A novel InSAR-based method for retrieving active layer thickness: Emphasizing soil pore ratio and unfrozen water content

Abstract

Active Layer Thickness (ALT) is a crucial indicator for assessing the status of permafrost. Large-scale monitoring of ALT is of significant importance for the ecological environment and engineering projects in permafrost regions. Interferometric Synthetic Aperture Radar (InSAR) has emerged as a vital tool for retrieving ALT. However, due to the harsh natural conditions in permafrost areas, the understanding of the mechanisms governing ALT formation remains incomplete, leading to inaccuracies in InSAR-based ALT retrieval. In this study, we developed an InSAR retrieval model for ALT that integrates surface deformation and soil water content. This model accounts for changes in the pore ratio of permafrost soil and the presence of unfrozen water during freeze–thaw cycles. Using Sentinel-1 ascending and descending data, we derived vertical displacements from 2018 to 2020. These displacements were incorporated into the model to estimate ALT along the Lanzhou-Urumqi High-Speed Railway (LUHR).The results showed that vertical displacements in the study area ranged from −0.061 m to 0.140 m, while ALT estimates varied from 0 to 4.553 m. The average ALT for the years 2018, 2019, and 2020 were 0.986 m, 0.994 m, and 1.099 m, respectively. Validation against ALT estimates derived from the Stefan model revealed mean absolute errors (MAE) of 0.212 m, 0.582 m, and 0.227 m for 2018, 2019, and 2020, respectively. These results demonstrate the high accuracy of our model. This study provides a new idea of using InSAR technology for large-scale ALT estimation.