An instrument that takes remote-sensing radar images from space. It is generally used to study the Earth's environment. SIR-C, one version built for the space shuttle in 2001, measured the Earth's surface at three different wavelengths, compared to one used by the European Space Agency's ERS-1 satellite. SIR-C is used in combination with a synthetic aperture radar to measure such phenomena as deforestation, desertification, soil moisture-retention, and ocean dynamics.

SIR was developed by NASA's Jet Propulsion Laboratory, and was first launched on 12 November 1981 as Shuttle Imaging Radar-A aboard the Columbia space shuttle.

http://www.jpl.nasa.gov/radar/sircxsar/ Presents recently released radar images obtained using SIR-C/X-Band SAR and processed at the Jet Propulsion Laboratory. The site has radar images organized by category (for example, archaeology, ecology); there are small browsable images for viewing online and high-resolution versions for a much closer look.