Spectral Reflectance Corrections for Satellite Intercalibrations Using SCIAMACHY Data

High-resolution spectra measured by the ENVISAT SCanning Imaging Absorption spectroMeter for Atmospheric CartograpHY (SCIAMACHY) are used to develop spectral correction factors for satellite imager solar channels to improve the transfer of calibrations from one imager to another. SCIAMACHY spectra averaged for various scene types demonstrate the dependence of reflectance on imager spectral response functions. Pseudo imager radiances were computed separately over land and water from SCIAMACHY pixel spectra taken over two tropical domains. Spectral correction factors were computed from these pseudo imager radiance pairs. Intercalibrations performed using matched 12th Geostationary Operational Environmental Satellite and Terra MODerate-resolution Imaging Spectroradiometer (MODIS) visible (similar to 0.65 mu m) channel data over the same domains yielded ocean and land calibration gain and offset differences of 4.5% and 41%, respectively. Applying the spectral correction factors reduces the gain and offset differences to 0.1% and 3.8%, respectively, for free linear regression. Forcing the regression to use the known offset count reduces the land-ocean radiance differences to 0.3% or less. Similar difference reductions were found for matched MODIS and Meteosat-8 Spinning Enhanced Visible and Infrared Imager channel 2 (similar to 0.86 mu m). The results demonstrate that SCIAMACHY-based spectral corrections can be used to significantly improve the transfer of calibration between any pair of imagers measuring reflected solar radiances under similar viewing and illumination conditions.