFFIC SEPARATION SCHEMES, DEEP-DRAUGHT ROUTES, areas to be avoided, etc.).
o
204
4451
routeing guide. A document designed to be used in conjunction with nautical charts and other nautical publications in
areas where complex routeing systems have been established by the IMO.
4452
routeing system. Any system of one or more routes or routeing measures aimed at reducing the risk of casualties; it
includes traffic separation schemes, two-way routes, recommended tracks, areas to be avoided, inshore traffic zones,
roundabouts, precautionary areas and deep-water routes.
4453
rubble. Fragments of hard SEA ICE, roughly spherical and up to 1,5 METRES (5 FEET) in diameter, resulting from
the disintegration of larger ice formations. When afloat, commonly called BRASH ICE.
Loose angular rock fragment.
4454
rubidium vapour magnetometer. See MAGNETOMETER.
4455
rudite (or rudyte). Rock or sediment DEPOSITS composed of grains larger than 2 millimetres.
4456
ruin. A ruin is a structure in a decayed or deteriorated condition resulting from neglect or disuse, or a damaged structure
in need of repair. A ruin is considered hazardous if it extends over or into navigable waters and thus represents a danger
to surface navigation.
4457
ruling. A mechanically produced series of equally-spaced parallel lines at a predetermined 'angle of ruling'. Used to
distinguish particular areas of a MAP by providing a paler shade of the full printing colour.
4458
run. A BROOK, or small CREEK.
The distance travelled by a craft during any given time interval, or since leaving a designated place.
Complete performance of one PROGRAMME on a COMPUTER.
4459
run a line of soundings (v.t.) To obtain SOUNDINGS along a LINE OF SOUNDING, for surveying purposes.
4460
runnel. The smallest of natural STREAMS; a BROOK or RUN.
A TROUGH or corrugation formed in the FORESHORE or in the BOTTOM, immediately offshore, formed by
WAVES or TIDAL CURRENTS.
4461
running fix. See FIX.
4462
running survey. See SURVEY.
4463
run of micrometer. See ERROR OF RUN.
4464
run-up. The rush of water up a structure on the breaking of a WAVE. The amount of run-up is the vertical HEIGHT
above STILL WATER LEVEL that the rush of water reaches. See UPRUSH.
4465
runway. A defined rectangular area, on a land aerodrome, prepared for the landing and take-off run of aircraft along its
length.
4466
runway light(s). See LIGHT.
205
S
4467
sac. An INDENTATION in the CONTOURS on a CHART showing SUBMARINE RELIEF which is analogous to a
GULF on the surface. The opposite term is SUBMARINE PENINSULA.
4468
saddle. A COL or PASS or any land-form recalling in shape a saddle.
A low part on a RIDGE or between SEAMOUNTS.
4469
safety aids. See AID TO NAVIGATION.
4470
safety fairway. An area within which permits are not granted for the erection of oil or gas related structures. The use of
a safety fairway is not usually mandatory, but is recommended.
4471
safety zone. The area around an offshore installation within which vessels are prohibited from entering without
permission. Special regulations protect installations within a safety zone and vessels of all nationalities are required to
respect the zone.
4472
safe water mark. In the IALA Maritime Buoyage System a safe water mark indicates that there is navigable water
around its position.
4473
sag correction (tape). See TAPE: SAG CORRECTION.
4474
sailing. A method of solving the various problems involving COURSE, distance, DIFFERENCE OF LATITUDE,
DIFFERENCE OF LONGITUDE and DEPARTURE. The various methods are collectively spoken of as 'the sailings'.
4475
sailing: composite. A modification of GREAT-CIRCLE SAILING used when it is desired to limit the highest
LATITUDE.
4476
sailing: great circle. Any SAILING when a GREAT CIRCLE TRACK is involved.
4477
sailing: Mercator. A mathematical solution of the plot as made on a MERCATOR CHART. It is similar to PLANE
SAILING, but uses MERIDIONAL DIFFERENCE and DIFFERENCE OF LONGITUDE in place of DIFFERENCE
OF LATITUDE and DEPARTURE, respectively.
4478
sailing: meridian. Following a TRUE COURSE of 0°or 180°; SAILING along a MERIDIAN.
4479
sailing: middle-latitude. A method of converting DEPARTURE into DIFFERENCE OF LONGITUDE, or vice versa,
when the true COURSE is not 90°or 270°, by assuming that such a COURSE is steered at the MIDDLE LATITUDE.
4480
sailing: parallel. A method of converting DEPARTURE into DIFFERENCE OF LONGITUDE, or vice versa, when
the true COURSE is 90°or 270°.
4481
sailing: plane. A SAILING in which the EARTH or a small part of it is considered a plane.
4482
sailing: rhumb line. Any SAILING when a RHUMB LINE is involved.
4483
sailing: spherical. Any of the SAILINGS which consider the spherical or spheroidal shape of the EARTH.
4484
sailing: traverse. A method of determining the equivalent COURSE and distance made good by a craft following a
TRACK consisting of a series of RHUMB LINES. The problem is customarily solved by the principles of PLANE
SAILING.
4485
sailing chart. See under CHART.
4486
sailing directions. Information published in book form describing COASTS, waters, CHANNELS, harbour facilities,
etc., for use by mariners.
4487
Saint Elmo's fire. Faintly luminous electrical discharge in the ATMOSPHERE: this discharge, more or less continuous
and of slight or moderate intensity, emanates from objects which present a high surface electric field, in particular from
points and sharp edges.
4488
Saint Hilaire method. See MARCQ ST. HILAIRE METHOD.
206
4489
salina. A SALT MARSH or salt POND separated from the SEA but flooded by HIGH TIDES.
4490
salinity. A measure of the quantity of dissolved salts in SEA WATER. It is normally defined as the total amount of
dissolved solids in SEA WATER in parts per thousand (‰ ) by WEIGHT when all the carbonate has been converted to
oxide, the bromide and iodide to chloride, and all organic matter is completely oxidized.
These qualifications result from the chemical difficulty in drying the salts in SEA WATER. In practice, salinity is
not determined directly but is computed from CHLORINITY, electrical conductivity, refractive index, or some other
property whose relationship to salinity is well established.
Because of the Law of Constancy of Proportions, the amount of CHLORINITY in a sea water sample is used to
establish the sample's salinity.
The relationship between chlorinity Cl and salinity S as set forth in Knudsen's Tables is S = 0.03 + 1.805 Cl.
A joint committee of IAPO, UNESCO, ICES, and SCOR proposed the universal adoption of the following equation
for determining salinity from CHLORINITY: S = 1.80655 Cl. It was adopted by IAPO in 1963 and ICES in 1964.
4491
salinometer. Any device or instrument for determining SALINITY, especially one based on electrical conductivity
methods.
4492
sallying ship. Producing rolling motion of a vessel by the running in unison of a group from side to side. This is usually
done to help float a vessel which is aground or to assist it to make HEADWAY when it is BESET by ICE.
4493
salt marsh. Flat, poorly drained coastal SWAMPS which are flooded by most HIGH TIDES.
4494
salt pans. Shallow POOLS of brackish water used for the natural evaporation of SEA WATER to obtain salt.
4495
sample. A representative part or single item from a larger whole or group especially produced for inspection or to give
evidence of quality.
4496
sampling. The process of taking samples.
4497
sand. Loose material consisting of small but easily distinguishable, separate grains, between 0.0625 and 2.000
millimetres in diameter.
4498
sand dune. A RIDGE of SAND piled up by the action of WIND on sea coasts or in deserts.
4499
sanding. An irregular dot pattern used on some of the early HYDROGRAPHIC SURVEYS to accentuate the area
between the HIGH- and LOW-WATER LINES.
4500
sandwave. A large wavelike sediment feature in very shallow water and composed of sand. The wavelength may reach
100 meters; the amplitude is about 0.5 meter. Also called mega-ripple.
4501
sargasso (or sargassum). A certain type of SEAWEED, or more generally, a large floating mass of this SEAWEED.
4502
saros. The eclipse cycle of about 18 YEARS, almost the same length as 223 SYNODICAL MONTHS. At the end of
each saros the SUN, MOON, and LINE OF NODES return to approximately the same relative positions, and another
series of ECLIPSES begins, closely resembling the series just completed.
4503
satellite. A relatively small CELESTIAL BODY revolving around a PLANET.
Name sometimes given to the fictitious bodies assumed in the HARMONIC ANALYSIS OF TIDES.
4504
satellite: artificial. An object placed by man in ORBIT around the EARTH, or other CELESTIAL BODY. See
NAVIGATIONAL (or NAVIGATION) SATELLITE.
4505
satellite: navigational (or navigation). See NAVIGATIONAL (or NAVIGATION) SATELLITE.
4506
satellite boat. A subsidiary boat used in PARALLEL SOUNDING.
4507
satellite geodesy. See GEODESY.
4508
satellite navigation. A positioning method using satellites.
4509
satellite sounding. SOUNDING effected by means of instruments placed on board an ARTIFICIAL SATELLITE.
4510
satellite station. See ECCENTRIC STATION.
207
4511
saturation. The condition existing when the greatest possible amount of anything has been reached, as a magnetic
substance which cannot be further magnetized, or an electronic AID TO NAVIGATION which is being used by all the
craft it can handle.
At given temperature and pressure, state of moist air whose mixing ratio is such that the moist air can co-exist in
neutral EQUILIBRIUM with an associated condensed phase (liquid or solid) at the same temperature and pressure, the
surface of separation being plane.
4512
Savonius rotor current meter. A low-threshold current speed sensor composed of two cylindrical VANES disposed to
form an S-shaped rotor responsive to a wide SPECTRUM of horizontal flow components.
4513
scale. A series of marks or GRADUATIONS at definite intervals.
The ratio between the linear dimensions of a CHART, MAP, drawing, etc., and the actual dimensions represented. It
may be called chart scale or map scale when applied to a CHART or a MAP.
In PHOTOGRAMMETRY, the ratio of a distance on a PHOTOGRAPH to a corresponding distance on the ground.
The scale of a PHOTOGRAPH varies from point to point because of DISPLACEMENTS caused by TILT and
RELIEF; but it is usually taken as f/H where f is the PRINCIPAL DISTANCE of the CAMERA and H is the HEIGHT
of the CAMERA above mean ground elevation.
4514
scale: bar. A graduated line on a MAP, PLAN, PHOTOGRAPH, or MOSAIC, by means of which actual ground
distances may be determined. Also called graphic scale or linear scale.
4515
scale: border. A SCALE drawn along the BORDER OF CHART.
4516
scale: equivalent. The relationship which a small distance on a MAP, CHART or graphic bears to the corresponding
distance on the EARTH, expressed as an equivalence.
4517
scale: fractional. See SCALE: NATURAL.
4518
scale: graphic. See SCALE: BAR.
4519
scale: large. A SCALE involving a relatively small reduction in size. A large scale CHART is one covering a small
area. The opposite is SMALL SCALE. See SCALE: NATURAL.
4520
scale: latitude. The subdivided east and west borders of a MERCATOR CHART into DEGREES and MINUTES. A
variant of the BAR SCALE, since a MINUTE of LATITUDE is very nearly equal to a NAUTICAL MILE.
4521
scale: linear. See SCALE: BAR.
4522
scale: logarithmic. A SCALE graduated in the logarithms of uniformly-spaced consecutive numbers.
4523
scale: log factor. In HYDROGRAPHIC SURVEYS, a proportional DIAGRAM constructed for the SCALE of the
SURVEY sheet by means of which the LOG FACTOR can be quickly determined.
4524
scale: natural. The ratio between the linear dimensions of a CHART, drawing, etc., and the actual linear dimensions
represented, expressed as a proportion. Occasionally called representative fraction, fractional scale or numerical scale.
4525
scale: numerical. See SCALE: NATURAL.
4526
scale parallel. Used in mercator projection charts to indicate the parallel at which the noted scale of the chart is exact.
The scale parallel itself need not necessarily be depicted within the chart.
4527
scale: particular. The relation between an infinitesimal linear distance in any direction at any point on a map
PROJECTION and the corresponding linear distance on a GLOBE.
4528
scale: principal. The SCALE of a reduced or generating globe representing the sphere or SPHEROID defined by the
fractional relation of their respective radii.
4529
scale: small. A SCALE involving a relatively large reduction in size. A small scale chart is one covering a large area.
The opposite is LARGE SCALE. See SCALE: NATURAL.
4530
scale: speed. A graphic SCALE by means of which the rate of SPEED of a SURVEY SHIP, or the distance travelled in
a given time can be determined quickly and accurately.
208
4531
scale error. The difference between the PRINCIPAL SCALE and the PARTICULAR SCALE resulting from projection
DISTORTION.
4532
scale factor. A multiplier for reducing a distance obtained from a MAP by computation or scaling to the actual distance
on the DATUM of the MAP.
A conventional modification which may be applied to the majority of map PROJECTIONS. This is the multiplication of the PRINCIPAL SCALE by some numerical constant which is slightly less than unity. This has the effect of
changing all PARTICULAR SCALES by a corresponding amount and, since both maximum and minimum PARTICULAR SCALES are similarly modified, the special properties of the PROJECTION are unaffected. The effect is to
produce a better balance of positive and negative SCALE ERRORS over the mapped area.
4533
scale of hydrographic survey. That SCALE at which the POSITIONS of the SOUNDINGS in the area are plotted on
the HYDROGRAPHIC SURVEY SHEET. Suitable survey scales are selected in each case in accordance with the
nature of the SURVEY and the average DEPTHS prevailing in the area.
4534
scan. See SCOPE.
4535
scanner. A device for directing a BEAM of RADIANT ENERGY successively over all points of a given region.
In data processing a photo-electronic device for digital reproduction of pictures. The picture is scanned linewise and
decomposed into a matrix-like raster of individual pixels. In contrast to vectorial DIGITIZERS, the information to
coherent elements of the picture (lines, symbols) is lost by this rasterization process. To retrieve these elements the
rasterized picture has to be vectorized by pattern recognition methods and manual post-processing.
4536
scanning. Directing a BEAM of RADIANT ENERGY successively over all points of a given region.
4537
scar. A lofty, steep face of ROCK upon a mountain-side; a precipice; CLIFF.
4538
scarp. The steep face of a HILL.
See also ESCARPMENT.
4539
scattering. In physics, the change in direction of a particle or WAVE, because of a collision with another particle or
system.
In electromagnetism, diffusion of ELECTROMAGNETIC WAVES in a random manner by air masses in the upper
ATMOSPHERE. See also: TROPOSPHERIC SCATTERING.
4540
scend. Upward motion of a vessel, either upward motion of the bow and stern associated with pitching, or lifting of the
entire vessel by WAVES or SWELL, when it may be called send.
4541
schist. A foliated metamorphic ROCK which can be split into thin flakes or flat lenticles. Schists are usually named
from the dominant mineral, e.g. mica schist.
4542
school. See SHOAL.
4543
Scientific Committee on Antarctic Research (SCAR). A committee established by ICSU to promote and coordinate
antarctic research.
4544
scintillation. Rapid variations, often in the form of pulsations, of the brightness of the STARS or terrestrial light
sources.
4545
scope. The face of a CATHODE-RAY TUBE of electronic equipment. The various methods of presenting the
information on a radar scope are usually designated by letter, as A-scope, B-scope, etc. Also called INDICATOR, scan,
SCREEN, although the alphabetical designations are not generally used with SCREEN.
4546
scoria (pl. scoriae). Volcanic rock fragments usually of basic composition, characterized by marked vesicularity, dark
colour, high density, and a partly crystalline texture.
4547
scour. The action of a CURRENT or FLOW of water in clearing away MUD or other DEPOSIT; in civil engineering an
artificial CURRENT or FLOW produced for this purpose.
4548
scree. A mass of DETRITUS, forming a precipitous, strong SLOPE upon a mountain-side. Also the material composing
such a SLOPE. See also TALUS.
209
4549
screen. A device to shield or separate one part of an apparatus from other parts, or to separate the effects of one part on
others.
In electronic charting, a device connected to a COMPUTER displaying information either under computer control,
or under user control, e.g. on a CATHODE-RAY TUBE. Devices allowing for high resolution are capable of displaying
also graphics.
4550
scribing. A method of preparing a MAP by cutting the lines into a prepared coating.
4551
sea. The great body of salt water in general, as opposed to LAND; OCEAN.
One of the smaller divisions of the OCEANS.
The state of the surface of the OCEAN with regard to WAVE or SWELL, as a calm sea. See CROSS SEA, HEAD
SEA, BEAM SEA, FOLLOWING SEA, QUARTERING SEA, SUGAR LOAF SEA.
4552
seabed sampler. A device used to obtain samples of the SEA FLOOR.
4553
seabed texture chart. A tracing showing the nature and texture of the BOTTOM, DEPTH CONTOURS and SEABED
features including WRECKS and obstructions. Also called bottom texture tracing.
4554
seabed topography. See TOPOGRAPHY.
4555
sea bottom temperature. The temperature measured at or close to SEA FLOOR.
4556
seaboard. A general term for the rather extensive coastal region bordering the SEA.
4557
sea bed. See SEA FLOOR.
4558
sea (or lake) breeze. WIND of coastal regions, blowing by day from a large water surface (sea or lake) towards the
LAND as a result of diurnal heating of the land surface.
4559
sea bottom. See SEA FLOOR.
4560
sea bottom sediment chart. See CHART: SEA BOTTOM SEDIMENT.
4561
sea buoy. See FAREWELL BUOY.
4562
sea channel. See CHANNEL.
4563
sea floor. The BOTTOM of the OCEAN when there is a generally smooth gentle GRADIENT. Also referred to as sea
bed, sea bottom.
4564
sea fog. See FOG.
4565
seagrass. Any grasslike marine ALGA. Eelgrass is one of the best known seagrasses.
4566
sea ice. Any form of ICE which has originated from SEA WATER. Generally, any ICE in the SEA.
4567
sea level. The height of the sea surface uninfluenced by wind waves and swell, which is frequently measured relative to
a reference horizon. Observations of the sea level over a certain period are often evaluated to render minimum,
maximum, and mean sea level.
4568
sea level datum. A determination of MEAN SEA LEVEL that has been adopted as a standard DATUM of HEIGHTS
although it may differ from a later determination over a longer period of time.
4569
seamanship. A general term for the art by which vessels are handled.
4570
seamark. An AID TO NAVIGATION located with the express purpose of being visible from a distance to
SEAWARD. Often erected in shoal water rather than on LAND.
4571
sea mile. The length of one MINUTE of arc, measured along the MERIDIAN in the LATITUDE of the POSITION; its
length varies both with the LATITUDE and with the FIGURE OF THE EARTH in use.
Used in NAVIGATION to measure distances on sea charts using the MERCATOR PROJECTION. Not to be
confused with NAUTICAL MILE or INTERNATIONAL NAUTICAL MILE.
4572
sea moat. See MOAT.
210
4573
seamount (or peak). An isolated or comparatively isolated ELEVATION rising 1 000 METRES or more from the SEA
FLOOR and of limited extent across the SUMMIT.
4574
seamount chain. Several SEAMOUNTS in a line with bases separated by a relatively flat SEA FLOOR.
4575
seamount group. Several closely spaced SEAMOUNTS not in a line.
4576
seamount range. Several SEAMOUNTS having connected bases and aligned along a RIDGE or RISE.
4577
seaport. A PORT on or near the SEA and readily accessible to seagoing vessels.
4578
sea reach. The straight part of a RIVER between the last bend and the SEA.
4579
sea scarp. See ESCARPMENT.
4580
seashore. The SHORE of a SEA or OCEAN.
4581
seasonal current. See CURRENT.
4582
sea state. Numerical scale of the average surface WAVE HEIGHT as defined by the WMO code. Also called state of
the sea.
4583
sea valley. See VALLEY.
4584
sea wall. An EMBANKMENT or wall for protection against WAVES or tidal action along a SHORE or WATER
FRONT.
4585
seaward (adj. and adv.). Away from the LAND; toward the SEA.
4586
sea water. The water of the SEAS, distinguished from fresh water by its appreciable SALINITY. The degree of the
SALINITY greatly affects the water's physical characteristics.
4587
sea water: colour of. The apparent colour of the surface layers of the SEA caused by the REFLECTION of certain
components of the visible light spectrum coupled with the effects of dissolved material, concentration of PLANKTON,
DETRITUS, or other matter. Colour of oceanic water varies from deep blue to yellow and is expressed by number
values which are a variation of the FOREL SCALE. Plankton concentrations may cause a temporary appearance of red,
white, green, or other colours. Also called water colour. See also DISCOLOURED WATER.
4588
seaway. A moderately rough SEA. Used chiefly in the expression 'in a seaway'.
HEADWAY of a vessel.
The SEA as a route of travel from one place to another; a shipping LANE.
4589
seaweed. Any macroscopic marine ALGA or SEAGRASS.
4590
Secchi disc. A white, black, or varicoloured disc, 30 centimetres in diameter, used to measure water transparency
(clarity). The disc is lowered in the water and the DEPTH (in METRES) at which it disappears from sight is averaged
with the DEPTH at which it reappears. This average value is used to represent sea water transparency.
4591
second. The unit of TIME in the SI system.
A sixtieth part of a MINUTE, an angle or an arc.
4592
secondary port. See STATION: SUBORDINATE.
4593
secondary radar. See RADAR: PRIMARY.
4594
secondary station. See STATION: SUPPLEMENTARY.
4595
secondary tide(s). See TIDE.
4596
secondary tide station. See STATION: TIDE.
4597
second nodal point. See NODAL POINT.
4598
second order triangulation. See TRIANGULATION CLASSIFICATION.
211
4599
section. Process of locating and coordinating a point from at least two existing control stations by observing horizontal
directions from the control stations to the point. Also called intersection.
4600
sector scan sonar. A horizontal aperture SONAR used to detect obstructions ahead of the vessel by mechanical or
electronic scanning in the horizontal plane.
4601
secular change. An increase or decrease of intensity and/or change of direction of the total MAGNETIC FIELD over a
period of many years.
4602
sediment. Particulate organic and inorganic matter which accumulates in a loose unconsolidated form. It may be
chemically precipitated from solution, secreted by organisms, or transported by air, ICE, WIND, or water and deposited.
4603
sediment(s): bottom. In general all sedimentary material regardless of origin found on or in the submarine BOTTOM,
including ballast or other material dumped into the SEA by man. More specifically it is limited to unconsolidated
mineral and organic material forming the sea bottom, not including CORAL REEFS or BEDROCKS.
4604
sediment survey. A survey to determine the nature and distribution of types of sea bottom SEDIMENTS.
4605
sedimentary (adj.). Formed by the deposition of SEDIMENT.
4606
sedimentary rocks. ROCKS formed by the accumulation of SEDIMENT in water (aqueous DEPOSITS) or from air
(eolian DEPOSITS). The SEDIMENTS may consist of rock fragments or particles of various sizes (conglomerate,
sandstone, shale); of the remains or products of animals or plants (certain LIMESTONES and coal); of the product of
chemical action or of evaporation (salt, gypsum, etc.); or of mixture of these materials.
4607
sedimentation. The process of breakup and separation of particles from the parent ROCK, their transportation,
deposition, and consolidation into another ROCK.
4608
sediment core. See CORE.
4609
sedimentology. The science concerned with the description, classification, origin, and interpretation of sediments and
sedimentary rock.
4610
sediment trap. A device used to measure the rate and amount of SEDIMENTATION in a location.
4611
seiche. A STANDING WAVE oscillation of an enclosed or semi-enclosed water body that continues, pendulum
fashion, after the cessation of the originating force, which may have been either seismic, atmospheric, or wave induced.
4612
seismic reflection. The study of the shallower internal structure of the earth by generating acoustic waves and
registering their reflection from subsurface layers.
4613
seismic refraction. The study of the shallower internal structure of the earth by generating acoustic waves and
registering their return at increasing distances from the acoustic source, thus detecting waves that have been transmitted
along deeper layers of greater elasticity and rigidity .
4614
seismic sea wave. See TSUNAMI.
4615
seismograph. An instrument that records the direction, intensity and TIME of EARTHQUAKES.
4616
seismology. The science and study of EARTHQUAKES, and their causes and effects and related PHENOMENA.
4617
selectivity. The degree of decrease in the RESPONSE of a resonant device with departure from RESONANCE. Selectivity determines the ability of a RADIO RECEIVER to differentiate between SIGNALS of different carrier
FREQUENCY.
4618
selenotrope. A device used in geodetic SURVEYING for reflecting the MOON's RAYS to a distant point, to aid in
long-distance OBSERVATIONS.
4619
self-aligning level. See LEVELLING INSTRUMENT: SELF-ALIGNING LEVEL.
4620
semaphore. Any apparatus for signalling.
212
4621
semicircular deviation. See DEVIATION.
4622
semidiameter. Half the angle at the observer subtended by the visible disk of a CELESTIAL BODY. SEXTANT
ALTITUDES of the SUN and MOON should be corrected for semidiameter unless the centre is observed, as with a
BUBBLE SEXTANT.
4623
semidiameter correction. A CORRECTION due to SEMIDIAMETER, particularly that sextant altitude correction
resulting from OBSERVATION of the upper or lower LIMB of a CELESTIAL BODY, rather than the centre of
that body.
4624
semidiurnal current. See CURRENT.
4625
semidiurnal tide. See TIDE.
4626
semi-enclosed sea. See ENCLOSED SEA.
4627
semimajor axis. One-half of the longest diameter of an ellipse.
4628
semiminor axis. One-half of the shortest diameter of an ellipse.
4629
send. See SCEND.
4630
sensibility of magnetic compass. The ability of a magnetic compass card to align itself with the MAGNETIC
MERIDIAN after deflection.
4631
sensibility (or sensitivity) of spirit level. The ACCURACY and PRECISION which a SPIRIT LEVEL is capable of
producing. Sensibility depends on the radius of curvature of its longitudinal section; the longer the radius, the more
sensitive the level.
4632
sensible horizon. See HORIZON.
4633
sensitive bubble. See LEVEL: SPIRIT.
4634
sensitivity of electronic equipment. The ability of electronic equipment to amplify a SIGNAL, measured by the
minimum strength of signal INPUT capable of causing a desired value of OUTPUT. The lower the INPUT signal for a
given OUTPUT, the higher the sensitivity.
4635
sensitivity of spirit level. See SENSIBILITY OF SPIRIT LEVEL.
4636
separation effect. In ECHO SOUNDING instruments with separate transmitting and receiving units, the effect caused
by such separation. This introduces an ERROR depending on the distance between the acoustic units and varying with
the DEPTH of water. Such ERROR makes the registered DEPTH greater than the actual DEPTH. Separation also
causes a LAG in registration of the transmitted SIGNAL.
4637
separation line. See SEPARATION ZONE.
4638
separation zone (or line). A zone or line separating the traffic LANES in which ships are proceeding in opposite, or
nearly opposite directions; or separating a traffic lane from the adjacent sea area; or separating traffic lanes designated
for particular classes of ships proceeding in the same direction.
