Sciamachy Reflectance and Solar Irradiance Validation

The top-of-atmosphere spectral reflectance measured by SCIAMACHY has been validated by comparisons between calibrated SCIAMACHY V6 Level 1 data and corresponding reflectances from AATSR and MERIS. The AATSR analysis is currently restricted to part of one specifically processed orbit containing a scene over a hurricane with high and homogeneous clouds for which results for V5 data are already available. The MERIS intercomparison is based on one individual state over Europe. These first comparisons between AATSR/MERIS and SCIAMACHY reflectances show a substantial improvement of the radiometric calibration of SCIAMACHY, although discrepancies still remain, especially at the wavelength 1600 nm. Furthermore, SCIAMACHY solar irradiances from the V6 Level 1 product have been compared with calibrated solar measurements by the LPMA/DOAS spectrometer which has been flown during various balloon campaigns (Kiruna 2003, Aire Sur l’Adour 2003, Kiruna 2004, Teresina 2004, 2005), SIM (Spectral Irradiance Monitor) UV/Vis/NIR spectra, the Atlas-3 shuttle composite spectrum, and the Kurucz solar reference spectrum. From these comparisons we conclude that an overall substantial improvement of SCIAMACHY V6 irradiances has been achieved, in particular with respect to the known irradiance offset (10-20%) in V5. The data in the overlap regions between channels have also improved but results are still not satisfactory there.