What is synthetic aperture radar (SAR)?

How it works

Optical satellite imagery is passive. Radar supplies its own signal. NASA's Earthdata program describes SAR as active data collection, in which the instrument emits pulses of energy and measures how much returns from the surface. Because radar uses wavelengths from centimeters to meters, NASA says it can produce high-resolution images at night, in any weather and over cloud-covered ground.

The word synthetic refers to a workaround for antenna size. NASA says radar resolution depends on the ratio of wavelength to antenna length. It calculates that a satellite using a wavelength of about 5 centimeters would need an antenna roughly 4,250 meters long to resolve details 10 meters across. SAR instead merges successive acquisitions from a short antenna so they act like a much longer one.

NASA lists uses of C-band (3.8 to 7.5 centimeters) that include global mapping and change detection. It lists L-band (15 to 30 centimeters) uses including biomass and vegetation mapping. Interferometric SAR, or InSAR, measures distance to the ground. NASA describes those measurements as accurate up to the centimeter level.

Who flies it

The European Space Agency (ESA) says Europe's Copernicus Sentinel-1 satellites carry a 12-meter-long C-band SAR. Its default land mode covers a 250-kilometer swath at 5 by 20 meters ground resolution. ESA said on June 30, 2026 that Sentinel-1A, launched on April 3, 2014, had ended operations on June 29, leaving Sentinel-1C and Sentinel-1D working in tandem.

NISAR, a joint mission of NASA and the Indian Space Research Organization, launched on July 30, 2025, with L-band and S-band radars. NASA gives an average revisit time of about six days over land and ice-covered regions, at 3 to 10 meters resolution. It entered science operations in early January 2026. NASA's mission page lists a provisional data release on July 20, 2026.

Where AI comes in

ESA reported on June 4, 2026 on Tessera, a foundation model developed by University of Cambridge researchers and partners. It said Tessera combines Sentinel-1 SAR with Sentinel-2 optical data into embeddings, compressed summaries at 10 meters resolution. It said they cover each year from 2017 to 2025, offered at no cost.

Some processing is moving into orbit. TechCrunch reported in April 2026 that Kepler Communications had 10 operational satellites carrying about 40 Nvidia Orin processors. Chief executive Mina Mitry cited SAR as a power-hungry sensor that could benefit from offloading its processing, it reported.