Monitoring permafrost deformation in the upstream Heihe River, Qilian Mountain by using multi-temporal Sentinel-1 InSAR dataset

Changes in active layer thickness (ALT) over permafrost regions lead to a large-scale ground deformation, affecting infrastructure stability and hydrogeological conditions. Therefore, accurate measurements of such deformation are urgently needed for characterizing the seasonal freeze-thaw process. In this paper, we present a time-series InSAR method for monitoring permafrost deformation, named "DSs-SBAS", which combines both cut-edge algorithms for identification of radar distributed scatters (DSs) and eigenvalue-decomposition-based optimization of DS interferometric phases to improve the spatial and temporal resolutions of deformation measurements. Taking into account difficulty in selecting reference points for the InSAR analysis in the permafrost region, we introduce a new strategy based on the relationship between ground temperature and deformation to improve the reliability of the selected reference point. This DSs-SBAS InSAR method is applied to investigate ground deformation over permafrost regions at the upstream west branch of the Heihe River, Qilian Mountain. A total of 27 Sentinel-1 SAR images are employed to derive deformation time series and annual deformation rates between 2014 and 2016. In addition, the Stefan model constrained by the ground temperatures is adopted to calculate the seasonal deformation amplitude. The results indicate that (1) most of the permafrost in the study area was stable (-1. 0 similar to+1. 0 cm.a(-1)), and large deformations occurred in the southern slope and the bottom part of the upper reaches of the Yeniugou River, (2) there are two main temporal processes of deformation with annual cycles, namely seasonal cycle deformation and seasonal subsidence. The largest deformation rate and maximum deformation amplitude were up to 6. 0 cm and -3. 0 cm.a(-1), respectively, (3) a significant heterogeneous pattern in freeze-thaw cycles and permafrost deformation is found, which is mainly controlled by permafrost landscapes, soil types and ALT. This proposed DSs-SBAS InSAR method has a great potential for monitoring large-scale deformation and retrieving ALT variations over permafrost regions in the Tibetan Plateau.