Radar deployed aboard aircraft and satellites that produces a two-dimensional image of the target surface. The position of an object along the direction parallel to the movement of the observing platform is determined by the Doppler shift of the received signal. Phenomena observed by SAR include swell waves, current patterns imaged because of the varying sea surface roughness due to wave– current interaction, and oil spills and natural films that appear as areas of low image intensity as a result of their damping effect on centimeter-scale surface waves. See also Doppler radar, marine radar, microwave radar, high-frequency radar.