4639
sequence of current. The order of occurrence of the TIDAL CURRENT strengths of a day, with special reference to
whether the greater FLOOD immediately precedes or follows the greater EBB.
4640
sequence of tide. The order in which the TIDES of a day occur, with special reference to whether the HIGHER HIGH
WATER immediately precedes or follows the LOWER LOW WATER.
4641
serial temperatures. The OBSERVATIONS required to determine the vertical distribution of temperature and
SALINITY with DEPTH at any one place in the OCEAN.
4642
set. The direction toward which a CURRENT flows.
4643
set (v.i.). Of a CELESTIAL BODY, to cross the APPARENT HORIZON while descending. The opposite is RISE.
To establish, as to set a COURSE.
213
4644
set of observations. A set of two or more OBSERVATIONS at different settings of the apparatus made in order to
eliminate certain ERRORS which, for the apparatus concerned, are inherent in a single OBSERVATION.
4645
settlement. The general lowering in level of a moving vessel, relative to what its level would be were it motionless.
Settlement is due to the regional depression of the surface of the water in which the ship moves. It is not an increase in
displacement. Settlement is a factor to be reckoned in ECHO SOUNDING.
4646
sexagesimal. An angular division whereby a circle is divided in 360 equal parts called degrees. A degree is divided in
60 minutes and one minute in 60 seconds.
4647
sextant. A double-reflecting instrument for measuring angles, primarily ALTITUDES of CELESTIAL BODIES. The
sextant has an arc of 60°, a sixth of a circle, from which it derives its name, and a RANGE of 120°. In modern practice
the term also applies to a similar instrument, regardless of its RANGE. See also OCTANT, QUADRANT and
QUINTANT.
4648
sextant: air. A SEXTANT designed primarily for AIR NAVIGATION. Air sextants are generally provided with some
form of ARTIFICIAL HORIZON.
4649
sextant: bubble. A SEXTANT with a bubble or SPIRIT LEVEL to indicate the horizontal.
4650
sextant: gyro. A SEXTANT provided with a GYROSCOPE to indicate the horizontal.
4651
sextant: hydrographic. See SEXTANT: SOUNDING.
4652
sextant: marine. A SEXTANT designed primarily for MARINE NAVIGATION.
4653
sextant: pendulum. A SEXTANT provided with a PENDULUM to indicate the horizontal.
4654
sextant: sounding (British terminology). A simplified and more robustly constructed version of the marine sextant
intended primarily for use in HYDROGRAPHIC SURVEY. It has no SHADES, a wide angle low magnification
telescope and is generally graduated in MINUTES of arc. It may be fitted with either a VERNIER or a MICROMETER
reading device. Both mirrors are silvered all over to enable angles up to 180°to be measured. Some sounding sextants
have a 90°prism attachment which reflects the normal direct LINE OF SIGHT 90°to the left. Called surveying sextant,
or hydrographic sextant in U.S. terminology.
4655
sextant: surveying. See SEXTANT: SOUNDING.
4656
sextant adjustment. The process of checking the ACCURACY of a SEXTANT and removing or reducing its ERROR.
4657
sextant altitude. See under ALTITUDE.
4658
sextant altitude correction. Any of several CORRECTIONS applied to a SEXTANT ALTITUDE in the process of
converting it to TRUE ALTITUDE.
4659
sextant chart. See CIRCLE SHEET.
4660
sextant error. See ERROR.
4661
sextometer method. A substitute for PLANE TABLE TRAVERSE for short distances in unimportant areas where the
use of the PLANE TABLE is impracticable and the survey party operates in a LAUNCH. AZIMUTH is carried forward
by means of angles accurately measured with a SEXTANT. Distance is determined by measuring, also with the
SEXTANT, the small horizontal angle between fixed TARGETS on a special rod held horizontally. The angle may be
converted into a distance by means of a HYPSOGRAPH.
4662
shade. A coloured glass that can be moved into the LINE OF SIGHT of an optical instrument, such as a SEXTANT, to
reduce the intensity of light reaching the eye. Also called shade glass. See HORIZON SHADE, and INDEX SHADE.
4663
shaded relief. See ILLUMINATED RELIEF.
4664
shade glass. See SHADE.
4665
shading. Gradations of light, colour, or thickness of lines; or indications of shadows. Shading of lines is sometimes used
on CHARTS to produce the effect of HEIGHT or DEPTH. See also HILL SHADING.
214
4666
shadow pin. A small rod or pin used to cast a shadow on an instrument, such as a MAGNETIC COMPASS or SUN
COMPASS, to determine the direction of the luminary; a GNOMON.
4667
shadow zone. A region into which very little sound energy penetrates.
4668
shallow (adj.). Having little DEPTH.
4669
shallow (n.). An area composed of unconsolidated material where the DEPTH of water is relatively slight. It may be a
hazard to SURFACE NAVIGATION.
4670
shallows. An indefinite term applied to expanses of SHOAL or SHALLOW WATER.
4671
shallow water. Commonly, water of such a DEPTH that SURFACE WAVES are noticeably affected by bottom topography. It is customary to consider water of DEPTHS less than half the surface WAVE LENGTH as shallow water.
4672
shallow water constituent. A short-period harmonic term introduced into the formula of ASTRONOMICAL TIDE
constituents to take account of the change in the form of a TIDE WAVE resulting from SHALLOW WATER conditions. Shallow water constituents include OVERTIDES and COMPOUND TIDES. See HARMONIC CONSTITUENT.
4673
shallow water corrections. Quantities to be applied to a TIDE PREDICTION to correct for the QUARTER
DIURNAL TIDES.
4674
shallow water tide(s). See TIDE.
4675
shallow water wave. See WAVE: TRANSITIONAL WATER.
4676
shear strength. The internal resistance of a body to shear stress.
4677
shelf. Geologically an area adjacent to a continent or around an island and extending from the low-water line to the
depth at which there is usually a marked increase of slope towards greater depth. See also CONTINENTAL SHELF.
4678
shelf break. See SHELF EDGE.
4679
shelf edge (or shelf break). The line along which there is a marked increase of SLOPE at the outer margin of a
CONTINENTAL (or ISLAND) SHELF.
4680
shell. The hard outside covering of an animal. Part of the ocean bed is composed of numerous shells of marine animals.
4681
shelving. A gently sloping area.
4682
shimmer. Apparent fluttering of objects at the EARTH's surface, when they are viewed in an almost horizontal
direction above strongly heated surfaces.
4683
shingle. Rounded, often flat waterworn rock fragments larger than approximately 16 millimetres.
4684
ship of opportunity. An expression designating ships of commercial lines employed in gathering oceanographic
DATA.
4685
ship-to-shore triangulation. See TRIANGULATION.
4686
shipyard. A place where ships are built or repaired.
4687
shoal (adj.). SHALLOW.
4688
shoal (n.). An offshore hazard to NAVIGATION on which there is a DEPTH of ten FATHOMS or twenty METRES or
less, composed of unconsolidated material, except CORAL or ROCK. See REEF.
A great number of fish or aquatic animals swimming in company or considered as a group. Also called school.
4689
shoal (v.i.). To proceed from a greater to a lesser DEPTH.
To cause to become less deep.
215
4690
shoaling effect. The alteration of a WAVE proceeding from deep water to SHALLOW WATER.
4691
shoot (v.t.). To observe the ALTITUDE of (a CELESTIAL BODY).
4692
shore. The narrow strip of LAND in immediate contact with any body of water including the area between HIGH and
LOW WATER lines.
4693
shoreface. The narrow zone seaward from the low tide shoreline, permanently covered by water, over which the beach
sands and gravels actively oscillate with changing wave conditions.
4694
shore lead. A LEAD between PACK ICE and the SHORE, or between PACK ICE and a narrow fringe of FAST ICE.
4695
shoreline. The line where SHORE and water meet. Although the terminology of COASTS and SHORES is rather
confused, shoreline and coastline are generally used as synonymous.
4696
shoreline map. Shoreline maps are the graphic representation of planetable and photogrammetric surveys. The maps
contain graphic data relating to the shoreline, alongshore natural and man-made features, and a narrow zone of natural
and man-made features inland from the shoreline. The original sources of a shoreline map are ground survey data and
photographs. Utilizing these sources, photogrammetric map compilation techniques, and instruments, cartographers
generate shoreline maps, overlays, and associated data. The data are primarily generated to support nautical chart
maintenance, new nautical chart construction, and hydrographic survey operations.
4697
shore station. See FIXED STATION.
4698
short baseline acoustic system. An underwater acoustic position fixing system comprising a minimum of three
hydrophones on the hull of a surface vessel. Three ranges are measured to a beacon either mounted on the seabed or a
submersible to obtain a three-dimensional position fix.
4699
short range navigation. See NAVIGATION.
4700
short wave. See WAVE.
4701
shower. PRECIPITATION, often short-lived and heavy, falling from convective CLOUDS; the drops or solid particles
in showers are usually bigger than the corresponding elements in other types of PRECIPITATION. Showers are
characterized by their sudden beginning and ending, generally by large and rapid changes of intensity, and, most
frequently, by the appearance of the sky; namely, rapid alternations of dark, menacing CLOUDS (cumulonimbus) and
of CLEARANCES of short duration.
4702
shuga. An accumulation of spongy white ice lumps, a few centimetres across; the lumps are formed from grease ice or
slush and sometimes from anchor ice rising to the surface.
4703
shutter. In PHOTOGRAPHY, the mechanism of a CAMERA which controls the length of time the EMULSION is
exposed.
4704
shutter: between-the-lens. A SHUTTER located between the lens elements of a CAMERA; usually consisting of thin
metal leaves which open and close or revolve to make the EXPOSURE.
4705
shutter: focal-plane. A SHUTTER located near the FOCAL PLANE; usually consisting of a curtain with a slot which
is pulled across the FOCAL PLANE to make the EXPOSURE.
4706
shutter: louver. A SHUTTER consisting of a number of thin metal strips or louvers which operate like a venetian blind
to make the EXPOSURE; usually located just in front of or just behind the LENS.
4707
side echo(es). See ECHO(ES): FALSE.
4708
side lap. See OVERLAP.
4709
side-looking airborne radar (SLAR). A radar system using a stabilized antenna orientated at right angles to the
aircraft flight path.
4710
side scan sonar. A form of active sonar in which fixed acoustic beams are directed into the water perpendicularly to the
direction of travel to scan the bottom and generate a record of the bottom configuration.
216
4711
side scan sonar mosaic. An assembly of side scan sonar images whose edges have been cut or torn and matched to
form a continuous side scan sonar image.
4712
sidereal (adj.). Of or pertaining to the STARS.
4713
sidereal chronometer. See CHRONOMETER.
4714
sidereal day. See DAY.
4715
sidereal hour angle. See HOUR ANGLE.
4716
sidereal month. See MONTH.
4717
sidereal time. See TIME.
4718
sidereal year. See YEAR.
4719
side shot. A reading or measurement from a survey station to locate a point which is not intended to be used as a base
for the extension of the SURVEY. A side shot is usually made for the purpose of determining the POSITION of some
object which is to be shown on the MAP.
4720
siemens. The unit of conductance in the SI SYSTEM.
4721
sight. OBSERVATION of the ALTITUDE, and sometimes also the AZIMUTH of a CELESTIAL BODY for a LINE
OF POSITION, or the DATA obtained by such OBSERVATION.
Any of various devices used to aid the eyes in lining up an optical instrument on its OBJECTIVE.
4722
sight line. See COLLIMATION: LINE OF.
4723
sight (or sighting) vane. See VANE.
4724
sigma-t. (Symbol s t). A conveniently abbreviated value of the DENSITY of a sea water sample of TEMPERATURE t
and SALINITY S:
st = (rho(S,t)-1) * 103
where rho(S,t) is the value of the sea water density in CGS units at standard ATMOSPHERIC PRESSURE. If, for
example, rho(S,t) = 1.02648, then st = 26.48.
4725
signal. As applied to electronics, any transmitted electrical IMPULSE.
That which conveys intelligence in any form of communication, such as a TIME SIGNAL, a PIP on the SCOPE of
electronic equipment, or an object marking the location of a surveying STATION.
4726
signal: eccentric. See ECCENTRIC SIGNAL.
4727
signal: fog. See FOG SIGNAL.
4728
signal: hydrographic. Any object, existing or specially erected, for the CONTROL of HYDROGRAPHIC SURVEY.
See also SOUNDING MARK.
4729
signal: longitude. A sign indicating a time event, observable at different stations, and used in comparing LOCAL
TIMES of those stations, and determining the difference of their LONGITUDES.
4730
signal: luminous. In SURVEYING, a SIGNAL consisting of HELIOTROPE or HELIOSTAT by day, and
SELENOTROPE or SIGNAL LAMP by night.
4731
signal: sound. See SOUND SIGNAL.
4732
signal: survey. A natural or artificial object or structure whose horizontal and sometimes vertical POSITION is
obtained by surveying methods. Survey signals are given special designation according to the kind of SURVEY in
which they are determined, or which they may later serve.
4733
signal: tidal current. A SIGNAL or message conveying information on condition of TIDAL CURRENT in the area in
question.
4734
signal: tide. A SIGNAL or message conveying information on tidal conditions in the area in question.
217
4735
signal: time. An accurate SIGNAL marking a specified TIME or time interval. It is used primarily for determining
ERRORS of TIMEPIECES. Such SIGNALS are usually sent from an observatory by RADIO or telegraph, but visual
SIGNALS are used at some PORTS.
4736
signal: topographic. Any object, existing or specially erected, used for the CONTROL of TOPOGRAPHIC SURVEY.
4737
signal: triangulation. A rigid structure erected close or over a TRIANGULATION STATION. Also any object, natural
or artificial, whose POSITION is obtained in a triangulation survey. The term may be applied to a structure whose
POSITION is determined by TRIANGULATION, but whose primary purpose is to serve later in a HYDROGRAPHIC
or TOPOGRAPHIC SURVEY, when it may become known as a HYDROGRAPHIC or TOPOGRAPHIC SIGNAL.
4738
signal: tripod. A three-legged TRIANGULATION SIGNAL. It is usually constructed in such a manner that an observer can set up his THEODOLITE and make OBSERVATIONS without moving any of the structure.
4739
signal: water. A HYDROGRAPHIC SIGNAL erected in SHALLOW WATER.
4740
signal: weather. A visual SIGNAL displayed to indicate a WEATHER FORECAST.
4741
signal lamp. See LAMP.
4742
signal station. A place on SHORE from which SIGNALS are made to ships at sea.
4743
signi. Abbreviation for Signalisation de Navigation Intérieure. A system of buoyage used in certain inland waters in the
Netherlands.
4744
sill. The low part of the RIDGE or RISE separating ocean basins from one another or from the adjacent SEA FLOOR.
4745
sill depth. The greatest depth over a sill.
4746
silt. An unconsolidated SEDIMENT whose particles range in size from 0.0039 to 0.0625 millimetres in diameter
(between CLAY and SAND size).
4747
siltation. The deposition or accumulation of silt that is suspended in a body of water.
4748
simplex. A method in which TELECOMMUNICATION between two stations takes place in one direction at a time.
4749
simultaneous altitudes. ALTITUDES of two or more CELESTIAL BODIES observed at the same TIME.
4750
simultaneous comparison of depths. The comparison of echo sounding depths with simultaneous direct vertical
measurements of DEPTH. Simultaneous comparisons are periodically made to determine the INSTRUMENTAL
ERROR of ECHO SOUNDERS.
4751
single buoy mooring (SBM). A large mooring buoy used by tankers to load and unload in port approaches or in
offshore oil and gas fields.
4752
single day tide. See TIDE: DIURNAL.
4753
single point mooring (SPM). A mooring structure used by tankers to load and unload in port approaches or in offshore
oil and gas fields. The size of the structure can vary between a large mooring buoy and a manned floating structure.
4754
sinker. WEIGHT used to sink fishing line or SOUNDING LINE.
4755
sinking. A downward movement of surface water generally caused by converging CURRENTS or when water mass
becomes more dense than the surrounding water. See UPWELLING, and CONVERGENCE.
An apparent lowering of distant terrestrial objects by abnormal ATMOSPHERIC REFRACTION. Because of
sinking, objects normally visible at or near the HORIZON sometimes disappear below the HORIZON. The opposite is
LOOMING.
4756
siren. A type of FOG SIGNAL apparatus which produces SOUND by virtue of the passage of air through slots or holes
in a revolving disk.
218
4757
SI System. See SYSTÈME INTERNATIONAL.
4758
sketch map. See MAP.
4759
sketch survey. See SURVEY.
4760
skew convergence. The angle, on a SKEWED PROJECTION, between TRUE NORTH and skew north.
4761
skewed projection. See PROJECTION.
4762
sky compass. See COMPASS.
4763
sky wave. See WAVE.
4764
sky-wave correction. The CORRECTION to be applied to the time difference reading of received SKY WAVES to
convert it to an equivalent GROUND WAVE reading.
4765
slack tide. See SLACK WATER.
4766
slack water. The interval when the SPEED of the TIDAL CURRENT is very weak or zero; usually refers to the period
of reversal between EBB and FLOOD currents. Also called slack tide.
4767
slant distance. The straight-line distance from one point to another, as contrasted with GROUND DISTANCE. This
expression is customarily used only when the straight line connecting the two points lies above the surface of the
EARTH. Also called slant range.
4768
slant range. See SLANT DISTANCE.
4769
slave. A SLAVE STATION.
4770
slave station. In a radio navigation system, the transmitting station controlled or triggered by the SIGNAL received
from the MASTER STATION. Often shortened to slave.
4771
slide: dark. A thin PLATE (usually metal or fibre, rigid or flexible) which, after insertion in a camera magazine,
renders it light-tight.
4772
slide (or sliding) rule. A device used for performing rapid computations involving multiplication, division, proportion,
roots, and powers. It has a body like a ruler, but with a sliding section. Both body and sliding section are graduated with
numbers according to LOGARITHMIC SCALES.
4773
slime. Soft, fine, oozy MUD or other substance of similar consistency.
4774
slip. See DOCK.
4775
slipway. The prepared and usually reinforced inclined surface on which keel- and bilge-blocks are laid for supporting a
vessel under construction.
4776
slope. An inclined surface or line.
The degree of INCLINATION to the horizontal. Usually expressed as a ratio.
4777
slope and height factor. In the measurement of distances with Tellurometer, a factor to be reckoned when reducing
distances to the SPHEROID. It takes into account the mean HEIGHT of the stations (master and remote units) and the
SLOPE of the line.
4778
slope angle. The angle between a SLOPE and the horizontal.
4779
slope correction (tape). See TAPE: GRADE CORRECTION.
4780
slotted-template triangulation. In PHOTOGRAMMETRY, a graphical RADIAL TRIANGULATION using slotted
TEMPLATES.
4781
slough. A minor marshland or tidal WATERWAY which usually connects other tidal areas; often more or less
equivalent to a BAYOU.
Quagmire, SWAMP, miry place.
219
4782
sludge. Spongy whitish ice lumps, a few centimetres across; they consist of SLUSH, of snow slush and sometimes of
spongy ice lumps formed on the BOTTOM of the SEA and emerging on the surface.
4783
sluice. Sliding gate or other contrivance for changing the level of a body of water by controlling FLOW into or out of it.
4784
slush. An accumulation of ice crystals which remain separate or only slightly frozen together. It forms a thin layer and
gives the sea surface a greyish or leaden-tinted colour. With light WINDS no RIPPLES appear on the surface.
4785
small circle. See CIRCLE.
4786
small correction (British terminology). Minor corrections made to the chart plates. They have been discontinued since
1954.
4787
small craft chart. Chart designed for easy reference and plotting in limited spaces. It portrays regular nautical chart
detail and other specific details of special interest to the small craft operator, such as enlargements of harbours; tide,
current and weather information; rules of the road information; locations of marine facilities; anchorages; courses; and
distances.
4788
small diurnal range. See RANGE.
4789
small halo. See HALO.
4790
small scale. See SCALE.
4791
small tropic range. See RANGE.
4792
smoothing. Averaging of data in space or time, designed to compensate for random errors or fluctuations of a scale
smaller than that presumed significant to a specific problem.
4793
smooth sheet (U.S. terminology). See FAIR CHART.
4794
snag. A tree or branch embedded in a river or lake bottom and not visible on the surface, forming thereby a hazard to
boats.
4795
snapper. A bottom sampling device used to collect a small amount (less than 1 pint) of material from the ocean floor. It
has metal jaws that snap shut when the device touches the BOTTOM. Also called clamshell snapper.
4796
snapper: mud. A small clamshell SNAPPER which is attached to the bottom of SOUNDING LEAD by means of a
hole drilled in the LEAD.
4797
snow. PRECIPITATION of ice crystals, most of which are branched (sometimes starshaped).
4798
snowstorm. STORM of blowing SNOW.
4799
soft iron. Iron or steel which is easily magnetized by induction, but loses its MAGNETISM when the MAGNETIC
FIELD is removed. The opposite is HARD IRON.
4800
software. All programs which can be used on a computer system. In particular the system software (i.e. the
OPERATING SYSTEM) consists of all programs which are necessary for the proper functioning of the computer. The
application software consists of all programs developed for special user applications.
4801
soil. The EARTH or GROUND; the face or surface of the EARTH.
The GROUND with respect to its composition, quality, etc., or as the source of vegetation.
4802
solar apex. See APEX.
4803
solar cell. A cell using the solar light or other light energy for conversion into electric energy.
4804
solar day. See DAY.
4805
solar eclipse. See ECLIPSE.
4806
solar parallax. See PARALLAX.
220
4807
solar radiation. RADIATION emitted by the SUN.
4808
solar system. The SUN and other CELESTIAL BODIES within its gravitational influence, including PLANETS,
PLANETOIDS, SATELLITES, COMETS, and METEORS.
4809
solar tide. See TIDE.
4810
solar time. See TIME.
4811
solar year. See YEAR: TROPICAL.
4812
solenoid. A coil of wire, often helical in form, which becomes an electromagnet when an electric current is passed
through it.
4813
solid. Matter of stable shape, not liquid or fluid.
4814
solitary wave. See WAVE.
4815
solstice. One of the two points of the ECLIPTIC farthest from the CELESTIAL EQUATOR; one of the two points on
the CELESTIAL SPHERE occupied by the SUN at maximum north or south DECLINATION. That in the northern
hemisphere is called the summer solstice or first point of Cancer, and that in the southern hemisphere, the winter
solstice or first point of Capricorn. Also called solsticial point.
That instant at which the SUN reaches one of the solstices, about June 21 (summer solstice) or December 22 (winter
solstice).
4816
solsticial colure. See COLURE: SOLSTICIAL.
4817
solsticial point. See SOLSTICE.
4818
solsticial tide(s). See TIDE.
4819
sonar. A system of determining distance of an underwater object by measuring the interval of time between
transmission of an underwater sonic or ultrasonic SIGNAL and the return of its ECHO. Direction may also be
determined by noting the direction of transmission of the SIGNAL. The name sonar is derived from the words sound
navigation and ranging. See ECHO RANGING.
4820
sonargram. The analog echo record produced by the side scan sonar recording device on special chemically-treated
paper.
4821
sonar target. An object which reflects a sufficient amount of a sonar signal to produce a detectable echo signal at the
sonar equipment.
4822
sonic bearing. See BEARING.
4823
sonic depth finder. See ECHO SOUNDER.
4824
sonic frequency. See AUDIOFREQUENCY.
4825
sonic line of position. A LINE OF POSITION determined by means of SOUND WAVES. Also called acoustic line of
position.
4826
sonic navigation. See NAVIGATION.
4827
sonic wave. See WAVE: SOUND.
4828
sono-buoy. A BUOY with equipment for automatically transmitting a radio signal when triggered by an underwater
SOUND SIGNAL.
4829
sono-radio buoy. See SONOBUOY.
4830
sound. A relatively long ARM OF THE SEA forming a CHANNEL between an ISLAND and a MAINLAND or
connecting two larger bodies of water, as a SEA and the OCEAN, or two parts of the same body but usually wider and
more extensive than a STRAIT.
A vibratory disturbance in air or some other elastic medium, capable of being heard by the human ear, and thus of
any FREQUENCY between about 20 and 20,000 CYCLES PER SECOND.
221
4831
sound (v.i.). To measure the DEPTH of the water.
4832
sound buoy. See BUOY.
4833
sound channel. The region in the water column where SOUND VELOCITY first decreases to a minimum value with
DEPTH and then increases in value as a result of pressure. Above the minimum value SOUND RAYS are bent
downward, and below the minimum value SOUND RAYS are bent upward; the RAYS are thus trapped in this CHANNEL. SOUND travelling in a deep channel can be detected thousands of MILES from the sound source.
4834
sounder. A machine or apparatus for SOUNDING. An ECHO SOUNDER.
4835
sounder: echo. See ECHO SOUNDER.
4836
sounding. Measured or charted DEPTH of water, or the measurement of such a DEPTH.
In METEOROLOGY, determination of one or several upper-air meteorological elements by means of instruments
carried up by balloon, aircraft, kite, glider, ROCKET, SATELLITE, etc.
4837
sounding: acoustic. See ECHO SOUNDING.
4838
sounding: danger. A minimum SOUNDING chosen for a vessel of specific DRAFT in a given area to indicate the
limit of safe NAVIGATION.
4839
sounding(s): detached. Those SOUNDINGS, including least DEPTHS on SHOALS, whose POSITIONS were
accurately located. See POSITION: DETACHED.
4840
sounding: doubtful. A DEPTH shown on a CHART over a SHOAL, a ROCK, etc., that may be less than that
indicated.
4841
sounding: drift. A method of finding the least DEPTH in a shoal area by letting the boat drift along a series of closely
spaced, previously run parallel SOUNDING LINES, while the LEADSMAN sounds or 'feels' along the BOTTOM. The
operation is repeated until the SHOAL is found or the area is covered.
4842
sounding: echo. See ECHO SOUNDING.
4843
sounding: fixed angle. A method consisting in sounding along the arcs of circles subtended by two objects whose
POSITION is known. For each arc, an angle remains constant (fixed angle) and the second angle, between another pair
of objects, defines the POSITION of the vessel along the arc. By varying the fixed angle successively by equal amounts,
a series of LINES OF SOUNDING covering the area systematically can be run. See FIXED ANGLE PLOT.
4844
sounding: formation. SOUNDING carried out by two or more ships in formation searching for a reported danger.
4845
sounding: hand lead. SOUNDING with HAND LEAD. Hand lead soundings are usually taken from a slowly moving
vessel.
4846
sounding: line of. See LINE OF SOUNDING.
4847
sounding(s): minus (U.S. terminology). SOUNDINGS that reduce to HEIGHT above the SOUNDING DATUM (plane
of reference) when corrected for HEIGHT OF TIDE. Minus soundings are shown on the SMOOTH SHEET preceded
by a minus sign.
4848
sounding(s): no bottom (U.S. terminology). SOUNDINGS where the BOTTOM was not reached because the general
DEPTHS were too great for the method of measurement.
