NASA - National Aeronautics and Space Administration

The Clouds and the Earth’s Radiant Energy System (CERES), Multiangle Imaging Spectroradiometer (MISR), and Moderate-resolution Imaging Spectroradiometer (MODIS) instruments aboard the Terra satellite make critical measurements of cloud and aerosol properties and their effects on the Earth’s radiation budget. In this study, a new multiangle, multichannel data set that combines measurements from all three instruments is created to assess uncertainties in instantaneous shortwave (SW) top-of-atmosphere (TOA) radiative fluxes inferred from CERES Angular Distribution Models (ADMs). MISR Level 1B2 ellipsoid-projected radiances from nine viewing directions in four spectral bands are merged with CERES by convolving the MISR radiances with the CERES Point Spread Function. The merged CERES-MISR data are then combined with the CERES Single Scanner Footprint TOA/Surface Fluxes and Clouds (SSF) product to produce the first merged CERES-MISR-MODIS data set. CERES and MISR data are used to generate narrow-to-broadband regression coefficients to convert narrowband MISR radiances to broadband SW radiances as a function of MODIS-based scene type. The regression uncertainty for all-sky conditions over ocean is approximately 4%. Up to nine SW TOA fluxes for every CERES footprint are estimated by applying the CERES Terra ADMs to each MISR angle. Assuming that differences along the line-of-sight from the different MISR angles are small, the consistency of the TOA fluxes provides an indication of the instantaneous TOA flux uncertainty. The overall relative consistency of all-sky ocean TOA fluxes is 6% (17 W m-2). When stratified by cloud type, TOA fluxes are consistent to 2–3% (<10 W m-2) for moderately thick overcast clouds, which make up 15% of the total population.