A 20-Year Monitoring of Seasonal and Long-Term Surface Elevation Changes in Permafrost Areas Using GPS Interferometric Reflectometry

Permafrost areas are affected by the annual freeze–thaw cycle, where water-ice phase changes cause surface uplift or subsidence. Global navigation satellite system interferometric reflectometry can effectively quantify these changes. In this study, we retrieved continuous surface elevation changes induced by the dynamics of the active layer and near-surface permafrost (frozen ground dynamics) using global positioning system (GPS) interferometric reflectometry. The SG27 site in a permafrost area (Utqiaġvik, formerly Barrow) was selected, and GPS signal-to-noise ratio observations from the snow-free thaw seasons between 2005 and 2024 were processed. We focused on seasonal and long-term trends in surface elevation changes and proposed a stage-specific analysis of seasonal changes using the timing of active layer thickness (ALT; defined as the seasonally maximum thaw depth) measurements. The results revealed: 1) Seasonal trends: the surface experienced obvious subsidence trends during the pre-ALT measurement period, followed by varying trends during the post-ALT measurement period. 2) Long-term trends: although the surface exhibited an overall uplift trend of 0.26 ± 0.01 cm year⁻¹ from 2005 to 2024, a detailed analysis revealed a subsidence trend from 2005 to 2012 (−0.83 ± 0.03 cm year⁻¹), an uplift trend from 2012 to 2018 (1.29 ± 0.05 cm year⁻¹), and a return to subsidence from 2018 to 2024 (−0.55 ± 0.04 cm year⁻¹). This study provides further insights into the active layer thaw subsidence patterns and the dynamics of near-surface permafrost.