Regional map of InSAR-based active layer thickness of permafrost in Qinghai-Tibet Plateau

Abstract

Accurate assessment of the state and changes of permafrost active layer thickness (ALT) on the Qinghai-Tibet Plateau (QTP) is critical to understanding the underlying processes driven by the global climate change. The Interferometric Synthetic Aperture Radar (InSAR) technology has been proven to be a method for quantifying deformation caused by natural and degradational processes of permafrost changes. Given its high accuracy, this method has been applied to monitoring local and regional permafrost deformation in QTP. However, there is a lack of improved large-scale regional ALT mapping algorithm using the accurate InSAR deformation data. Here, we examine the complex processes where the active layer melts spatio-temporally in depth during the thawing season, and the ground subsides due to the volume difference induced by the ice - water conversion. We developed a new model that infers ALT from the surface subsidence with help of other parameters in the process. This model takes the advantage of long-term InSAR derived deformation data, including both seasonal signal and inter-annual trend. In addition, it introduces an empirical parameter to represent the contribution of the ice-water phase change with consideration of additional water contribution from other sources. We implemented the developed method in Kekexili regional of the QTP. The seasonal deformation was obtained from radar images of Sentinel-1 by using the Small Baseline Subset Interferometry (SBAS-InSAR) technology. The thawing water was estimated in combination with soil moisture, precipitation, evapotranspiration and runoff data. Based on deformation data, vegetation cover information and existing ALT products, the empirical parameter was obtained by a data-driven regression method. Finally, a new InSAR-derived permafrost ALT map in the Kekexili region from 2015 to 2020 is produced. The results show that the average ALT is of 1.94 m with a standard deviation of 0.35 m. A comparative discussion with permafrost maps produced using other methods is given.