The calibration of GOES visible sensors using MODIS as a reference to provide consistent clouds and fluxes for CERES

CERES will be on NPP and the JPSS follow on missions to maintain a complete climate record of TOA fluxes starting with Terra-MODIS in the year 2000. 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. Monthly regional fluxes can be biased on the order of 30 Wm-2, for example over maritime stratus regions. CERES has successfully normalized the geostationary derived broadband fluxes with CERES fluxes to maintain the CERES instrument calibration. Even after artificially altering the geostationary calibration by ±5% the resulting monthly mean flux difference is less than 0.1%. CERES uses MODIS as a reference to inter-calibrate all the geostationary satellite to retrieve consistent cloud properties across the earth, which are used in the narrowband to broadband conversion of geostationary radiances. The CERES visible inter-calibration techniques will be employed by CLARREO, which has the added advantage of having NIST traceable hyper-spectral radiances. However, CERES uses hyper-spectral SCIAMACHY measurements to take into the spectral band differences after inter-calibration. In addition CERES uses invariant desert sites and deep convective clouds to monitor the stability of operational visible sensors, and validate the MODIS inter-calibration technique. As CERES progresses to NPP and JPSS these calibration techniques will be modified to take into account the new sensors. The current CERES calibration methodology will be presented with emphasis on the calibration of the GOES imagers. We are confident these techniques can easily be applied to GOES-R and JPSS follow on instruments.