psInSAR

PSInSAR, or Permanent Scatterer Interferometric Synthetic Aperture Radar, is a remote sensing technique used to measure and monitor ground deformation over time by analyzing long sequences of SAR images. The method builds on the concept of stable, strongly reflecting targets, known as permanent scatterers, which maintain high radar backscatter coherence across many acquisitions.

By modeling the interferometric phase of many image pairs, PSInSAR estimates, for each scatterer, a time series of line-of-sight displacement and corrections for topography, orbital errors, and atmospheric phase delays. The core idea is that most atmosphere-induced phase delays behave as broad-area, image-wide components, while the deformation signal and the topographic phase are localized to each scatterer.

PSInSAR requires an archive of high-quality SAR images with similar geometry and sufficient temporal sampling. It identifies a network of PS points (urban surfaces, exposed rock, infrastructure) and uses a statistically robust solution to separate per-image atmospheric terms from the per-scatterer deformation signal. The result is a set of displacement time series at each PS, often expressed in millimeters of line-of-sight motion, and an associated uncertainty.

Applications include monitoring subsidence and uplift due to mining, groundwater extraction, or hydraulic fracturing; landslides; volcanic deformation; and structural health monitoring of cities. The method is robust to decorrelation and long revisit times, but it requires areas with stable scatterers and careful handling of decorrelation in vegetated or mountainous terrain. Limitations include sensitivity to decorrelation, phase unwrapping ambiguities, and the need for accurate DEM for topographic phase removal.

PSInSAR has inspired subsequent approaches, such as Small Baseline Subset (SBAS) and time-series InSAR methods, and remains widely used in geodesy and Earth observation.