High-Resolution Subsidence Zonation in Joshimath Using Complementary DInSAR and UAV Dem Analysis

Ground subsidence in Joshimath, a geologically fragile town in Uttarakhand's Chamoli district situated on an ancient landslide zone (Mishra Committee Report, 1976), poses severe risks to infrastructure and residents, exacerbated by aquifer disruption, deforestation, heavy development, and a muddy water outburst on 2 January 2023. Major subsidence and cracking occurred between 3–8 January 2023, necessitating precise monitoring methods amid complex Himalayan terrain. While Differential SAR Interferometry (DInSAR) excels in wide-area millimeter-scale Line-of-Sight (LOS) displacement detection using Sentinel-1 SLC data, it struggles with high-gradient deformations; conversely, UAV photogrammetry, which generated high-resolution orthomosaics and DEMs for detailed zone mapping.This study proposes an integrated DInSAR–UAV approach to leverage complementary strengths, achieving higher accuracy than either method alone, akin to strategies validated in this region. Results delineate subsidence patterns, refine zoning of affected areas, and inform risk mitigation for sustainable urban planning in hazard-prone Himalayan settlements.