Directed Infrared Countermeasures (DIRCM)

Transcription

Slides From ATI Professional Development Short Course
Directed Infrared Countermeasures (DIRCM) Principles
Instructor:
John L. Minor
ATI Course Schedule:
ATI's DIRCM:
http://www.ATIcourses.com/schedule.htm
http://www.aticourses.comDirected_Infrared_Countermeasures_DIRCM_Principles.htm
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Course Overview
0.
1.
2.
3.
4.
5.
6.
Intro, Administrative, and Course Overview
Electromagnetic Spectrum & Infrared Fundamentals
The Infrared Threat
Missile Warning Receivers
Aircraft Signatures
Infrared Missile System Principles
DIRCM Systems
–
–
–
Increasing J/S Requirement
Legacy DIRCM (Broadband and Flash Lamp) Systems
Laser Jam (Closed Loop) DIRCM Systems
7. Test and Evaluation of DIRCM Systems
© Copyright 2010 by John L. Minor, American Eagle Aerospace LLC.
End of Module 0
QUESTIONS?
Next Up
1. Electromagnetic Spectrum & Infrared Fundamentals
Module 1
The Electromagnetic Spectrum
& IR Fundamentals
Course Overview
1.
2.
3.
4.
5.
6.
The Infrared Threat
Aircraft Signatures
DIRCM Systems
–
–
–
Module 1 Overview
•
•
•
•
•
Electromagnetic (EM) Wave Basics
Properties of EM Waves and Light
Regions of Interest in the EM Spectrum
Infrared Basics
Blackbody Radiation Physics and Terminology
Propagation of Light as EM Waves
•
•
•
ALL Electromagnetic radiation consists of an electric (E) field and a magnetic (H) field
The wave propagates at the speed of light, at right angles to the E/H field planes
If you cross the E Field vector with the H Field vector, you get the direction of travel of the EM
wave (known as the right hand rule)
The Speed of Light
• Light, like all electromagnetic waves, travels at the same fixed
velocity (in a vacuum)  186,000 miles/second = 3 X 108 meters/second
• C = the speed light = 3 X 108 meters/second
• C = f or you can always remember the 2 Greeks >> C =

