Era-shifting in space altimetry with the Swot satellite, which will be launched in December. Built by Thales Alenia for Cnes and NASA, Swot contains breakthrough technology that will revolutionize knowledge of the water cycle on a planetary scale. Lakes, rivers, reservoirs and oceans, 90% of the earth’s surface waters are surveyed. Commentary by Christophe Duplay, Swot program manager for TAS, and Charlotte Emery, design engineer at CS Group France, working for Cnes on the Swot mission.
Thirty years after the launch of the Topex Poseidon satellite, which marked the beginning of precision altimetry, Thales Alenia Space is supplying the Swot satellite to Cnes and NASA. This mission is a continuation of the Jason missions and will be the ” very accurate measurement of sea level over a long period of time, which is a very good indicator of climate change explains Christophe Duplay, Swot program manager for Thales Alenia Space.
It opens a new era in ” Watch after continental surface waters, lakes and rivers with revolutionary perspectives in the area‘continental hydrology and‘oceanography “. This broad swath altimetry survey of oceanic and continental surface water topography ” should revolutionize the discipline on the same scale as Topex-Poseidon to whom we owe the first precise measurements of sea level rise “which allowed us to see that climate change was happening”.
Launch is scheduled for early December aboard a SpaceX Falcon 9 launch vehicle. The satellite will be installed in a 77.6° inclined orbit at an altitude of 890 kilometers for at least three years and will have a repeatability of 20.86 days. From this height, Swot will make a complete map,” today new » Earth-scale topography of oceanic and continental water surfaces every 10 days!
After Topex-Poseidon, the series of satellites Jason 1, 2 and 3 and Sentinel 3 and 6, which are considered first generation missions, Swot launches the ” Second generation altimetry satellites “. These last will be characterized by very wide swath altimeters that will become the standard for all other satellites that will follow Swot, while current altimeter radars are limited to a swath a few kilometers vertically from the satellite.”
120 kilometers for Swot!
To carry out his mission, Swot has several instruments on board, including the KaRIn radar for Ka-band radar interferometer. It is based on the technological legacy of the SRTM mission’s SAR interferometers and the WSOA instrument and enables a wide swath of 120 kilometers, a significant technological gap compared to previous missions “. Swot also carries the Poseidon (3C) nadir altimeter, which operates on two frequencies (Ku and C band), similar to that carried on Jason-3.
KaRIn consists of two Ka-band SAR antennas (frequency at 35.75 GHz for a wavelength of 8.6 mm) separated by a 10-meter mast and surfaces at near-nadir angles of incidence between 0.6° and 3 .9° observe. To achieve a 120-kilometer swath, Karin observes ground surfaces over two 50-kilometer swaths, each 20 kilometers apart.
New scientific goals
Swot wants ” I‘overall observation of‘Fresh water on continents and oceans with dissolving capacities ten times greater than today’s “. This mission arose from the need to develop new tools to closely observe continental surface waters, ” which current satellites and instruments do not allow “. For hydrology, Swot will represent a first measuring instrument dedicated to the observation of continental surfaces.
In the field of oceanography, Swot is said to be the ” spatio-temporal coverage of data compared to currently used altimeters, in particular to observe mesoscale ocean variability and a better view of ocean circulation ”, explains Charlotte Emery in her thesis, currently design engineer at CS Group France working for Cnes on the Swot mission.
Understanding ocean circulation is important because it transfers half of the heat and carbon from the upper ocean to the deep sea, a key process in global climate change. The accuracy of the measurements could be improved to discover new phenomena that require further resolution according to the granularity of the phenomena in question “ emphasizes Christophe Duplay!
With improved ocean circulation models and, in particular, a better understanding of small-scale phenomena including waves, eddies, currents and ocean fronts, swot data will be Offshore shipping, fishing and commercial activities “. They will also allow it Plan new, more economical trade routes across the oceans “.
Swot will collect data on the surface of the earth, fresh water and salt water. This will help measure the impact of climate change. © NASA/JPL-Caltech, Cnes, Thales Alenia Space
Better understanding of the water cycle on a global scale
In the field of hydrology, it becomes a before and after swot in a ” A proportion that we cannot measure because the scientific yield promises to be “enormous”. ! »
“There will be a before and after swot in a ‘proportion that we cannot measure as the scientific yield looks ‘enormous’!”
Charlotte Emery, who has worked on contributing Swot data to improve large-scale hydrological modelling, states that Swot has the ” First coherent images of inventory variants d‘surface water and river currents and for which it will provide a significant amount of new data I‘Surface hydrology, lakes, expanses of‘Water, streams and rivers, improving the estimation of surface water availability “.
Never-before-seen data will be available with Swot.” To study rivers, particularly those that are poorly monitored locally, poorly equipped with on-site measuring stations, or whose information is not shared with the international community for geopolitical reasons “. In addition, Swot will provide information ” crucial to the‘Effects of currents and their fluctuations on human societies “. This information includes the properties of the ” Floods and droughts in poorly monitored catchment areas, and fluctuations in the flow of transboundary rivers concludes the scientist.
The Swot data allows for a ” better management of water resources and the deployment of new prevention models for water-related natural disasters such as floods, storms, coastal erosion, but also models for predicting flood risks, such as drought », Christophe Duplay would like to point out.
Swot is not just a scientific satellite. His data is under ” Core of the challenges of sustainable development and human adaptation to climate change ” and useful for a variety of uses ” many of these have yet to be invented “. As a matter of fact ” It is estimated that only a part of the applications that will use swot data is known !
Swot will be the first satellite capable of controlled re-entry into the‘Atmosphere at end-of-life under the Space Operations Act (LOS), which came into force in 2020 to address the space debris problem “. You should also know that given the mass of the satellite ” more than 2 tons, of which 850 kg represent the mass of the instruments », some of its elements are unlikely to be destroyed in the atmosphere. The controlled re-entry set up on Swot makes it possible to deorbit the satellite in 10 days and ensure the landing of potential debris in an uninhabited area. But that comes at a price. ” Impeccable reliability of the propulsion and avionics system at the end of its service life and 80% of the fuel reserves carried by the satellite (366 kg) are dedicated to this task. »
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