An improved active layer thickness retrieval method over Qinghai-Tibet permafrost using InSAR technology: With emphasis on two-dimensional deformation and unfrozen water

Abstract

The increasing warming and humidification have caused the dramatic degradation of Qinghai-Tibet Plateau permafrost. The active layer thickness (ALT) is particularly crucial to be monitored with a wide range as an indispensable variable to characterize permafrost status. Interferometric synthetic aperture radar (InSAR) technology has recently been widely used for ALT retrieval. However, these studies are mostly limited by the accuracy of one-dimensional deformation measurements and ignore the presence of unfrozen water in the negative temperature state of the soil. Therefore, an improved ALT retrieval model using InSAR technology is proposed considering the influence of two-dimensional deformation and unfrozen water. This paper first employed the multidimensional small baseline subset (MSBAS) technology to monitor two-dimensional surface deformation over the Beiluhe-Wudaoliang permafrost region. We observed that the study area underwent surface subsidence of up to 60 mm in the thawing season. Considering the influence of unfrozen water, the ALT was subsequently estimated using the InSAR-observed subsidence. The estimated ALT varied from 50 to 500 cm, with ALT in the Wudaoliang area being higher than that in the Beiluhe Basin. Based on in situ data, the improved method is better than the traditional InSAR-based methods with a mean absolute error of 0.404 m. Our study demonstrates that considering the influence of two-dimensional deformation and unfrozen water can effectively improve the accuracy and reliability of InSAR-based ALT retrieval.

Keywords

• Active layer thickness
• Two-dimensional deformation
• Unfrozen water
• Multidimensional small baseline subset
• Qinghai-Tibet Plateau permafrost