Improvements in the Shortwave Cloud-free Radiation Budget Accuracy. Part I: Numerical Study Including Surface Anisotropy

Abstract The shortwave radiation field, i.e., in the solar spectral range, emerging at the top of the atmosphere is anisotropic due to the optical properties of the atmosphere and the reflectance characteristics of the underlying surface. Thus, anisotropy conversion factors are used to account for anisotropy in the derivation of flux densities from satellite measured broadband radiances. Uncertainties in the conversion factors due to uncertainties of the actual parameters of the atmosphere and the surface lead to errors in the derived net fluxes at the top and the bottom of the atmosphere and in the derived surface albedo. The errors for cloud-free situations over land, which this paper is only concerned with, are analyzed by simulation, using measured surface bidirectional reflectance functions and realistic values of the optical parameters of the atmosphere, including gas and aerosol absorption and multiple Battering. To derive surface albedo from planetary albedo, a linear relationship is commonly used...