LADI: Landslide Activity Detection Index Based on InSAR Coherence and Sensitivity

Abstract

Interferometric synthetic aperture radar (InSAR) coherence loss can be indicative of fast surface deformations on active landslides (LSs). In this context, this letter introduces an InSAR-based approach for detection of statistically significant LS activity windows. It combines InSAR geometric sensitivity with coherence into an index, referred hereby as the LSs Activity Detection Index (LADI), that acts as a proxy of LS activity. It is defined as the harmonic mean of the sensitivity and loss of coherence. Experimentation is performed on 90 Sentinel-1 C-band interferograms (2023–2025) with a 12-day temporal baseline, over Lohar Gali in Northern Pakistan. Independent optical validation using PlanetScope imagery confirms LADI-detected active periods, with velocity increases up to sixfold. The proposed approach is computationally simple as no phase unwrapping or time-series inversion is needed; it, therefore, provides a potential means for operational large-scale monitoring of fast activity detection on unstable slopes.