SWOT team moving in on radar ocean mission

SWOT will improve accuracy of surface water elevation measurements by a factor of 10 (NASA)

18 October 2018

The long-gestation US-French SWOT mission to improve radar altimetry measurements from space of Earth’s surface water got a boost this week with the delivery of a critical, UK-built system component. The Honeywell-built duplexer – which isolates signals from the radar receiver and transmitter, allowing them to share a single antenna, and in this case operates at a record 1,500W – will be integrated by Thales Alenia Space in France into a radio frequency unit, before ultimately featuring in SWOT’s Ka-band Radar Interferometer (KaRIn) instrument.

SWOT – Surface Water and Ocean Topography – promises to measure the ocean’s surface with 10 times the resolution of current technologies and survey 90 percent of the globe, twice every 21 days. The mission will use wide swath altimetry technology to produce high-resolution elevation measurements of the ocean surface and the surface of lakes, reservoirs, and wetlands. According to NASA, only 15 percent of lakes around the world are currently measured from space, but SWOT will inventory most medium to large lakes as well as the discharge volumes of rivers.

The two-tonne spacecraft will be positioned at an altitude of 890 kilometers, with an inclination of 77.6°.

By the time SWOT is launched in 2021 – by SpaceX Falcon 9 – the mission will have been nearly 15 years in the making. It was recommended in the US National Research Council’s 2007 decadal survey of Earth science priorities. NASA and France’s CNES space agency began initial joint studies in 2009, and formally agreed in 2014 to jointly build, launch, and operate the spacecraft.

The two agencies have been collaborating on ocean monitoring missions since the 1980s, and launched TOPEX/Poseidon in 1992. Jason-1 followed in 2001 and Jason-2/Ocean Surface Topography Mission in 2008.

SWOT is a technology demonstration mission with a planned three-year service life and is understood to be costing the US and French governments some $1.1 billion.

The spacecraft bus is a new-generation unit being developed by Thales Alenia Space to comply with the French Space Operations Act, set to take effect in 2020 with the goal of limiting space debris and improving the likelihood that end-of-life manoeuvres will put the spacecraft into the Pacific Ocean, with no debris falling into inhabited areas. Thales Alenia Space is building the spacecraft with NASA’s Jet Propulsion Laboratory in California.

The Canadian and UK space agencies are also SWOT partners.

The Amazon delta, captured by Landsat in 2006; SWOT will help measure the discharge volume of rivers (NASA/USGS)