EM Wave Terminology
• The amplitude is related to the intensity of the light in Volts/Meter.
• The period (T) is the time between crests of the wave in seconds.
• The wavelength ( ) is the physical distance between wave crests
• The frequency (or f ) is the inverse of the period, and vice-versa.
Polarization
E
Direction of E field determines the
polarization of an EM wave.
With E field in vertical direction
wave is said to be vertically polarized
Direction of travel by the right hand
rule crossing the E vector into the H
vector
H
E
Horizontal
Circular
Can be right or left
hand circularly
polarized
EM Wave Polarization Video
Diffraction
• When light passes through a narrow opening, it tends to spread out
as if the opening itself were a very small point source of light
•The bending of light when it passes through a narrow opening or
along the edge of a barrier is known as diffraction
Note: Diffraction limits the resolution of an optical system
The Electromagnetic Spectrum
Optical Band of the
Electromagnetic Spectrum
ROYGBV
Optical frequencies, or light can be both visible and invisible to the unaided eye
Note: Boundaries, UV, & IR Band Nomenclature are somewhat arbitrary and are
author/text dependent
Red, orange, yellow, green, blue, violet
Electromagnetic Spectrum Charts (cont.)
This is the
IR Threat
X-Band Radar
10 GHz, 3 cm
EO Wavelengths shown in microns (m)
UV MWS
0.1-0.4
NVG
(0.65-0.95)
CCD TV
0.55-0.95
Older IR
Missiles
Near IR
Modern
IR Missile
Threat
3-5
FLIR
3-5, 8-12
Diffraction Limited Resolution
1.22 
~
R D
Phase Angle Properties
Interference Properties of Light
• When two or more light waves meet
at the same place and time, their
amplitudes will add by the principle of
superposition
• If crests meet crests they add
together to produce a larger amplitude
and this is constructive interference
• If crests meet with troughs they add
together to produce a smaller
amplitude and this in know as
destructive interference
The Interaction of Light With Matter
When light (EM energy) strikes the boundary of some type of matter,
three things can happen:
3
Medium 1
1
Medium 2
2
Boundary between two different media such as air/glass or air/water
1. REFLECTION -
Radiation is turned back into the first medium ()
2. REFRACTION -
Radiation is passed or transmitted into the second media
(also called transmission). If the index of refraction is
different between the two medium, the light will be bent
or refracted () according to Snell’s Law
3. ABSORPTION -
Process in which the energy of the incident photons are
absorbed and changed into molecular energy & heat ( )
Note: The sum of these three coefficients ( must = 1
The Discovery of Infrared
On 11 February 1800, Sir William Herschel was
testing filters for viewing the sun so he could observe
sun spots
When using a red filter he found there was a lot of
heat produced
Herschel discovered infrared radiation by passing
sunlight through a prism and holding a thermometer
just beyond the red end of the visible spectrum
This thermometer was meant to be a control to
measure the ambient air temperature in the room
He was shocked when it showed a higher
temperature than the visible spectrum
Further experimentation led to Herschel's conclusion
that there must be an invisible form of light beyond
the visible spectrum.
The Infrared Spectrum
When we speak of infrared, we mean that portion of the electromagnetic
spectrum that lies between visible light on one side and microwaves on the
other. Quantitatively, is is expressed as the region extending from a
wavelength of ~ 0.7 microns to ~1000 microns
~0.7-1000 microns
IR
Radiometry
A2
R1
A1
P0
R2
• A source at the origin radiates
optical power such that P0 is
radiated into a cone as shown
• Other powers may be radiated in
other directions.
• For the first cone, the power per
unit area at a distance R1 away is…
P0/A1
and is called the “Irradiance”
• The Irradiance at distance R2 is
P0/A2
• Since the illuminated area increases as the square of R, i.e. A2/A1=(R2/R1)2,
in a non-absorbing medium the Irradiance produced by the source varies
as inverse R-squared.
Radiometry (cont.)
• Irradiance is given the symbol “E”
and is expressed in the units W/cm2.
A2
R1
A1
P0
R2
• Missiles care about the quantity
“Irradiance” because the power
they receive Pr is determined by
that value and by the missiles’s
collection area Am. That is…
Pr2=E2 x Am =(P0/A2) x Am
is the power the missile receives
when it is at the range R2
• Since the Irradiance increases as the inverse-square of R, the missile
receives greater and greater power as it flies toward the source.
Radiometry (cont.)
A2
R1
=A/R2.
A1
P0
• The angular region contained in the
cone is called the “solid angle” of the
cone,  and is given by
R2
• This definition is true for any arbitrary
angular region which can differ from
that of a cone.
• Since the illuminated area varies as Rsquared, the solid angle of the
illuminated region does not change
with range.
• A radiometric quantity called “Radiant Intensity” has been defined and is
calculated using the expression P/.. Since the power P0 uniformly fills
the solid angle region, in a non-absorbing medium, the Radiant Intensity
does not vary with range.
Radiometry (cont.)
• Radiant intensity is given the
symbol “I” and is expressed in the
units W/sr.
A2
R1
A1
P0
R2
• IRCM engineers care about the
quantity “Radiant Intensity”
because that value describes the
strength of target and jammer
sources without specifying range *
• Irradiance can be found from
Radiant Intensity by dividing by
the range-squared. That is…
E2=I/(R2)2
Is the Irradiance produced at a
range R2 by a source of Radiant
Intensity “I”.
* This is true for a non-absorbing medium.
Radiometry (cont.)
• Aircraft targets and jamming transmitters are optical sources whose
radiation strengths may be expressed in terms of Radiant Intensity or
Irradiance.
