Synthetic Aperture Radar (SAR) sends out microwave pulses and coherently combines their echoes along the satellite’s flight path to “synthetically” create a very long “virtual antenna”, generating sharp images–independent of daylight and largely independent of clouds–even though microwave radar uses much longer wavelengths than visible light. Changes in backscatter amplitude (i.e. the strength of the returned signal) reflect variations in surface roughness, geometry, moisture and dielectric properties (and, over land, vegetation structure). When complex images from two (or more) acquisitions are interferometrically compared (e.g. with InSAR), differences in phase—after accounting for topography and atmospheric effects—reveal surface deformation or ground displacement along the radar line of sight.
