The Use of Cloud Reflectance Functions with Satellite Data for Surface Radiation Budget Estimation

The bidirectional reflectance distribution function (BRDF) of an overcast atmosphere above an ocean surface has been calculated as a function of wavelength using a discrete-ordinates radiative transfer model. This plane-parallel BRDF appears qualitatively similar to the empirically derived angular dependence models from the Earth Radiation Budget Experiment. But when these two different BRDFs are used to estimate net shortwave flux at the ocean surface, discrepancies of 20–60 W m−2 can occur between the respective net surface flux estimations. When using either BRDF with Advanced Very High Resolution Radiometer data for surface radiation budget estimation, this uncertainty can be minimized by restricting the satellite viewing (polar) angle to between 30° and 50°. Accurate measurements of the planetary BRDF would help resolve these differences.