(Paris) His distant predecessor had highlighted the phenomenon El Nino In 1994 ; the Franco-American SWOT satellite, whose launch is scheduled for Thursday, should further the understanding of the water cycle and its impact on the climate.
For the French space agency, Cnes, and its American counterpart NASA, which have been collaborating in this field for 30 years, and the Topex-Poseidon satellite, this is an “emblematic” mission, just in terms of of its billion dollar budget.
This cooperation was highlighted during a visit by French President Emmanuel Macron to Washington, at NASA headquarters on November 30.
The 2.2-ton juggernaut is to be put into orbit by a SpaceX rocket launched from Vandenberg, California. Once in space, SWOT, for Surface Water and Ocean Topography, will measure the surface water level of the oceans, but also of lakes and rivers.
For this, the satellite is equipped with a revolutionary instrument, a wide-swath interferometer called KaRin: two radar antennas, located at arm’s length ten meters from each other, scan the surface of the water on a 120 km wide band, providing a two-dimensional image. The slightly different signal received by each of the two antennas makes it possible to know the water level.
Thanks to the distance between the two antennas and the stability of the satellite, “we will have a resolution ten times greater than what current technologies produce for measuring the height of the oceans and understanding how fronts and oceanic eddies influence the climate,” explains Karen St. Germain, director of Earth observation at NASA.
“It’s like observing a license plate from space when you could only distinguish one street before,” says Thierry Lafon, head of the SWOT project at Cnes.
The stakes are high: if the impact on the climate of major ocean currents such as the Gulf Stream is known, this is not the case for more localized currents and eddies, over ten kilometres. These affect sea surface temperature, heat transfer, and ocean uptake of CO2 present in the atmosphere, he explains.
This will help to better model weather and climate conditions and better observe coastal erosion and future climate change.
End of life without debris
Its orbit at an altitude of 890 kilometers is “optimal because it makes it possible to discriminate all the components that affect the height of the water, such as the tides or the sun”, according to him.
SWOT also has a hydrological role: it will be able to monitor the height, surface area and changes in the quantity of water of more than 20 million lakes with sides of at least 250 metres. And observe rivers over 100 meters wide and calculate their flow.
The management of water resources and the prevention of floods and droughts will be improved, adds Thierry Lafon.
Getting the satellite to Vandenberg from the Thales Alenia Space (TAS) site in Cannes, where it was assembled, was a headache.
“With the war in Ukraine, there were no more Antonov transport planes available and he couldn’t fit in a Boeing 747,” says Christophe Duplay, project manager at TAS. It was therefore necessary to rely on NASA for the American Air Force to detach one of its rare C-5 Galaxy air giants to convey the marvel.
At the end of its life, scheduled to last three years – “even if nothing prevents the mission from continuing for five to eight years” according to Thierry Lafon – SWOT will be the first satellite to perform a controlled re-entry into the atmosphere to fight against the proliferation of debris in space, under the French law on space operations.
Nearly 80% of the 400 kilos of fuel it carries are devoted to this.