Experimental and theoretical study of multi-angular, polarimetric brightness temperature observation during thaw and frozen soil condition at frequency of 1.4 GHz

In this study, an experimental testing of the possibility of retrieving of soil temperature, which is in the process of freezing and thawing, from the multi-angular, polarimetric observations of brightness temperature on 1,4 GHz are presented. The sensitivity of multi-angular, polarimetric brightness temperature observations with respect to the depth of freezing of the surface soil layer was experimentally investigated. The possibility of identification of thawed and frozen states of soil on the basis of brightness temperature observations was experimentally demonstrated. The study period covers the 62 hours from October 27 to 30, 2016. Brightness temperature measurements were performed near the city of Omsk in the agricultural field. Brightness temperature measurements were carried out on the vertical and horizontal polarization at an observation angle of 10, 25 and 40 degrees. The calibration of the radiometer was performed by the standard method over the water basin and metal sheets. Synchronously with the radiometric measurements, the measurements of soil moisture, soil temperature and the depth of soil freezing were carried out. Furthermore, in the field using a portable network analyzer, synchronously with radiometric measurements, the permittivity of the soil surface at the test site was measured. To simulate the brightness temperature used simple model of radio emission of soil uncovered vegetation. As the dielectric pattern of the complex permittivity of mineral soils with a high content of clay fraction the permittivity model was used. The temperature recovery method and soil moisture is based on the minimization of the residual norm between measured and calculated values of brightness temperature. As a result of the inverse problem reduces to obtain time series of reconstructed values of temperature, humidity and the roughness of the surface of the soil. The standard deviation and the square of the correlation coefficient between the recovered and measured values of the temperature of the soil in frozen condition appeared to be 0.6 K and 0.63, respectively.