• Whatever radiometric quantity is used, IRCM engineers refer to the
aircraft radiation strength as “S” for signature, and to the Jammer
strength as “J”. The IRCM system’s J/S is then determined as the
ratio.
• Since aircraft and jamming systems can radiate different amounts in
different directions, the apparent values of S, of J, and of J/S, can vary
with the observer’s viewing perspective.
• As an example, a fixed-wing aircraft signature may be 1000 W/sr at a
tail perspective where aircraft engines are unobscured, but may be
only 100 W/sr when viewed nose-on.
• Since the atmosphere will typically remove power from any radiating
cone through absorption, values of J and S may change with range
beyond the standard R-squared multiplier.
RADIOMETRIC UNITS
Watts
• The watt is the fundamental unit of optical power and
measurement, and is defined as a rate of energy of one
joule per second
• It is a function of both the number of photons and the
wavelength of the photons
• Each photon carries an energy = h = hc/
where h = Planck’s constant = 6.623 x 10 -34 Joule-sec
c = speed of light = 3 x 10 8 meters / sec
 wavelength of the photons
Radiator Response Curves
(Watt/cm3 - micron)
Monochromatic
Energy Density
Emissivity () = 1 (black body at 300° 
 = 0.9 (gray body)
 = varies as wavelength
(Selective Radiator)
0
10
20
30
 (m)
Need to specify the  for the spectral band of interest
• Usually specified as an average  over a given spectral band
• For example:  = 0.3avg at 8-12 microns
Important Laws of Radiation
• Inverse Square Law
• Lambert’ s Cosine Law
• Stefan-Boltzman’s Law
• Wien’s Law
• Planck’s Law
Inverse Square Law
Defines the relationship between the irradiance (illuminance) from
a point source and the distance to it
The intensity per unit
area varies in inverse
proportion to the square
of the distance -- why?
Inverse Square Law
Inverse Square Law & Divergence
Stefan-Boltzman’s Law
(Thermal Radiation Law)
The amount of radiation emitted by a body is
proportional to the emissivity and to the fourth
power of the absolute temperature of the body
W
Note that if T is doubled, the
radiated emittance is
increased sixteen times
4
T
=
Stefan Boltzman’s Constant
W
5.670 x 10-8
cm2 k4
=
Emissivity
T=
Temperature (absolute)
FOR A BLACKBODY
 = 1.0
Wien’s Displacement Law
The wavelength at which the maximum radiance
occurs is inversely proportional to the absolute
temperature of the body (Kelvin):
9.6m
300
8
12
max
 2900/T microns
Planck’s Law
• In physics, Planck's law describes the spectral radiance of
electromagnetic radiation at all wavelengths from a black
body at temperature T. As a function of frequency ν,
Planck's law is written as:
Planck’s Law
Weins Law
Solar
All bodies emit radiation at all
wavelengths as
a function of the bodies absolute
temperature
Rocket
Exhaust
Jet Engine
Exhaust
Earth
(terrain)
Lambert’s (Cosine) Law
• The irradiance or the
illuminance falling on any
surface varies as the cosine
of the incident angle
• Maximum at 90 degrees to
the surface (shown as 0
degrees here)
The perceived measurement
area orthogonal to the incident
flux is reduced at oblique
angles causing the light to
spread out over a wider area
than it would if perpendicular
to the measurement plane
IRCM Terminology
Common IRCM Terms
•
•
•
•
•
•
IR spectrum
Band pass
Radiant intensity
Watts per steradian
Watts per cm2
IR signature
•
•
•
•
•
Open loop IRCM
Closed loop IRCM
Optical break lock
Guidance suppression
J/S ratio
Module 1
Questions?
Next Up
1.
2.
3.
4.
5.
6.
The Infrared Threat
Aircraft Signatures
DIRCM Systems
–
–
–
Module 5
Infrared Missile Systems
Course Overview
0.
1.
2.
3.
4.
5.
6.
Intro, Administrative, and Course Overview
The Infrared Threat
Aircraft Signatures
DIRCM Systems
–
–
–
Module 5 Overview
•
•
•
•
•
How IR Missiles Work
Video – Basics of How IR Missiles Work
Threat Development Timeline & History
Missile Guidance Basics
Intro to IRCM Basics to Defeat IR Missiles
IR Missile Guidance Loop Description
Detector
Spin
Carrier
AMP Band Pass Envelope Band Pass
Steering Commands
To Fins
Guidance
Processing
Precession
Pointing Commands To Seeker Gyro
Reticle, Mirror/Gyro
MODULATION
• Tracks small targets (points sources)
more efficiently than large sources
• Has problems with extended sharply
defined edges (horizon line)
IR Missile Threat Evolution
Threat Development Timeline vs. Band
1960s
1970s
1970/80s
1980s
1990s
2000
Scanning
Imagers
Spin Scan
Con Scan
Cooled
Seeker
FRCCM
PseudoImagers
2005
reticle-based seekers
SA-7
HN-5
Band I
(hot metal)
Redeye
Band II
(hot metal)
1st Gen
Staring Imagers
SA-14
SA-16
Stgr-BASIC
Stgr-POST
SA-18
Mistral
Band IV
(jet engine plume)
2010
2nd Gen
Spectral Imagers
Rosette
Detector IFOV
• Pseudo Imaging
• Small Field-of-View Detector
Scanning a Rosette Pattern Using
Two-Counter-Rotating Optical
Elements
Target
Image
Petal
A Rosette Scanning Pattern
• Small IFOV
–
–
–
Provides Greater Sensitivity
Resistant to Jammers
Resistant to False Targets
S(t)
Petal Scan
Time
1
t
0
Normalized Signal Pulse
Sequence for On-Axis Image
Imaging
• Produces an Image
• Takes Advantage of State-of-the-Art Technology
– Processing Capability
– Software Track Algorithms
Rectangular Detector Arrays
Linear Detector Array
Target Scene
Image
Target Scene
Linear Detector Array Scanning
of a Target Scene
Rectangular Detector Array
and Target Scene
Illustration of Imaging Detectors
Flare Decoy
Objective: Present a more attractive
IR target to the missile
• Shortcomings
-Flares operate at higher
temperatures than aircraft, emitting
primarily in Bands 1 & 2 (versus
modern Band 4 threats)
-Very effective against Band 1 & 2
(1st and 2nd Generation) missiles
-Limited performance against newer
Band 4 missiles due to output
energy limitations and inclusion of
flare CCM techniques in missile
design

Directed Infrared Countermeasures (DIRCM)

Transcription

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