Influence of 3D cloud effects on satellite derived solar irradiance estimation

3D cloud effects influencing the surface solar irradiance are investigated using the radiative transfer model SHDOM. The calculations are motivated by improving the Heliosat method which is used for the estimation of surface solar irradiance from satellite data. The modelled results lead to the assumption that it is possible to find a correction for moderate viewing and solar geometries for the current Heliosat method. Based on these results an empirical study is done, comparing ground measurements with Heliosat derived data. It is shown that a correction of the current Heliosat method for 3D cloud effects is possible. The proposed corrections decrease the error of the irradiance derived by the Heliosat method in a range of about 2 %. The use of a site specific correction for other locations shows that the corrections depend on the specific local ”cloud” climate, which governs e.g. the existence of certain cloud types.