From sub-daily to multi-year: permafrost ground surface deformation processes revealed by collocated multi-sensor observations at a supersite on the Tibetan Plateau

Abstract. Ground surface deformation in permafrost terrain provides critical information on heat and mass transfer during soil freezing and thawing, and serves as a key indicator of permafrost dynamics. However, continuous observations at minute-scale resolution remain extremely rare, sub-daily deformation processes are still poorly documented, and the consistency among remote sensing, contact, and non-contact in situ measurements has not been systematically evaluated. To address these gaps, we established an intensively instrumented permafrost deformation monitoring supersite in an alpine meadow on the central Tibetan Plateau. Ground surface deformation was measured using collocated linear variable differential transformer (LVDT) sensors, ultrasonic ranging, GNSS interferometric reflectometry (GNSS-IR), and Sentinel-1 SBAS-InSAR, together with multi-layer soil temperature and moisture observations. Automated LVDT-based observations provided continuous 5 min deformation records with sub-millimetre precision from 2022 to 2026, thereby resolving, for the first time, sub-daily deformation processes across different freeze–thaw stages. Results show that active layer thaw settlement commonly develops in a stepwise manner within a day, whereas late-thaw-season subsidence associated with excess ground ice melt is more continuous, reflecting sustained drainage and compression. This process also gives rise to a breakpoint-style acceleration in subsidence during the late thaw season. The sub-daily record further clarifies the origin of short-lived late-winter heave events, which are most consistent with infiltration and rapid refreezing of liquid water in shallow soil. The four deformation datasets show broadly consistent temporal patterns. LVDT and InSAR agree closely (r = 0.91), whereas GNSS-IR and ultrasonic ranging show even stronger agreement (r = 0.96). InSAR maintains strong agreement with the other observation methods in both the freezing and thawing seasons, with correlation coefficients consistently exceeding 0.86. GNSS-IR and ultrasonic ranging are more affected by snow and vegetation and require substantial filtering, making them more suitable for seasonal- to multi-year monitoring than for resolving subtle sub-daily signals. At our site, settlement during the active layer thaw stage is strongly correlated with the square root of thawing degree days across all four thaw seasons (R² > 0.96), and ice–water phase change within the active layer can explain more than 78 % of the observed seasonal deformation. These results provide a valuable observational benchmark for permafrost deformation from sub-daily to multi-year timescales and support improved process-based modelling and interpretation of GNSS-IR and InSAR observations in permafrost regions.