Identification of thawed and frozen soil state in some Siberia regions by multi-temporal Sentinel 1 radar data in 2017-2018

The paper deals with the identification of thawed/frozen soils in the topsoil layer for three stations in Siberia: Salekhard, Tiksi and Norilsk by using Sentinel 1B C-band radar data for the period of 2017-2018. Determination of the frozen/thawed soil state is carried out in three ways: 1) by multi-temporal radar data on the basis of a significant in 3-5 dB difference in the backscatter coefficient 0 in the transition of freezing/thawing soil state, 2) by finding the threshold value of 0  at which the temperature in the topsoil layer falls below 00C, 3) by texture features. The first method allows determining the period of time during which the process of freezing/thawing of the soil occurs. The second and third methods allow making local maps of frozen/thawed soils. It is shown that for the studied areas the Spearman correlation coefficient between 0  and air temperature for cross - polarization exceeds the correlation coefficient for co-polarization. The graphs of the AFI (air freezing index) for the period of 2012-2018 are constructed based on the archive data of air temperature for the study areas.