Validation of Top-of-Atmosphere Radiative Fluxes Using Multiangle Measurements from the Clouds and the Earth's Radiant Energy System (CERES) Satellite Instrument

Nine months of measurements from the Clouds and the Earth's Radiant Energy System (CERES) instrument aboard the Tropical Rainfall Measuring Mission (TRMM) satellite are used to assess uncertainties in shortwave (SW), longwave (LW) and window (WN) top-of-atmosphere (TOA) radiative flux estimates based on recently developed CERES Angular Distribution Models (ADMs). CERES has the unique capability of being able to acquire measurements over a region in either a crosstrack, alongtrack or rotating azimuth plane (RAP) scan mode. CERES's multiangle sampling capability is exploited to determine errors in instantaneous and regional mean TOA fluxes over the tropics. Results are compared with those obtained from the CERES ERBE-Like product, which uses algorithms from the Earth Radiation Budget Experiment (ERBE) applied to the same CERES data. Instantaneous fluxes from the new CERES ADMs for days when CERES samples radiances in the alongtrack scan mode show a factor of 4 improvement in consistency with angle compared to CERES ERBE-Like fluxes. Similarly, mean albedos based on the new CERES ADMs show very little dependence on viewing geometry, whereas ERBE-like albedos show a 10% (relative) increase with viewing zenith angle. Regional mean flux errors from all nine months of CERES/TRMM are generally less than 0.5 W m-2 (1 sigma), a 40% improvement over CERES ERBE-Like. Flux uncertainties are also examined as a function of cloud and clear sky properties inferred using measurements from the Visible Infrared Radiometer (VIRS), which flies alongside CERES on the TRMM spacecraft.