Impact of Level 1 quality on SCIAMACHY Level 2 retrieval

Abstract

The SCIAMACHY instrument is suitable to retrieve vertical column densities (VCDs) and profiles of atmospheric gases from the UV/VIS to the SWIR spectral range. The quality of VCD retrievals depends on theoretical, computational and observational issues. Realistic atmospheric data as well as efficient yet accurate, robust radiation transfer models and inversion methods have to be used. The quality of the measured spectra greatly affects the accuracy of the retrievals. Since model parameters are optimally varied during the inversion process to mimic the measured values, errors in the input spectra will lead to wrong retrievals. SCIAMACHY spectra are spectrally and radiometrically calibrated and corrected for several effects, namely: Leakage current, pixel-to-pixel gain, non-linear response, straylight, polarisation and damaged pixels. Reflectances are calculated using in-flight sun diffuser spectra. Addition- ally, the degradation of the instrument is being monitored and the quality of the individual spectral pixels assessed. In the past it was shown that - depending on the retrieved trace gas and the spectral region used - a good correction of effects like stray light in the UV or bad pixels in the SWIR channels is essential for the quality of the level 2 data. In this paper we want to show the first results of a systematic study of the impact of calibration (errors) and instrumental effects on trace gas retrievals.