4849
sounding: wire. SOUNDING with a SOUNDING MACHINE. To obtain a vertical wire sounding the ship or boat must
be stopped while the wire is running out.
4850
sounding(s): zero (U.S. terminology). SOUNDINGS that reduce to HEIGHTS above the SOUNDING DATUM but
shown on the SMOOTH SHEET as zero soundings regardless of HEIGHT. A practice now discontinued. See
SOUNDING: MINUS.
4851
sounding apparatus. Any apparatus designed for use in measuring the DEPTH of water.
4852
sounding board. See FIELD BOARD.
222
4853
sounding book. See SOUNDING RECORD.
4854
sounding bottle. A strong metal container fitted with non-return valves for taking WATER SAMPLES at great
DEPTHS. See also WATER BOTTLE.
4855
sounding datum. See DATUM.
4856
sounding interval. The interval between successive SOUNDINGS along a LINE OF SOUNDING. See DENSITY OF
SOUNDINGS.
4857
sounding lead. A LEAD used for determining DEPTH of water. Also referred to as plummet.
4858
sounding line. A LINE OF SOUNDING.
A LEAD LINE.
4859
sounding machine. An instrument for measuring DEPTH of water, consisting essentially of a reel of wire to one end of
which is attached a WEIGHT which carries a device for recording the DEPTH. A crank or motor is provided for reeling
in the wire.
4860
sounding mark (British terminology). A MARK erected for CONTROL of SOUNDING; its POSITION is determined
by plotting using INTERSECTIONS from sextant FIXES.
4861
sounding pole. A graduated pole or rod used for SOUNDING in SHALLOW WATER. Also called sounding rod.
4862
sounding record. Bound record book in which all of the DATA taken on a HYDROGRAPHIC SURVEY are entered,
and become part of the permanent records of the SURVEY. Also called sounding book.
4863
sounding rod. See SOUNDING POLE.
4864
sounding selection. 1. Water depths numerically displayed on a CHART.
2. The process of choosing individual water depths from a hydrographic survey in the compilation of a chart.
4865
sounding tube. A glass tube of small diameter, used with certain types of SOUNDING MACHINES in determining
DEPTH.
4866
sounding wire. A wire used with a SOUNDING MACHINE in determining DEPTH.
4867
sound intensity. See INTENSITY.
4868
sound pressure. See PRESSURE.
4869
sound ray. A line perpendicular at each of its points to the fronts of a sound WAVE.
4870
sound signal. Any SOUND produced to convey intelligence, as a FOG SIGNAL.
4871
sound signal: submarine. A SOUND SIGNAL transmitted through water.
4872
sound velocity. The rate of motion at which sound energy moves through a medium.
The velocity of sound in SEA WATER is a function of temperature, SALINITY, and the changes in pressure
associated with changes in DEPTH. An increase in any of these factors tends to increase the VELOCITY.
4873
sound wave. See WAVE.
4874
source. The point where a RIVER rises.
4875
source diagram. A small scale map or index placed on a chart to indicate the coverage area, and textual description, of
the source data, used in construction of the chart. Also called compilation diagram.
4876
south celestial pole. See POLE: CELESTIAL.
4877
south geographical pole. See POLE: GEOGRAPHICAL.
4878
southing. The distance a craft makes good to the south. The opposite is NORTHING.
4879
south magnetic pole. See MAGNETIC POLE.
223
4880
space coordinates. See COORDINATES.
4881
space modulation. See MODULATION.
4882
spar buoy. A BUOY made of a tapered log or metal shaped like a tapered log, and secured so as to float in an
approximately vertical position.
4883
sparker. An ECHO SOUNDER which uses an electrical spark discharge as the sound source. A RECORDER produces
a CHART which represents a vertical cross section of the geological structure beneath the water bottom.
4884
spatial (adj.). Pertaining to or limited by space.
4885
special mark. In the IALA Maritime Buoyage System a special mark indicates an area or feature referred to in nautical
documents; it is not primarily intended to assist navigation.
4886
special purpose map. See MAP.
4887
specific gravity. The ratio of the density of a substance at a given temperature and the density of some other substance
used as a STANDARD. For liquids and solids, the STANDARD assumed is the density of distilled water at 4°C.
4888
spectroscope. An optical instrument for forming SPECTRA. It is very useful in studying the characteristics of
CELESTIAL BODIES.
4889
spectrum (pl. spectra). A series of IMAGES formed when a BEAM of RADIANT ENERGY is separated into its
various WAVE LENGTH components, as when a BEAM of white light is refracted and dispersed by a prism.
The entire RANGE of electromagnetic RADIATIONS, or any part of it used for a specific purpose, as the RADIO
SPECTRUM (10 kilohertz to 300,000 MEGAHERTZ).
4890
specular reflection. The type of reflection, in optics or microwave theory, characteristic of a highly polished plane
surface from which all rays are reflected at an angle equal to the angle of incidence.
4891
speed. Rate of motion. The terms speed and VELOCITY are often used interchangeably, but speed is a scalar, having
magnitude only, while VELOCITY is a vector quantity, having both magnitude and direction. Speed may either be the
ship's speed through water, or the SPEED MADE GOOD over ground.
4892
speed: angular. Change of direction per unit time. Also called angular rate or angular velocity.
4893
speed: ground. See GROUND SPEED.
4894
speed: linear. Rate of motion in a straight line.
4895
speed: relative. See RELATIVE MOTION.
4896
speed line. A LINE OF POSITION approximately perpendicular to the COURSE.
4897
speed made good. The actual velocity of the ship along a course measured in relation to the ocean bottom or to fixed
objects ashore.
4898
speed of lens. See APERTURE: RELATIVE.
4899
speed of propagation. The speed with which waves of energy travel through or along a medium other than a specially
constructed path.
4900
speed of relative movement. See RELATIVE MOTION.
4901
speed of sound. The SPEED OF PROPAGATION of sound waves .
4902
speedometer. An ODOMETER recording the SPEED of a craft by a process of differentiation.
4903
speed scale. See SCALE.
4904
sphere. A curved surface all points of which are equidistant from a fixed point within, called the centre.
4905
spherical aberration. See ABERRATION OF LIGHT.
224
4906
spherical buoy. See BUOY.
4907
spherical coordinates. See COORDINATES.
4908
spherical excess. The amount by which the sum of the three angles of a spherical triangle exceeds 180°.
4909
spherical sailing. See SAILING.
4910
spherical wave. See WAVE.
4911
spheroid. An ellipsoid; a figure resembling a sphere. Also called ellipsoid or ELLIPSOID OF REVOLUTION, from
the fact that it can be formed by revolving an ellipse about one of its axes. In GEODESY, this term is frequently used to
mean REFERENCE SPHEROID. See also SPHEROID: OBLATE and SPHEROID: PROLATE.
4912
spheroid: oblate. An ELLIPSOID OF REVOLUTION, the minor AXIS of which is the AXIS of REVOLUTION. The
EARTH is approximately an oblate spheroid.
4913
spheroid: prolate. An ELLIPSOID OF REVOLUTION, the major AXIS of which is the AXIS of REVOLUTION.
4914
spheroid of reference. See REFERENCE SPHEROID.
4915
spicule. A minute needlelike or multiradiate calcareous or siliceous body in sponges, radiolarians, primitive chitons, and
echinoderms. They frequently are identified in marine sediment samples.
4916
spilling breaker. See BREAKER.
4917
spindle. A spar serving as a BEACON.
A slender pin or rod, as one constituting part of a machine.
4918
spire. A pointed structure extending above a building. The spire is seldom less than two-thirds of the entire height and
its lines are rarely broken by stages or other features. The term is not applied to short pyramid-shaped structures rising
from a tower or belfry.
4919
spirit bubble. See LEVEL: SPIRIT.
4920
spirit compass. See COMPASS: LIQUID.
4921
spirit level. See LEVEL.
4922
spirit level axis. See AXIS OF SPIRIT LEVEL.
4923
spirit levelling. See LEVELLING.
4924
spit. A small point of land or narrow SHOAL projecting into a body of water from the SHORE.
4925
splines. Flexible rulers or interpolation algorithm used to draw smooth curves between points when constructing e.g.
hyperbolic lattices.
4926
split fix. See FIX.
4927
split line of sounding. A LINE OF SOUNDING run to fill a void when the maximum spacing of principal lines is
exceeded.
4928
spoil. MUD, SAND, SILT or other DEPOSIT obtained from the BOTTOM of a CHANNEL or HARBOUR by
dredging.
4929
spoil banks. Submerged accumulations of dumped material dredged from CHANNELS or HARBOURS.
4930
spoil ground. A sea area where dredged material is deposited. Also called dumping ground.
4931
spoil ground buoy. A BUOY marking the limit of a SPOIL GROUND.
4932
spot elevation. A point on a MAP or CHART whose ELEVATION is noted. It is usually indicated by a dot
accompanied by a number indicating the vertical distance of the point from the reference DATUM. Spot elevations are
used principally to indicate points higher than their surroundings. Also called spot height.
225
4933
spot height. See SPOT ELEVATION.
4934
spout. Phenomenon consisting of an often violent WHIRLWIND, revealed by the presence of a cloud column or
inverted cloud cone (funnel cloud), protruding from the base of a cumulonimbus and of a 'bush' composed of water
drops raised from the surface of the SEA or of DUST, SAND, or litter, raised from the GROUND.
4935
spray. Ensemble of water droplets torn by the WIND from the surface of an extensive body of water, generally from the
CRESTS of WAVES, and carried up a short distance into the air.
4936
spring. SPRING TIDE.
A natural issue of water or other substances from the EARTH. One on the BOTTOM of the SEA is called a submarine spring.
4937
spring high water. See MEAN HIGH WATER SPRINGS.
4938
spring low water. See MEAN LOW WATER SPRINGS.
4939
spring range. The mean semidiurnal RANGE OF TIDE when SPRING TIDES are occurring. The mean difference in
HEIGHT between MEAN HIGH WATER SPRINGS and MEAN LOW WATER SPRINGS. Also called mean spring
range.
4940
spring rise. See MEAN SPRING RISE.
4941
spring tide(s). See TIDE.
4942
spur. A subordinate ELEVATION, RIDGE or RISE projecting outward from a larger feature.
4943
squall. Atmospheric phenomenon characterized by a very large variation of wind speed: it begins suddenly, has a
duration of the order of minutes, and decreases rather suddenly in SPEED. It is often accompanied by a SHOWER or
THUNDERSTORM.
4944
squall line. Fictitious moving line, sometimes of considerable extent, along which squall phenomena occur.
4945
squares: method of. A method of transferring one SURVEY to another of different SCALE. Also called squaring
down or squaring up depending on whether the SCALE is being decreased or increased.
4946
squaring down. See SQUARES: METHOD OF.
4947
squaring up. See SQUARES: METHOD OF.
4948
squat. For a ship underway, the change of level of the bow and stern from the still water condition in response to the
elevation and depression of the water level about the hull resulting from the bow and stern wave systems.
4949
stability. Property of the state of rest or continuous movement of a system such that any disturbance introduced into this
state decreases. In METEOROLOGY, the term is often used as a synonym of STATIC STABILITY.
4950
stability: static. State of hydrostatic equilibrium of the ATMOSPHERE in which a particle of air moved from its initial
level undergoes a hydrostatic force which tends to restore it to this level. Also called hydrostatic stability.
4951
stabilization: gyroscopic. See GYROSCOPIC STABILIZATION.
4952
stabilizer: marine. A device installed on ships to reduce rolling.
4953
stadia. A graduated rod used in the determination of distance by observing the intercept on the rod subtending a small
known angle at the point of observation. In practice the angle is usually defined by two fixed lines in the RETICLE of a
TELESCOPE. Also called stadia rod.
4954
stadia constant. The constant which is multiplied by the STADIA INTERVAL to obtain the length of a sight in
METRES.
4955
stadia interval. The length of rod subtended between the top and the bottom CROSS WIRES in the LEVELLING
INSTRUMENT as seen projected against the face of the LEVELLING ROD.
4956
stadia lines. Two or more horizontal wires fixed in the DIAPHRAGM at equal distances from the AXIS of
TELESCOPES, of THEODOLITES and LEVELS. Also called stadia wires.
226
4957
stadia rod. See STADIA.
4958
stadia wires. See STADIA LINES.
4959
stadimeter. An instrument used to measure the distance from the observer to a more-or-less distant object, such as a
vessel, when the HEIGHT of a specified part of the latter (e.g. the mast) is known. It is in effect a hand-held RANGE
FINDER.
4960
stake. An elongated wood or metal pole embedded in the bottom to serve as a marker or support for fish nets.
4961
stand. See STAND OF TIDE.
4962
standard. An exact value (a physical entity or an abstract concept) established and defined by authority, custom, or
common consent, to serve as a reference, model, or rule in measuring quantities or qualities, establishing practices or
procedures, or evaluating results.
In chart construction, a master copy of a CHART upon which are marked all corrections affecting the CHART
between printings (U.S. terminology).
4963
standard atmosphere. See ATMOSPHERE.
4964
standard chronometer. See CHRONOMETER.
4965
standard circle sheet. See CIRCLE SHEET.
4966
standard compass. See COMPASS.
4967
standard depth. See DEPTH.
4968
standard deviation. See ERROR: STANDARD.
4969
standard error. See ERROR.
4970
standard meridian. See MERIDIAN.
4971
standard parallel. See PARALLEL.
4972
standard port. See STATION: REFERENCE.
4973
standard sea water. See NORMAL WATER.
4974
standard station. See STATION: REFERENCE.
4975
standard tape. See REFERENCE TAPE.
4976
standard time. See TIME.
4977
standardization. The comparison of an instrument or device with a STANDARD to determine the value of the
instrument or device in terms of an adopted unit. See CALIBRATION.
4978
standing wave. See WAVE.
4979
stand of tide. The condition at HIGH TIDE or LOW TIDE when there is no change in the HEIGHT of the water. It may
be called high water stand if it occurs at the TIME of HIGH TIDE, and low water stand if it occurs at LOW TIDE.
Also called stand.
4980
standpipe. A tall cylindrical structure in a waterworks system, whose height is several times greater than its diameter. It
extends from the ground and may be supported by a skeleton-type framework.
4981
star. CELESTIAL BODIES which appear as points of light due to their great distance from the EARTH. They are
self-luminous whereas PLANETS shine only by reflection light.
4982
starboard. The right side of a craft facing forward. The opposite is PORT.
4983
star chart. See CHART.
227
4984
star finder. A device to facilitate the identification of STARS. Sometimes called a star identifier. See PLANISPHERE.
4985
star globe. A small globe representing the CELESTIAL SPHERE, on which the apparent positions of the STARS are
indicated. It is usually provided with graduated arcs and a suitable mount for determining the approximate ALTITUDE
and AZIMUTH of the STARS, to serve as a STAR FINDER. Also called celestial globe.
4986
star identifier. See STAR FINDER.
4987
starred lines of sounding. LINES OF SOUNDING which are 'starred' round a ROCK or ISLET.
4988
state of sea scale. Numerical SCALE of average WAVE HEIGHT in which the numbers increase with the WAVE
HEIGHT.
4989
state of sky. State of the ATMOSPHERE in respect of the amount, genus, height, etc. of the CLOUDS which are
present.
4990
state of the sea. See SEA STATE.
4991
static instability. See INSTABILITY.
4992
static stability. See STABILITY.
4993
station. Generally, a permanent or temporary location where scientific OBSERVATIONS and measurements are made.
In SURVEYING, a point whose POSITION has been (or is to be) determined. A station may be a marked station
(i.e., a point more or less permanently marked for recovery) or an unmarked station, one which is not recoverable. Also
called survey station.
4994
station: astronomical. A point on the EARTH whose POSITION has been determined by OBSERVATIONS of
CELESTIAL BODIES.
4995
station: control. See CONTROL.
4996
station: eccentric. See ECCENTRIC STATION.
4997
station: electronic navigation. A STATION emitting radio signals which are used in electronic navigational systems.
4998
station: intersection. In SURVEYING, an object whose horizontal POSITION is determined by OBSERVATIONS
from other STATIONS, no OBSERVATIONS being made at the object itself. Where the object is observed from only
two stations, the position is termed a no check position as there is no proof that such OBSERVATIONS are free from
BLUNDERS. Intersection stations are either objects which would be difficult to OCCUPY with an instrument, or
SURVEY SIGNALS whose POSITIONS can be determined with sufficient ACCURACY without being occupied. Also
called intersected point.
4999
station: Laplace. A TRIANGULATION or TRAVERSE STATION at which a LAPLACE AZIMUTH is determined.
At a Laplace station both ASTRONOMICAL LONGITUDE and ASTRONOMICAL AZIMUTH are determined.
5000
station: 'lost'. See STATION: UNRECOVERABLE.
5001
station: magnetic. The geographic location at which any set of MAGNETIC OBSERVATIONS was taken.
5002
station: main scheme. A STATION through which the main computations and ADJUSTMENTS of the survey data are
carried and serve for the continued extension of the SURVEY.
5003
station: oceanographic. The geographic location at which any set of oceanographic observations are gathered. The
STATION may be occupied by a mobile PLATFORM (a ship) or a fixed platform such as a tower.
5004
station: recoverable. A STATION artificially marked by well defined natural or artificial objects, whose
GEOGRAPHIC POSITION has been accurately determined and which has been described.
228
5005
station: reference. A place where tide or tidal current constants have been determined from OBSERVATIONS, and
which is used as a STANDARD for the comparison of simultaneous OBSERVATIONS at a SUBORDINATE
STATION. It is also a place for which independent daily predictions are given in the tide or tidal current tables, from
which corresponding predictions are obtained for other locations by means of differences or factors. Also called
standard station and standard port (British terminology).
5006
station: resection. A STATION located by RESECTION methods.
5007
station: satellite. See ECCENTRIC STATION.
5008
station: secondary. See STATION: SUPPLEMENTARY.
5009
station: subordinate. One of the places for which tide or tidal current predictions are determined by applying a
CORRECTION to the predictions of a REFERENCE STATION.
A tide or tidal current station at which a short series of OBSERVATIONS was made and reduced by comparison
with simultaneous OBSERVATIONS at a REFERENCE STATION.
Called secondary port in British terminology. See STATION: TIDE.
5010
station: subsidiary. A STATION established to overcome some local obstacle to the progress of a SURVEY, and not
to determine position data for the station point.
5011
station: supplementary. An auxiliary STATION, established to increase the number of CONTROL STATIONS in a
given area, or to place a STATION in a desired location where it is impracticable or unnecessary to establish a principal
STATION. Also called secondary station.
5012
station: survey. See STATION.
5013
station: tide. A place where TIDAL OBSERVATIONS are obtained. It is a primary tide station when continuous
OBSERVATIONS are available for a sufficient number of years to determine the characteristic tide features for the
locality. A secondary tide station is operated during a short period of time to obtain DATA for a specific purpose.
5014
station: topographic. A definite point on the EARTH, whose GEOGRAPHIC POSITION has been determined by graphic methods, usually by PLANE TABLE TRAVERSE or graphic TRIANGULATION. Also a point located by geodetic methods but with less than third-order ACCURACY.
5015
station: traverse. A definite point on the EARTH whose POSITION has been determined from another known point by
linear measurements controlled in AZIMUTH by angular measurements.
5016
station: triangulation. A recoverable point on the EARTH, whose GEOGRAPHIC POSITION has been determined by
angular methods with geodetic instruments. A triangulation station is a selected point, which has been marked with a
STATION MARK, or it is a conspicuous natural or artificial object. Also called trigonometric station or triangulation
point.
5017
station: trigonometric. See STATION: TRIANGULATION.
5018
station: unrecoverable. A TRIANGULATION STATION that cannot be found and cannot be included in the
TRIANGULATION to connect it with a new DATUM. Sometimes called 'lost' station.
5019
stationary wave. See WAVE: STANDING.
5020
stationary wave theory. A theory which assumes that the basic tide motion in the open OCEAN consists of a system of
STANDING WAVE oscillations; PROGRESSIVE WAVES are of secondary importance except where the TIDE
advances into tributary waters.
5021
station buoy. A BUOY used to mark the approximate POSITION of an important BUOY or LIGHTSHIP should it be
carried away or temporarily removed. Also called MARKER BUOY, watch buoy.
5022
station error. See DEFLECTION OF THE VERTICAL.
5023
station mark (or marker). A buried mark-stone, a metal plug or disk, or any kind of permanent MARK intended to
provide a means of re-identifying main CONTROL STATIONS. See SURFACE MARK and
UNDERGROUND MARK.
229
5024
station pointer (British terminology). A metal instrument with three legs, a circle graduated in degrees and 1/2 degrees,
and a VERNIER or MICROMETER for setting the angles. See also PROTRACTOR: THREE ARM.
5025
statoscope. A highly sensitive BAROMETER or ALTIMETER for measuring slight variations in pressure or
ALTITUDE.
5026
statute mile. A unit of distance equal to 1,760 YARDS or 5,280 FEET (1,609.35 m). This MILE is generally used on
LAND, and is sometimes called land mile.
5027
steel tape. See TAPE.
5028
steep-to (adj.). Precipitous. The term is applied particularly to a SHORE, BANK or SHOAL that descends steeply to a
lower level.
5029
steerageway. The condition wherein the ship has sufficient way on that it will respond to rudder movements to maintain
desired COURSE.
5030
steering compass. See COMPASS.
5031
steering repeater. A COMPASS REPEATER by which a craft is steered. See also COMPASS: STEERING.
5032
stellar parallax. See PARALLAX: ANNUAL.
5033
stellite. A trade name for an alloy of chromium, cobalt and tungsten. Stellite mirrors, free of imperfection and
practically indestructible, are frequently used in hydrographic SEXTANTS.
See SEXTANT: SOUNDING.
5034
steradian. The unit of a solid angle in the SI system.
5035
stereocomparator. In PHOTOGRAMMETRY, a stereoscopic instrument for measuring PARALLAX; usually
includes a means of measuring PHOTOGRAPH COORDINATES of IMAGE POINTS.
5036
stereocompilation. See COMPILATION.
5037
stereogram. A STEREOSCOPIC PAIR of photographs or drawings correctly oriented and mounted or projected for
stereoscopic viewing.
5038
stereographic horizon projection. See PROJECTION: STEREOGRAPHIC.
5039
stereographic meridional projection. See PROJECTION: STEREOGRAPHIC.
5040
stereographic polar projection. See PROJECTION: STEREOGRAPHIC.
5041
stereographic projection. See PROJECTION.
5042
stereometer. A measuring device comprising a micrometer movement by means of which the separation of two INDEX
MARKS can be changed to measure PARALLAX DIFFERENCE on a STEREOSCOPIC PAIR of photographs. Also
called parallax bar.
5043
stereometric camera. See CAMERA.
5044
stereomodel. See STEREOSCOPIC IMAGE.
5045
stereopair. See STEREOSCOPIC PAIR.
5046
stereophotogrammetry. PHOTOGRAMMETRY utilizing stereoscopic equipment and methods.
5047
stereoscope. A binocular optical instrument for helping an observer to view PHOTOGRAPHS, or DIAGRAMS, to
obtain the mental impression of a three-dimensional model.
5048
stereoscopic fusion. The mental process which combines the two perspective views to give an impression of a threedimensional model.
5049
stereoscopic image. The mental impression of a three-dimensional model which results from viewing two overlapping
perspective views. Also called stereoscopic model or stereomodel.
230
5050
stereoscopic model. See STEREOSCOPIC IMAGE.
5051
stereoscopic pair. In PHOTOGRAMMETRY, two PHOTOGRAPHS of the same area taken from different AIR
STATIONS so as to afford STEREOSCOPIC VISION. Frequently called a stereopair.
5052
stereoscopic plotting instrument. An instrument for compiling a MAP or obtaining spatial solutions by observation of
STEREOSCOPIC IMAGES formed by STEREOSCOPIC PAIRS. See COMPILATION.
5053
stereoscopic vision. The particular application of BINOCULAR VISION which enables the observer to obtain the
impression of depth, usually by means of two different perspectives of an object, as two PHOTOGRAPHS taken from
different AIR STATIONS.
5054
stereoscopy. The science and art which deals with the use of BINOCULAR VISION for observation of a pair of
overlapping PHOTOGRAPHS or other perspective views, and with the methods by which such viewing is produced.
5055
stereotriangulation. A triangulation procedure that uses a STEREOSCOPIC PLOTTING INSTRUMENT to obtain the
successive ORIENTATION of the STEREOSCOPIC PAIRS of photographs into a continuous strip. The spatial solution for the extension of horizontal and/or vertical CONTROL using these STRIP COORDINATES may be obtained by
either graphical or computational procedures. Also called bridging.
5056
sternway. Making way through the water in a direction opposite to the HEADING.
5057
still water level. The LEVEL that the sea surface would assume in the absence of WIND WAVES; not to be confused
with MEAN SEA LEVEL or HALF-TIDE LEVEL.
5058
stippling. Graduation of SHADING by numerous separate touches. Shallow areas on CHARTS, for instance, are
sometimes indicated by numerous dots decreasing in density as the DEPTH increases.
5059
stone. A general term for ROCK and rock fragments ranging in size from PEBBLES and GRAVEL to BOULDERS or
large rock masses.
5060
stooping. Apparent decrease in the vertical dimension of an object near the HORIZON, due to large inequality of
ATMOSPHERIC REFRACTION in the LINE OF SIGHT to the top and bottom of the object. The opposite is TOWERING.
5061
stop. See APERTURE STOP.
5062
stop watch. See WATCH.
5063
storage. In a COMPUTER, a device in which DATA can be inserted and preserved, and from which DATA can be
retrieved. Common storage devices are magnetic tapes, drums, disks and cores.
5064
storm. WIND with a SPEED between 44 and 50 KNOTS (Beaufort scale wind force 10).
NOTE: The term 'storm' has been substituted for the term 'whole gale' in U.S. Weather Bureau Warnings. This term
refers to wind speeds of 48-63 KNOTS.
5065
storm high water. See HIGH WATER.
5066
storm surge. A RISE above normal water level on the OPEN COAST due only to the action of WIND stress on the
water surface. Storm surge resulting from a HURRICANE or other intense STORM also includes the RISE in level due
to ATMOSPHERIC PRESSURE reduction as well as that due to wind stress. A storm surge is more severe when it
occurs in conjunction with a HIGH TIDE. Also called storm tide, storm wave, tidal wave.
5067
storm tide. See STORM SURGE.
5068
storm warning. See WARNING.
5069
storm wave. See WAVE.
5070
straight-edge. A bar of wood, metal, etc. with one edge accurately straight for drawing straight lines in cartographic
applications.
5071
straight line. Mathematically the line of shortest distance between two points in a specified space or on a specified
surface.
231
5072
strait (also straits). A PASSAGE connecting two larger bodies of water.
5073
straits used for international navigation. Geographically, a narrow passage between two land masses or islands or
group of islands connecting two larger sea areas.
5074
strand. The portion of the SEASHORE between high and low water line.
