ANNOUNCEMENTS
Ground subsidence in steep Himalayan settlements threatens infrastructure and public safety, yet systematic measurements are rare. This study delivers the first wall-to-wall, satellite-derived assessment of deformation in Reckong Peo, Himachal Pradesh, by applying the Small Baseline Subset (SBAS) InSAR technique to 154 Sentinel-1A/B Interferometric Wide-mode scenes acquired between January 2021 and December 2023. A network of 318 interferograms, generated through ASF HyP3 and processed in MintPy, was rigorously corrected for orbital ramps, stratified tropospheric delays, and residual DEM error. The resulting time-series exposes a bowl-shaped lobe of cumulative line-of-sight subsidence reaching −90 mm—approximately −115 mm of true vertical motion— beneath the town’s lower terraces and National Highway-5 corridor, while surrounding gneissic ridges remain essentially stable. Temporal decomposition reveals three acceleration episodes that coincide with monsoon rainfall maxima and a six-to-eight-metre fall in groundwater head, implicating poro-elastic compaction of Quaternary colluvium and anthropogenic fill. Cross-validation against differential levelling (±3 mm) and building-crack surveys (5–12 mm separations) confirms millimetre-scale accuracy, with median temporal coherence exceeding 0.70 across the deforming zone. The derived displacement and velocity mosaics offer an actionable hazard layer: they pinpoint priority sectors for micropiling, slope buttressing, and groundwater-management interventions, and establish a geodetic baseline for forthcoming NISAR and ALOS-4 missions. Beyond its local relevance, the work demonstrates how freely available C-band SAR archives and open-source processing can transform geohazard surveillance in data-scarce mountain environments, moving risk management from reactive to predictive mode.
