Members of the international Surface Water and Ocean Topography (SWOT) mission test one of the antennas for the Ka-band Radar Interferometer (KaRIn) instrument in a clean room at NASA's Jet Propulsion Laboratory in Southern California. The mission is a collaborative effort between NASA and the French space agency Centre National d'Études Spatiales (CNES) – with contributions from the Canadian Space Agency (CSA) and the UK Space Agency.

KaRIn is the scientific heart of the SWOT satellite, which will survey the water on more than 90% of Earth's surface, measuring the height of water in lakes, rivers, reservoirs, and the ocean. To do that, KaRIn will transmit radar pulses to Earth's surface and use its two antennas to triangulate the return signals that bounce back. Mounted at the ends of a boom 33 feet (10 meters) long, the antennas will collect data along a swath 30 miles (50 kilometers) wide on either side of the satellite.

KaRIn will operate in two modes: A lower-resolution mode over the ocean will involve significant onboard processing of the data to reduce the volume of information sent during downlinks to Earth; a higher-resolution mode will be used mainly over land.

Scheduled to launch from Vandenberg Space Force Base in Central California on Dec. 15, 2022, SWOT is being jointly developed by NASA and CNES, with contributions from the CSA and the UK Space Agency. NASA's Jet Propulsion Laboratory, which is managed for the agency by Caltech in Pasadena, California, leads the U.S. component of the project. For the flight system payload, NASA is providing the Ka-band Radar Interferometer (KaRIn) instrument, a GPS science receiver, a laser retroreflector, a two-beam microwave radiometer, and NASA instrument operations. CNES is providing the Doppler Orbitography and Radioposition Integrated by Satellite (DORIS) system, the dual frequency Poseidon altimeter (developed by Thales Alenia Space), the KaRIn radio-frequency subsystem (together with Thales Alenia Space and with support from the UK Space Agency), the satellite platform, and ground control segment. CSA is providing the KaRIn high-power transmitter assembly. NASA is providing the launch vehicle and associated launch services.