5075
strand (v.t. & i.). To run aground. The term strand usually refers to a serious grounding, while the term GROUND
refers to any grounding, however slight.
5076
stranded. 1. The terms "stranded" and "sunken" apply exclusively to items that once were afloat but which are now
resting on the bottom. Stranded items project above the sounding datum while sunken items do not project above the
sounding datum. These terms apply most often to wrecks. Masts, funnels, and other extensions of wreck superstructure
should be disregarded when applying the above definition; i.e., such features may project above the sounding datum and
still have the wreck classified as sunken.
2. The grounding of a vessel so that it is not soon refloated; a serious grounding.
5077
strath. A broad elongated DEPRESSION with relatively steep walls located on a CONTINENTAL SHELF. The longitudinal profile of the floor is gently undulating with greatest DEPTHS often found in the inshore portion.
5078
stratification. The state of a fluid that consists of two or more horizontal layers arranged according to their density.
5079
stratocumulus. See CLOUD GENERA.
5080
stratopause. Top of the INVERSION LAYER in the upper STRATOSPHERE, at about 50-55 km.
5081
stratosphere. Region of the ATMOSPHERE, situated between the TROPOPAUSE and the STRATOPAUSE, in which
the temperature generally increases with HEIGHT.
From an imperfect analogy with the ATMOSPHERE, the term is sometimes applied in OCEANOGRAPHY to the
nearly uniform masses of cold, deep and bottom water of middle and low LATITUDES. This LAYER is separated from
the TROPOSPHERE by the THERMOCLINE.
5082
stratum (pl. strata). A single sedimentary bed or LAYER of generally homogenous ROCK, independent of thickness.
5083
stratus. See CLOUD GENERA.
5084
strays. In ECHO SOUNDING, false indications occasionally appearing on the DIAL or FATHOGRAM of an ECHO
SOUNDER. They may be caused by the motion of the vessel through the water, by acoustic or electric NOISES in the
ship, or by electric NOISES in the echo sounding equipment. Strays may be mistaken for the true echo or may be of
such a nature as to prevent the identification of the true echo.
5085
stream. Any RIVER, BROOK, RIVULET or course of running water.
A steady CURRENT in the SEA or in a RIVER, especially the middle or most rapid part of a TIDE or CURRENT.
A steady FLOW of a fluid, small solid particles, or RADIANT ENERGY.
5086
stream (v.t.). To place overboard and secure, as to stream a LOG, or stream a sea anchor.
5087
stream: ebb. See EBB STREAM.
5088
stream: flood. See FLOOD STREAM.
5089
stream: ingoing. See FLOOD STREAM.
5090
stream: outgoing. See EBB STREAM.
5091
stream: rectilinear. See CURRENT: REVERSING.
5092
stream: rotary. See CURRENT: ROTARY.
5093
stream: tidal. See CURRENT: TIDAL.
5094
stream current. See CURRENT.
232
5095
streamer. A string of hydrophones towed behind a ship.
5096
streamline. A LINE OF FLOW.
In METEOROLOGY, line envelope in space of the tangents to the instantaneous wind directions at a given time.
Also written as two words.
See also TRAJECTORY.
5097
streamline flow. See LAMINAR FLOW.
5098
strength of current. The PHASE of a TIDAL CURRENT at which the SPEED is a maximum; also the SPEED at this
time.
5099
strength of figure. In GEODESY, the comparative PRECISION of computed lengths in a TRIANGULATION NET as
determined by the size of the angles, the number of conditions to be satisfied, and the distribution of BASES and points
of fixed POSITION.
5100
striding level. See LEVEL.
5101
strip. In ice terminology, a long narrow area of PACK ICE, about 1 km or less in width, usually composed of small
fragments detached from the main mass of ICE, and run together under the influence of WIND, SWELL or CURRENT.
5102
strip coordinates. See COORDINATES.
5103
strip film (or stripping film). A film which has the emulsion coated on an extremely thin membrane which is in turn
supported on a normal-thickness film base. The emulsion and the membrane can be stripped (separated) from the base
after exposure and processing. The thin image so obtained can be mounted face down on a new support for lateral image
reversal or used for combining with, or inserting in, other image elements.
5104
stripes (of colour). Areas of contrasting colour separated from one another by straight lines, and used as distinguishing
characteristic for navigation marks. In British terminology horizontal stripes are denoted as bands.
5105
strong gale. Wind with a speed between 41 and 47 KNOTS (Beaufort scale wind force 9).
5106
structure. The term "structure" shall include, without limitation, any pier, wharf, dolphin, weir, boom, breakwater,
bulkhead, revetment, riprap, jetty, permanent mooring structure, power transmission line, permanently moored floating
vessel, piling, aid to navigation, or any other obstacle or obstruction.
5107
stylus. A pointer that is operated by placing it in a display space or a tablet.
5108
subastral point. See SUBSTELLAR POINT.
5109
sub-bottom profiler. A form of active, low frequency sonar in which acoustic beams penetrate the BOTTOM. A
recorder produces a chart which represents a cross section of the geological structure of the subbottom. See also: ECHO
SOUNDER.
5110
sub-celestial point. See SUB-POINT.
5111
sublunar point. The GEOGRAPHICAL POSITION of the MOON. That point on the surface of the EARTH at which
the MOON is in the ZENITH at a specified TIME. See SUB-POINT.
5112
submarine bell. A bell whose SIGNAL is transmitted through water.
5113
submarine cable. See CABLE.
5114
submarine canyon. See CANYON.
5115
submarine geology. See GEOLOGY.
5116
submarine navigation. See NAVIGATION.
5117
submarine oscillator. See OSCILLATOR.
5118
submarine peninsula. See PENINSULA.
233
5119
submarine pipeline. See PIPELINE.
5120
submarine relief. See RELIEF.
5121
submarine ridge. An elongated elevation of the sea floor, with either irregular or relatively smooth topography and
steep sides which constitutes a natural prolongation of land territory.
5122
submarine sentry. A form of underwater KITE towed at a predetermined constant DEPTH in search of ELEVATIONS
of the BOTTOM. The KITE rises to the surface upon encountering an OBSTRUCTION.
5123
submarine sound channel. A water layer with minimum sound velocity and high concentration of sound energy in
which sound waves are propagated without reflection from sea surface or bottom.
5124
submarine sound signal. See SOUND SIGNAL.
5125
submarine spring. See SPRING.
5126
submarine valley. See VALLEY.
5127
submarine volcano. A seabed volcano, submerged at the chart sounding datum, which may or may not be active.
5128
submerged (adj.). Under water; not showing above water. The opposite is UNCOVERED.
5129
submerged rock. A rock covered at the chart sounding datum and considered to be potentially dangerous to navigation.
5130
subordinate station. See STATION.
5131
subpermanent magnetism. See MAGNETISM: PERMANENT.
5132
subplan. An INSET on a SURVEY SHEET used to extend the survey coverage shown on the sheet, or to show small
congested areas at enlarged SCALES.
5133
sub-point. That point on the surface of the EARTH at which a particular CELESTIAL BODY is in the ZENITH at a
specified TIME. Also called 'geographical position of a celestial body'. Called sub-celestial point in Canadian
terminology. See SUBLUNAR POINT, SUBSOLAR POINT, SUBSTELLAR POINT.
5134
sub-sea completion. See WELL: PRODUCTION.
5135
subsidiary station. See STATION.
5136
subsoil. All naturally occurring matter lying beneath the sea-bed or deep ocean floor.
5137
subsolar point. The GEOGRAPHICAL POSITION of the SUN; that point on the EARTH at which the SUN is in the
ZENITH at a specified TIME.
5138
subsonic (adj.). Designating or of SPEEDS that are less than that of SOUND.
5139
substellar point. The GEOGRAPHICAL POSITION of a STAR; that point on the surface of the EARTH at which the
STAR is in the ZENITH at a specified TIME. Also called subastral point.
5140
substitute centre. A point which, because of its ease of identification on overlapping PHOTOGRAPHS, is used instead
of the PRINCIPAL POINT as a RADIAL CENTRE.
5141
substitute map. See MAP.
5142
subsurface current. See CURRENT.
5143
subsurface mark. See UNDERGROUND MARK.
5144
subsurface sound channel. The SUBMARINE SOUND CHANNEL which is adjacent to the water surface.
5145
subtense bar. A horizontally held bar of precisely determined length, used to measure distances by observing the angle
it subtends at the distance to be measured.
234
5146
subtense method. A procedure by which distance measurements are obtained by use of a SUBTENSE BAR.
5147
sue. The vertical amount which a vessel aground dries due to the fall of the TIDE.
5148
sugar loaf. A descriptive term for a conical HILL.
5149
sugar loaf sea. Waves that rise into sugar loaf shapes, with little WIND, possibly resulting from intersecting WAVES.
5150
summer solstice. See SOLSTICE.
5151
summer time. See TIME: DAYLIGHT SAVING.
5152
summit. The highest point, part or ELEVATION; top or APEX.
5153
Sumner line. A CELESTIAL LINE OF POSITION, particularly one established by the SUMNER METHOD. Named
after Captain Thomas H. Sumner, the discoverer of the LINE OF POSITION by celestial observation.
5154
Sumner method. The establishing of a LINE OF POSITION from the OBSERVATION of the ALTITUDE of a
CELESTIAL BODY by assuming two LATITUDES (or LONGITUDES) and calculating the LONGITUDES (or
LATITUDES) through which the LINE OF POSITION passes.
5155
sun. The luminous CELESTIAL BODY at the centre of the SOLAR SYSTEM, around which other CELESTIAL
BODIES revolve.
5156
sun: apparent. The actual SUN as it appears in the sky. Also called true sun.
5157
sun: mean. A fictitious SUN conceived to move eastward along the CELESTIAL EQUATOR at a rate that provides a
uniform measure of TIME equal to the average APPARENT TIME. It is used as a reference for reckoning MEAN
TIME, ZONE TIME, etc.
5158
sun: true. See SUN: APPARENT.
5159
sun compass. See COMPASS.
5160
sundial. An instrument that indicates TIME by the position of the shadow of a pointer or GNOMON cast by the SUN
on the face of a DIAL marked in HOURS.
5161
sunken rock. A ROCK potentially dangerous to SURFACE NAVIGATION, the SUMMIT of which is below the lower
limit of the zone for ROCK AWASH.
5162
sunrise. The crossing of the APPARENT HORIZON by the upper LIMB of the ascending SUN.
5163
sunset. The crossing of the APPARENT HORIZON by the upper LIMB of the descending SUN.
5164
sunshine recorder. See HELIOGRAPH.
5165
sunspot. Any of the dark spots sometimes seen at the surface of the SUN; they are believed to have some connection
with magnetic disturbances on EARTH.
5166
sunspot cycle. The time interval (11.2 YEARS) during which the number of SUNSPOTS progresses from a minimum
to a maximum and decreases again to a minimum.
5167
super high frequency (SHF). See FREQUENCY: RADIO.
5168
superior conjunction. See CONJUNCTION.
5169
superior mirage. See MIRAGE.
5170
superior planet(s). See PLANET(S): SUPERIOR.
5171
superior transit. See MERIDIAN TRANSIT.
5172
superjacent waters. The waters lying immediately above the sea-bed or deep ocean floor up to the surface.
235
5173
super-short baseline acoustic system. A variation of the short baseline system with three sensors incorporated in a
single transducer.
5174
supersonic (adj.). Designating or of a SPEED greater than the SPEED of SOUND.
5175
supplemental control. See CONTROL.
5176
supplemental control point. A photoimage point for which an ELEVATION or a horizontal POSITION, or both, is to
be, or has been determined. See also CONTROL POINT.
5177
supplementary station. See STATION.
5178
surf. Collective term for BREAKERS.
The wave activity in the area between the SHORELINE and the outermost limit of BREAKERS.
5179
surface boundary layer. See GROUND LAYER.
5180
surface current. See CURRENT.
5181
surface duct. A zone immediately below the sea surface where SOUND RAYS are refracted toward the surface and
then reflected. They are refracted because the SOUND VELOCITY at some DEPTH near the surface is greater than at
the surface. The RAYS alternately are refracted and reflected along the duct to considerable distances from the sound
source.
5182
surface mark. A STATION MARK used in addition to the UNDERGROUND MARK, over which it is plumbed.
5183
surface navigation. See NAVIGATION.
5184
surface of position. A surface on some point of which a craft is located.
5185
surface reflection. The return of SOUND RAYS to depth after striking the sea surface.
5186
surface temperature. Temperature of the water of the surface layer of the SEA (or LAKE, RIVER, etc.).
5187
surface wave. See WAVE.
5188
surf zone. The area between the outermost BREAKER and the limit of wave UPRUSH.
5189
surge. A ship's bodily motion forward and backward along the longitudinal axis, caused by the force of the sea acting
alternately on the bow and stern.
The name applied to wave motion with a period intermediate between that of the ordinary WIND WAVE and that of
the TIDE, from about 1/2 to 60 minutes.
Horizontal oscillation of water with comparative short period accompanying a SEICHE.
5190
surge (v.i.). To rise and fall, as a vessel at anchor.
To vary abruptly and momentarily in amount, as an electric current in a circuit.
5191
surge: negative. An occasion when the level of the sea is lower than the predicted level. It is caused by meteorological
conditions.
5192
surge: positive. An occasion when the level of the sea is higher than the predicted level. It is caused by meteorological
conditions.
5193
surging breaker. See BREAKER.
5194
surround. See MARGIN.
5195
survey. The orderly process of determining DATA relating to the physical or chemical characteristics of the EARTH.
The act or operation of making measurements for determining the RELATIVE POSITION of points on, above or
beneath the EARTH's surface.
The result of such operations.
An organization for making surveys.
236
5196
survey: aerial. A SURVEY using AERIAL PHOTOGRAPHS as part of the surveying operation; also the taking of
AERIAL PHOTOGRAPHS for surveying purposes.
5197
survey: cadastral. A SURVEY relating to land boundaries and subdivisions, made to create units suitable for transfer
or to define the limitations of title. Also called land survey.
5198
survey: coastal. HYDROGRAPHIC SURVEY of coastal area including COASTLINING.
5199
survey: exploratory. A SURVEY executed for the purpose of obtaining general information concerning areas about
which such information was not, previously, a matter of record.
5200
survey: geodetic. A SURVEY in which the figure and size of the EARTH is considered. It is applicable for large areas
and long lines and is used for the precise location of basic points suitable for controlling other SURVEYS.
5201
survey: geologic(al). A SURVEY or investigation of the character and structure of the EARTH, of the physical changes
which the EARTH'S CRUST has undergone or is undergoing, and of the causes producing those changes.
5202
survey: graphic control. A skeleton SURVEY made by PLANE TABLE for the purpose of (a) locating the
HYDROGRAPHIC SIGNALS, (b) locating additional CONTROL from AERIAL SURVEYS and clarification of
indefinite detail on PHOTOGRAPHS, of (c) a combination of the two.
5203
survey: gravimetric. A SURVEY made to determine the ACCELERATION OF GRAVITY at various places on the
EARTH's surface.
5204
survey: ground. A SURVEY made by ground methods, as distinguished from an AERIAL SURVEY. A ground survey
may or may not include the use of PHOTOGRAPHS.
5205
survey: harbour. HYDROGRAPHIC SURVEY of a harbour area.
5206
survey: hydrographic. A SURVEY having for its principal purpose the determination of DATA relating to bodies of
water. A hydrographic survey may consist of the determination of one or several of the following classes of DATA:
DEPTH of water; configuration and NATURE OF THE BOTTOM; directions and force of CURRENTS; HEIGHTS
and TIMES of TIDES and water stages; and location of topographic features and fixed objects for survey and navigation
purposes.
5207
survey: land. See SURVEY: CADASTRAL.
5208
survey: large scale. A HYDROGRAPHIC SURVEY at a LARGE SCALE. Large scale surveys are usually intended to
furnish detailed information for dredging, or other types of harbour improvement.
5209
survey: magnetic. A SURVEY conducted to measure the strength and direction of the EARTH'S MAGNETIC FIELD
at specific points on or near the surface of the EARTH.
5210
survey: magnetometer. A SURVEY wherein the EARTH'S MAGNETIC FIELD is mapped by the use of a
MAGNETOMETER.
5211
survey: new. See RESURVEY.
5212
survey: oceanographic. A study or examination of any physical, chemical, biological, geological or geophysical
condition in the OCEAN, or any part of it.
An expedition to gather DATA, samples or information to conduct such studies or examination.
5213
survey: offshore. HYDROGRAPHIC SURVEYS conducted in areas beyond a certain distance from the shore, e.g. in
the HIGH SEAS.
5214
survey: photogrammetric. A SURVEY utilizing either TERRESTRIAL or AERIAL PHOTOGRAPHS.
5215
survey: preliminary. See SURVEY: RECONNAISSANCE.
5216
survey: reconnaissance. A hasty preliminary SURVEY of a region made to provide some advance information regarding the area which may be useful, pending the execution of more complete SURVEYS. Also called preliminary
survey.
237
5217
survey: revisory. Hydrographic surveys conducted for the revision of charts including checking depths, aids to
navigation, existence of land and water features, and any changes or additions such as new features constructed that are
important to the mariner. A revisory survey is not considered to be a detailed resurvey.
5218
survey: running. A HYDROGRAPHIC SURVEY in which the greater part of the work is done from the ship steaming
along the COAST. A LINE OF SOUNDING is run on the COURSE MADE GOOD and any additional information of a
hydrographic nature which can be obtained whilst under way, is collected.
5219
survey: sketch. A HYDROGRAPHIC SURVEY made (due to lack of time or facilities) to a lower degree of
ACCURACY and detail than the chosen SCALE would normally indicate.
5220
survey: sonar. HYDROGRAPHIC SURVEY using a SONAR.
5221
survey: tagline. A LARGE SCALE SURVEY made by employing a TAGLINE. An accurate method sometimes
adopted in river and harbour work.
5222
survey: topographic. A SURVEY which has for its major purpose the determination of the configuration (RELIEF) of
the surface of the EARTH and the location of natural and artificial objects thereon.
5223
survey: wire-drag. A HYDROGRAPHIC SURVEY made utilizing a WIRE DRAG. In areas of rocky BOTTOM or
where submerged obstacles such as WRECKS are present, a wire-drag survey represents the most practical way of
making sure that all OBSTRUCTIONS or dangers have been found and least DEPTHS over them obtained. Also called
wire drag sweep.
5224
survey buoy. See BUOY.
5225
survey boat. A boat used for hydrographic surveys.
5226
surveying. Specifically, the science or art of making such measurements as are necessary to determine the RELATIVE
POSITION of points above, on, or beneath the surface of the EARTH, or to establish such points. Generally, the art of
making a SURVEY.
5227
surveying: plane. A branch of the art of SURVEYING in which the surface of the EARTH is considered a plane
surface. In plane surveying, curvature of the EARTH is neglected, and computations are made using the formulae of
plane geometry and plane trigonometry.
5228
surveying (or mapping) camera. See CAMERA.
5229
surveying sextant. See SEXTANT: SOUNDING.
5230
survey mark. An object placed at the site of a station to identify the surveyed location of that station. In particular, an
object whose coordinates are used for control in a geodetic network. Also called MARKER, geodetic marker, and
MONUMENT.
5231
survey net. See LEVEL NET, TRIANGULATION NET.
5232
surveyor. A person engaged in SURVEYING.
5233
surveyor's compass. See COMPASS.
5234
survey sheet. See HYDROGRAPHIC SURVEY SHEET.
5235
survey (or surveying) ship (or vessel). A ship or vessel specially equipped for carrying out HYDROGRAPHIC and/or
OCEANOGRAPHIC SURVEY.
5236
survey signal. See SIGNAL.
5237
survey station. See STATION.
5238
survey traverse. See TRAVERSE.
5239
Swallow float. A tubular BUOY, usually made of aluminium, that can be adjusted to remain at a selected density level
to drift with the motion of that water mass. The FLOAT is tracked by shipboard listening devices and current velocities
can be determined.
238
5240
swamp. An area of spongy land saturated with water. It may have a shallow covering of water, usually with a
considerable amount of vegetation appearing above the surface.
5241
swash. A narrow CHANNEL or SOUND within a sand bank, or between a sand bank and the SHORE. Also called
swashway.
A BAR over which the SEA washes.
The rush of water up onto a BEACH following the breaking of a WAVE.
5242
swash channel. A CHANNEL across a BANK, or among SHOALS.
5243
swash mark. The thin wavy line of fine SAND, mica scales, bits of SEAWEED, etc., left by the UPRUSH when it
recedes from its upward limit of movement on the BEACH.
5244
swashway. See SWASH.
5245
swath(e). The strip or lane on the ground scanned by a multi-beam sounder when the survey vessel proceeds along its
course.
5246
swath(e) sounding system. A multi-beam system which is capable of obtaining a lane of soundings from a single ship's
track.
5247
sway. The side-to-side bodily motion of a ship, independent of ROLLING, caused by uniform pressure being exerted all
along one side of the hull.
5248
sweep (v.t. & i.). To tow a line or object below the surface, to determine the least depth in an area or to insure that a
given area is free from navigational dangers to a certain depth; or the removal of such dangers.
5249
sweeping. The process of towing a line or object below the surface, to determine whether an area is free from isolated
submerged dangers to vessels and to determine the position of any dangers that exist, or to determine the least depth of
an area.
5250
swell. Ocean waves which have travelled out of their generating area. Swell characteristically exhibits a more regular
and longer PERIOD and has flatter CRESTS than WAVES within their FETCH.
Rising of the water of a RIVER above its usual LEVEL.
Gently rising GROUND or a rounded HILL above the surrounding GROUND.
5251
swing. In PHOTOGRAMMETRY, a rotation of a PHOTOGRAPH in its own plane about its camera axis.
5252
swinger. See FIX: CIRCULAR.
5253
swinging buoy. See COMPASS ADJUSTMENT BUOY.
5254
swinging ship. The process of placing a vessel on various HEADINGS and comparing MAGNETIC COMPASS readings with the corresponding magnetic DIRECTIONS, to determine DEVIATION. This usually follows COMPASS
COMPENSATION (or ADJUSTMENT), and is done to obtain information for making a DEVIATION TABLE. Also
called compass calibration, or calibration of compass. See COMPENSATION OF MAGNETIC COMPASS.
5255
swirl error. See ERROR.
5256
symbol. A CHARACTER, letter, or similar graphic representation used on a CHART, MAP, HYDROGRAPHIC
SURVEY SHEET, or DIAGRAM to represent some object, quantity, characteristic, etc.
5257
synodical month. See MONTH.
5258
synodic (or synodical) period. The interval of time between any planetary configuration of a CELESTIAL BODY,
with respect to the SUN, and the next successive same configuration of that body, as from INFERIOR CONJUNCTION
to INFERIOR CONJUNCTION.
5259
synoptic analysis. Sea WEATHER ANALYSIS.
5260
synoptic chart (or map). See CHART (or MAP): WEATHER.
5261
synoptic forecast. WEATHER FORECAST based on SYNOPTIC OBSERVATION.
239
5262
synoptic hour. Hour, expressed in terms of UT, at which, by international agreement, METEOROLOGICAL
OBSERVATIONS are made simultaneously throughout the globe.
5263
synoptic meteorology. Branch of METEOROLOGY which is concerned with the study of METEOROLOGICAL
ELEMENTS in space. It is based on the analysis of the SYNOPTIC CHARTS on which are plotted SYNOPTIC
OBSERVATIONS for the purpose of the WEATHER ANALYSIS or WEATHER FORECAST.
5264
synoptic observation. METEOROLOGICAL OBSERVATION made at the same time (SYNOPTIC HOUR) at
numerous stations to obtain general representation of the state of the atmosphere at the given time.
5265
synthetic aperture radar (SAR). A RADAR with a synthetic aperture antenna which is composed of a large number
of elementary transducing elements. The signals are electronically combined into a resulting signal equivalent to that of
a single antenna of a given aperture in a given direction.
5266
syntony. The situation of two or more oscillating circuits having the same RESONANT FREQUENCY.
5267
systematic error. See ERROR.
5268
system development. The development of a program system comprising analysis, design, programming, testing, and
implementation.
5269
systems of sounding lines. The predetermined lines that the SURVEY VESSEL is to follow for the best development
of the DEPTH CONTOURS in an area.
5270
Système International (SI System). System of metric measures consisting of seven basic units which are METRE,
KILOGRAMME, SECOND, AMPERE, Kelvin, MOLE and CANDELA.
5271
syzygy. In ASTRONOMY, either of two opposing points in the ORBIT of a PLANET or SATELLITE, especially of
the MOON, at which it is in CONJUNCTION with or in OPPOSITION to the SUN.
5272
syzygy tide. See TIDE.
240
T
5273
table. An orderly, condensed arrangement of numerical or other information, usually in parallel vertical columns. See
CONVERSION TABLE, CURRENT TABLES, TIDE TABLES, TRAVERSE TABLE.
5274
tableland. An elevated region of LAND with a generally level surface of large or considerable extent; a lofty PLAIN; a
PLATEAU.
5275
tablemount. A SEAMOUNT having a comparatively smooth flat top. Also called guyot.
5276
tabular berg. A flat-topped ICEBERG. Most tabular bergs form by breaking from an ICE SHELF and show horizontal
banding.
5277
tabulation. Orderly arrangement as in a TABLE.
5278
tachometer. A device that indicates or measures the revolutions per MINUTE of a revolving shaft or the VELOCITY
of a machine.
5279
tachymeter (or tacheometer). A surveying instrument designed for use in the rapid determination of distance,
DIRECTION, and difference of ELEVATION from a single OBSERVATION, using a short base which may be an
integral part of the instrument.
5280
tachymetry. A method of SURVEYING for the rapid determination of distance, DIRECTION, and relative ELEVATION of a point with respect to the instrument station by a single OBSERVATION on a rod or other object at the point.
The stadia method of SURVEYING is an example of tachymetry.
5281
tach stave (levelling staff). A staff with a length of about 2m with subdivisions. It is used in combination with a
levelling instrument or theodolite.
5282
taffrail. The after rail at the stern of a vessel.
5283
taffrail log. See LOG.
5284
tagline. A line, either marked at equal intervals or run over a registered sheave, used in LARGE-SCALE SURVEYS to
take equally spaced SOUNDINGS at predetermined distances from the CONTROL STATIONS.
5285
tagline survey. See SURVEY.
5286
tail wind. WIND which blows in the same direction as that in which an object is moving, with respect to the EARTH's
surface.
5287
talus. A SLOPE. A sloping mass of DETRITUS lying at the base of a CLIFF or the like, and consisting of material
which has fallen from its face; also the SLOPE or inclination of the surface of such a mass.
5288
talweg (or thalweg). The line joining the lowest points of a VALLEY throughout its length. Sometimes called valley
line.
5289
tandem control. In HYDROGRAPHIC SURVEY, a system of obtaining two or more adjacent SOUNDING LINES
run simultaneously and controlled by one ship, the other ships, or LAUNCHES being merely referenced to it.
