Revision of ground albedo estimation in Heliosat scheme for deriving solar radiation from SEVIRI HRV channel of Meteosat satellite

Methodologies for computing ground albedo from geostationary satellite images are investigated within the framework of models for deriving solar radiation components from satellite information. A revision of Heliosat-3 approach for determining ground albedo and its implication in the cloud index estimation is done using two close pixels of quite different reflectivity in the Nile delta surroundings in Egypt. The analysis done has revealed that the way in which Heliosat-3 approaches the ground albedo and especially its dependence with the viewing angle is not very precise when dealing with high reflective sites. A simple method for fitting, individually for every pixel, the angular dependence and the ground albedo estimations is proposed here and applied to different points in the Mediterranean area. The results of the revised method show rather good estimations of ground albedo in every kind of terrain in terms of reflectivity. These results are translated to cloud index estimations and finally to surface solar irradiance and they show improvements in solar radiation estimation over high reflective pixels.