DSM Testing at IASI level
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Transcript DSM Testing at IASI level
IASI Level 0 and 1 processing
algorithms description
B. Tournier
D. Blumstein
F. Cayla
ITSC-XII – 27/2-5/3/2002 – Melbourne
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Fourier transform spectroscopy
Physical measurement is not a spectrum
Lots of transformations are necessary to retrieve the spectrum
Interferogram
1
I ( x) S ( )1 cos2x d
2
raw spectrum computation
TF ( I ) : S ( ) I ( x)e2ix dx
1
calibrations ...
Michelson interferometer
ITSC-XII – 27/2-5/3/2002 – Melbourne
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Radiometric calibration
Non linearity correction
Radiometric calibration done in the complex space using
cold calibration view SCS
hot calibration view SBB
First step done on board
Post-calibration on ground
(level 1 processing)
Radiometric calibration
ITSC-XII – 27/2-5/3/2002 – Melbourne
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Field of View effects and spectral properties
Basic fact
Wave number at an angle q from the axis of the instrument
Wave number cos q on the axis
give the same raw spectrum (first order only)
Consequences
angle between pixel and interferometric axis must be taken into account in the
spectral calibration (off axis pixel)
broadening and deformation of the Instrument Spectral Response Function
(ISRF) due to the extension of the IASI pixel (approx. 0.8 degree wide)
non uniform distribution of radiance in the field of view of the instrument
must be taken into account at user level
ITSC-XII – 27/2-5/3/2002 – Melbourne
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Instrument spectral response function
Level 1b ISRF
is not the same for the 4 IASI pixels
is dependant of the wave number
depends on a lot of possibly varying instrument characteristics
Level 1c ISRF removes this complexity (is uniq and constant)
IASI Level 1c Instrument Spectral Response Function
4
2,00E+00
3
2
645 cm-1
2000 cm-1
2700 cm-1
1
-3
-2
-1
1,00E+00
5,00E-01
0,00E+00
-2,00E+00
0
-4
ISRF Shape Variation
1,50E+00
0
1
2
3
-1,50E+00
-1,00E+00
-5,00E-01
0,00E+00
5,00E-01
1,00E+00
1,50E+00
2,00E+00
4
-5,00E-01
ISRF Definition Domain Width in cm-1
-1
Level 1b ISRF
ITSC-XII – 27/2-5/3/2002 – Melbourne
Level 1c ISRF
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Level 1 processing architecture
IASI scientific telemetry
IIS images (64x64 pix.)
coded spectra
Spectra
decoding
IIS images
radiometric
calibration
30 images
/ line
AVHRR images
4 x 30 spectra / line (8 sec.)
interferometric
axis estimation
1 (Y,Z)
/ line
spectral
functions
interpolation
spectra l
calibration
function
radiometric
post calibration
Spectra 1A
Resampling
Spectra 1B
apodisation function
AVHRR / IIS
coregistration
AVHRR
radiances
analysis
Apodisation
Spectra 1C
(4 x 30 / line)
sounding products
annotations
ITSC-XII – 27/2-5/3/2002 – Melbourne
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Input to level 1 processing
System parameters are computed off-line by the IASI Technical
Expertise Center (TEC) based in Toulouse
Parameters used by the level 1 processing are mainly
Spectral data base (ISRF, apodisation functions, spectral calibration functions)
Input for radiometric post-calibration (reflectivity of scan mirror, emissivity of
reference black body)
Spectrum coding/decoding tables
Geometry information for localisation of IASI products
Co-registration Imager/Sounder information
Input for NRT spectral calibration algorithm
Limits of spectral bands
NB: Noise and noise covariance matrix are provided for higher level
processing
ITSC-XII – 27/2-5/3/2002 – Melbourne
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