5290
tank. A fixed structure for storing liquids.
5291
tangent screw. A slow motion screw of a surveying instrument or SEXTANT.
5292
tape. In SURVEYING, a ribbon of steel, INVAR, or other suitable material on which GRADUATIONS are placed for
the measurement of lengths or distances. See also BASE TAPE (or WIRE).
5293
tape: alignment correction. A CORRECTION applied to the measured length of a line to allow for the TAPE not
being held exactly in a vertical plane containing the line.
5294
tape: base. See BASE TAPE (or WIRE).
5295
tape: catenary correction. See TAPE: SAG CORRECTION.
241
5296
tape: grade correction. A CORRECTION applied to a distance measured on a SLOPE to reduce it to a horizontal
distance between the vertical lines through its end points. Also termed slope correction or correction for inclination of
tape.
5297
tape: invar. Any survey TAPE made of INVAR.
5298
tape: length correction. The difference between the nominal length of a TAPE and its effective length under conditions
of STANDARDIZATION.
5299
tape: reference. See REFERENCE TAPE.
5300
tape: sag correction. The difference between the effective length of a TAPE (or part of a TAPE) when supported
continuously throughout its length and when supported at a limited number of independent points. Also called catenary
correction.
5301
tape: standard. See REFERENCE TAPE.
5302
tape: steel. Any survey TAPE made of steel.
5303
tape: temperature correction. The quantity applied to the nominal length of a TAPE to allow for a change in its
effective length because of its being used at a temperature other than that for which its standard length is given.
5304
tape: tension correction. The CORRECTION applied to the nominal length of a TAPE to allow for a change in
effective length because of its being used at a tension other than that for which its standard length is known.
5305
tape correction(s). CORRECTIONS applied to a distance measured with a TAPE to eliminate ERRORS caused by the
physical condition of the TAPE, and to the manner in which it is used.
5306
tape stretcher. A mechanical device which facilitates holding a TAPE at a prescribed tension and in a prescribed
position.
5307
tape thermometer. See under THERMOMETER.
5308
taping. The operation of measuring a distance on the GROUND using a TAPE or ribbon of metal or other material.
Also called chaining.
5309
target. Any object, point, etc., toward which something is directed.
An object which reflects a sufficient amount of a radiated SIGNAL to produce an echo signal on detection
equipment. See RADAR TARGET, SONAR TARGET.
The distinctive marking or instrumentation of a ground point to aid in its identification on a PHOTOGRAPH. In
PHOTOGRAMMETRY, target designates a material marking so arranged and placed on the GROUND as to form a
distinctive pattern over a geodetic or other control point marker, on a property corner or line, or at the position of an
identifying point above an underground facility or feature. A target is also the image pattern on AERIAL
PHOTOGRAPHS of the actual MARK placed on the GROUND prior to PHOTOGRAPHY.
5310
target: false. See ECHO: FALSE.
5311
tartan plots. LATTICES resulting from the enlargement of small parts of Two Range and hyperbolic LATTICES, used
for work which has to be carried out on a SCALE larger than that being used for the main SURVEY.
5312
taut wire measuring gear. An apparatus designed for measuring horizontal distances at sea. It is constructed so that a
wire of small diameter, one end of which is anchored on the BOTTOM, passes around a calibrated sheave as the ship
steams along the route to be measured.
5313
taut wire mooring. A mooring arrangement in which a submerged FLOAT provides the upward force necessary to
maintain the system in a fixed position with reference to the sea bottom.
5314
tectonics. The study of origin and development of the broad structural features of the EARTH.
5315
telecommunication. Any transmission, emission, or reception of signs, SIGNALS, writing, IMAGES and SOUNDS or
intelligence of any nature by wire, RADIO, visual or other electromagnetic systems.
5316
telegraph buoy. A BUOY used to mark the position of a submarine telegraph cable.
5317
telemeteorograph. General term for meteorological instruments whose indications are recorded at a distance.
242
5318
telemeter. An instrument for determining the distance from one point to another. Some such instruments employ a
TELESCOPE and measure the angle subtended by a short base of known length.
The complete equipment for measuring any quantity, transmitting the results electrically to a distance point, and
there recording the values measured.
5319
telemeter: electronic. An electronic device that measures the phase difference or transit time between a transmitted
electromagnetic IMPULSE of known FREQUENCY and SPEED and its return.
5320
telemetry. The study and technique involved in measuring a quantity or quantities in place, transmitting this value to a
station, and there interpreting, indicating, or recording the quantities; and transmitting commands from the station to
control the measurement device.
5321
telemotor. A hydraulic or electrical device controlling the action of power at a distance, specifically, a device which
controls the steering gear of a ship.
5322
telescope. An optical instrument used as an aid in viewing or photographing distant objects, particularly celestial
objects.
5323
telescope: meridian. A TELESCOPE whose motion along a VERTICAL CIRCLE is intended to lie in the plane of the
MERIDIAN.
5324
telescope: photo zenithal. An instrument designed to take photos of stars culminating close to the zenith of a station in
order to determine the position of the station with high accuracy.
5325
telescope: reflecting. A TELESCOPE which collects light by means of a concave MIRROR.
5326
telescope: refracting. A TELESCOPE which collects light by means of a LENS or system of LENSES.
5327
telescope: zenith. An astronomical instrument for determining the LATITUDE by observing ZENITH DISTANCES of
two STARS that culminate as close as possible in TIME, and at nearly the same ALTITUDE on opposite sides of the
ZENITH.
5328
telescopic alidade. See ALIDADE.
5329
telltale compass. See COMPASS.
5330
telluric current(s). See CURRENT: TELLURIC.
5331
temperature. The intensity or degree of heat.
5332
temperature correction (levelling). That CORRECTION which is applied to an observed difference of ELEVATION
to correct for the ERROR introduced when the temperature at which the LEVELLING RODS are used in the field is
different from the temperature at which they were standardized.
5333
temperature correction (tape). See TAPE: TEMPERATURE CORRECTION.
5334
temperature inversion. In OCEANOGRAPHY, a LAYER in which temperature increases with DEPTH. Also called
inversion layer.
5335
temperature lapse rate. Rate of decrease of temperature with increasing HEIGHT; usually an average rate over a
distance, for example 100 METRES, is considered.
5336
temperature-salinity diagram. The plot of temperature versus SALINITY data of a water column. The result is a
DIAGRAM which identifies the water masses within the column, the column's stability, and indicates the st value, and
allows an estimate of the ACCURACY of the temperature and salinity measurements.
5337
template (or templet). A pattern or guide, usually constructed of paper, plastic, or metal, used to shape, delimit, or
locate an area.
A device used in RADIAL TRIANGULATION to represent the AERIAL PHOTOGRAPH; the template provides a
record of the directions of RADIALS taken from the PHOTOGRAPH.
5338
temporal (adj.). Pertaining to or limited by TIME.
5339
temporal variation. See MAGNETIC TEMPORAL VARIATION.
243
5340
temporary magnetism. See MAGNETISM.
5341
tension correction (tape). See TAPE: TENSION CORRECTION.
5342
tented ice. PRESSURE ICE in which two ICE FLOES have been pushed into the air, leaving an air space underneath.
5343
terminal. A number of berths grouped together, providing facilities for handling a particular form of cargo, e.g. oil
terminal, container terminal.
5344
terrace. A relatively flat horizontal or gently inclined surface, sometimes long and narrow, bounded above and below
by rather abrupt SLOPES.
5345
terrain. Standing GROUND.
A tract of country considered with regard to its natural features, configuration, etc.
5346
terrestrial camera. See CAMERA.
5347
terrestrial equator. See EQUATOR.
5348
terrestrial globe. See GLOBE.
5349
terrestrial latitude. See LATITUDE.
5350
terrestrial longitude. See LONGITUDE.
5351
terrestrial magnetic field. See GEOMAGNETIC FIELD.
5352
terrestrial magnetism. See GEOMAGNETISM.
5353
terrestrial meridian. See MERIDIAN: ASTRONOMICAL.
5354
terrestrial navigation. The kind of NAVIGATION which uses marks ashore for positioning.
5355
terrestrial photogrammetry. See PHOTOGRAMMETRY.
5356
terrestrial photograph. See PHOTOGRAPH.
5357
terrestrial pole. See POLE.
5358
terrigenous (adj.). Derived from the LAND.
Applied to marine DEPOSITS, originating from the EROSION of the LAND as opposed to pelagic DEPOSITS.
5359
terrigenous sediments. DEPOSITS consisting of DEBRIS derived from the EROSION of land areas and usually
deposited in the shallow parts of the SEA.
5360
territorial sea. A belt of water of a defined breadth but not exceeding 12 nautical miles measured seaward from the
territorial sea baseline.
5361
territorial waters. See TERRITORIAL SEA.
5362
tesla. The unit of magnetic flux density in the SI SYSTEM.
5363
test. The hard covering or supporting structure of many invertebrates; it may be enclosed within an outer layer of living
tissue; a SHELL.
5364
Texas tower. A fixed tower mounted on the CONTINENTAL SHELF or on a SHOAL, used to drill and operate gas or
petroleum wells, and to provide a platform for AIDS TO NAVIGATION and meteorological or oceanographic instrumentation.
5365
thalweg. See TALWEG.
5366
thaw. Melting of SNOW and/or ICE, at the EARTH's surface, following a temperature rise above 0°C.
5367
thematic map. See MAP.
244
5368
theodolite. A precision surveying instrument consisting of an ALIDADE with a TELESCOPE. It is mounted on an
accurately graduated CIRCLE and is equipped with necessary LEVELS and reading devices. Sometimes, the
ALIDADE carries a graduated VERTICAL CIRCLE.
5369
theodolite: direction. A THEODOLITE in which the graduated HORIZONTAL CIRCLE remains fixed during a series
of OBSERVATIONS, the TELESCOPE being pointed on a number of SIGNALS or objects in succession, and the
DIRECTION of each read on the CIRCLE, usually by the use of MICROMETER MICROSCOPES.
5370
theodolite: face(s) of. See FACE(S) OF THEODOLITE.
5371
theodolite: repeating. A THEODOLITE so designed that successive measures of an angle may be accumulated on the
graduated CIRCLE, and a final reading of the CIRCLE made which represents the sum of the repetitions. The observed
value of the angle is obtained by dividing the total arc passed through in making the series of OBSERVATIONS by the
number of times the angle has been observed. Also called repeating instrument. See REPETITION METHOD OF
OBSERVATION.
5372
theodolite: transit. See TRANSIT.
5373
theodolite axes. See AXIS: HORIZONTAL and AXIS: VERTICAL.
5374
theodolite drag. See DRAG (of THEODOLITE).
5375
theoretical error. See ERROR.
5376
thermal equator. See EQUATOR.
5377
thermal layer. See THERMOCLINE.
5378
thermocline. A vertical negative temperature gradient in some LAYER of a body of water, which is appreciably greater
than the GRADIENTS above and below it; also a LAYER, in which such a GRADIENT occurs. The principal
thermoclines in the OCEAN are either seasonal, due to heating of the surface water in summer, or permanent. Also
called discontinuity layer, or thermal layer.
5379
thermocline: transient. A small decrease in vertical temperature observed above the THERMOCLINE. It is a shortterm PHENOMENON associated primarily with diurnal heating and wind mixing.
5380
thermogram. Record made by a THERMOGRAPH.
5381
thermograph. THERMOMETER used to give a graphical record of the time variations of temperature.
5382
thermohygrograph. See HYGROTHERMOGRAPH.
5383
thermometer. Instrument used in the measurement of temperature.
5384
thermometer: deep sea. A THERMOMETER for ascertaining the temperature of SEA WATER at any DEPTH. See
THERMOMETER: PROTECTED REVERSING, THERMOMETER: REVERSING, THERMOMETER:
UNPROTECTED REVERSING.
5385
thermometer: dry-bulb. That of the two THERMOMETERS of a PSYCHROMETER whose bulb is bare and which
indicates the air temperature.
5386
thermometer: maximum. THERMOMETER used for measuring the highest temperature attained during a given interval of time, for example, a day.
5387
thermometer: minimum. THERMOMETER used for measuring the lowest temperature attained during a given interval of time, for example, a day.
5388
thermometer: protected reversing. A REVERSING THERMOMETER enclosed in a heavy glass case to protect it
from HYDROSTATIC PRESSURE.
5389
thermometer: reversing. A DEEP-SEA THERMOMETER that records temperature at the desired DEPTH upon being
inverted and thereafter retains its reading until returned to the first position. Reversing thermometers are generally used
in pairs on WATER BOTTLES.
245
5390
thermometer: tape. A precision THERMOMETER fitted in a specially designed case to clip on and against a metal
TAPE in order to determine TEMPERATURE CORRECTIONS for precision BASE or TRAVERSE tape
measurements.
5391
thermometer: unprotected reversing. A REVERSING THERMOMETER which is not protected against
HYDROSTATIC PRESSURE. Used in conjunction with PROTECTED REVERSING THERMOMETERS to
determine THERMOMETRIC DEPTH.
5392
thermometer: wet-bulb. That of the two THERMOMETERS of a PSYCHROMETER whose bulb is wet and covered
by a film of pure water or ICE.
5393
thermometric depth. See DEPTH.
5394
thermometric levelling. See LEVELLING.
5395
thermoprobe. A TRANSDUCER used to measure temperature 'in situ' of ocean BOTTOM SEDIMENTS at DEPTHS
beneath the BOTTOM. Such measurements when combined with heat conductivity information provide a measurement
of heat flow through the ocean bottom.
5396
third order triangulation. See TRIANGULATION CLASSIFICATION.
5397
three-arm protractor. See PROTRACTOR: THREE-ARM.
5398
three-point fix. See FIX.
5399
three-point fix method. One of the principal methods used on inshore HYDROGRAPHIC SURVEYS for establishing
the POSITION of the SURVEY VESSEL. It involves the measurement with SEXTANTS of two angles between three
known STATIONS, the middle STATION being common to both angles, and plotting the vessel's POSITION graphically with a THREE-ARM PROTRACTOR.
5400
three-point problem. The determination of the horizontal POSITION of a point of observation from DATA comprising
two observed horizontal angles between three objects of known POSITION. The problem is solved either graphically by
the use of a THREE-ARM PROTRACTOR, or analytically by trigonometrical computation.
5401
threshold. In aeronautical terminology, the beginning of that portion of the RUNWAY usable for landing.
5402
threshold speed. The minimum SPEED of CURRENT at which a particular CURRENT METER will measure at its
rated reliability.
5403
thunder. Sharp or rumbling SOUND which accompanies LIGHTNING.
5404
thunderstorm. One or more sudden electrical discharges manifested by the flash of light (LIGHTNING) and a sharp or
rumbling sound (THUNDER).
5405
tidal basin. See BASIN.
5406
tidal bore. See BORE.
5407
tidal constants. Tidal relations that remain essentially constant for any particular locality. Tidal constants are classed as
harmonic and non-harmonic, the HARMONIC CONSTANTS consisting of the AMPLITUDES and EPOCHS, and the
NON-HARMONIC CONSTANTS including those values determined directly from OBSERVATIONS, such as tidal
ranges and intervals.
5408
tidal constituent. See HARMONIC CONSTITUENT.
5409
tidal current. See CURRENT.
5410
tidal current chart. See CHART.
5411
tidal current signal. See SIGNAL.
5412
tidal (or tide) cycle. A complete set of tidal conditions, as those occurring during a TIDAL DAY, LUNAR MONTH or
METONIC CYCLE.
5413
tidal datum. See DATUM.
246
5414
tidal day. LUNAR DAY.
The period of the daily CYCLE of the TIDES, differing slightly from the LUNAR DAY because of PRIMING and
LAGGING OF THE TIDE.
5415
tidal difference. Difference in TIME or HEIGHT of a HIGH or LOW WATER at a SUBORDINATE STATION and
at a REFERENCE STATION for which predictions are given in the TIDE TABLES. The difference, when applied
according to sign to the prediction at the REFERENCE STATION, gives the corresponding TIME or HEIGHT for the
SUBORDINATE STATION.
5416
tidal epoch. See PHASE LAG.
5417
tidal flat. A MARSH or sandy or muddy coastal flatland which is covered and uncovered by the RISE and fall of the
TIDE.
5418
tidal harbour. See HARBOUR.
5419
tidal light(s). See LIGHT.
5420
tidal movement. The movement which includes both the vertical RISE and fall of the TIDE, and the horizontal FLOW
of the TIDAL CURRENTS. This movement is associated with the astronomical TIDE-PRODUCING FORES of the
MOON and SUN acting upon the rotating EARTH.
5421
tidal observations. See OBSERVATION.
5422
tidal prediction. See TIDE PREDICTION.
5423
tidal range. See RANGE OF TIDE.
5424
tidal rise. See RISE OF TIDE.
5425
tidal stream. See CURRENT: TIDAL.
5426
tidal theories. The different theories trying to describe the tidal phenomena.
5427
tidal water. Any water the level of which changes periodically due to tidal action. See TIDEWATER.
5428
tidal wave. See WAVE.
5429
tide. The periodic RISE and fall of the surface of OCEANS, BAYS, etc., due principally to the gravitational interactions
between the MOON, SUN and EARTH.
5430
tide: analysis. The mathematical processes by which the observed TIDE or TIDAL CURRENT are analyzed to obtain
constituents and statistics.
5431
tide(s): apogean. TIDES of decreased RANGE occurring when the MOON is near APOGEE.
5432
tide: astronomical. TIDE due to the attraction of the SUN and MOON, in contrast to a METEOROLOGICAL TIDE,
caused by meterological conditions.
EQUILIBRIUM TIDE.
5433
tide: compound. A tide constituent with a SPEED equal to the sum or difference of the SPEEDS of two or more basic
constituents. Compound tides usually occur in SHALLOW WATER regions. See SHALLOW WATER
CONSTITUENT.
5434
tide: diurnal. A TIDE in which the TIDAL CYCLE consists of one HIGH WATER and one LOW WATER each
TIDAL DAY. In British terminology also called single day tide.
5435
tide: double. A double-headed TIDE. Also called agger. See HIGH WATER: DOUBLE and LOW WATER:
DOUBLE.
5436
tide: earth. Periodic movement of the EARTH's CRUST caused by the TIDE-PRODUCING FORCES of the MOON
and SUN.
5437
tide: ebb. See TIDE: FALLING.
247
5438
tide(s): equatorial. TIDES that occur approximately every two weeks when the MOON is over the EQUATOR. At
these times, the MOON produces minimum DIURNAL INEQUALITY in the TIDE.
5439
tide: equilibrium. A hypothetical TIDE based upon the assumption that the water responds, instantly to the TIDEPRODUCING FORCES of the MOON and SUN, and forms a surface of EQUILIBRIUM under the action of these
forces, disregarding friction, inertia and the irregular distribution of the land masses.
5440
tide(s): equinoctial spring. Those TIDES occurring near the EQUINOXES when the FULL or NEW MOON and the
SUN have little or low DECLINATION and SPRING TIDES of greater RANGE than the average occur, particularly if
the MOON is also nearly in PERIGEE.
5441
tide: falling. The portion of the TIDE CYCLE between HIGH WATER and the following LOW WATER. Also called
ebb tide. The opposite is RISING TIDE.
5442
tide: flood. See TIDE: RISING.
5443
tide: half. The condition or TIME of the TIDE when at the level midway between any given HIGH TIDE and the
following or preceding LOW TIDE.
5444
tide: high. See HIGH WATER.
5445
tide: leeward (or lee). A TIDAL CURRENT setting in the same direction as that in which the WIND is blowing. Also
called leeward tidal current.
5446
tide: low. See LOW WATER.
5447
tide: lunar. That part of the TIDE due solely to the TIDE-PRODUCING FORCES of the MOON, as distinguished
from that part caused by the forces of the SUN. See TIDE: SOLAR.
5448
tide: meteorological. A change in water level caused by local meteorological conditions, in contrast to an
ASTRONOMICAL TIDE caused by the attraction of the SUN and MOON.
5449
tide: mid-extreme. A level midway between the extreme HIGH WATER and extreme LOW WATER occurring at a
place. See HALF-TIDE LEVEL.
5450
tide: mixed. The TYPE OF TIDE in which a diurnal WAVE produces large INEQUALITIES in HEIGHTS and/or
durations of successive HIGH and/or LOW WATERS. This term applies to the TIDES intermediate to those predominantly semidiurnal and those predominantly diurnal.
5451
tides: mixed diurnal. Diurnal tides which become semidiurnal with a considerable decrease of range when the moon's
declination is small.
5452
tides: mixed semidiurnal. Semidiurnal tides with noticeable inequality in corresponding extremes.
5453
tide(s): neap. The TIDES of decreased RANGE occurring near the TIMES of FIRST and LAST QUARTER.
5454
tide: oceanic. The periodic rise and fall of the earth's oceans resulting from gravitational interactions between the sun,
moon, and earth.
5455
tide: partial. One of the harmonic components comprising the TIDE at any point. The periods of the partial tides are
derived from various combinations of the ANGULAR VELOCITIES of EARTH, SUN, MOON, and STARS relative to
each other. See HARMONIC CONSTITUENT.
5456
tide(s): perigean. TIDES of increased RANGE occurring when the MOON is near PERIGEE.
5457
tide(s): predicted. The expected TIMES and HEIGHTS of the TIDE as given in the TIDE TABLES in advance of their
occurrence.
5458
tide: primary. That part of a tidal UNDULATION that is the direct response to a TIDE-PRODUCING FORCE.
5459
tide(s): quarter-diurnal. The TIDE resulting from the distortion of the normal TIDE in SHALLOW WATER with four
HIGH WATERS and four LOW WATERS during one day. See also TIDE(S): SHALLOW WATER.
5460
tide: rising. The portion of the TIDE CYCLE between LOW WATER and the following HIGH WATER. Also called
flood tide. The opposite is FALLING TIDE.
248
5461
tide(s): secondary. Those additional TIDES HIGHER LOW WATERS and LOWER HIGH WATERS that occur twice
a MONTH (when the MOON is over the EQUATOR) in a general pattern of DIURNAL TIDES.
5462
tide: semidiurnal. A TIDE in which the TIDAL CYCLE consists of two HIGH WATERS and two LOW WATERS
each TIDAL DAY, with comparatively little DIURNAL INEQUALITY.
5463
tide(s): shallow water. A distortional effect upon astronomically generated TIDE caused by SHALLOW WATERS.
See also TIDE(S): QUARTER-DIURNAL.
5464
tide: single day. See TIDE: DIURNAL.
5465
tide: slack. See SLACK WATER.
5466
tide: solar. That part of the TIDE due solely to the TIDE-PRODUCING FORCES of the SUN, as distinguished from
that part caused by the forces of the MOON.
5467
tide(s): solsticial. TIDES occurring near the TIMES of the SOLSTICES, when the TROPIC RANGE is especially
large.
5468
tide(s): spring. The TIDES of increased RANGE occurring near the TIMES of FULL MOON and NEW MOON.
5469
tide: storm. See STORM SURGE.
5470
tide: syzygy. The TIDE which takes place on the afternoon of the day the SUN and MOON are in SYZYGY. (This
term is now little used).
5471
tide: tropic. The TIDE that occurs twice monthly when the effect of the MOON's maximum DECLINATION north or
south of the EQUATOR is greatest.
5472
tide: vanishing. The PHENOMENON occurring when a HIGH and LOW WATER 'melt' together into a period of
several hours with a nearly constant water level. The TIDE is in the diurnal category but is known as a 'vanishing tide'.
5473
tide: weather. See TIDE: WINDWARD.
5474
tide: windward. A TIDAL CURRENT setting to windward. Also called weather tide.
5475
tide-bound (adj.). Unable to proceed because of insufficient DEPTH of water due to tidal action.
5476
tide bulge. See TIDE WAVE.
5477
tide crack. The fissure at the line of junction between an immovable ICEFOOT or ICE WALL and FAST ICE, the
latter being subject to the RISE and fall of the TIDE.
5478
tide curve. Any graphic representation of the RISE and fall of the TIDE. TIME is generally represented by the
abscissae and the HEIGHT of the TIDE by ordinates. For normal TIDES the curve so produced approximates a sine
curve. Also called marigram.
5479
tide cycle. See TIDAL CYCLE.
5480
tide gate. A restricted passage through which water runs with great SPEED due to tidal action.
5481
tide gauge. See GAUGE.
5482
tide-generating force. See TIDE-PRODUCING FORCE.
5483
tideland. LAND which is under water at HIGH TIDE and uncovered at LOW TIDE.
5484
tide lock. A LOCK situated between a BASIN or CANAL and TIDEWATER to maintain the water at a desired level as
the HEIGHT of the TIDE changes. Also called guard lock.
5485
tidemark. A HIGH WATER MARK left by TIDAL WATER.
The highest point reached by a HIGH TIDE.
A MARK placed to indicate the highest point reached by a HIGH TIDE, or, occasionally, any specified state of
TIDE.
249
5486
tide pole. See TIDE STAFF.
5487
tide-predicting machine. An instrument that computes, sometimes for years in advance, the TIMES and HEIGHTS of
HIGH and LOW WATERS at a REFERENCE STATION by mechanically summing the HARMONIC
CONSTITUENTS of which the TIDE is composed.
5488
tide (or tidal) prediction. The mathematical process by which the TIMES and HEIGHTS of the TIDE are determined
in advance from the HARMONIC CONSTITUENTS at a place. See HARMONIC ANALYSIS OF TIDE.
5489
tide-producing force(s). That part of the gravitational attraction of a CELESTIAL BODY which is effective in
producing the TIDES on EARTH. The SUN and MOON are the principal astronomic bodies that have a tide-producing
effect. The force varies approximately as the mass of the attracting body and inversely as the cube of its distance. Also
called tide-generating force.
5490
tide race. A strong TIDAL CURRENT or a CHANNEL in which such a CURRENT flows.
5491
tide range. See RANGE OF TIDE.
5492
tide reducer. The CORRECTION that must be applied to a recorded SOUNDING for the HEIGHT OF TIDE above or
below the DATUM of reference at the TIME of SOUNDING.
5493
tide register. See GAUGE: TIDE.
5494
tide rip(s). Small WAVES formed on the surface of water by the meeting of opposing TIDAL CURRENTS or by a
TIDAL CURRENT crossing an irregular BOTTOM. Vertical oscillation, rather than PROGRESSIVE WAVES, is
characteristic of tide rips.
5495
tide signal. See SIGNAL.
5496
tide staff. A TIDE GAUGE consisting of a vertical graduated pole from which the HEIGHT OF TIDE at any TIME can
be read directly. Also called tide pole.
5497
tide staff: multiple. A succession of TIDE STAFFS on a sloping SHORE, so placed that the vertical GRADUATIONS
on the several staffs form a continuous scale with reference to the same DATUM.
5498
tide station. See STATION.
5499
tide tables. TABLES listing daily predictions, usually a year in advance, of the TIMES and HEIGHTS of the TIDE.
