Snow, Hydrology and Forests in EBtfi Alpine Areas (Proceedings of the Vienna Symposium, August 1991). IAHS Publ. no. 205,1991. Use of microwave radiometiy for monitoring the alpine environment ASHOK K. KESHARI & RAMESH P. SINGH Department of Civil Engineering, Indian Institute of Technology, Kanpur - 208 016, INDIA ABSTRACT Variations of physical parameters which may affect the monitoring of Alpine environment using microwave radiometry are discussed in the present paper. We consider four different models of snow surfaces in the Alpine regions and have study the nature of variations observed by the passive radiometric device. Usually the air-snow interface is considered for evaluating radiometeric response. It is shown that this assumption is not strictly valid and a transition interface is formed due to changes in the atmospheric variations over the snow covered Alpine surface. Radiometeric implications of remote sensing in the frequency range of 5-37 GHz are discussed. INTRODUCTION Alpine ground surface is generally covered with varying types of snow and ice. The thickness of the snow and ice varies from one season to another, which is responsible for changes in climatic conditions changing throughout the year and also from one year to another year. The changes in the thickness of the snow and ice cover in the alpine areas serve as precursors for river flooding and a consequent sea level change. In winter snow accumulates and layering of snow causes compaction of previous layers of snow and this densification goes on until the incidence of summer. The density of snow increases with depth in the direction of gravity. In summer the snow melts due to warming of the atmosphere, which decreases the snow thickness and increases the water vapour in the atmosphere, manifesting snowfall at higher latitude regions. The decrease of snow cover thickness is also found due to avalanches which cause deforestation in alpine areas. The variations in the incidence of snow and ice not only affect the living conditions of human beings in alpine areas but its effect can be seen in other parts of the region. In the present paper, we consider four different models representative of planer smooth alpine areas covered with snow of various thicknesses and have studied the implications of microwave remote sensing for monitoring the climatic conditions of alpine areas. We find that the microwave radiometers are useful in monitoring of climatic conditions and in delineating the snow thickness of the alpine areas. MICROWAVE RESPONSE OVER ALPINE AREAS Alpine areas with snow cover are represented as a multi-layer 81