Comparative Assessment of Landslide Deformation Using UAV-derived DSM differencing and InSAR: A Case Study from the Prashar Landslide site, Himachal Pradesh

The precise monitoring of landslide deformation is essential to understand slope dynamics and its stability condition in mountainous terrain. It affects transportation, communication, and waterways directly, and associated damages hinder economic growth in the region. The study presents a comparative assessment of surface deformation at the Prashar landslide site (Himachal Pradesh) using high-resolution unmanned aerial vehicle (UAV) photogrammetry and satellite-based Interferometric Synthetic Aperture Radar (InSAR). Drone-based surveys were conducted in two time frames (April 2024 and March 2025) to obtain high-resolution Digital Surface Models (DSMs). Sentinel-1 C-band images (from May 2023 to November 2024) were used for getting time-series deformation using EZ-InSAR and MintPy workflows. Results from both methods revealed consistent results signifying that the landslide site is deforming at a creeping rate. Rate of deformation from DSM differencing revealed surface deformation ranging from -55 cm to +46 cm over 13 months. The zone of erosion is concentrated along the crown portion of the landslide, accumulating debris along the body of the landslide. InSAR results showed mean line-of-sight deformation values between -3.35 and +4.68 cm/year, with the highest subsidence concentrated at the crown portion, however additional deformation was detected on the opposite valley flank. Despite differences in spatial resolution, both techniques consistently identify the same active deformation zones with a comparable deformation rate of approximately 8 cm per month when temporal averaging is considered. UAV-based DSMs provide centimeter-scale details of crack propagation, displacement, and associated local geomorphic changes. On the other hand, InSAR captures continuous regional-scale deformation trends, particularly effective over sparsely vegetated areas. The close agreement between UAV and InSAR-derived deformation patterns demonstrates the robustness of integrating high-resolution drones with satellite-based time-series analysis. This multi-sensor approach enhances the reliability of landslide monitoring in rugged terrain and offers a practical framework for long-term hazard assessment and early warning applications.

Keywords: UAV differencing, InSAR deformation, high-resolution DSM, Landslide monitoring, Prashar landslide site.