Angular distribution models anisotropic correction factors and sun glint: a sensitivity study

Abstract

Because radiometers do not measure the Earth's outgoing fluxes directly, angular distribution models (ADMs) are used to invert measured radiances at the top of atmosphere (TOA) to fluxes. In this study, we have investigated if the use of the newly developed clear ocean Clouds and the Earth's Radiant Energy System (CERES) broadband short wave (SW) ADMs from the Tropical Rainfall Measuring Mission (TRMM) satellite will allow reliable estimation of the instantaneous reflected SW fluxes at the TOA when the measured radiances are contaminated by sun glint. Using SW fluxes estimations computed from Meteosat‐7 visible radiances as a surrogate of the forthcoming Geostationary Earth Radiation Budget SW fluxes, our results indicate that while CERES‐TRMM ADMs angular resolution presents an advance over the previously built Earth Radiation Budget Experiment (ERBE) ADMs, the angular resolution is still too coarse to suitably define anisotropic correction factors in the sunlight region. SW fluxes are overestimated in the strong sun glint region and underestimated in the surrounding regions. Nevertheless, we show that by combining the high temporal sampling of the sun glint regions afforded by the geostationary orbit of the instrument with information contained in the clear ocean wind‐speed‐dependent CERES‐TRMM ADMs, an improved estimation of the reflected SW flux at the TOA is possible by comparison to a simple ADM flux interpolation.