Model of emission from melting snowpack in the microwave range

To model the emission, the snowpack is considered as a two-layer medium, of which the top layer is melting, and the lower layer is dry snow. The model is based on experimental data at frequencies of 22.2 GHz, 37.5 and 140 GHz. The recording of the radio brightness temperature of the melting snow cover was accompanied by measurements of the volume density of the liquid phase of water in the top layer of snow. It has been experimentally established that the volumetric moisture content of the upper layer of snow increases linearly from zero to 3 % during the first hour of its melting in sunny weather conditions. In order to accurately reproduce the time dependence of the brightness temperature of the melting snow cover during modeling, it was necessary to assume that the effect of volume scattering in the melting layer is negligible compared to its absorption. It is shown that the model of a melting layer as a mixture of wet ice particles and inclusions of the liquid phase of water embedded in an air background is able to reproduce at frequencies of 37.5...140 GHz the properties of a medium with the dominance of absorption in comparison with volume scattering at wetness of ice particles of at least 2.5 %. Thus, the increase in the radio brightness temperature of melting snow is due to an increase in the contribution of the melting layer’s own radiation and an exponential weakening of the contribution of the radiation of the underlying dry snow by the melting layer. Retrieval of the melting layer thickness based on the developed model showed that the maximum value of the radio brightness temperature of melting coarse-grained snow cover, close to 273 K, is achieved with a layer thickness of 1 cm at 140 GHz, 5...7 cm at 37.5 GHz and 8 cm at 22.2 GHz.