Verification of SCIAMACHY's polarisation correction over the Sahara desert

The justification for doing the work presented in this paper lies in the recent and disturbing rumours regarding the reflectivity of the current SCIAMACHY Level 1b product. The reflectivity was claimed to show an overall 20-percent loss in magnitude compared to GOME. We will show that the reported discrepancy in the reflectivity is indeed not a fictional one, but that it is certainly not caused by the failing polarisation correction. We also concentrate on the polarisation correction itself. Unfortunately, the current version of the polarisation correction algorithm is not reliable, and shows severe errors in the applied correction.