Unlike optical systems that rely on reflected solar radiation or thermal radiation emitted by Earth, imaging radar instruments work independently of light and heat. Radar is an active system that transmits a beam of radiation in the microwave region of the electromagnetic spectrum.
SAR can provide day-and-night imagery of Earth. In addition, clouds, fog and precipitation do not have any significant effect on microwaves, so images can also be acquired independent of weather conditions.
The Copernicus Contributing Missions carrying SAR sensors complement the Sentinel-1 mission. Sentinel-1 operates at C-band to provide SAR imagery at medium resolution. Its wide swath offers fast global coverage.