Fusion of CERES, MISR, and MODIS measurements for top‐of‐atmosphere radiative flux validation

Abstract

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.