On Evaluating the Depth of Soil Freezing Based on SMOS Satellite Data

The results of a comparative analysis of the brightness temperatures obtained by the SMOS (Soil Moisture and Ocean Salinity) satellite and the soil-freezing depths corresponding to them, which were measured at weather stations located on test sites of the Kulunda plain, are presented. Based on daily satellite measurements of brightness temperatures, the influence of soil-freezing processes on the microwave radiation of the underlying surface has been studied. Using a model of microwave radiation of a plane-layered inhomogeneous nonisothermal medium, a theoretical calculation of the dependence of the brightness temperature of the soil on the depth of freezing has been performed. Real soil parameters of the Kulunda plain and climatic characteristics of the studied areas obtained at weather stations during the same period were used as input parameters of the model. According to the analysis of satellite and field data, as well as model calculations, it follows that, to estimate the depth of freezing of the soil from daily satellite microwave radiometry data, it is necessary to know the date on which the freezing of the soil cover begins, as well as the dielectric characteristics of frozen and unfrozen soil in those areas where the SMOS product is issued by brightness temperature. Based on satellite data and a model of microwave radiation of the soil with the upper frozen layer, a method for determining the depth of freezing of the soil cover is proposed.