IASI Level 0 and 1 processing algorithms description

IASI Level 0 and 1 processing algorithms description B. Tournier D. Blumstein F. Cayla ITSC-XII – 27/2 -5/3/2002 – Melbourne 1

Fourier transform spectroscopy ï Physical measurement is not a spectrum ï Lots of transformations are necessary to retrieve the spectrum ï Interferogram ï raw spectrum computation ï calibrations. . . Michelson interferometer ITSC-XII – 27/2 -5/3/2002 – Melbourne 2

Radiometric calibration ï Non linearity correction ï Radiometric calibration done in the complex space using â cold calibration view SCS â hot calibration view SBB ï First step done on board ï Post-calibration on ground (level 1 processing) Radiometric calibration ITSC-XII – 27/2 -5/3/2002 – Melbourne 3

Field of View effects and spectral properties ï Basic fact â Wave number n at an angle q from the axis of the instrument â Wave number n cos q on the axis give the same raw spectrum (first order only) ï Consequences â angle between pixel and interferometric axis must be taken into account in the spectral calibration (off axis pixel) â broadening and deformation of the Instrument Spectral Response Function (ISRF) due to the extension of the IASI pixel (approx. 0. 8 degree wide) â 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 4

Instrument spectral response function ï Level 1 b ISRF â is not the same for the 4 IASI pixels â is dependant of the wave number â depends on a lot of possibly varying instrument characteristics ï Level 1 c ISRF removes this complexity (is uniq and constant) Level 1 b ISRF ITSC-XII – 27/2 -5/3/2002 – Melbourne Level 1 c ISRF 5

Level 1 processing architecture ITSC-XII – 27/2 -5/3/2002 – Melbourne 6

Input to level 1 processing ï System parameters are computed off-line by the IASI Technical Expertise Center (TEC) based in Toulouse ï Parameters used by the level 1 processing are mainly â Spectral data base (ISRF, apodisation functions, spectral calibration functions) â Input for radiometric post-calibration (reflectivity of scan mirror, emissivity of reference black body) â Spectrum coding/decoding tables â Geometry information for localisation of IASI products â Co-registration Imager/Sounder information â Input for NRT spectral calibration algorithm â Limits of spectral bands ï NB: Noise and noise covariance matrix are provided for higher level processing ITSC-XII – 27/2 -5/3/2002 – Melbourne 7