Differential Synthetic Aperture Radar Interferometry (DInSAR) aims the determination of deformation of the Earth’s surface that happened between two or more complex-valued SAR acquisitions. The phase of an interferogram issued from the complex multiplication of a SAR image with the complex conjugate of a second SAR image contains five distinct components, or layers of information: Two phase components arise from the geometrical baseline (slightly different position of both sensor positions): a topographical information representing the surface relief, a “flat earth” pattern coming from the orbital distance of both sensor positions. Two phase components result of the temporal baseline (time between both acquisitions): a deformation component, representing a possible displacement of the Earth’s surface between both acquisitions, an atmospheric component coming from different atmospheric conditions between both acquisitions. A phase component corresponding to intrinsic sensor noise Both parameters related to the temporal baseline can be retrieved using DInSAR on repeat-pass acquisitions. DInSAR cannot be used with single-pass interferometry (e.g. both acquisitions acquired at the same time). The deformation component of the interferometric phase corresponds to the modification of the phase of the second SAR image compared to the first due to an additional range difference between the sensor position and the Earth’s surface that is induced by the motion of the Earth’s surface towards or away from the initial sensor position. Using DInSAR, the phase components related to the geometrical baseline can be eliminated from the interferogram using an existing DEM and orbit information, or an additional interferogram showing no deformation. After DInSAR processing, neglecting the remaining sensor noise, only the deformation and atmospheric components remain. The resulting deformation image is called differential and is characterized by color bands, or fringes, from whom the amount of the displacement can be retrieved. DInSAR can be used for mapping displacements and deformations due to earthquakes, landslides, or other geophysical processes inducing deformation of the Earth’s surface. Using only one differential interferogram, mainly sudden and large scale changes between two acquisition can be mapped and quantified. However, the atmospheric phase component remains and may induce interpretation errors if it is not possible to eliminate it through e.g. precise weather models. Techniques of differential interferogram stacking (e.g. Persistent Scatterer Interferometry and Small-Baseline Subset) have been developed for long-term deformation monitoring which allow to filter the atmospheric phase component out.
Explain the fundamentals of Differential SAR Interferometry
Discuss advantages of SAR techniques over traditional measuring techniques
Discuss limitations of interferometric measurement
Apply DInSAR method
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