How is InSAR used for ground subsidence monitoring?

InSAR (Interferometric Synthetic Aperture Radar) measures ground displacement from phase differences between SAR images acquired at different times. Differential InSAR (DInSAR) removes topographic phase using DEM. Persistent Scatterer InSAR (PSInSAR) analyzes stable reflectors (buildings, infrastructure) over long time series, achieving millimeter-level precision. Applications: mining subsidence, groundwater extraction impacts, landslide monitoring, and urban settlement. Limitations include atmospheric artifacts, temporal decorrelation in vegetated areas, and satellite revisit times. Sentinel-1 provides free data every 6 days. Results validate against leveling/GPS for critical applications.