Satellite-derived snow coverage related to hydropower production in Norway: present and future

Hydropower derived from snow-melt runoff is a major source of electricity i n Norway. Therefore, amount of snow-melt runoff is key to the prediction of available water. The prediction of water quantity may be accomplished thro ugh the use of hydrological models. These models, which may be run for indi vidual basins, use satellite-derived snow-covered area in combination with snow-cover depletion curves. While it is known that snow albedo information would increase the accuracy of the models, large-scale albedo measurements have not yet been obtained from satellites on a regular basis. This paper presents Landsat-5 Thematic Mapper (TM) reflectances recorded in May 1989 f rom a mountainous catchment at Kvikne, Norway. Satellite-derived albedo val ues are analysed, and compared with simultaneously measured in situ albedo. The satellite-derived shortwave snow albedo is comparable with bare ground albedo and values as low as 0.19 were found in areas where the snow was hi ghly metamorphosed and heavily blackened by organic material. To map snow-c overed areas, the contrast between snow and snow-free areas can be improved by using a normalized TM Band 2-5 difference image. While TM Band 2 alone shows varying degrees of snow surface contamination within the study area, the normalized difference snow index (NDSI) is not affected by impurities. This paper also discusses the use of NASA's EOS (Earth Observing System) Mo derate Resolution Imaging Spectroradiometer (MODIS) sensor, which is planne d to be launched in the summer of 1999 for mapping of large-scale geophysic al parameters including snow-cover. MODIS will enable snow cover and albedo to be mapped in Norway on a daily basis, and should enhance our ability to estimate snow coverage and thus manage hydropower production.