Evaluation of the ATCOR methods for ENMAP and EMIT atmospheric correction

Kurzfassung

The ATCOR method has been established as a widely used tool for atmospheric and topographic correction of both airborne and spaceborne instruments. With the availability of new spaceborne instruments, the correction methods within ATCOR have been updated for optimal processing of the high spectral resolution instruments such as ENMAP and EMIT. This contribution at first focuses on recent developments for optimal atmospheric correction for such instruments. Recent developments include adaption of the topographic correction approaches, the correction of aerosol scattering, the influence of scattered clouds, spectral recalibration, and the BRDF correction. The bottom of atmosphere reflectance and the spectral albedos retrieved from such optimized corrections are evaluated against standard reflectance products from ENMAP and EMIT for a limited number of sample data sets. For ENMAP, the standard product for land applications is retrieved by a re-implementation of the ATCOR methods. Therefore, only small differences due to different configurations are to be expected. In the EMIT case, the standard reflectance products is based on JPL's ISOFIT algorithm. This algorithm integrates physical processing in an optimization routine, what results in significantly different reflectance products than achievable by strictly physical band-by-band inversion of radiative transfer models. For both instruments, available evaluation results of standard products against ground reference targets have shown a good agreement to reference spectra. Therefore, the focus of this analysis is on cross-comparison of reflectance outputs with a special focus on critical wavelength ranges such as water vapor absorption bands, the CO-2 bands, the blue to UV spectral range, and the SWIR range above 2300nm. Also, the detectability of spectral features in mineralogy is compared to evaluate the impact of polishing and spectral fitting on spectral accuracy. The evaluation shall help for a better understanding of the quality of reflectance data from current spaceborne imaging spectrometers.