A REVIEW OF SATELLITE METHODS TO DERIVE SURFACE SHORTWAVE IRRADIANCE

Shortwave radioative fluxes at the earth's surface are of primary inte rest in climate research because they control the total energy exchang e between the atmosphere and the land/ocean surface. Information on th ese fluxes is needed on a global scale, and therefore, has to be obtai ned by methods of remote sensing from observations made with instrumen ts carried on satellites. The primary objective of this paper is to re view current capabilities and activities to infer these forcing functi ons 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 increa singly to address climate issues, such as in determining the role of s olar forcing in oceanic and atmospheric processes, hydrological modeli ng, and in carbon cycling. Based on extensive comparisons with ground- truth it is believed that estimates of DSSR fluxes can be obtained wit hin 20 Wm(-2) or better on monthly time scales, for areas of an averag e climate model grid size. Methods for deriving NSSR fluxes seem promi sing, but need to be further evaluated.