These predictions are usually supplemented by TIDAL DIFFERENCES and TIDAL CONSTANTS by means of which
additional predictions can be obtained for numerous other places. See TIDE PREDICTION.
5500
tidewater. Water affected by TIDES or sometimes that part of it which covers the TIDELAND. The term is sometimes
used broadly to designate the SEABOARD. See TIDAL WAVES.
5501
tide wave. A long-period wave associated with the TIDE-PRODUCING FORCES of the MOON and SUN; identified
with the rising and falling of the TIDE. Also called tide bulge. See TIDE, TIDAL MOVEMENT, STAND OF TIDE.
5502
tideway. A CHANNEL through which a TIDAL CURRENT runs.
5503
tie. A survey connection from a point of known POSITION to a point whose POSITION is desired. A tie is made to
determine the POSITION of a supplementary point whose POSITION is desired for mapping or reference purposes, or
to close a SURVEY on a previously determined point. To tie in is to make such a connection. The point to which the
connection is made is termed a TIE POINT.
5504
tie in (v.i.). See TIE.
5505
tie net. See TRIANGULATION NET.
5506
tie point. Point of closure of a SURVEY either on itself or on another SURVEY.
5507
till. Unstratified glacial DRIFT consisting of CLAY, SAND, GRAVEL, and BOULDERS intermingled in any proportions. Also called boulder clay.
250
5508
tillite. ROCK formed of consolidated or lithified TILL and generally a record of a glacial EPOCH, older than that of the
quarternary.
5509
tilt. The angle which anything makes with the horizontal.
In PHOTOGRAMMETRY, the angle at the PERSPECTIVE CENTRE between the photograph perpendicular and
the PLUMB LINE, or other exterior REFERENCE DIRECTION; also, the dihedral angle between the plane of the
PHOTOGRAPH and the horizontal plane.
5510
tilt: base. In PHOTOGRAMMETRY, the INCLINATION of the AIR BASE with respect to the horizontal.
5511
tilt: relative. The angular relationship between two overlapping VERTICAL PHOTOGRAPHS with no reference to an
established DATUM.
5512
tilting level. See LEVELLING INSTRUMENT: TILTING LEVEL.
5513
time. The measurable aspect of duration.
The HOUR of the DAY reckoned by the position of a celestial reference point relative to a reference CELESTIAL
MERIDIAN.
An elapsed interval.
5514
time: apparent. See TIME: APPARENT SOLAR.
5515
time: apparent solar. TIME measured by the apparent diurnal motion of the (true) SUN. Also called true solar time,
and often apparent time.
5516
time: astronomic(al). SOLAR TIME in a DAY (ASTRONOMICAL DAY) that begins at NOON.
5517
time: civil. SOLAR TIME in a DAY (CIVIL DAY) that begins at MIDNIGHT.
5518
time: daylight saving. A variation of ZONE TIME, usually one HOUR ahead of that TIME. Sometimes called summer
time.
5519
time: geologic(al). The division into a number of great ERAS, each represented by a group of ROCKS.
5520
time: Greenwich. TIME based upon the GREENWICH MERIDIAN as reference.
5521
time: Greenwich civil. See TIME: GREENWICH MEAN.
5522
time: Greenwich mean (GMT) (or Greenwich civil). MEAN SOLAR TIME at the GREENWICH MERIDIAN. See
UNIVERSAL TIME (UT).
5523
time: local. TIME based upon the LOCAL MERIDIAN as reference, as contrasted with that based upon a ZONE
MERIDIAN, or the MERIDIAN of Greenwich.
Any TIME kept locally.
5524
time: local apparent. The APPARENT SOLAR TIME for the MERIDIAN of the observer.
5525
time: local mean. The MEAN SOLAR TIME for the MERIDIAN of the observer.
5526
time: local sidereal. The SIDEREAL TIME for the MERIDIAN of the observer.
5527
time: mean. See TIME: MEAN SOLAR.
5528
time: mean solar. TIME measured by the diurnal motion of the MEAN SUN, which is supposed to move uniformly in
the CELESTIAL EQUATOR, completing the circuit in one TROPICAL YEAR. Often termed simply mean time.
5529
time: sidereal. TIME measured by the apparent diurnal rotation of the (true) VERNAL EQUINOX. It is counted from
0 HOUR, when the VERNAL EQUINOX is on the MERIDIAN, through 24 HOURS. Naming the MERIDIAN of
reference is essential to its complete identification.
5530
time: solar. TIME based upon the ROTATION of the EARTH relative to the SUN. See TIME: APPARENT SOLAR,
TIME: ASTRONOMICAL, TIME: CIVIL, TIME: MEAN SOLAR.
251
5531
time: standard. A variation of ZONE TIME adapted for use on or near LAND, with irregular but well-defined zone
limits.
5532
time: summer. See TIME: DAYLIGHT SAVING.
5533
time: true solar. See TIME: APPARENT SOLAR.
5534
Time: Universal. See UNIVERSAL TIME (UT).
5535
time: zone. The LOCAL MEAN TIME of a reference or zone meridian, whose TIME is kept throughout a designated
ZONE. The ZONE MERIDIAN is usually the nearest MERIDIAN whose LONGITUDE is exactly divisible by 15°.
5536
time ball. A visual TIME SIGNAL in the form of a ball.
5537
timepiece. An instrument for measuring TIME. See CHRONOMETER, CLOCK, WATCH.
5538
time signal. See SIGNAL.
5539
time tag. Reference assigned to each measurement input from a sensor to identify the time (either CPU, GPS, or UTC)
when a measurement was actually made by that particular sensor; time tags allow adjustment of data from different
sensors to a common time reference.
5540
time zone. See ZONE.
5541
tinted areas. Those areas on the NAUTICAL CHART that are symbolized by a flat colour to indicate the nature of the
area.
5542
title. In CARTOGRAPHY, an inscription, on the CHART or FAIR CHART, including any useful information and details concerning the HYDROGRAPHIC SURVEY, the NATURAL SCALE, and geodetic, magnetic and tidal DATA.
5543
titration. A chemical method for determining the concentration of a substance in solution. In OCEANOGRAPHY, the
most common titration is that for CHLORINITY.
5544
tolerance. The maximum allowable variation from a STANDARD or from specified conditions.
5545
ton. A unit of WEIGHT equal to 1,000 KILOGRAMS ('metric ton'), 2,240 POUNDS ('long ton'), or 2,000 POUNDS
('short ton').
5546
tongue. A projection of the ICE EDGE up to several kilometres in length, caused by WIND and CURRENT.
A relatively narrow strip of LAND.
An INLET.
A narrow, rapid CURRENT.
A protrusion of water into a region of different temperature.
5547
tonnage. The carrying capacity of ships.
5548
topmark. A characteristic shape secured at the top of a BUOY or BEACON to aid in its identification.
5549
topmark buoy. A BUOY with a TOPMARK, or characteristic shape secured at the top to aid in its identification.
5550
topoangulator. An instrument used to measure vertical angles in the PRINCIPAL PLANE of an OBLIQUE PHOTOGRAPH.
5551
topographic feature. A single feature of the surface of the EARTH such as a MOUNTAIN or VALLEY.
5552
topographic map. See MAP.
5553
topographic model. See RELIEF MODEL.
5554
topographic signal. See SIGNAL.
5555
topographic station. See STATION.
5556
topographic survey. See SURVEY.
252
5557
topography. The configuration of the surface of the EARTH, including its RELIEF, the position of its STREAMS,
roads, cities, etc. The EARTH's natural and physical features collectively.
In OCEANOGRAPHY, the term is applied to a surface such as the sea bottom or a surface of given characteristics
within the water mass.
5558
topography board. See FIELD BOARD.
5559
toponymy. The place names or the study of place names of a country or district.
5560
tornado. In North America, the name for an intense SPOUT of large diameter.
5561
torrent. Rushing STREAM of water; great downpour of RAIN.
5562
torrid zone. That part of the EARTH between the TROPIC OF CANCER and the TROPIC OF CAPRICORN. Also
called the tropics.
5563
torsion balance. A device for measuring very small forces of attraction resulting from GRAVITATION,
MAGNETISM, etc., and consisting of a bar suspended horizontally by an elastic filament, one end of the bar being
subjected to the influence of the attracting force to a greater degree than the other end. The attracting force is balanced
and its comparative strength measured by the torsional reaction of the filament.
5564
total eclipse. See ECLIPSE.
5565
total magnetic intensity. The vector resultant of the intensity of the horizontal and vertical components of the
EARTH's MAGNETIC FIELD at a specified point.
5566
towering. Apparent increase in the vertical dimension of an object near the HORIZON, due to large inequality of
ATMOSPHERIC REFRACTION in the LINE OF SIGHT to the top and bottom of the object. The opposite is STOOPING.
5567
tracer. Foreign substance introduced into the water by natural or artificial means which enables determination of water
movement through measurement of distribution and location of the substance at the same time.
5568
tracing cloth. A fine semitransparent linen or cotton cloth sized on one side and dull on the other.
5569
tracing paper. A thin tough semitransparent paper suitable for making tracings of drawings, or for miscellaneous use in
hydrographic work, where permanence is not important or when pencil work is sufficient.
5570
track. The actual path or route of a craft over the GROUND or sea bottom, or its graphic representation. In AIR
NAVIGATION also called track made good.
5571
track (v.t.). To follow the movements of an object as by RADAR or an optical system.
To navigate by keeping a record, tabular or graphical of the past POSITIONS of a craft without regard for future
POSITIONS.
5572
track: dead reckoning. A line representing successive DEAD RECKONING POSITIONS of a craft.
5573
track: great-circle. The TRACK of a craft following a GREAT CIRCLE, or a GREAT CIRCLE which a craft intends
to follow approximately.
5574
track: intended. The anticipated path of a vessel relative to the EARTH.
5575
track: radar guided. See RADAR.
5576
track: recommended. A track, shown on a chart by either a dashed or a continuous line, recommended to all or only
certain vessels.
5577
track chart. A chart showing recommended, required, or established tracks, and usually indicating turning points,
courses, and distances.
5578
tracking. The process of observing the sequential changes in the position of a target to establish its motion.
5579
tracking camera. See CAMERA: BALLISTIC.
253
5580
track line of sounding. A continuous record of SOUNDINGS obtained by a ship on an extended voyage en route
between its home port and the working ground. Also called cruise line of sounding.
5581
track made good. See TRACK.
5582
track plotter. A PLOTTER used to plot the track or course of a craft.
5583
trade winds. Persistent WINDS, mainly in the lower ATMOSPHERE, which blow over vast regions from a subtropical
ANTICYCLONE toward the equatorial regions. The predominant directions of the trade winds are from NE in the
northern hemisphere and from SE in the southern hemisphere.
5584
traffic lane. An area within defined limits in which one-way traffic is established. Natural obstacles, including those
forming separation zones, may constitute a boundary.
5585
traffic separation scheme. A scheme which aims at reducing the risk of collision in congested and/or converging areas
by separating traffic moving in opposite, or nearly opposite, directions.
5586
training wall. A wall, BANK, or JETTY, often submerged, built to direct or confine the FLOW of a RIVER or TIDAL
CURRENT.
5587
trajectory. The curved path of something hurtling through space.
In METEOROLOGY, curve traced by the successive positions of a moving particle of air. Curve traced by the
successive positions of the centre of a selected synoptic system, such as a DEPRESSION.
In OCEANOGRAPHY, the path followed by moving water particles.
In electronics the path followed by electrons emanating from the cathode as in an electron tube.
5588
transceiver. A combination transmitter and receiver in a single housing, with some components being used by both
parts. See TRANSPONDER.
5589
transducer. Any device for converting energy from one form to another (electrical, mechanical, or acoustic).
5590
transducer: magnetostriction. A TRANSDUCER that depends for its operation on the interaction between the magnetization and the deformation of a material having magnetostrictive properties.
5591
transformation. In PHOTOGRAMMETRY, the process of projecting a PHOTOGRAPH (mathematically, graphically,
or photographically) from its plane onto another plane by translation, rotation, and/or scale change. The projection is
made onto a plane determined by the angular relations of the camera axes and not necessarily onto a horizontal plane.
See also RECTIFICATION.
5592
transforming printer. A specially designed projection printer of fixed geometry used for transforming the oblique
components of a coupled camera installation, a MULTIPLE-LENS CAMERA, or a panoramic camera onto a plane
perpendicular to the axis of the system.
5593
transhipment or lightening area. An area designated for transfer of cargo from one vessel to another to reduce the
draught of the larger vessel. Also called cargo transfer area.
5594
transient magnetism. See MAGNETISM: TEMPORARY.
5595
transient thermocline. See THERMOCLINE.
5596
transit. In ASTRONOMY, the apparent passage of a STAR or other CELESTIAL BODY across a defined line of the
CELESTIAL SPHERE, as a MERIDIAN, PRIME VERTICAL, or ALMUCANTAR. When no line is specified, a
transit across the MERIDIAN is usually intended. See MERIDIAN TRANSIT.
The apparent passage of a STAR or other CELESTIAL BODY across a line in the RETICLE of a TELESCOPE, or
some LINE OF SIGHT.
The apparent passage of a smaller CELESTIAL BODY across the disk of a larger CELESTIAL BODY.
A surveying instrument composed of a HORIZONTAL CIRCLE graduated in circular measure and an ALIDADE
with a TELESCOPE which can be reversed in its supports without being lifted therefrom. Also, the act of making such
a reversal. A THEODOLITE having a TELESCOPE that can be transited in its supports is a transit, and is sometimes
termed a transit theodolite. All modern THEODOLITES are transits.
An astronomical instrument having a TELESCOPE which can be so adjusted in position that the LINE OF SIGHT
may be made to define a VERTICAL CIRCLE. A transit used in astronomical work is usually termed either an astronomic(al) transit or a transit instrument.
In NAVIGATION, the position of two distant, fixed objects when they are in line to an observer; the line passing
through them and the observer being a LINE OF POSITION. See also RANGE.
254
5597
transit: broken telescope. A precise astronomic TRANSIT or THEODOLITE in which the light passing through the
OBJECTIVE LENS is reflected through a right angle by a prism placed in the HORIZONTAL AXIS. This hollow axis
is continued beyond the supports, and the EYEPIECE is fitted at one end.
5598
transit: local. The apparent passage of a CELESTIAL BODY across the MERIDIAN of the observer. See also
MERIDIAN TRANSIT.
5599
transit axis. See AXIS: HORIZONTAL.
5600
transit bearing. See BEARING.
5601
transit instrument. See TRANSIT.
5602
transitional water wave. See WAVE.
5603
transition layer. A water layer with a distinct change of the vertical gradient of a given parameter relative to adjacent
layers.
5604
transition zone. The water area between two opposing CURRENTS manifested by EDDIES, UPWELLING, RIPS, and
similar turbulent conditions occurring either vertically or horizontally; or a zone between two water masses of differing
physical characteristics such as temperature and/or SALINITY.
5605
transit magnetometer. See MAGNETOMETER.
5606
transit micrometer. See MICROMETER.
5607
transit passage. In straits used for international navigation, all ships and aircraft enjoy the unimpeded right of transit
passage. This means the freedom of navigation and overflight solely for the purpose of continuous and expeditious
transit of the strait between one part of the high seas or an exclusive economic zone and another part of the high seas or
an exclusive economic zone. See also INNOCENT PASSAGE.
5608
transit theodolite. See TRANSIT.
5609
transit traverse. See TRAVERSE.
5610
translocation. A method to improve the accuracy of satellite positioning by simultaneously using several receivers. One
receiver is deployed on a known position to obtain corrections required to match the known position and that derived
from satellite signals. These corrections are then transmitted to the other receivers.
5611
transmitter. One who or that which transmits or sends anything, particularly a RADIO TRANSMITTER.
5612
transparency. In OCEANOGRAPHY, the property of water to transmit light of different WAVE LENGTHS. Transparency sometimes is measured in percent of RADIATION that penetrates a distance of one METRE. Sometimes it is
expressed as the average DEPTH at which a SECCHI DISC disappears and reappears.
In PHOTOGRAPHY, a photographic PRINT on a clear base, especially adaptable for viewing by transmitted light.
Also, the light-transmitting capability of a material.
5613
transponder. A combined RECEIVER and TRANSMITTER whose function is to transmit SIGNALS automatically
when triggered by an INTERROGATOR. See TRANSCEIVER.
5614
transponder beacon. A beacon having a TRANSPONDER. Also called responder beacon.
5615
transport. The process by which a substance or quantity is carried past a fixed point, or across a fixed plane. In
OCEANOGRAPHY and METEOROLOGY, such quantities are: Heat, MOMENTUM, mass, dissolved impurities,
suspended particles, etc.
5616
transverse cylindrical orthomorphic projection. See PROJECTION: TRANSVERSE MERCATOR.
5617
transverse Mercator grid. The grid on a chart using the transverse Mercator projection.
5618
transverse Mercator projection. See PROJECTION.
5619
transverse wave. See WAVE.
5620
travelling wave. See WAVE: PROGRESSIVE.
255
5621
traverse. A method of surveying in which a sequence of lengths and DIRECTIONS of lines between points on the
EARTH are obtained from field measurements, and used in determining POSITIONS of the points. Also called survey
traverse.
5622
traverse: astronomical. A TRAVERSE in which the GEOGRAPHIC(AL) POSITIONS of the STATIONS are
obtained from ASTRONOMICAL OBSERVATIONS, and lengths and AZIMUTHS of lines are obtained by
computation.
5623
traverse: closed. A TRAVERSE which starts and ends upon the same STATION, or upon STATIONS whose relative
positions have been determined by other SURVEYS.
5624
traverse: hanging. See TRAVERSE: OPEN.
5625
traverse: open (or open end). A TRAVERSE which starts from a STATION of known or adopted POSITION, but
does not end upon such a STATION. Also called hanging traverse.
5626
traverse: plane table. A graphical TRAVERSE executed by PLANE TABLE methods.
5627
traverse: transit. A TRAVERSE in which the angles are measured with a TRANSIT or THEODOLITE and the
lengths with a suitable measuring device.
5628
traverse net. See TRIANGULATION NET.
5629
traverse point. See TURNING POINT.
5630
traverse sailing. See SAILING.
5631
traverse station. See STATION.
5632
traverse table. A TABLE giving relative values of various parts of plane right triangles, for use in solving such
triangles, particularly in connection with various SAILINGS.
5633
trench. A long, narrow and deep DEPRESSION of the SEA FLOOR with relatively steep sides.
A long narrow VALLEY between two MOUNTAIN RANGES, especially a rift valley or a U-shaped valley.
5634
trend. The general direction of something, such as a coastline.
5635
triangle of error. See COCKED HAT.
5636
triangulate. The process of TRIANGULATION.
5637
triangulation. A method of surveying in which the STATIONS are points on the GROUND at the vertices of a chain or
NETWORK of triangles. The angles of the triangles are measured instrumentally and the sides are derived by
computation from selected triangle sides called BASES (or BASE LINES), the lengths of which are obtained from
direct measurements on the GROUND.
5638
triangulation: arc of. A system of TRIANGULATION of limited width designed to progress in a single general
direction. Also called chain of triangulation.
5639
triangulation: flare. A method of TRIANGULATION in which simultaneous OBSERVATIONS are made on
parachute flares. This method is used for extending TRIANGULATION over lines too long to be observed by ordinary
methods.
5640
triangulation: floating. In hydrographic SURVEYING, a TRIANGULATION that may be carried out by means of
anchored BUOYS when surveying at such a distance from the LAND that the SIGNALS on the SHORE cannot be directly used for locating the SOUNDINGS. Floating triangulation can be either connected to and extended from the
STATIONS of a shore triangulation or of a fully floating type in which case the POSITIONS of the BUOYS are
obtained by means of OBSERVATIONS and measurements taken at sea. BUOYS are anchored in such a position as to
provide a framework for surveying the area.
5641
triangulation: order of. See TRIANGULATION CLASSIFICATION.
5642
triangulation: radial. See RADIAL TRIANGULATION.
256
5643
triangulation: ship-to-shore. A method of TRIANGULATION involving simultaneous OBSERVATIONS from three
shore STATIONS on a target carried by a ship offshore of the middle STATION. The middle STATION must be visible
from each of the two end STATIONS.
5644
triangulation classification. The classifying of TRIANGULATIONS into first-order, second-order, and third-order
triangulation, according to the ERROR OF CLOSURE OF TRIANGLES. In first-order work, the average closure is not
in excess of 1 SECOND; in second order work, it does not exceed 3 SECONDS; and in third-order work, it does not
exceed 5 SECONDS. For the basic first-order work, the computed length through the NETWORK must agree with the
measured BASE within 1 part in 50 000, as a minimum, and average about 1 in 75 000, or better.
5645
triangulation net. ARCS OF TRIANGULATION, sometimes with lines of TRAVERSE, connected together to form a
system of loops or circuits extending over an area. Sometimes called tie net when used to tie small ISLANDS together.
Also called traverse net or survey net.
5646
triangulation point. See STATION: TRIANGULATION.
5647
triangulation signal. See SIGNAL.
5648
triangulation station. See STATION.
5649
triangulation tower. A TRIANGULATION SIGNAL consisting of two separate structures, independent of one another
an inner structure which supports the THEODOLITE and sometimes the TARGET or SIGNAL LAMP, and an outer
structure which supports the observer and his assistants and sometimes the TARGET or SIGNAL LAMP. Triangulation
towers are used to elevate the LINE OF SIGHT above trees, topographic features, and other obstacles that might
interfere with the OBSERVATIONS. See BILBY STEEL TOWER.
5650
tribrach plate. A demountable, three-armed plate which is attached to an instrument stand or survey tower and on
which the bottoms of the FOOTSCREWS of the instrument rest in milled grooves.
5651
tributary. A RIVER which joins a larger one.
5652
trigonometric levelling. See LEVELLING.
5653
trigonometric station. See STATION: TRIANGULATION.
5654
trilaterate. The process of TRILATERATION.
5655
trilateration. A method of surveying wherein the lengths of the triangle sides are measured, usually by electronic
methods, and the angles are computed from the measured lengths. Compare with TRIANGULATION.
5656
trim. The way in which a ship floats on the water, in relation to her fore-and-aft line, whether on an even keel or down
by the bow or by the stern.
5657
tripod. A three-legged stand for THEODOLITE, CAMERA, SIGNALS, etc.
5658
tripod signal. See SIGNAL.
5659
tripping device. A device to pull equipment out of or to lower it into water.
5660
tripton. Collectively, all of the dead suspended particulate matter in aquatic habitats.
5661
trivet. A low support for a surveying instrument which is used where a TRIPOD cannot be used.
5662
trochoidal wave. See WAVE.
5663
tropical cyclone. CYCLONE of tropical origin of small diameter (some hundreds of kilometers). It is characterized by
violent WIND and torrential RAIN. Sometimes accompanied by a THUNDERSTORM.
5664
tropical month. See MONTH.
5665
tropical year. See YEAR.
5666
tropic higher high water. The HIGHER HIGH WATER of TROPIC TIDES.
5667
tropic higher low water. The HIGHER LOW WATER of TROPIC TIDES.
257
5668
tropic high water inequality. See DIURNAL INEQUALITY.
5669
tropic lower high water. The LOWER HIGH WATER of TROPIC TIDES.
5670
tropic lower low water. The LOWER LOW WATER of TROPIC TIDES.
5671
tropic low water inequality. See DIURNAL INEQUALITY.
5672
tropic of Cancer. The northern PARALLEL OF DECLINATION, approximately 23°27' from the CELESTIAL
EQUATOR, reached by the SUN at its maximum northerly DECLINATION, or the corresponding PARALLEL on the
EARTH.
5673
tropic of Capricorn. The southern PARALLEL OF DECLINATION, approximately 23°27' from the CELESTIAL
EQUATOR, reached by the SUN at its maximum southerly DECLINATION, or the corresponding PARALLEL on the
EARTH.
5674
tropic range. Short for GREAT TROPIC RANGE.
5675
tropics. See TORRID ZONE.
5676
tropic tide. See TIDE.
5677
tropopause. Upper limit of the TROPOSPHERE.
5678
troposphere. Lower part of the terrestrial ATMOSPHERE, extending from the surface up to a HEIGHT varying from
about 9 km at the POLES to about 17 km at the EQUATOR, in which temperature decreases fairly regularly with
HEIGHT.
From an analogy with the ATMOSPHERE, the term is sometimes applied in OCEANOGRAPHY to the upper ocean
layer of relatively high temperature that is found in middle and lower LATITUDES and within which strong
CURRENTS are present. See STRATOSPHERE.
5679
tropospheric scattering. Diffusion of electromagnetic waves when traversing the troposphere. See also:
SCATTERING.
5680
trough. A long DEPRESSION of the SEA FLOOR normally wider and shallower than a TRENCH.
The lowest part of a WAVE between successive WAVE CRESTS. Also called wave trough.
Region of the ATMOSPHERE in which the pressure is low relative to the surrounding regions at the same level. It is
represented on a WEATHER CHART by a system of nearly parallel ISOBARS or CONTOURS, of approximately Vshape, which are concave towards a DEPRESSION.
5681
trough compass. See DECLINATOIRE.
5682
true (adj.). Related to TRUE NORTH.
Actual, as contrasted with fictitious, as true SUN.
Related to a fixed point, either on the EARTH or in space, as TRUE WIND; in contrast with relative, which is
related to a moving point.
Corrected, as TRUE ALTITUDE.
5683
true altitude. See ALTITUDE.
5684
true azimuth. See AZIMUTH.
5685
true bearing. See BEARING.
5686
true course. See COURSE.
5687
true horizon. See HORIZON.
5688
true meridian. See MERIDIAN.
5689
true north. See NORTH.
5690
true solar time. See TIME: APPARENT SOLAR.
5691
true sun. See SUN: APPARENT.
258
5692
true wind. WIND VECTOR in relation to the EARTH's surface. For a moving object it is the vector sum of the
RELATIVE WIND and the VELOCITY of the object.
5693
trumpet buoy. See BUOY: SOUND.
5694
trunnion axis. See AXIS: HORIZONTAL.
5695
tsunami. A long-period sea wave produced by a submarine EARTHQUAKE or volcanic eruption. It may travel
unnoticed across the OCEAN for thousands of MILES from its point of origin. It builds up to great HEIGHTS over
shoal water. Also called tunami, TIDAL WAVE, seismic sea wave.
5696
tubular compass. See COMPASS.
5697
tufa. A chemical SEDIMENTARY ROCK composed of calcium carbonate or silica, precipitated from percolating
ground water or from a SPRING.
5698
tuff. A ROCK formed of fragments of volcanic origin, DUST, ashes, etc., thrown out of a volcano during an eruption,
frequently hardened to a ROCK. Hence tuff-cone, a volcanic cone built up of such material.
5699
tuff-cone. See TUFF.
5700
tunny net. A net built at sea for catching tunnies.
5701
turbidite. Turbidity current deposits, characterized by both vertically and horizontally graded bedding.
5702
turbidity. Reduced water clarity resulting from the presence of suspended matter. Water is considered turbid when its
load of suspended matter is visibly conspicuous, but all waters contain some suspended matter and therefore are turbid.
