Monitoring freeze/thaw cycles using ENVISAT ASAR Global Mode

Due to the high temporal sampling rate of ASAR Global Monitoring (GM) mode, it has a high application potential for analyzing the land surface freeze/thaw process in high latitudes. This study aims to develop effective methods of extracting freeze/thaw transition dates of permafrost areas from ASAR GM data sets. In order to use ASAR GM time-series for analyzing freeze/thaw states, a least square fitting of piecewise step function is introduced. The thawing date can be determined by minimizing the sum of squared residuals between measured backscattering time-series and a pre-defined step function. An experimental result for a Siberian permafrost region illustrates that it can be a promising approach in monitoring permafrost ecosystems.

► ENVISAT ASAR GM has high application potential for analyzing freeze/thaw process.
► We examine usability of ASAR GM to analyze seasonal processes in high latitudes.
► Threshold approaches can be hardly applicable to the ASAR GM data.
► Rigorous method of extracting freeze/thaw dates from GM time-series is presented.
► The method is validated against meteorological data and snowmelt timing.