Improving the CERES Derivation of Broadband Fluxes from GEO Narrowband Radiances with the Anticipation of the Next Generation GEO Sensors

The Clouds and the Earth's Radiant Energy System (CERES) project provides top of atmosphere (TOA) broadband fluxes for the modeling community for climate studies and model validation. The daily averaged TOA fluxes account for the diurnal flux cycle in between CERES observations by using 3-hourly geostationary (GEO) derived fluxes. The GEO narrowband radiances are converted to broadband radiances using theoretical and empirical models based on scene types derived from the GEO cloud properties. The broadband radiances are converted to fluxes using the same angular directional models that CERES observed radiances use. The GEO derived broadband fluxes are then normalized to the CERES flux to maintain the CERES instrument calibration. The advent of the next generation GEO multi-band sensors, which will have onboard calibration for both the visible and IR sensors, will greatly improve these GEO derived BB fluxes for incorporation in CERES datasets. A similar CERES MODIS cloud retrieval algorithm can be applied to the next generation GEO sensors and narrowband to broadband relationships can be developed with multiple bands in the SW. In preparation the CERES project is reformulating the narrowband (NB) to broadband (BB) relationships using DISORT to take into account various GEO spectral response functions used in the CERES data record in order to derive uniform and consistent GEO fluxes. The NB to BB model will be presented along with validation using both MODIS and GEO visible radiances compared with coincident CERES radiances.