DInSAR

DInSAR, short for differential interferometric synthetic aperture radar, is a radar remote sensing technique used to measure ground deformation by analyzing phase differences between SAR images acquired at different times. By forming an interferogram from two complex SAR scenes and removing the topographic contribution with a digital elevation model, the remaining phase encodes deformation that occurred between acquisitions along the radar line of sight. Phase unwrapping converts the wrapped phase to a continuous value, which is then translated into line-of-sight displacement using the radar wavelength and geometry.

Data requirements and process: DInSAR relies on SAR images with similar viewing geometry and wavelength. The workflow includes co-registering scenes, generating an interferogram, removing orbital and topographic errors, correcting for atmospheric effects, and unwrapping the phase to yield a quantitative displacement signal along the radar line of sight. The resulting measurements are typically expressed as millimeters to centimeters of motion per unit time. Obtaining vertical or horizontal components often requires additional observations or modeling because DInSAR inherently provides LOS (line-of-sight) displacement.

Applications: DInSAR is widely used to monitor geophysical and engineering processes such as earthquakes, volcanic inflation or deflation, ground subsidence from aquifer depletion or mining, landslides, infrastructure monitoring (bridges, dams, urban areas), glacier and ice sheet dynamics, and slow surface deformation in urban environments.

Limitations and developments: The technique is sensitive to decorrelation from vegetation, surface change, or moisture, and to atmospheric phase fluctuations, requiring careful processing and sometimes multiple images. Phase unwrapping can be challenging in steep terrains. Multitemporal approaches, such as Persistent Scatterer Interferometry (PSInSAR) and SBAS (Small Baseline Subset) InSAR, improve noise reduction and allow time-series analysis to retrieve deformation histories.