An Improvement of the IGMK Model to Derive Total and Diffuse Solar Radiation at the Surface from Satellite Data

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Abstract
For a better understanding, of climate, as well as all kinds of solar power applications it is necessary to know about incoming solar radiation at the surface (global radiation) and its partition into disuse and direct components Over the last ten years, several studies have been undertaken to demonstrate the capability of satellite-based methods for analyzing the downward solar radiation at the surface. At the University of Köin the so-called IGMK model was developed by Möser and Raschke to determine global radiation from geostationary satellite data. We now present some improvements of this IGMK model. These improvements include a totally new treatment of cloud transmittance in combination with the clear-sky atmospheric state. In this new algorithm we now explicitly account for multiple reflections between surface and atmospheric layers, which is most important for the diffuse component of global radiation. Thus, one additional major advantage of the new IGMK model is that the diffuse component of the global radiation can be derived from satellite data. Moreover, in this new version the clear-sky background atmospheric treatment includes more variables, which account for regional and temporal variations of all atmospheric constituents as well as the dependence of incoming radiation on the elevation of the surface. By use of METEOSAT ISCCP-B2 it is demonstrated, that over a period of two years (1985, 1986), the deviations between the IGMK model results and surface measurements are less than 10%. As a result, the interannual differences in global and diffuse radiation are presented, and the differences in both of the components, which are directly linked to changes in the large-scale circulation patterns are discussed.

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