On the angular correction of satellite radiation measurements: The performance of ERBE angular dependence model in the arctic

An angular dependence model (ADM) is needed to convert radiance measurements into fluxes. This paper provides an overview on the progress and issues related to the angular correction of radiation data at the top-of-the-atmosphere (TOA), followed by an investigation on the performance of the Earth Radiation Budget Experiment (ERBE) ADMs in the Arctic during summer. The variation of inferred albedo with viewing geometry indicates the merit of an ADM. The ERBE ADM for land does well as it leads to near constant albedos for given solar zenith angles. The ADM for snow/ice is least satisfactory when applied to the Arctic in summer. The performance of the ocean ADM is acceptable except at large solar zenith angles for which albedo increases with viewing zenith angle. Significant and systematic variation of albedo with viewing angle and relative azimuth angle are manifest when the overcast ERBE ADM is applied to over-cast-over-snow/ice scenes. A methodology for correcting ERBE ADMs was proposed by normalizing the anisotropic factor over bins containing sufficient measurements.