Development of a correlated-k distribution band model scheme for the radiative transfer program GOMETRAN/SCIATRAN for retrieval of atmospheric constituents from SCIAMACHY/ENVISAT-1 data

GOMETRAN/SCLATRAN is a radiative transfer forward model developed for retrieval of atmospheric trace gas concentrations, aerosol and cloud parameters, and surface reflectance from the spectral radiance measurements of the SCIAMACHY/ENVISAT-1 and GOME/ERS-2 UV-Vis-NIR multi-channel spectrometers. For radiative transfer modeling of the line absorptions of O-2, H2O, CO2, CH4, N2O, and CO, two different schemes are under development: an accurate but rather slow line-by-line (LBL) implementation and a significantly faster correlated-k(c-k) distribution scheme. The c-k scheme has been matched to the resolution of the instruments, which is channel dependent. In spectral regions free of overlapping line-absorbers the multiply scattered radiance calculated with both, the LBL and the c-k scheme, agrees within 1-2%. Calculations in c-k mode are a factor of 25-800 faster depending on spectral interval. Good agreement has been found with the MODTRAN/DISORT radiative transfer model. First results concerning a new method are presented indicating that overlapping line-absorbers can be modeled with similar accuracy and speed as single line-absorbers.