A review of satellite methods to derive surface shortwave irradiance

Shortwave radiative fluxes at the earthʹs surface are of primary interest in climate research because they control the total energy exchange between the atmosphere and the land/ocean surface. Information on these fluxes is needed on a global scale, and therefore, has to be obtained by methods of remote sensing from observations made with instruments carried on satellites. The primary objective of this paper is to review current capabilities and activities to infer these forcing functions from satellite observations and to discuss future needs. Discussed will be fluxes of downward surface shortwave radiation (DSSR) and net surface shortwave radiation (NSSR). Methods for deriving DSSR fluxes on a global scale are becoming operational. They are being used increasingly to address climate issues, such as in determining the role of solar forcing in oceanic and atmospheric processes, hydrological modeling, and in carbon cycling. Based on extensive comparisons with ground-truth it is believed that estimates of DSSR fluxes can be obtained within 20 Wm−2 or better on monthly time scales, for areas of an average climate model grid size. Methods for deriving NSSR fluxes seem promising, but need to be further evaluated.