Passive Remote sensing in the IR spectral range

Transcription

Remote sensing in IR spectral range
• Overview
• trace gas spectra
• spectrometer concepts
• Trace gas measurements from different platforms
• Imaging satellite instruments
Lecture on atmospheric remote sensing
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Remote sensing in IR spectral range
Cloud droplets
rain droplets
aerosols
molecules
Wavelengths from ~1 to 1000μm
-vibrational + rotational transitions
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In the IR spectral
range, typically
emission spectra are
analysed
In some cases also
absorption spectra of
the solar radiation
are measured
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Infrared emission spectrum of the Earth atmosphere in the mid-infrared region (700–2250 cm−1) calculated
with the radiative transfer model LBLRTM for mid-latitude conditions (summer, unpolluted scenario). The
most important absorption bands of different trace gases (O3, CO, CO2, H2O, CH4, N2O) are indicated.
(Orphal et al.,
2005)on atmospheric remote sensing
Lecture
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The observed Intensity is:
=0
if only emission
is observed
Optical depth
-emission and absorption plays a role
-typically no simple inversion (like in the UV/vis)
is possible
-complex radiative transfer modelling has to be
applied
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α: absorption coefficient
α ij (ν , p, T , N ) = N ⋅ σ (ν ij , T )⋅ S (ν − ν ij , p, T )
N: Number density
T: Temperature
p: Pressure
σ: absorption cross section
S: Line width
gl is the degeneracy and El the energy for state l,
μis the overall dipole (or other) moment coupling to the radiation field
Q(T)= Σgl exp (- El /kT) is the partition function
φij² is the transition matrix element
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Scheme of rotational-vibrational transitions
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Zu sehen sind die Rotationsschwingungsspektren von HCl (2800 cm-1) und DCl (2200 cm-1) sowie deren
erste Obertöne (HCl bei 5600 cm-1 und DCl bei 4400 cm-1) sowie Wasserbanden (3600 cm-1) und CO2Banden (2600
cm-1).on atmospheric remote sensing
Lecture
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Example of an absorption FTIR- measurement
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The rotational-vibrational spectra are determined by the molecules symmetry and complexity
Methyl ethyl ketone
(13 atoms, nonsymmetric)
Benzene
(12 atoms, symmetric)
Formaldehyde
(4 atoms, non-linear)
Acetylene
(4 atoms, linear)
Nitric oxide
(heteronuclear, diatomic)
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Subtraction sequence
of an absorption
measurement
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Example of an emission FTIR- measurement
http://www-imk.fzk.de:8080/imk2/mipas-b/bestfit.gif
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MIPAS-HNO3-observation
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Beispiel:
N2OIsotope
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Natural line width:
It can be ignored compared to collision (pressure) broadening at lower
altitudes and Doppler (thermal motion) broadening at higher altitudes.
Collision (pressure) broadening:
-collission between molecules shortens lifetimes for specific states
-for increasing pressure towards lower altitudes the probability to be scattered
increases
-the line shape for pressure broadening can be approximated by a Lorentzian
line shape:
(Δν: line width for pressure broadening)
The Lorentian line shpae can be retrievd from the *van Vleck and Weisskopf*
line shape assuming that the duration of a collision is much shorter than the
time between two collisions (impact-approximation)
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Lorentian line width:
Typical value: 2.5 MHz
p0: 1hPa
T0: 300K
Typical value: 0.75
The Lorentian line width is temperature dependent
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Doppler broadening
-is caused by thermal motion of molecules. The Maxwell distribution depends
on temperature and the molecular mass:
According to the Doppler-effect, the line width becomes:
With line width:
By convolution of the Lorentian and Doppler line shape one gets the so called
Voigt line shape:
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www2.nict.go.jp/kk/e414/shuppan/ kihou-journal/journal-vol49no2/4-06.pdf
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Different types of spectrometers:
-Grating spectrometer: simple setup, medium spectral
resolution, typical for early measurements, today satellite
instrument CRISTA
-FTIR, e.g. MIPAS: complex system with moving parts, high
spectral resolution (typical instruments today)
-Etalon spectrometers (e.g. CLAES): high spectral resolution in
selected wavelength windows
-gas correlation filter radiometer (e.g. satellite instrument
MOPITT)
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Michelson-Interferometer
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Prinzip des Michelson- Interferometers
Wellenzahl:
ν ≡
1
λ
=
ν
c
Überlagerung zweier monochromatischer Wellen mit Phasenverschiebung Δx:
a1 = A ⋅ cos(2π ⋅ν ⋅ x)
a2 = A ⋅ cos(2π ⋅ν ⋅ ( x − Δx))
a = a1 + a2 = 2 A ⋅ cos(2π ⋅ν ⋅ Δx) ⋅ cos(2π ⋅ν ⋅ ( x + Δx / 2))
Intensität:
I = a 2 = 4 ⋅ A2 ⋅ cos 2 (2π ⋅ν ⋅ Δx) = 2 ⋅ I in ⋅ [1 + cos(2π ⋅ν ⋅ Δx)]
1.0
a1
Amplitude
0.5
a2
Δx
0.0
-0.5
-1.0
0
1
2
3
4
Phase in W ellenlängen
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Polychromatische Interferenz
Da Spektrometer Licht vieler Wellenlängen verarbeiten, entsteht die oben beschriebene
Interferenz für jede Wellenlänge. Entsprechend überlagern sich die InterferenzIntensitäten der einzelnen Wellenlängen zusätzlich.
