The use of desert sites to validate the current CERES geostationary calibration approach based on MODIS

CERES primary calibration technique involves inter-calibrating geostationary sensors with MODIS as an absolute reference. The ray-matched radiances effectively transfers the MODIS calibration to the geostationary sensors mitigating discontinuities between satellite boundaries and providing consistent geostationary derived cloud properties. CERES will be on NPP and the JPSS follow on missions to provide TOA fluxes for the climate community. CERES uses geostationary satellites imager radiances converted to broadband flux to infer the diurnal signal in between CERES measurements for a given region to derive the daily mean flux. These geostationary derived broadband fluxes need to free of any geostationary sensor artifacts, which can be interpreted as a climate signal. The CERES calibration approach needs to be validated with invariant targets such as deserts and deep convective clouds. These independent calibration approaches provides confidence that the geostationary calibration is stable over time.

The CERES desert methodology incorporates multiple desert sites across the earth. The desert sites are selected by first characterizing them for stability with 10 years of MODIS radiances. The trend of the desert geostationary radiance should match the gain derived from MODIS. Usually two simultaneous geostationary satellites can view the same desert target and after applying the gain from the MODIS calibration to each satellite should reveal the stability of the desert. This stability should match the stability derived from the MODIS characterization. This validation approach will be presented at the conference using the Sonoran desert with the GOES East and West satellites. The techniques learned from characterizing deserts sites with MODIS can easily be applied to the JPSS sensors.