Comparison of coherent radar phases from repeated observations to infer relative line-of-sight displacement. A complete deformation fringe represents half a radar wavelength after other phase contributions have been removed.
An image of the relative radar phase between co-registered coherent observations. A displacement changes the two-way path length, giving phase change proportional to , with sign set by the adopted range convention. A full wrapped phase cycle therefore corresponds to half a radar wavelength of line-of-sight displacement. Orbital geometry, topography, atmospheric delay and scattering changes must be separated from deformation; a fringe is not uniquely an elevation contour or an earthquake displacement.[ref]
Interferometry by NASA. Interferograms, half-wavelength fringes and removal of orbital and topographic contributions
A normalized measure of consistency of complex radar returns over a neighborhood. Low coherence makes interferometric phase unreliable and can arise from vegetation, surface changes, viewing differences or extreme displacement gradients.
The component of a displacement vector along a specified sensor–target viewing direction. Its sign must state whether motion toward or away from the sensor is positive.
The phase difference of complex radar returns. It includes deformation, topography, orbital geometry and propagation contributions; the displayed wrapped phase is defined modulo .
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Interferometric Synthetic Aperture Radar (InSAR) is a remote sensing technique used to create high-resolution images of the Earth's surface and to measure ground deformation. It combines the principles of synthetic aperture radar (SAR) and interferometry to gain detailed insights into topography, land subsidence, tectonic activity, and other geological processes.