CNES projects library

June 16, 2023

Swot

The SWOT satellite (Surface Water and Ocean Topography) was sent into orbit on 16 December 2022 by a Falcon 9 launcher operated by SpaceX from U.S. Vandenberg Space Force Base in California.

From its 891-kilometre orbit, SWOT is set to revolutionize the science of hydrology with its altimeter capable of surveying Earth’s lakes and rivers.

Satellites have already revolutionized oceanography, and tomorrow they will do the same for hydrology. The French-U.S. SWOT mission will be at the forefront, carrying a wide-swath Ka-band radar interferometer dubbed KaRIn that marks a break with today’s technologies.

With its two radar antennas perched at the end of a 10-metre boom, KaRIn will afford continuous coverage of a 120-kilometre swath where current radar altimeters are restricted to a strip of a few kilometres directly beneath the satellite. Thanks to this wide ground track, KaRIn will be able to acquire measurements of surface water height in rivers wider than 100 metres, as well as in lakes and flood zones covering an area of more than 250 metres x 250 metres, with an accuracy better than 10 metres, and to quantify slopes with an accuracy better than 1.7 cm/km (averaged out over an area of surface water greater than 1 sq.km).

Combined with high-precision geoid models from the GOCE satellite and precise digital terrain models, SWOT data will radically improve hydrodynamic models used to estimate river discharges. They will also help to determine temporal variations in surface water stocks—lakes, reservoirs and wetlands—and in flow dynamics. To give an idea, it is estimated there are more than 30 million lakes larger than 1 hectare in the world.

Besides hydrologists, oceanographers are also going to benefit from SWOT, as KaRIn can see mesoscale and sub-mesoscale circulation patterns covering several hundred down to several tens of kilometres, like eddies and filaments, to characterize their very dynamic vertical transport, and to study coastal circulation and refine current ocean and climate prediction models, all with centimetre accuracy.

The key technical, scientific and practical innovations of the SWOT mission draw on the heritage that NASA and CNES have built together in the field of satellite altimetry over more than 20 years.