Pronounced Underestimation of Surface Deformation Due To Unwrapping Errors Over Tibetan Plateau Permafrost by Sentinel-1 InSAR: Identification and Correction

Surface deformation plays an important role in permafrost studies as it is closely associated with the hydrological-thermal dynamics of the active layer and permafrost, affecting the stability of infrastructure. In this study, we have identified a significant underestimation of surface deformation over permafrost using Sentinel-1 InSAR, which is attributed to unwrapping errors in interferograms. Specifically, the inclusion of interferograms with longer temporal baselines in the SBAS network will cause unwrapping errors to occur more frequently and severely, leading to a more pronounced underestimation, exceeding 3 times in severe cases. To address this issue, we propose a novel correction strategy to mitigate unwrapping errors by correcting long-span interferograms with reliable short-span interferograms in the temporal domain. Here, 12-day interferograms are utilized as the reliable interferograms for the correction. The results show that the seasonal deformation amplitude over an ice-rich permafrost location on the Tibetan Plateau increases to approximately 110 mm after applying the correction, compared to the previous underestimation of only about 28 mm. The proposed correction method facilitates accurate retrieval and verification permafrost products from InSAR time series, such as the ground ice/water storage and thickness of the active layer. This in turn deepens our understanding of surface deformation in permafrost regions under a warming climate. Moreover, the proposed correction method demonstrates its promise as an effective strategy for mitigating underestimation issues in various InSAR studies that suffer from unwrapping errors.