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Fourier Transformation
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Atmospheric observations
-ground based measurements
-balloon-borne observations of IR emission
-satellite observations of scattered sun light (NIR)
-satellite observations of direct sun light
-satellite observations of IR emission (limb)
-satellite observations of IR emission (nadir)
-satellite observations imagers (IR emission nadir)
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Schematic illustration of the
instrumental setup used. The
solar/lunar tracker follows the
course of the sun/moon and feeds a
parallel light beam into the
spectrometer. In the interferometer
the light beam is splitted into the
two rays by the beamsplitter.
Several detectors are mounted
which allow to record the whole
spectral region from the IR at
700/cm (14 µm) up to the UV at
33000/cm (300 nm).
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Increase of free tropospheric CO
from 1951 to 1985
(ISSJ Jungfraujoch)
Early measurements were carried
out with a grating spectrometer; the
spectral resolution was limited
A spectrum from 1985
mathematically degraded to the
resolution from 1951
Original spectrum from 1985
measured with a FTIR high
reolution spectrometer
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CO and CH4 column
above the
Jungfraujoch station
1985 - 1996
Mahieu et al., 1997
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Total column CO abundance
over Zvenigorod (right scale)
and corresponding mean
tropospheric mixing ratio
(left scale). Regression lines
for 1970-1984 and for 19851997 are shown.
http://www.igac.noaa.gov/newsletter/igac21/trends.html
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Seasonal cycle of free
tropospheric CO from 1950/51
and 1985-87
(ISSJ Jungfraujoch)
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www.ifjungo.ch/reports/1999_2000/pdf/09.pdf
Increase of several species from 1951 to
2000 (ISSJ Jungfraujoch)
Early measurements were carried out with
a grating spectrometer; the spectral
resolution was limited
A spectrum from 2000 mathematically
degraded to the resolution from 1951
Original spectrum from 2000 measured
with a FTIR high reolution spectrometer
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1951
1988
2000
1951
1988
2000
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Total column densities of HCl, measured in Spitsbergen between 1992 and 2000.
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Griesfeller, A.: Validierung von ENVISAT-Daten mit Hilfe von bodengebundenen FTIR-Messungen,
Dissertation, FZK Report No. 7072, Forschungszentrum Karlsruhe, Germany, 2004.
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MIPAS Balloon
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MIPAS ClONO2-Messung
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SCIAMACHY-Spectral regions
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SCIAMACHY on ENVISAT measures backscattered sunlight in the near-IR
How does the earth look like in the NIR spectral region?
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Unterer Häufungspunkt der Reflektivität als Maß für wolkenfreie Messungen
1508-1645
Lecturenm
on atmospheric remote sensing
M. Grezeorski
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Unterer Häufungspunkt der Reflektivität als Maß für wolkenfreie Messungen
2265-2380
Lecturenm
on atmospheric remote sensing
M. Grezeorski
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Panel (a) shows the spectrally fully resolved total optical densities for a vertical path for CH4 (V = 3.6 · 1019molec/cm-2) and H2O (V =
6.5 · 1022molec/cm-2) while panel (b) depicts the vertical optical densities of CH4 for different height layers in the atmosphere. The
expected total slant optical density (here for A=2.41) is now shown in panel c). Shown is the high resolution optical density and the
convolved one that is seen by the instrument, i.e. convolved with I (here: SCIAMACHY slit function in channel 8: Gaussian,
FWHM=0.24nm). Starting from this linearisation point, the effect of a change in the vertical column density of CH4 of +1018molec/cm2
(i.e. 3% of the total column) in different height layers is shown in panel (d). Panel (e) shows the derivatives (also with respect to CH4
perturbations) for different linearisation points, viz. for different water vapour columns (1.3, 6.5 and 32.5 1022molec/cm-2, respectively).
The optical densities in (a) and (b) are not convolved.
