Sentinel-6A monitors the level of the oceans

Sentinel-6A monitors the level of the oceans

Made by Airbus and equipped with a precision altimeter made by Thales Alenia Space, this European satellite launched by SpaceX will measure sea levels, a key indicator of climate change.

On 21 November at 9.17 a.m., Californian time, a SpaceX Falcon 9 launcher left the Vandenberg base and successfully took the Sentinel-6 satellite into orbit, more accurately Sentinel-6A, since its Sentinel-6B twin is already scheduled to relieve it from 2026. All this since the issues at stake are proving to be of the utmost importance: it is about monitoring precisely the rise in sea levels which is related to climate change.


An American launch, but a European satellite! Sentinel-6A joins the other Sentinel family satellites in the Earth observation programme initiated by the European Commission. The aim is to collect essential data to take our planet’s pulse and thus obtain a factual baseline for political decision-makers. Free dissemination of Copernicus measurements encourages companies to derive concrete services via their expertise (e.g., weather forecasts and monitoring of soils suitable for agriculture) which creates jobs.
Sentinel-6A was built by the European company, Airbus Defence and Space, while its cutting-edge altimeter, Poseidon-4, was supplied by another European company, Thales Alenia Space. Below, the full video of the SpaceX launch. Take-off takes place at 37:00. The return of the first stage is at 44:55 and entry to orbit at 1:35:30.



For Sentinel-6A, as for the other Copernicus satellites, the European Space Agency (ESA) is responsible for developing the satellite. CNES, the French Space Agency and the European Meteorology by Satellite Organisation, EUMETSAT are also involved in this mission. The United States is involved via their agency for studying the atmosphere and oceans, NOAA, and NASA, whose Jet Propulsion Laboratory (JPL) supplies the GNSS-RO instrument (for measuring atmospheric pressure and water vapour). The American agency also pays for the launch, sub-contracted to SpaceX, which explains the take-off using a Falcon 9. Furthermore, Sentinel-6A was named Michael Freilich as a tribute to this oceanographer who was Director of Earth Science for NASA from 2006 to 2019. He passed away on 5 August 2020 after pancreatic cancer, a few months after learning that this satellite to study sea levels (a type of measure whose importance he often defended) would bear his name. It should be noted that his children Sarah and Daniel were present at the launch. In the above video, they speak with emotion about their father from 55:55.


Once in orbit, control of the satellite was in the hands of ESOC, ESA’s control centre for probes and satellites in Darmstadt in Germany. Here, teams will carry out a series of delicate alterations to the trajectory so that Sentinel-6A Michael Freilich reaches an altitude of 1336 km by positioning itself 230 km behind Jason-3 which carries out same kind of sea-level measurements. The aim is to ensure the continuity of this level measurement which is so important to monitor climate change. Just think that up there, while Jason-3 and Sentinel-6A are separated by 230 km, one follows the other gap only 30 seconds apart!

Le centre de contrôle ESOC de l’Agence Spatiale Européenne était prêt le 21 novembre à commencer les délicates manœuvres orbitales de Sentinel-6A. La photo date du 12 novembre lors d’une répétition des procédures. L’organisme européen EUMETSAT prendra ensuite le relais pour les ultimes ajustements et la gestion opérationnelle de la mission. Crédit : ESA

The ESOC European Space Agency control centre was ready to start the delicate orbital manoeuvres of Sentinel-6A on 21 November. The photo dates from a procedural rehearsal on 12 November. The European EUMETSAT organisation will then take over for the final adjustments and operational management of the mission. Credit: ESA

Precision is the keyword for Sentinel-6A’s mission. By cross-checking the data from its Poseidon-4 altimeter, scientists will be able to follow the rise of sea levels which has already reached an alarming 3.5 mm per year. While the figure seems extremely modest, it will end up gradually making coastal areas uninhabitable. According to ESA, cities like New York and Shanghai will have to take protective measures and countries like Bangladesh will face serious problems. These issues are described in the ESA video below (in English).


As this video details, while this rise in sea levels seems very gradual, it is, however, estimated that children who have just been born could suffer its consequences! Sea level has emerged as a real “thermometer” for climate change since the level is rising with the melting of continental ice and the increase of water, due to the increase in average temperature. Moreover, this rise is not uniform, making it all the more essential that it be monitored.
Finally, Sentinel-6A’s measurements, like those of its predecessors, such as Topex-Poseidon and Jason-1, 2 and 3, are also useful in the short term in improving marine meteorology, assessing seasonal trends and monitoring the speed of sea currents.




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