A method to generate near real time UV-Index maps of Austria

A method is presented that combines individual ground based ultraviolet (UV) measurements and satellite data from MSG (Meteosat Second Generation) to generate a UV-Index map all over the region of Austria. Cloud modification factors (CMFs) gathered from satellite images give an area wide information of the cloud situation but compared to ground based measurements significant discrepancies have been found. These discrepancies are especially large for high mountain stations but also for low altitude sites differences between satellite derived and ground based data in the order of 15% have been found. To overcome these discrepancies a correction procedure based on the correlation of both data sets at the pixel of the measurement stations is developed. The uncertainty of the final UV-Index map is evaluated exemplarily for the pixel of the measurement sites Bad Vöslau and München by eliminating the information of both sites from the UV-Index map generation process and comparing afterwards calculated and measured results. More than 5000 maps for all weather conditions have been evaluated leading to a mean agreement of 1.02 (standard deviation ±0.31, Bad Vöslau) and 1.01 (standard deviation ±0.34, München) between calculated and measured UV-Indexes.