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Typical modelled and measured differential slant optical densities (DSOD) in the CO2 (a)
and CH4 (b) fit windows are shown. In panel (a), CO2 contributes most to the depicted total
DSOD, while there are also very weak absorptions by water vapour. In panel (b),
absorptions by CO2 and H2O marginally add to the strong CH4 signal. In both panels, all
species are fitted simultaneously and make up the total DSOD using a gaussian slit function
with 1.35 nm full width at half maximum.
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CO absorption detected in SCIAMACHY spectra
C. Frankenberg, IUP
Heidelberg
Example of a CO fit. The upper panel shows the differential slant optical
density of all absorbers (CH4, H2O and CO), the middle panelthat of CO.
The lower panel shows the residual of the fit.
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CO maps correlate well with maps of fire counts
C. Frankenberg, IUP Heidelberg
Fire counts measured by MODIS aboard Terra.
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CH4 maps from SCIAMACHY
CO2
CH4
CH4 columns are normalised with respect to CO2 columns
Aug-Nov 2003
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Comparison with model results
Aug-Nov 2003
J.F. Meirink, KNMI, Utrecht
Aug-Nov 2003
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Difference SCIAMACHY – Model, Aug-Nov 2003
The largest differences can
be seen in tropical
broadleaf evergreen forests
Science, March 2005
In agreement with recent
findings of a new CH4
source from plants under
aerobic conditions
Keppler et al., Nature 2006
MODIS Enhanced Vegetation Index
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Different viewing geometries and wavelength ranges:
Direct sun observations
provide a high signal to
noise ratio
The light path is well
defined
High requirements on
telescope adjustement
Only special parts of the
earth can be monitored
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The platform for SAGE II is the Earth Radiation Budget Satellite (ERBS).
Nominal orbit parameters for ERBS are:
•Launch Date: October 5, 1984
•Planned Duration: 2 years
•Actual Duration: ongoing
•Orbit: non-sun synchronous, circular at 650 km
•Inclination: 57 degrees
•Nodal Period: 96.8 minutes
Channel
Wavelength (nm)
1
2
3
4
5
6
7
1020
935
600
525
452
448 (nominal)
386
SAGE II Channels
http://www-sage2.larc.nasa.gov/instrument/
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Approximate
Altitude Range (km)
3-6
O3, NO2
45-60
1, 3-6
O3, NO2, Aerosol (3)
15-45
1, 3-5
O3, Aerosol(3)
10-15
1, 3 ,4
O3, Aerosol (2)
5-10
1
Aerosol (1)
1-5
Table 2. Algorithm Species and Altitude Range. (3) 1020, 525, and 452nm extinction profiles; (2) 1020 and 525 nm; (1) 1020 nm only.
Channels
Species
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http://www-sage2.larc.nasa.gov/data/v6_data/
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Limb-Beobachtung
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THE (Cryogenic Limb Array Etalon Spectrometer ) CLAES INSTRUMENT
CLAES infers the amounts of gases in the stratosphere from the measurement of the unique infrared emission
features by combining a telescope with an infrared spectrometer and solid state detectors, and cryogenically
cooling the whole instrument below 150 Kelvin to minimise its own thermal infrared emissions. The
spectrometer operates over the wavelength range 3.5 to 12.9 microns.Spectroscopy is performed by tilt
scanning one of the four solid etalons between one or more of the nine blocking filters. The nine filters are
centered at 2843, 1897, 1605, 1257, 925, 879, 843, 792 and 780 cm-1.
http://www.lmsal.com/
9120/CLAES/mission.
html
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24 hours of ClONO2 (top) and HNO3 (bottom)
data at 21 km as measured by CLAES in the
Arctic stratosphere for individual days between
July 1992 and May 1993.
(Roche et al., J. Atmos. Sci., 51, 2877-2902, Oct. 15, 1994.] )
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http://www.crista.uni-wuppertal.de/images/space.png
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Measured CRISTA spectra of a single altitude scan in the tropical upper
troposphere. Shaded spectral signatures originate from H2O emissions of
weak lines.
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CRISTA ist in der Ladebucht des
Space Shuttles eingebaut
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N20-Karte am 06. November 1994 in 30 km Höhe
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Assimilated water vapor field at 215 hPa on August 12, 1997.
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MIPAS/ENVISAT
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MIPAS on Envisat
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13.5km
16.4km
19.4km
40.3km
ClO emission
http://www-imk.fzk.de/asf/ame/ClosedProjects/assfts/P_III_12_Glatthor_N.pdf
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17.9.2002
20.9.2002
13.10.202
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Model simulation O3
(TM3-DAM, KNMI)
GOME O3
GOME NO2
GOME OClO
(IUP Bremen)
(IUP Heidelberg)
(IUP Heidelberg)
21.09.
