Variation of snow/ice-extent and cloud coverage of the Alps as seen from NOAA operational satellites imager
The extent of snow and glacier ice in the Alps is characterized by annual, seasonal and - at least for snow - inner-seasonal variations. The knowledge of these variations is of increasing importance for the water management of the Alpine and abutting countries. By classifying imager data of the polar orbiting satellites and the additional use of a Geographical Information System (GIS) a monitoring of snow/ice extent is possible. This is exemplary performed in this study using AVHRR/3 data of the time range December 2002 to May 2003. The classification of the satellite data is done by multispectral threshold techniques taking account for underlying landuse and topography data and recent atmospheric profiles as forecasted by the global model GME of the German Weather Service (DWD). The automatic cloud masking based on NOAA 15 and 16 scenes fulfilling the condition of a sun zenith angle less than 90 turned out to be in good agreement to cloud coverage estimated by central Alpine SYNOP-stations. Applying the GIS functionality enables the evaluation of the snow/ice conditions with regard to the given topography. Time series of the relative coverage for predefined regions-of-interests reveal an accumulation phase in early winter, fluctuations of the order of several percent during the winter and the beginning of the snow melt in March and its continuation, interrupted by a late winter intermezzo happening in the first days of April 2003.