Stammes, P.: Verification of the radiometric calibration of SCIAMACHY in the UV for two alternative key data sets

This document deals with the well-known radiometric calibration error of SCIAMACHY. Two new key data products have recently become available and we investigate their performance in the UV. The use of the new key data results in a smaller calibration error in the reflectance, but some additional spectral features are introduced. These changes are mainly due to changes in the solar irradiance. The radiance has not changed significantly. 1. REFLECTANCE VALIDATION METHOD For the work presented in this report we rely on a radiative transfer model to provide us with a reference spectrum in order to validate the reflectance measured by SCIAMACHY. The reference spectrum is calculated by the radiative transfer model Doubling-Adding KNMI (DAK). The approach we followed is described in [1]. There it is explained that a comparison with model calculations is most reliable in the UV. The SCIAMACHY data were calibrated using SciaL1C 2.2.7. Polarisation correction was not applied; instead, we corrected the spectrum using our own polarisation correction. The latter procedure is described in [2]. 2. CURRENT STATE OF THE REFLECTANCE Figure 1 explains the current situation. Plotted are the reflectances of the ‘eastern ’ and ‘western ’ Sahara regions (cf. Reference [2]), according to the model calculations and the SCIAMACHY instrument. The DAK reflectanc