Top-of-atmosphere albedo estimation from angular distribution models: a comparison between two approaches

Empirical angular distribution models (ADMs) are commonly used to convert s atellite-measured radiances to top-of-atmosphere (TOA) radiative fluxes. Th is study compares two methods of developing ADMs: (I) the radiance pairs me thod (RPM), which composits ratios of near-simultaneous radiance measuremen ts over the same scene to construct the ADMs; (2) the sorting-into-angular- bins (SAB) method, which estimates ADM anisotropic factors from the ratio o f the mean radiance in each angular bin to the mean flux determined by dire ct integration of the mean radiances. Theoretical simulations and analyses of measurements from the CERES (Clouds and Earth's Radiant Energy System) s atellite instrument show that the RPM method provides a better estimate of the true mean ADM for a population of scenes, while the SAB method is bette r suited for top-of-atmosphere flux estimation. The CERES results also show that a variable field of view size with viewing zenith angle can cause an approximate to 10% (relative) change in estimated all-sky mean albedo with viewing zenith angle.