ITSC-XII – 27/2-5/3/2002 – Melbourne1 IASI Level 0 and 1 processing algorithms description B. Tournier D. Blumstein F. Cayla

ITSC-XII – 27/2-5/3/2002 – Melbourne2 Fourier transform spectroscopy ïPhysical measurement is not a spectrum ïLots of transformations are necessary to retrieve the spectrum ïInterferogram ïraw spectrum computation ïcalibrations... Michelson interferometer

ITSC-XII – 27/2-5/3/2002 – Melbourne3 Radiometric calibration ïNon linearity correction ïRadiometric calibration done in the complex space using âcold calibration view S CS âhot calibration view S BB ïFirst step done on board ïPost-calibration on ground (level 1 processing) Radiometric calibration

ITSC-XII – 27/2-5/3/2002 – Melbourne4 Field of View effects and spectral properties ïBasic fact  Wave number  at an angle  from the axis of the instrument  Wave number  cos  on the axis give the same raw spectrum (first order only) ïConsequences âangle between pixel and interferometric axis must be taken into account in the spectral calibration (off axis pixel) âbroadening and deformation of the Instrument Spectral Response Function (ISRF) due to the extension of the IASI pixel (approx. 0.8 degree wide) ânon 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 – Melbourne5 Instrument spectral response function ïLevel 1b ISRF âis not the same for the 4 IASI pixels âis dependant of the wave number âdepends on a lot of possibly varying instrument characteristics ïLevel 1c ISRF removes this complexity (is uniq and constant) Level 1b ISRFLevel 1c ISRF

ITSC-XII – 27/2-5/3/2002 – Melbourne6 Level 1 processing architecture

ITSC-XII – 27/2-5/3/2002 – Melbourne7 Input to level 1 processing ïSystem parameters are computed off-line by the IASI Technical Expertise Center (TEC) based in Toulouse ïParameters used by the level 1 processing are mainly âSpectral data base (ISRF, apodisation functions, spectral calibration functions) âInput for radiometric post-calibration (reflectivity of scan mirror, emissivity of reference black body) âSpectrum coding/decoding tables âGeometry information for localisation of IASI products âCo-registration Imager/Sounder information âInput for NRT spectral calibration algorithm âLimits of spectral bands ïNB: Noise and noise covariance matrix are provided for higher level processing