Using Sentinel-L Sar Measurements to Detect High Resolution Freeze and Thaw States in Alaska

The states of the earth surface in terms of freeze and thaw (FT) cycles especially in high-latitude regions have a crucial role in many applications such as biogeochemical transitions, hydrology and ecosystem studies. This study uses Synthetic Aperture Radar (SAR) c-band backscatterdata from Sentinel 1 from April 2014 to December 2017 to detect high-resolution freeze/thaw states in Alaska. The contrasts between frozen and thawed seasons are used to define FT states. Comprehensive in situ observations of soil temperature, air temperature, snow depth, and soil moisture were obtained to develop appropriate sigma (dB) thresholds of backscatteringbetween freeze and thaw states. The developed thresholds were used to detect FT in Alaska, USA. The results of this method revealed that the estimates are reasonably able to detect the states of surface when compared with ground measurements from SNOw TELemetry ( SNOTEL) observations. The developed method that mainly relies on using ground measurements from different land cover type shows an improvement with respect to previous methods that had used the average of frozen and thawed backscatteringscenarios as FT references.