22.09.
23.09.
Walburga Wilms-Grabe
[email protected]
Model simulation O3
(TM3-DAM, KNMI)
GOME O3
GOME NO2
GOME OClO
(IUP Bremen)
(IUP Heidelberg)
(IUP Heidelberg)
24.09.
25.09.
26.09.
Walburga Wilms-Grabe
[email protected]
www.copernicus.org/EGU/acp/acpd/4/6283/acpd-4-6283.pdf
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MOPITT measures emitted (4.6 μm) and and reflected (2.3 μm) radiation
http://www.atmosp.physics.utoronto.ca/MOPITT/MATR.pdf
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MOPITT
instrument
LMC: length modulated
gas correlation cell
PMC: pressure modulated
gas correlation cell
Transmission
convolved with the
detector sensitivity
(4.6 μm) for
different CO
absorptions
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Global CO distribution from SCIAMACHY (top) and
MOPITT (bottom)
Buchwitz et al., 2004
Averaging kernels
Remedios et al., 2005
Global CO on 23 March 2000
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Clerbaux et al., 2003
IMG spectrum (in transmittance units) in the 600–2500 cm−1 spectral range recorded over South
Pacific (−75.24, −28.82) on 4 April 1997, 04:00:42GMT (top). Radiative transfer simulations for
absorption contributions due to strong (middle) and weak (bottom) absorbers are also provided.
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Detection of HNO3 from IMG data.
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Surface temperature retrieved from IMG at 976.75 cm−1
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Coheur et al.,
JGR 2005
(a) Best ozone spectral fits for IMG observations above the Uccle (left plot) and Ny-Alesund (right
plot) sites. The selected scenes correspond to surface temperatures of 280 and 255 K, respectively. The
dashed lines at ±107 W/(cm2 sr cm1) correspond to the se value selected to constrain the retrievals.
(b) Retrieved ozone profiles in number density units and relative differences calculated with respect to
the smoothed
ozone
sonde profiles
the two [email protected]
The a priori profile is also shown.
Lecture on
atmospheric
remoteat
sensing
Turquety et al., ACP, 2004
Global distributions of IMG O3
total and partial columns for the
April 1–10, 1997 IMG
period, filtered and averaged over a
5 5 grid and the time period.
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Global distributions of IMG
CH4 and CO total columns
for the April 1–10, 1997 IMG
period. The data are averaged
over the time period and a 5
5 grid. The corresponding
available NDSC
measurements are represented
by colored circles on each
map.
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Tropospheric
Emission
Spectrometer (TES)
From Beer, 2005
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First TES global map of
tropospheric O3 (9/21/2004)
GEOS-CHEM model
for 9/21/2004
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CO Column from TES, 9-20-04
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CO Column from MOPITT, 9-20-04
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Nimbus-1
Launch Date
Operational Period
August 28, 1964
Operational until September 23, 1964
Nimbus-1 High Resolution Infrared
Radiometer (HRIR) image, taken at night
over western Europe - note the distortion that
enlarges Germany and Sweden relative to
southern countries - the Italians might be
aggrieved by the shrinking of the "boot".
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Nimbus-4
Launch Date
April 8, 1970
Operational Period
Over 10 years until it was deactivated on
September 30, 1980
700-mile Long Thermometer. Nimbus-4 took temperature readings of three continents (Africa, Europe and
Asia) from 700 statute miles with an infrared camera. The temperature data were reconstructed into a
photograph. White dots on the photo are grid marks which provide scientists with precise latitude and
longitude information. Since the images were measured in heat emitted from Earth, dark areas are land,
grey are water and white are clouds.
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AVHRR 23 Jan 2005 at 1245 UTC
Dundee Satellite Receiving Station
http://www.sat.dundee.ac.uk/abin/browse/avhrr/2005/1/23/1245
visible, 0.58-0.68µm
near infra-red,
0.725-1.10µm
short wave
infra-red,
1.58-1.64 or
3.55-3.93µm
thermal
infra-red,
10.3-11.3µm
thermal
infra-red,
11.512.5µm
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High Resolution Infrared Radiation Sounder Version 2 (HIRS/2)
on he TIROS Operational Vertical Sounder (TOVS)
Sensitivity of TOVS H2O
observation for different IR
wavelengths
Soden and Bretherton, 1996
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Retrieved water vapor between 1000 - 700 mb, 700 - 500 mb, and 500 - 300 mb for CSU
algorithm, NVAP algorithm, and Susskind's algorithm.
Engelen and
Graeme, 2002
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Set up of an interferometer
Monochromatic interference
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Passive Remote sensing in the IR spectral range

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