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Synthetic aperture radar (SAR) is a means of using a moving radar antenna (e.g., on a satellite or airplane) to produce images of a stationary target with a higher angular resolution than possible with a stationary antenna of the same size. The resolution of a single signal (radio pulse sent and sensed) is determined by the wavelength and antenna diameter (aperture), but if this is done at multiple locations, additional processing can produce image data with a higher angular resolution, as if the aperture were as large as the distance between the locations at which the pulses were sent/received. Typical radar wavelengths used are in the 1 mm to 1 m range.
A number of algorithms are used to produce images from the raw data, some undoubtedly sharing techniques of radio interferometry, but the term interferometric synthetic aperture radar (InSAR) is used for further processing of multiple such images, that makes use of the phase information to determine distances to the objects imaged, e.g., to produce a topographical map.
These techniques are used in spacecraft (e.g., satellites) that gather data on Earth and other solar system bodies. They are similarly used on Earth with radar carried by aircraft.