Strahlungstransport und Inversions-Algorithmen zur Ableitung atmosphaerischer Spurengasinformationen aus Erdfernerkundungsmessungen in Nadirgeometrie im ultravioletten bis nahinfraroten Spektralbereich am Beispiel SCIAMACHY

Abstract

Retrieval of atmospheric constituents from remote sensing measurements requires a radiative transfer forward model and appropriate inversion algorithms. A fast and accurate correlated-k (c-k) distribution radiative transfer scheme has been developed for the simulation of radiance spectra to be measured in nadir viewing geometry by the SCIAMACHY satellite diode array grating spectrometer. SCIAMACHY is part of the atmospheric sciences payload of the European Space Agencies ENVISAT-1 satellite to be launched in mid 2001. SCIAMACHY covers the spectral region 240-2385 nm with moderate spectral resolution (0.2-1.6 nm FWHM) and observers solar radiation scattered and reflected back to space by the Earths atmosphere and surface. The spectral region 440-2385 nm is dominated by molecular line absorption due to CO, CO2, CH4, H2O, N2O, and O2. The most accurate approach for the calculation of the spectrally averaged radiance - if line absorption needs to be considered - is the line-by-line approach. This approach, however, is very time consuming and can only be used for reference purposes. Therefore, a much faster c-k scheme has been developed. It is based on parameters that can be interpreted as trace gas absorption cross-sections representative for narrows spectral intervals. In this context a new method (alpha-mixing scheme) has been developed to consider spectrally overlapping line absorption. This method is shown to be more accurate (at SCIAMACHY resolution) and flexiblethan any previously developed method. The c-k and a line-by-line schemes have been implemented in the radiative transfer.