Reduced transparency of the ATMOSPHERE, caused by absorption and SCATTERING of RADIATION by solid
or liquid particles, other than CLOUDS, held there in suspension.
5703
turbidity current. See CURRENT.
5704
turbulence. A state of fluid flow in which the instantaneous VELOCITIES exhibit irregular and apparently random
fluctuations, so that in practice only statistical properties can be recognized and submitted to analysis.
Superimposed on the mean motion of the air, an agitation composed of air motions which are uncoordinated and in a
state of continuous change.
5705
turbulent flow. A FLOW characterized by TURBULENCE.
5706
turning basin. An enlargement of a channel for turning vessels. Also called manoeuvering basin.
5707
turning buoy. A BUOY marking a turn, as in a CHANNEL.
5708
turning point. In LEVELLING, a point on which both a minus sight (FORESIGHT) and a plus sight (BACKSIGHT)
are taken on a line of DIRECT LEVELLING.
In TOPOGRAPHIC SURVEYS, any point on which the rod is held while the instrument (PLANE TABLE) is
moved to another STATION.
In a TRAVERSE, any point of junction of two LEGS. Also called traverse point.
5709
turn of the tide. See CHANGE OF TIDE.
5710
twilight. The periods of incomplete darkness following SUNSET (evening twilight) or preceding SUNRISE (morning
twilight). Twilight is designated as civil, nautical, or astronomical, as the darker limit occurs when the centre of the
SUN is 6°, 12°, or 18°below the CELESTIAL HORIZON, respectively.
5711
twilight stars. STARS suitably placed for ASTRONOMICAL OBSERVATION during morning or evening
TWILIGHT.
5712
two-way route. A route within defined limits inside which two-way traffic is established, aimed at providing safe
passage of ships through waters where navigation is difficult or dangerous.
5713
tyfon. See TYPHON.
259
5714
type. In printing (TYPOGRAPHY) a metal block having a raised letter or figure which, when inked, is used to make an
impression on paper or other material. Type can also be in the form of negative or positive stripping film.
5715
type face. A type of print, such as Roman, Egyptian, Caslon, etc.
5716
type of tide. The characteristic feature of the TIDE (TIDAL CURRENT) determined from the combination of its
diurnal and semidiurnal components. TIDES are classified as SEMIDIURNAL, MIXED and DIURNAL, but there are
no sharply defined limits separating the groups.
5717
typhon. A diaphragm HORN which operates under the influence of compressed air or steam. Called SIREN in
Canadian terminology. Also called tyfon.
5718
typhoon. Name given to TROPICAL CYCLONES of the China Sea and, more generally, of the north-west Pacific.
260
U
5719
ultra high frequency (UHF). See FREQUENCY: RADIO.
5720
ultrashort wave. See WAVE.
5721
ultrasonic (adj.). Having a FREQUENCY above the audible RANGE.
5722
ultrasonic depth finder. See ECHO SOUNDER.
5723
ultrasonics. The science and technology relating to SOUND WAVES of FREQUENCIES above the audible RANGE.
5724
ultraviolet (adj.). Having a FREQUENCY immediately beyond the violet end of the visible SPECTRUM. Said of
RAYS of shorter WAVE LENGTH than visible light but longer than X-RAYS.
5725
uncontrolled mosaic. A MOSAIC composed of uncorrected PRINTS, the detail of which has been matched from print
to print without GROUND CONTROL or other ORIENTATION.
5726
uncovered (adj.). Above water. The opposite is SUBMERGED.
5727
uncovers. See COVERS AND UNCOVERS.
5728
undercliff. A TERRACE or lower CLIFF formed by a LANDSLIDE. Also written as two words.
5729
undercurrent. A CURRENT below the surface, particularly one flowing in a direction or at a SPEED differing from
the SURFACE CURRENT.
5730
underground mark. A STATION MARK set and plumbed below the centre of a SURFACE MARK and separated
therefrom so as to preserve the STATION in case of accident to the SURFACE MARK. Also called subsurface mark.
5731
underkeel clearance. The distance between the lowest point of the ship's hull, normally some point on the keel, and the
sea bottom.
5732
underkeel allowance. The estimated minimum UNDERKEEL CLEARANCE in a given channel accounting for the
ship's squat, movement due to swell, tide height etc.
5733
undertow. A seaward FLOW near the BOTTOM of a sloping BEACH.
The subsurface return by gravity flow of the water carried up on SHORE by WAVES or BREAKERS. See also
BACKRUSH.
5734
underwater acoustics. A special field of technical acoustics dealing with the physics of sound propagation in the
water.
5735
underwater ice. See ANCHOR ICE.
5736
underwater navigation. See NAVIGATION.
5737
underwater photogrammetry. See PHOTOGRAMMETRY.
5738
underwater position fixing. A method of position fixing for surface vessels, submersibles or towed devices in relation
to a network of underwater acoustic beacons on the seabed with known relative positions.
5739
underwater sound projector. A TRANSDUCER used to produce SOUND in water. The conversion from electrical
energy to SOUND is achieved through the use of either the piezoelectric or magnetostrictive effect. See
MAGNETOSTRICTION and PIEZOELECTRICITY.
5740
underway (or under way) (adv.). Without MOORINGS; not secured in any way to the ground or a WHARF.
In motion, particularly the start of such motion after a standstill.
5741
undulating (adj.). Having the form of WAVES or SWELLS, as undulating LAND.
5742
undulation. A continuously propagated motion to and from, in any fluid or elastic medium, with no permanent
translation of the particles themselves.
261
5743
undulation of the geoid. The distance between the mathematical REFERENCE SPHEROID and the GEOID.
5744
unidirectional antenna. See ANTENNA.
5745
unifilar magnetometer. See MAGNETOMETER.
5746
uniform flow. Any CURRENT in which neither CONVERGENCE nor DIVERGENCE is present.
5747
unit magnetic pole. In magnetic theory, a fictitious entity analogous to a unit electric charge in electrostatic theory.
5748
United Nations (UN). The major international organization established to maintain international peace and security, to
develop friendly relations among nations, to achieve cooperation in solving international problems.
5749
United Nations Conference on Trade and Development (UNCTAD). Helps to restructure patterns of international
trade in order to enable developing countries to play their part in world commerce.
5750
United Nations Development Programme (UNDP). An UN agency which registers organizations and institutions
located in developing countries which have the capacity for cooperative technical activities with organizations in other
developing nations. The subject matter includes education and training courses, research and technological development
activities, consulting and expert services, and scientific and technical information and used primarily by institutions and
governments in developing countries.
5751
United Nations Educational, Scientific, and Cultural Organization (UNESCO). Organized in 1945 to promote
collaboration among nations in education, science, and culture; UNESCO is the parent agency for the
INTERGOVERNMENTAL OCEANOGRAPHIC COMMISSION.
5752
universal drafting machine. See PROTRACTOR: PARALLEL MOTION.
5753
universal level. See LEVEL: SPIRIT.
5754
Universal Time (UT). TIME as defined by the rotational motion of the EARTH and determined from the apparent
diurnal motions which reflect this ROTATION. Because of variations in the rate of rotation, Universal Time is not
rigorously uniform. Also called Greenwich mean time.
5755
Universal Time 0 (UT0). The uncorrected TIME of the EARTH's ROTATION as measured by the TRANSIT of
STARS across the observer's MERIDIAN. This ROTATION is referred to a fiducial mark on the ECLIPTIC which
approximates the position of the MEAN SUN.
5756
Universal Time 1 (UT1). UT0 corrected for polar motion.
5757
Universal Time 2 (UT2). UT1 corrected for seasonal variations in the EARTH's ROTATION.
5758
Universal Time Coordinated (UTC). The time scale that is available from most broadcast time signals. It differs from
INTERNATIONAL ATOMIC TIME by an integral number of seconds. UTC is maintained within 1 second of UT1 by
the introduction of 1-second steps (leap seconds) when necessary, normally at the end of December. DUT1, an
approximation to the difference UT1 minus UTC, is transmitted in code on broadcast time signals.
5759
Universal Transverse Mercator (UTM) grid. See GRID.
5760
unprotected reversing thermometer. See THERMOMETER.
5761
unrecoverable station. See STATION.
5762
unsurveyed area. An area where survey data is non-existent or very poor.
5763
unsurveyed clearance depth. The estimated depth over an unsurveyed wreck or obstruction over which the exact depth
is unknown but which is considered to have a safe clearance to the depth shown.
5764
upland. The higher GROUND of a region contrasted with the VALLEYS and PLAINS. Used in contrast to
LOWLAND.
5765
uplifted reef. A CORAL REEF exposed above water level.
262
5766
upper branch. That half of a MERIDIAN or CELESTIAL MERIDIAN from POLE to POLE which passes through a
place or its ZENITH.
5767
upper culmination. Upper TRANSIT.
5768
upper limb. See LIMB.
5769
upper limit of navigability. The character of a river will, at some point along its length, change from navigable to
non-navigable. Very often that point will be at a major fall or rapids, or other place where there is a marked decrease in
the navigable capacity of the river. The upper limit will therefore often be the same point traditionally recognized as the
head of navigation, but may, under some of the tests described above, be at some point yet farther upstream.
5770
upper transit. See MERIDIAN TRANSIT.
5771
uprush. The rush of water up onto the BEACH following the breaking of a WAVE. See RUN-UP.
5772
upstream (adj. & adv.). Toward the SOURCE of a STREAM. The opposite is DOWNSTREAM.
5773
upwelling. The process by which water rises from a lower to a higher DEPTH, usually as a result of DIVERGENCE
and offshore CURRENTS. See SINKING.
5774
upwind (adj. & adv.). In the direction from which the WIND is blowing. The opposite is DOWNWIND.
263
V
5775
vacuum lead. A CORER which makes use of HYDROSTATIC PRESSURE to force a tube into the BOTTOM
SEDIMENT.
5776
valley. A long DEPRESSION or hollow in the LAND lying between HILLS or stretches of high GROUND and usually
having a RIVER or STREAM flowing along the bottom.
5777
valley: median. See MEDIAN VALLEY.
5778
valley: submarine. A relatively shallow wide DEPRESSION with gentle SLOPES, the bottom of which grades continuously downward. This term is used for features that do not have canyon-like characteristics in any significant part of
their extent.
5779
valley line. See TALWEG.
5780
vane. A device to indicate the direction from which the WIND blows. Also called weather vane, wind vane. See
ANEMOMETER.
A SIGHT on an instrument used for observing BEARINGS, as on a PELORUS, BEARING CIRCLE, etc. Also
called sight (or sighting) vane.
A device to indicate the direction toward which the CURRENT flows.
5781
vanishing line. In PHOTOGRAMMETRY, the straight line on a PHOTOGRAPH upon which lie all the VANISHING
POINTS of all systems of parallel lines parallel to one plane.
5782
vanishing point. In PHOTOGRAMMETRY, the IMAGE in the plane of a PHOTOGRAPH, of the point toward which
a system of parallel lines in the object space converges.
5783
vanishing tide. See TIDE.
5784
variate. A variate is a quantity that may take on any of the values of a specified set with a specified relative frequency
or probability often known as random variable. It is to be regarded as defined not merely by a set of permissible values,
but by an associated frequency (probability) function expressing how often those values appear in a given situation.
5785
variation. The angle between the MAGNETIC and GEOGRAPHICAL MERIDIANS at any place, expressed in
DEGREES east or west to indicate the direction of MAGNETIC NORTH from TRUE NORTH. Also called magnetic
variation, or magnetic declination.
5786
variation: grid. Angular difference in direction between GRID NORTH and MAGNETIC NORTH. It is measured east
or west from GRID NORTH. Also called grivation, or grid magnetic angle.
5787
variation of the pole. A wandering of the POLES of the FIGURE OF THE EARTH with respect to its POLES of
ROTATION.
5788
variometer. An instrument for comparing magnetic forces, especially of the EARTH's MAGNETIC FIELD.
5789
varsol. An oil used as the liquid in some modern MAGNETIC COMPASSES.
5790
varve. A sedimentary DEPOSIT, bed, or lamination deposited in one season. It is usually distinguished by colour or
composition and used as an index to changes in the depositional environment.
5791
vectograph. A stereoscopic PHOTOGRAPH composed of two superimposed IMAGES which polarize light in planes
o
90 apart. When these IMAGES are viewed through polaroid spectacles with the polarization axes at right angles, an
impression of depth is obtained.
5792
vector. Direct connection between two points, either given as two sets of coordinates (points), or by direction and
distance from one given set of coordinates; or a point in a vector space defined by one set of coordinates relative to the
origin of a coordinate system.
5793
vector airborne magnetometer. See MAGNETOMETER.
5794
vector data presentation. Method of representing image features digitally by points, lines and polygons given through
their coordinates and appropriate code(s).
264
5795
vectorial angle. See COORDINATES: PLANE POLAR.
5796
veering wind. Clock-wise change of WIND direction, in either hemisphere.
5797
vein. A narrow LEAD or lane in PACK ICE.
In mineralogy, a crack or fissure in the ROCKS of the EARTH's CRUST in which highly heated waters from below
have deposited from solution crystalline minerals (especially vein quartz) and, under certain circumstances, metallic
minerals of economic importance.
5798
velocimeter. An instrument used for the 'in situ' measurement of the SPEED of SOUND in the SEA and other natural
waters.
5799
velocity. A vector quantity equal to SPEED in a given direction.
5800
velocity of sound. See SOUND VELOCITY.
5801
veneer. A thin LAYER of SEDIMENT covering a rocky surface.
5802
vent. The orifice through which molten LAVA reaches the CRATER of a volcano. Eventually it may become choked as
the LAVA solidifies to form a plug or neck.
5803
Venturi tube. The trade name for a short tube of smaller diameter in the middle than at the ends. When a fluid flows
through such a tube, the pressure decreases as the diameter becomes smaller, the amount of the decrease being
proportional to the SPEED of FLOW and the amount of restriction.
5804
vernal equinox. See EQUINOX.
5805
vernier. A short, auxiliary SCALE situated alongside the graduated SCALE of an instrument, by means of which
fractional parts of the smallest division of the primary SCALE can be measured accurately.
5806
vertex (pl. vertices). The highest point; the vertices of a GREAT CIRCLE are the points nearest the POLE. See APEX.
5807
vertical (adj.). In the DIRECTION OF GRAVITY; perpendicular to the plane of the HORIZON.
5808
vertical (n.). The direction in which the force of GRAVITY acts. A vertical line, plane, etc.
5809
vertical axis. See AXIS.
5810
vertical circle. See CIRCLE.
5811
vertical clearance. The minimum vertical space available for passage.
5812
vertical collimator. See COLLIMATOR.
5813
vertical control. See CONTROL.
5814
vertical control datum. See DATUM.
5815
vertical deflection. See DEFLECTION OF THE VERTICAL.
5816
vertical dilution of precision. See DILUTION OF PRECISION.
5817
vertical intensity of the earth's magnetic field. The strength of the vertical component of the EARTH's MAGNETIC
FIELD.
5818
vertical light(s). See LIGHT.
5819
vertical parallax. See PARALLAX: Y-.
5820
vertical photograph. See PHOTOGRAPH.
5821
vertical plane. See PLANE.
265
5822
very close pack ice. SEA ICE the CONCENTRATION of which is practically 10/10ths with little if any water present.
5823
very high frequency (VHF). See FREQUENCY: RADIO.
5824
very low frequency (VLF). See FREQUENCY: RADIO.
5825
very open pack ice. SEA ICE the CONCENTRATION of which ranges between 1/10ths 3/10ths.
5826
vessel traffic service (VTS). Any service implemented by a relevant authority primarily designed to improve safety and
efficiency of traffic flow and the protection of the environment. It may range from simple information messages, to
extensive organization of the traffic involving national or regional schemes.
5827
viaduct. A structure consisting of a series of arches or towers supporting a roadway, waterway, etc., across a
depression, etc.
5828
vibrating needle. A MAGNETIC NEEDLE used in compass adjustment to find the relative intensity of the horizontal
components of the EARTH'S MAGNETIC FIELD and the MAGNETIC FIELD at the compass location. Also called
horizontal force instrument. See COMPENSATION OF MAGNETIC COMPASS.
5829
vibration. Periodic motion of an elastic body or medium in alternately opposite directions from EQUILIBRIUM;
OSCILLATION.
The motion of a vibrating body during one complete CYCLE; two OSCILLATIONS.
5830
vigia. A PINNACLE, ROCK, or SHOAL the existence or POSITION of which is doubtful, or a warning note to this
effect on a CHART.
5831
vignetting. In PHOTOGRAPHY, a gradual reduction in DENSITY of parts of a photographic IMAGE due to the
stopping of some of the RAYS entering the LENS.
5832
violent storm. WIND with a speed between 56 and 63 KNOTS (Beaufort scale wind force 11).
5833
virtual image. See IMAGE.
5834
visibility. The extreme horizontal distance at which prominent objects can be seen and identified by the unaided eye.
5835
visibility: flight. The VISIBILITY forward from the cockpit of an aircraft in flight.
5836
visibility: meteorological. The greatest distance at which a black object of suitable dimensions can be seen and
recognized against the horizon sky, or, in the case of night observations, could be seen and recognized if the general
illumination were raised to the normal daylight level.
5837
visibility: radius of. The radius of a circle limiting the area in which an object can be seen under specified conditions.
5838
visible horizon. See HORIZON: APPARENT.
5839
visual display unit (VDU). See DISPLAY.
5840
visual line of position. A LINE OF POSITION determined by visual OBSERVATION of a LANDMARK, AID TO
NAVIGATION, etc.
5841
voe. An INLET, BAY, or CREEK.
5842
volcanic ash. Uncemented pyroclastic material consisting of fragments mostly under 4 millimetres in diameter. Coarse
ash is 1/4 to 4 millimetres in grain size; fine ash is below 1/4 millimetre. A constituent of some marine SEDIMENTS.
5843
volt. The unit of potential difference or electromotive force in the SI SYSTEM.
5844
vulgar (or common) establishment. See ESTABLISHMENT.
266
W
5845
wadi. A watercourse that is permanently dry or dry except for the rainy season.
5846
wake. The path of disturbed water or air behind a craft in motion.
5847
waning moon. See PHASES OF THE MOON.
5848
want of correspondence. See PARALLAX: Y-.
5849
warm front. Any non-occluded FRONT which moves in such a way that warmer air replaces colder air.
5850
warm pool. A body of warm water entirely surrounded by cold water.
5851
warning: gale. Meteorological message intended to warn those concerned of the occurrence or expected occurrence of
a WIND of Beaufort force 8 or 9 over a specified area.
5852
warning: hurricane. Meteorological message intended to warn those concerned of the occurrence or expected
occurrence of a WIND of BEAUFORT force 12 over a specified area.
Tropical cyclone warning relating to a HURRICANE.
5853
warning: navigation. See NAVIGATIONAL WARNING.
5854
warning: storm. Meteorological message intended to warn those concerned of the occurrence or expected occurrence
of a WIND of BEAUFORT force 10 or 11 over a specified area.
More generally, forecast of severe weather conditions.
5855
warping buoy. A BUOY so located that lines to it can be used for the movement of ships.
5856
wash. The visible or audible motion of agitated water; especially that caused by the passage of a vessel.
5857
washovers. Small DELTAS formed on the lagoon side of a BAR separating the LAGOON from the OPEN SEA.
STORM WAVES breaking over the BAR deposit SEDIMENT on the lagoon side in the form of DELTAS. Also called
wave deltas.
5858
watch. A small TIMEPIECE of a size convenient to be carried on the person.
5859
watch: comparing. A HACK WATCH, particularly one having its ERROR determined by comparison with a
CHRONOMETER.
5860
watch: hack. A WATCH used for timing OBSERVATIONS of CELESTIAL BODIES regulating ship's CLOCKS, etc.
5861
watch: stop. A WATCH that can be started, stopped, and reset at will, to indicate elapsed time.
5862
watch buoy. See STATION BUOY.
5863
water bottle. A device for collecting WATER SAMPLES from varying DEPTHS. They are lowered in an 'open' state
to the required DEPTH and can be closed before being hauled up by means of a MESSENGER. Water bottles can be
operated in series that is with more than one bottle on the wire rope so that WATER SAMPLES can be taken at a
number of DEPTHS on the same CAST. Also called water specimen cup.
5864
water bottle: insulated (or insulating). A WATER BOTTLE specially designed for measuring temperatures and
collecting WATER SAMPLES at moderate DEPTHS. This type of WATER BOTTLE is insulated to maintain the
temperature constant while being brought to the surface.
5865
water bottle: reversing. A WATER BOTTLE specially designed for use in deep sea waters. The bottle is lowered by
wire and can be closed watertight at any desired DEPTH, by means of a MESSENGER allowed to slide down the wire
and strike the reversing mechanism making the bottle turn upside down. Thus the enclosed WATER SAMPLE is not
contaminated by water at higher levels or lost by leakage after the bottle is brought on board. REVERSING
THERMOMETERS are attached to reversing water bottles. See EKMAN BOTTLE and NANSEN BOTTLE.
5866
water colour. See SEA WATER: COLOUR OF.
267
5867
water column. A vertical continuum of water from sea surface to sea-bed.
5868
water content. A ratio; 100 multiplied by the weight of water in a bottom sediment sample divided by the weight of the
dried sample, expressed as a percentage.
5869
watercourse. A STREAM of water, a RIVER or a BROOK; also an artificial CHANNEL for the conveyance of water.
5870
water front. LAND at the end of a STREAM, HARBOUR, etc. The part of a city or town on such LAND; WHARF or
dock area.
5871
water levelling. See LEVELLING.
5872
waterline. The line marking the junction of LAND and water.
The line along which the surface of the water touches a vessel's hull.
Also written as two words.
5873
water-parting. A summit or boundary line separating the drainage districts of two STREAMS or COASTS; a divide or
WATERSHED.
5874
water sample. A portion of water brought up from a certain DEPTH to determine its composition, or physical
properties viz: temperature, SALINITY and DENSITY.
5875
water sampler. Any device for obtaining a WATER SAMPLE. Also called water sampling device. See WATER
BOTTLE.
5876
watershed. WATER-PARTING.
The whole region or area contributing to the supply of a RIVER or LAKE; drainage area; catchment area or BASIN.
5877
water signal. See SIGNAL.
5878
water sky. Typical dark patches and strips on low CLOUDS over a water area enclosed in ICE or behind its edge.
5879
water specimen cup. See WATER BOTTLE.
5880
water vapor. Water in the gaseous phase.
5881
waterway. A line of water (RIVER, CHANNEL, etc.) which can be utilized for communication or transport.
5882
watt. The unit of power in the SI system.
5883
wave. A disturbance which moves through or over the surface of the medium with SPEED dependent upon the
properties of the medium.
A ridge deformation, or UNDULATION of the surface of a liquid.
5884
wave: capillary. A WAVE whose VELOCITY of propagation is controlled primarily by the surface tension of the
liquid in which the WAVE is travelling. Water waves of length less than one INCH are considered to be capillary
waves.
5885
wave: carrier. A RADIO WAVE used as a vehicle for conveying intelligence, generally by MODULATION. Also
called carrier.
5886
wave: cellular. System of SURFACE WAVES in which the OSCILLATION of water is limited as by solid
BOUNDARIES. The PERIOD is the same in adjacent cells.
5887
wave: compressional. A WAVE in an elastic medium which causes an element of the medium to change its volume
without undergoing rotation.
5888
wave: continuous. A series of WAVES of like AMPLITUDE and FREQUENCY. See WAVE: MODULATED,
PULSE.
5889
wave: cycloidal. A very steep, symmetrical WAVE whose CREST forms an angle of 120 DEGREES. The wave form
is that of a cycloid. A TROCHOIDAL WAVE of maximum steepness.
268
5890
wave(s): damped. WAVE(S) the AMPLITUDE of which becomes progressively smaller.
5891
wave: direct. A subdivision of the space wave component of the electromagnetic GROUND WAVE. This WAVE is
propagated directly through space, i.e., it follows the shortest path between TRANSMITTER and RECEIVER.
5892
wave: edge. An ocean wave travelling parallel to a COAST, with CRESTS normal to the COASTLINE. Such a WAVE
has a HEIGHT that diminishes rapidly seaward and is negligible at a distance of one WAVE LENGTH offshore.
5893
wave: electromagnetic. WAVE(S) of associated electric and magnetic fields characterized by variations of the fields.
The electric and magnetic fields are at right angles to each other and to the direction of propagation.
An electromagnetic wave is coherent if the phase-time relationship is constant throughout the propagation path.
5894
wave: forced. A WAVE generated and maintained by a continuous force, in contrast to a FREE WAVE that continues
to exist after the generating force has ceased to act.
5895
wave: free. A WAVE that continues to exist after the generating force has ceased to act, in contrast with a FORCED
WAVE that is generated and maintained by a continuous force.
A free wave on a water surface is one created by a sudden impulse, thereafter influenced only by friction, the
dimensions of the BASIN, and the dispersive character of the water medium it moves in. Most ocean surface waves
except TIDAL WAVES are free waves. See OSCILLATION.
5896
wave: gravity. A WAVE whose VELOCITY of propagation is controlled primarily by GRAVITY. Water waves of
length greater than 2 INCHES are considered gravity waves.
5897
wave: ground. That portion of a RADIO WAVE in proximity to and affected by the GROUND, being somewhat
refracted by the lower ATMOSPHERE, diffracted by the surface of the EARTH and retarded by the resistivity of the
EARTH. Such a WAVE travels more or less parallel to the surface of the EARTH. See WAVE: SKY.
5898
wave: indirect. Any WAVE which arrives by an indirect path having undergone an abrupt change of direction by
REFRACTION or REFLECTION. See WAVE: SKY.
5899
wave: internal. A WAVE that occurs within a fluid whose DENSITY changes with DEPTH, either abruptly at a sharp
surface of discontinuity (an INTERFACE) or gradually. Also called boundary wave.
5900
wave: longitudinal. A WAVE in which the direction of displacement of each particle in the medium is perpendicular to
the WAVE FRONT.
5901
wave: Love (or Q-wave). A TRANSVERSE WAVE propagated along the BOUNDARY of two elastic media which
both have rigidity, i.e. both media must be capable of propagating TRANSVERSE WAVES.
A surface seismic wave in which the particles of an elastic medium vibrate transverse to the direction of the
WAVE's travel, with no vertical component.
5902
wave: modulated. A WAVE which varies in some characteristic in accordance with the variations of a
MODULATING WAVE. See WAVE: CONTINUOUS.
5903
wave: modulating. A WAVE which modulates a CARRIER WAVE.
5904
wave: oscillatory. A WAVE in which each individual particle oscillates about a point with little or no permanent
change in position. The term is commonly applied to progressive oscillatory waves in which only the form advances, the
individual particles moving in closed ORBITS, as ocean waves in deep waters. Distinguished from a WAVE OF
TRANSLATION.
5905
wave(s): periodic. WAVES which are repeated at regular intervals.
