InSAR

Interferometric synthetic aperture radar (InSAR) uses phase differences between radar images to map ground deformation, elevation, or other surface changes.

Synthetic aperture radar: A radar imaging technique that combines measurements collected along a moving platform’s path to create high-resolution images. InSAR compares images produced by this radar technique.
Ground deformation: A change in the position or shape of Earth's surface over time. This is the principal surface motion that repeat-pass InSAR maps.
Electromagnetic wave: A wave of oscillating electric and magnetic fields that propagates through space. Radar phase measures position within the transmitted and returned electromagnetic wave.
Persistent scatterer interferometry: A multitemporal InSAR method that estimates motion using stable radar-reflecting points across many acquisitions. It addresses temporal decorrelation by focusing on persistent scatterers.
Decorrelation (radar): The loss of similarity between radar signals caused by changes in scattering, geometry, or time. Decorrelation erases usable phase, especially over vegetation, water, and rapidly changing surfaces.
Radar interferometry: A method that uses the phase difference between radar signals to infer distance or motion. InSAR applies interferometry to repeated radar images.
Earthquake: A sudden release of energy in Earth's crust that generates seismic waves and can displace the surface. Interferograms can reveal the spatial pattern of coseismic ground displacement.
Wavelength: The distance between successive corresponding points on a wave, such as adjacent crests. InSAR phase changes convert into displacement relative to the radar wavelength.
Small baseline subset: A multitemporal InSAR technique that links interferograms formed from acquisitions with small spatial and temporal separations. Its network of short-baseline pairs helps retain coherence over distributed terrain.
Tropospheric delay: A propagation delay caused by the refractive properties of the lower atmosphere. Its spatial variation can resemble deformation and remains difficult to remove perfectly.

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