Retrieving Soil Temperature at a Test Site on the Yamal Peninsula Based on the SMOS Brightness Temperature Observations

In this paper, the results of radiothermal remote sensing of soil temperature at a test site on the Yamal Peninsula using full-polarimetry multiangular brightness temperature (BT) observations at the frequency of 1.4 GHz are presented. The BT data were obtained from the Soil Moisture and Ocean Salinity (SMOS) satellite with the SMOS footprint near the Polar Weather Station Marresale, the Russia Federation. The SMOS data covered the period from January 1, 2013 to December 31, 2013. The method to retrieve the soil temperature was based on solving an inverse problem by minimizing the norm of the residuals between the observed and predicted values of the BTs. The calculation of the BT was performed using a semiempirical model of radiothermal emission, which incorporated an attenuation of the microwaves in the snow pack or the canopy and a temperature-dependent multirelaxation spectral dielectric model (TD MRSDM) for an organic-rich tundra soil. The TD MRSDM was specifically designed based on laboratory measurements of the complex permittivity of the organic-rich soil samples, which were collected at the test site on the Yamal Peninsula. As a result, the values of the root-mean-square error and the determination coefficient between the retrieved and measured soil temperatures were determined to be 2.2 °C and 0.70 and 3.5 °C and 0.52, respectively, for thawed frozen soil. These results indicate the perspectives of using the full-polarimetric multiangular BT observations in the L-band for the purpose of measuring the soil temperature in the Arctic region.