5906
wave: pressure. See PRESSURE WAVE.
5907
wave: progressive. A WAVE which is manifested by the progressive movement of the wave form. The opposite is a
STANDING WAVE. Also called travelling wave.
5908
wave: propagation. The travel of waves through or along a medium.
5909
wave(s): radio. ELECTROMAGNETIC WAVES of FREQUENCIES generally higher than those of audible SOUND
WAVES but lower than those of heat and light waves. Also called hertzian waves.
269
5910
wave: reflected. A WAVE that has had its direction of motion changed by REFLECTION.
5911
wave: refracted. A WAVE that has had its direction of motion changed by REFRACTION.
5912
wave: short. A RADIO WAVE shorter than those of the standard broadcasting band.
In OCEANOGRAPHY, WAVES under conditions where the relative DEPTH (water depth/wave length) is greater
than 0.5 and where the PHASE VELOCITY is independent of water depth, but dependent upon WAVE LENGTH.
5913
wave: sky. An indirect RADIO WAVE which travels from the transmitting ANTENNA into the sky, where the
IONOSPHERE bends it back toward the EARTH. Also called ionospheric wave. See WAVE: GROUND.
5914
wave: solitary. A WAVE OF TRANSLATION consisting of a single CREST rising above the undisturbed liquid level,
without any accompanying TROUGH, in contrast with a WAVE TRAIN.
5915
wave: sound. A mechanical disturbance advancing with finite VELOCITY through an elastic medium and consisting of
longitudinal displacements of the ultimate particles of the medium, that is, consisting of compressional and rarefactional displacements parallel to the direction of advance of the disturbance; a LONGITUDINAL WAVE. Also called
sonic wave, or acoustic wave.
5916
wave: spherical. A WAVE whose wave front surfaces are concentric spheres. Such WAVES propagate from a point
source.
5917
wave: standing. A type of WAVE in which the surface of the water oscillates vertically between fixed points, called
NODES, without progression. The points of maximum vertical RISE and fall are called antinodes or LOOPS. At the
NODES, the underlying water particles exhibit no vertical motion but maximum horizontal motion. At the antinodes the
underlying water particles have no horizontal motion and maximum vertical motion. They may be the result of two
equal progressive WAVE TRAINS travelling through each other in opposite directions. Also called stationary wave.
5918
wave: storm. A wind-generated sea surface wave of great HEIGHT. See STORM SURGE.
5919
wave: surface. A progressive GRAVITY WAVE in which the disturbance (that is, the particle movement in the fluid
mass as well as the surface movement) is confined to the upper limits of a body of water. Strictly speaking this term
applies to those progressive GRAVITY WAVES whose celerity depends only upon the WAVE LENGTH.
5920
wave: tidal. The wave motion of the TIDES.
In popular usage, any unusually high (and therefore destructive) water level along a SHORE. It usually refers to
either a STORM SURGE or TSUNAMI.
5921
wave: tide. See TIDE.
5922
wave: transitional water. A progressive GRAVITY WAVE in water whose DEPTH is less than 1/2 but more than
1/25 the WAVE LENGTH. Often called shallow water wave.
5923
wave: transverse. A WAVE in which the direction of propagation of the WAVE is normal to the displacements of the
medium, for example, a vibrating string. The GRAVITY WAVE in which fluid parcels move in circular ORBITS is an
example of a mixed transverse-longitudinal wave.
5924
wave: trochoidal. A progressive OSCILLATORY WAVE whose form is that of a prolate cycloid or trochoid. It is
approximated by WAVES of small AMPLITUDES.
5925
wave: ultrashort. A RADIO WAVE shorter than 10 METRES.
5926
wave: wind. A WAVE resulting from the action of WIND on a water surface. See FETCH.
5927
wave age. The state of development of a wind-generated sea surface wave, conveniently expressed by the ratio of wave
speed to wind speed. WIND SPEED is usually measured at about 8 METRES above STILL WATER LEVEL.
5928
wave base. The greatest DEPTH at which SEDIMENT on the SEA FLOOR can just be stirred by the oscillating water.
5929
wave crest. The highest part of a WAVE.
270
5930
wave deltas. See WASHOVERS.
5931
wave direction. The direction from which WAVES are moving.
5932
wave forecasting. The theoretical determination of future wave characteristics; usually from observed or predicted
meteorological or oceanographic PHENOMENA.
5933
waveform. The graphical representation of a WAVE, showing variation of AMPLITUDE with time. Also written as
two words.
5934
wave front. The leading side of a WAVE.
5935
wave generation. The creation of WAVES by natural or mechanical means.
In WAVE FORECASTING the growth of WAVES caused by a WIND blowing over a water surface for a certain
period of time. The area involved is called the generating area or FETCH.
5936
wave group. A series of WAVES in which the WAVE DIRECTION, WAVE LENGTH, and WAVE HEIGHT vary
only slightly.
5937
wave height. The vertical distance between a WAVE CREST and the preceding WAVE TROUGH.
5938
wave interference. The PHENOMENON which results when WAVES of the same or nearly the same FREQUENCY
are superposed. It is characterized by a spatial or temporal distribution of AMPLITUDE of some specified characteristic
differing from that of the individual superposed WAVES.
5939
wave length. The distance between corresponding points of two successive PERIODIC WAVES in the direction of
propagation, for which the OSCILLATION has the same PHASE. Unit of measurement in METRES. Also written as
one word.
5940
wavemeter. An instrument for measuring WAVES. One used for ocean waves usually measures HEIGHT and
PERIOD; one used for ELECTROMAGNETIC or SOUND WAVES usually measures length. Also written as two
words.
5941
wave of translation. A WAVE in which the individual particles of the medium are shifted in the direction of wave
travel, as ocean waves in shoal waters. Distinguished from an OSCILLATORY WAVE.
5942
wave period. The time, in SECONDS, required for a WAVE CREST to traverse a distance equal to one WAVE
LENGTH.
5943
wave refraction. See REFRACTION OF WATER WAVES.
5944
wave spectrum. In ocean wave studies, a graph showing the distribution of WAVE HEIGHTS with respect to FREQUENCY in a wave record.
5945
wave train. A series of WAVES moving in the same direction. See WAVE: SOLITARY.
5946
wave trough. See TROUGH.
5947
wave velocity. The SPEED at which the individual wave form advances.
A vector quantity that specifies the SPEED and direction with which a SOUND WAVE travels through a medium.
5948
waxing moon. See PHASES OF THE MOON.
5949
way. The motion of a vessel through the water.
5950
weather (adj.). Of or pertaining to the direction from which the WIND is blowing, as opposed to LEE.
5951
weather. State of the ATMOSPHERE at a given time, as defined by the various meteorological elements.
5952
weather analysis. Operation of studying the general state of the ATMOSPHERE over a region, with respect to
SYNOPTIC CHARTS. Also called synoptic analysis.
5953
weather buoy. An Ocean Data Acquisition System (ODAS) used for collecting oceanographic or meteorological
information. ODAS buoys are up to 40 feet in diameter.
271
5954
weather forecast. Statement of the expected meteorological conditions for a specified period, and for specified area or
portion of air space.
5955
weather chart (or map). See CHART.
5956
weathered ice. Hummocked POLAR ICE subjected to weathering which has given the HUMMOCKS and PRESSURE
RIDGES a rounded form. If the weathering continues, the surface may become more and more even.
5957
weather ship. See OCEAN STATION VESSEL.
5958
weather shore. SHORE that is to windward of a vessel. See LEE SHORE.
5959
weather side. The side of a vessel toward which, or the side of a CHANNEL from which the WIND is blowing.
5960
weather signal. See SIGNAL.
5961
weather tide. See TIDE: WINDWARD.
5962
weather vane. See VANE.
5963
weber. The unit of magnetic flux in the SI SYSTEM.
5964
wedge. In optics, a refracting prism of very small deviation such as those used in the EYEPIECE of some
STEREOSCOPES.
In METEOROLOGY, term synonymous with RIDGE, though usually applied to a fast-moving RIDGE between two
DEPRESSIONS or TROUGHS.
5965
weight. The force with which a body is attracted by GRAVITY.
Any block or mass of material used for its heaviness.
The relative value of an OBSERVATION, source, or quantity when compared with other OBSERVATIONS, sources, or quantities of the same or related quantities. The value determined by the most reliable method is assigned the
greatest weight.
5966
weighted mean. A value obtained by multiplying each of a series of values by its assigned WEIGHT and dividing the
sum of those products by the sum of the WEIGHTS.
5967
weir. A DAM erected across a RIVER to raise the level of the water.
A fence of stakes set in a RIVER or along the SHORE as a trap for fish.
The word is now restricted to smaller works, the larger are called DAMS.
5968
well: appraisal. A borehole drilled to evaluate an oil field or gas field.
5969
well: development. A borehole drilled, usually from a production platform, after an oil field or gas field has been
judged capable of economic production.
5970
well: deviated. A borehole drilled at an oblique angle to evaluate or remove oil or natural gas reserves not directly
below the drilling structure.
5971
well: offshore. A borehole that produces or is capable of producing oil or natural gas.
5972
well: plugged. A borehole which has been sealed with a plug and permanently abandoned.
5973
well: production. A borehole, producing oil or natural gas, which is covered by a seabed installation of valves and
pipelines for the controlled removal of the product. See also SUB-SEA COMPLETION.
5974
well: suspended. A borehole that has been temporarily abandoned pending future development. An obstruction up to 5
metres high may remain on the sea-floor.
5975
wellhead: offshore. See WELL: OFFSHORE.
5976
wellhead: submerged. A submarine structure projecting some distance above the seabed and capping a temporarily
abandoned or suspended oil or gas well.
272
o
o
5977
westerlies. Zone, lying between the approximate LATITUDES 35 and 65 in each hemisphere, in which the air motion
is mainly from west to east, especially in the high TROPOSPHERE and low STRATOSPHERE. Near the EARTH's
surface, the zone is particularly well marked in the southern hemisphere.
5978
westing. The distance a craft makes good to the west. The opposite is EASTING.
5979
wet-bulb thermometer. See THERMOMETER.
5980
wet compass. See COMPASS: LIQUID.
5981
wet density. The ratio of the WEIGHT of the solid particles of a BOTTOM SEDIMENT and the contained moisture to
its total volume.
5982
wet dock. See DOCK.
5983
wet fog. See FOG.
5984
wetlands. The term "wetlands" means those areas that are inundated or saturated by surface or ground water at a
frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of
vegetation typically adapted for life in saturated soil conditions. Wetlands generally include SWAMPS, MARSHES,
BOGS and similar areas.
5985
wharf. A structure serving as a berthing place for vessels.
5986
whirlpool. Water in rapid rotary motion. See EDDY.
5987
whirlwind. General term for a small-scale rotating column of air.
5988
whitecap. A CREST of a WAVE which becomes unstable in deep water, toppling over or breaking. See BREAKING
OF WAVES.
5989
wind. Air motion relative to the EARTH'S surface. Unless it is otherwise specified, only the horizontal component is
considered.
5990
wind circulation. The flow of air through a given area.
5991
wind direction. See DIRECTION OF WIND.
5992
wind driven current. See CURRENT.
5993
wind force. Number on a progressive scale (BEAUFORT WIND SCALE) corresponding to the effects produced by
WINDS within a range of speeds.
Force exerted by the wind on a construction, object, etc.
5994
wind rose. For a given STATION and period of time, a star-shaped DIAGRAM indicating the relative frequencies of
different DIRECTIONS OF WIND, sometimes also the frequencies of groups of WIND SPEEDS in different directions.
5995
wind set-up. The vertical rise in the STILL WATER LEVEL on the leeward side of a body of water caused by wind
stresses on the surface of the water.
The difference in STILL WATER LEVELS on the windward and the leeward sides of a body of water caused by
wind stresses on the surface of water.
Synonymous with wind tide. Wind tide is usually reserved for use on the OCEAN and large bodies of water. Wind
set-up is usually reserved for use on RESERVOIRS and smaller bodies of water. See TIDE: METEOROLOGICAL.
5996
wind speed. Ratio of the distance covered by the air to the time taken to cover it. The 'instantaneous speed' or, more
briefly, the 'speed', corresponds to the case of an infinitely small time interval. The 'mean speed' corresponds to the case
of a finite time interval.
5997
wind tide. See WIND SET-UP.
5998
wind vane. See VANE.
5999
wind velocity. See WIND VECTOR.
273
6000
wind vector (or wind velocity). Vector drawn in the sense and direction of the WIND and of length proportional to
WIND SPEED.
6001
window. In computer applications, a rectangular subdivision of the screen showing information without affecting other
parts of the screen; a method allowing to view different items of information (e.g. different data sets or graphics) at the
same time. On graphical displays a window may be selected with the cursor and subsequently be enlarged (ZOOM).
6002
windward (adj. & adv.). In the general direction from which the WIND blows; in the WIND; on the WEATHER SIDE.
The opposite is LEEWARD.
6003
windward tide. See TIDE.
6004
wind wave. See WAVE.
6005
winter ice. More or less unbroken, level SEA ICE of not more than one winter's growth originating from YOUNG ICE.
Thickness from 15 cm to 2 m.
6006
winter solstice. See SOLSTICE.
6007
wire: base. See BASE TAPE (or WIRE).
6008
wire: invar. A wire made of INVAR metal used in measurement of geodetic BASES.
6009
wire: sounding. See SOUNDING.
6010
wire and bar sweep. See BAR SWEEPING and WIRE DRAG SWEEP.
6011
wire angle. The angle measured between the SOUNDING WIRE, or the oceanographic wire, and the VERTICAL.
6012
wire angle indicator. A device used to measure the angle of the SOUNDING WIRE, or the oceanographic wire, from
the VERTICAL. It consists of a PROTRACTOR with a weighted plumb arm. The indicator is suspended from the wire
at two points and the plumb arm points to the WIRE ANGLE. Also called inclinometer.
6013
wire drag. An apparatus for surveying rocky areas where normal sounding methods are insufficient to insure the
discovery of all existing OBSTRUCTIONS, PINNACLES, ROCKS, etc., above a given depth or for determining the
least DEPTH of an area. It consists essentially of a buoyed wire towed at the desired DEPTH by two LAUNCHES.
Often shortened to drag. See DRAG (v.t.).
6014
wire drag survey. See SURVEY.
6015
wire drag sweep. See SURVEY: WIRE DRAG.
6016
wireless. See RADIO.
6017
wire sounding. See SOUNDING.
6018
witness mark. A MARK placed at a known distance and direction from a property corner, BASE TERMINAL, or
survey STATION, to aid in its recovery and identification.
6019
Wollaston current meter. A CURRENT METER similar but much larger and heavier than the EKMAN CURRENT
METER. It is equipped with recording mechanisms and is suitable for measuring CURRENTS up to six KNOTS. The
Wollaston current meter is designed for use from ships at anchor.
6020
word. An addressable subdivision of storage memory of a computer system. Usually an integer number of BYTES (e.g.
4 bytes = 32 bit) indicating the standard length of number representation in storage.
6021
working chart. See CHART.
6022
working pendulum. See PENDULUM.
6023
World Geodetic System. A global geodesic reference system developed by the USA for satellite position fixing and
recommended by IHO for hydrographic and cartographic use.
6024
World Meteorological Organization (WMO). Promotes international cooperation in the field of meteorology.
274
6025
World Wide Navigational Warning Service (WWNWS). A service established for the purpose of coordinating the
transmissions of radionavigational warnings in geographical areas using coastal and satellite communication services.
6026
wrack. See ROCKWEED.
6027
wreck. The ruined remains of a stranded or sunken vessel which has been rendered useless. See also DANGEROUS
WRECK, and DERELICT.
6028
wreckage. Goods or parts of a wrecked vessel washed ashore or afloat; remains of a WRECK.
6029
wreck buoy. A BUOY marking the location of a WRECK.
6030
w/t station. See RADIO STATION.
275
X
6031
x-axis. A horizontal axis in a system of RECTANGULAR COORDINATES; that line on which distances to the right or
left (east or west) of the reference line are marked, especially on a MAP, CHART, or graph.
6032
x-coordinates. See COORDINATES: PLANE RECTANGULAR.
6033
xerography. A process of electrostatic printing which employs a special selenium-coated PLATE, useable many times
over.
6034
x-parallax. See PARALLAX: ABSOLUTE STEREOSCOPIC.
6035
x-rays. Electromagnetic RADIATION of the same nature as visible radiation but of an extremely short WAVE
-2
LENGTH less than 10 micrometers. X-rays are used in radar technology.
276
Y
6036
yard. A unit of length equal to 3 FEET, 36 INCHES, or 0.9144 METRE.
6037
yaw (or yawing). The ship's oscillation about a vertical axis approximately through the center of gravity of the vessel.
6038
y-axis. A vertical axis in a system of RECTANGULAR COORDINATES; that line on which distances above or below
(north or south of) a reference line are marked, especially on a MAP, CHART, or graph.
The line which is perpendicular to the X-AXIS and passes through the ORIGIN.
6039
y-coordinates. See COORDINATES: PLANE RECTANGULAR.
6040
year. A period of one REVOLUTION of the EARTH around the SUN.
6041
year: anomalistic. The period of one REVOLUTION of the EARTH around the SUN, from PERIHELION to
PERIHELION, averaging 365 DAYS, 6 HOURS, 13 MINUTES, 53.0 SECONDS in 1900, and increasing at the rate of
0.26 second per century.
6042
year: civil. A YEAR of the Gregorian calendar of 365 DAYS in common YEARS, or 366 DAYS in leap (or bissextile)
years.
6043
year: sidereal. The period of one apparent REVOLUTION of the EARTH around the SUN, with respect to a fixed
point, or a distant STAR devoid of proper motion, being 365 DAYS, 6 HOURS, 9 MINUTES, and 9.5 SECONDS in
1900 and increasing at the rate of 0.0001 second annually.
6044
year: tropical. The period of one REVOLUTION of the EARTH around the SUN, with respect to the VERNAL
o
EQUINOX. Because of PRECESSION OF THE EQUINOXES, this is not 360 with respect to the STARS, but 50"3
less. A tropical year is about 20 minutes shorter than a SIDEREAL YEAR, averaging 365 DAYS, 5 HOURS, 48
MINUTES, and 46 SECONDS in 1900 and is decreasing at the rate of 0.00530 second annually. Also called
astronomical, equinoctial, natural, or solar year.
6045
Y-level. See LEVELLING INSTRUMENT: Y LEVEL.
6046
young ice. Newly formed LEVEL ICE in the transition stage of development from ICE RIND or PANCAKE ICE to
WINTER ICE. Thickness from 5 to 15 cm.
6047
y-parallax. See PARALLAX.
277
Z
6048
zenith. The point where the direction of the PLUMB LINE produced above the HORIZON meets the CELESTIAL
SPHERE.
6049
zenithal projection. See PROJECTION: AZIMUTHAL.
6050
zenith camera. A special CAMERA so designed that its OPTICAL AXIS may be pointed accurately toward the
ZENITH. It is used for the determination of ASTRONOMICAL POSITIONS by photographing the position of the
STARS.
6051
zenith distance. The vertical angle between the ZENITH and the object which is observed or defined. Zenith distance is
the complement of the ALTITUDE. See ZENITH DISTANCE: DOUBLE.
6052
zenith distance: double. A value of twice the ZENITH DISTANCE of an object, obtained by OBSERVATION and not
by mathematical process.
6053
zenith telescope. See TELESCOPE.
6054
zero sounding(s). See SOUNDING.
6055
zodiac. The band of the sky extending 8.5° either side of the ECLIPTIC. The SUN, MOON, and navigational
PLANETS are always within this band, with the occasional exception of Venus. The zodiac is divided into 12 equal
parts, called 'signs', each part being named for the principal CONSTELLATION originally within it.
6056
zodiacal light. White or yellowish light which spreads out, in the night sky, more or less along the ZODIAC from the
HORIZON on the side on which the SUN is hidden. It is observed when the sky is sufficiently dark and the
ATMOSPHERE sufficiently clear.
6057
zone. An area in all parts of which the same TIME is kept. In general, each zone is 15°of LONGITUDE in width, with
the GREENWICH MERIDIAN (0°LONGITUDE) designated as the central MERIDIAN of zone 0 and the remaining
zones centered on a MERIDIAN whose LONGITUDE is exactly divisible by 15°. Zones are used in connection with
ZONE, STANDARD, and DAYLIGHT SAVING TIMES. Also called time zone.
6058
zone: equiphase. That region in space within which the difference in PHASE of two radio signals is indistinguishable.
6059
zone: equisignal. That region in space within which the difference in AMPLITUDE of two radio signals (usually
emitted by a single STATION) is indistinguishable.
6060
zone meridian. The CENTRAL MERIDIAN of each zone of a grid system.
6061
zone of silence. See BLIND ZONE.
6062
zone time. See TIME.
6063
zoom. A method of enlarging graphics on a graphical display, usually a function provided by the hardware of the
screen. Either a selected WINDOW may be enlarged to cover the entire screen or by repeatedly pressing a key, a
stepwise or continuous enlargement of the screen contents can be invoked,keeping the graphics centered at the screen's
centre.
6064
Zulu time. See UNIVERSAL TIME.
278
ANNEX A
Acronyms
ASCII
BSHC
CCIR
CGS
CIRM
DOP
DORIS
DSL
DTM
EAHC
EAtHC
EBCDIC
ECDB
ECDIS
ED
ED
EEZ
EGC
EP
FAO
FIG
GDOP
GEBCO
GLOSS
GMDSS
HDOP
HO
IAC
IACOMS
IAG
IAGA
IAHR
IAL
IALA
IAMAP
IAPSO
IASPEI
IAT
IAVCEI
IBCCA
IBCEA
IBCM
IBCRSGA
IBCWIO
IBWM
ICA
ICAO
ICES
ICOS
ICSEM
ICSU
IERS
IGC
IGU
IHB
IHC
IHO
IIP
IMO
INMARSAT
American Standard Code for Information Interchange
Baltic Sea Hydrographic Commission
Comité Consultatif International des Radiocommunications
Centimetre-Gram-Second System
Comité International Radio-Maritime
(International Radio-Maritime Committee)
Dilution of Precision
Determination d'Orbite et Radiopositionnement intégrés par Satellite
Deep Scattering Layer
Digital Terrain Model
East Asia Hydrographic Commission
Eastern Atlantic Hydrographic Commission
Extended Binary Coded Decimal Interchange Code
Electronic Chart Data Base
Electronic Chart Display and Information System
European Datum
Existence Doubtful
Exclusive Economic Zone
Enhanced Group Call (INMARSAT)
Estimated Position
Food and Agricultural Organisation
Fédération Internationale des Geomètres
(International Federation of Surveyors)
Geometric Dilution of Precision
General Bathymetric Chart of the Oceans
Global Sea-Level Observing System
Global Maritime Distress and Safety System
Horizontal Dilution of Precision
Hydrographic Office
International Advisory Committee on Research in the Natural Sciences
International Advisory Committee on Marine Sciences
International Association of Geodesy
International Association of Geomagnetism and Aeronomy
International Association for Hydraulic Research
International Association of theoretical and applied Limnology
International Association of Lighthouse Authorities
International Association of Meteorology and Atmospheric Physics
International Association for the Physical Sciences of the Ocean
International Association of Seismology and Physics of the Earth's Interior
International Atomic Time
International Association of Volcanology and Chemistry of the Earth's Interior (IUGG)
International Bathymetric Chart of the Caribbean Sea and Gulf of Mexico
International Bathymetric Chart of the Eastern Atlantic
International Bathymetric Chart of the Mediterranean
International Bathymetric Chart of the Red Sea and Gulf of Aden
International Bathymetric Chart of the Western Indian Ocean
International Bureau of Weights and Measures
International Cartographic Association
International Civil Aviation Organization
International Council for the Exploration of the Sea
International Committee of Onomastic Sciences
International Commission for the Scientific Exploration of the Mediterranean Sea
International Council of Scientific Unions
International Earth Rotation Service
International Geological Congresses
International Geographical Union
International Hydrographic Bureau
International Hydrographic Conference
International Hydrographic Organization
International Ice Patrol
International Maritime Organization
International Maritime Satellite Organization
279
INT Chart
IOC
ISBA
ISLW
ISPRS
ISRU
ITU
IUGG
IUGS
IUPAP
LOP
LOS
MBSHC
MKS system
MSC
M.S.L.
M.T.L.
MWARC
NAD
Navarea
NAVTEX
NHG
NSHC
NtM
OECD
PA
PAIGH
PD
PDOP
PIANC
RHC
RMS
ROV
SAD
SAR
SCAR
SLAR
SCOR
SI
SON
SRC
SSS
SWPHC
TDOP
TSS
UNCLOS
ulcc
UN
UNCTAD
UNDP
UNEP
UNESCO
USCHC
UT0
UT1
UT2
UTC
UTM
VDOP
vlcc
VHO
VLBI
VTS
WGS
WMO
WWNWS
International Chart
Intergovernmental Oceanographic Commission of UNESCO
International Sea Bed Authority
Indian Spring Low Water
International Society of Photogrammetry and Remote Sensing
International Scientific Radio Union
International Telecommunications Union
International Union of Geodesy and Geophysics
International Union of Geological Sciences
International Union of Pure and Applied Physics
Line of Position
Law of the Sea
Mediterranean and Black Seas Hydrographic Commission
Meter Kilogram Second system
Maritime Safety Committee (IMO)
Mean Sea Level
Mean Tide Level
Maritime World Administrative Radio Conference
North American Datum
Navigational Warning Area
Automatic Narrow Band Printing System
Northern Hydrographic Group
North Sea Hydrographic Commission
Notice to Mariners
Organization for Economic Cooperation and Development
Position Approximate
Pan American Institute of Geography and History
Position Doubtful
Positioning Dilution of Precision
Permanent International Association of Navigation Congresses
Regional Hydrographic Commission
Root Mean Square Error
Remote Operated Vehicle
South American Datum
Synthetic Aperture Radar, Search and Rescue
Scientific Committee on Antarctic Researches
Side-looking Airborne Radar
Scientific Committee on Oceanographic Research
System International
Sub-Committee on Safety of Navigation (IMO)
Sub-Committee on Radio Communications (IMO)
Side Scan Sonar
South-West Pacific Hydrographic Commission
Time Dilution of Precision
Traffic Separation Scheme
United Nations Convention on the Law of the Sea
ultra large crude carrier (< 300 000 t)
United Nations
United Nations Conference on Trade and Development
United Nations Development Programme
United Nations Environmental Program
United Nations Educational, Scientific and Cultural Organization
U.S/Canada Hydrographic Commission
Universal Time 0
Universal Time 1
Universal Time 2
Universal Time Coordinated
Universal Transverse Mercator (Grid)
Vertical Dilution of Precision
very large crude carrier (> 200 000 t)
Voluntaring Hydrographic Office
Very Long Baseline Interferometry
Vessel Traffic Service
World Geodetic System
World Meteorological Organization
World Wide Navigational Warning Service
280