InSAR

InSAR, or Interferometric Synthetic Aperture Radar, is a remote sensing technique that derives ground surface deformation by measuring the phase difference between radar echoes recorded in one or more SAR images acquired from similar orbital geometry. The resulting interferogram encodes displacement along the radar line of sight. After removing the topographic contribution using a digital elevation model and unwrapping the phase, the data can be converted to a displacement map with millimeter to centimeter sensitivity over large areas.

Two main acquisition strategies are used. The classic two-pass approach forms an interferogram from a pair of images, typically a reference image and a later image, to reveal relative deformation. More recent methods use multi-temporal analyses such as SBAS (Small Baseline Subset) and PSI (Persistent Scatterer Interferometry) to produce stable deformation time series while reducing atmospheric noise and decorrelation. These approaches can produce deformation maps, coherence estimates, and temporal records of displacement.

Applications encompass a wide range of geophysical and engineering problems. InSAR is employed to monitor crustal deformation from earthquakes and volcanic activity, track land subsidence due to groundwater or mineral extraction, observe glacier and ice-shelf motion, and assess infrastructure stability and landslide movements. Its ability to cover large regions with frequent updates makes it a popular tool in geoscience, hazard assessment, and environmental monitoring.

Limitations include that measurements reflect motion only along the radar line of sight and may require multiple viewing geometries for full 3D displacement. Coherence loss from vegetation or rapid surface changes, atmospheric phase delays, and the need for accurate DEMs can complicate analysis. Data availability and processing requirements also influence practical application.