25 March 2021
Altimetry took on a new importance in the early 1980s, when the international scientific community realized that ocean and climate are intrinsically linked, and that sea level rise was a key indicator of global warming. The rise in sea level, averaging 8 cm over 30 years, reflects large-scale environmental and climatic effects, such as the melting of glaciers and ice caps. Therefore, we must have the ambition to measure the height of the seas to within a few centimeters at any point on the globe.
This is the challenge taken up by CNES nearly 40 years ago, and described in a recent article in the magazine La météorologie. CNES positions itself at the center of this oceanographic revolution, with the development of precision instruments, the Poseidon altimeter-radar and the DORIS orbitography system DORIS, and the development of cooperation with NASA and the industrialists Thales Alenia Space and Thales DMS. A new global vision of the oceans is then offered: from the height of the seas, we can deduce the ocean circulation, but also observe and anticipate El Niño and La Niña phenomena. An international scientific community in altimetry has been formed and gathers today nearly 350 members, and where SYRTE processes observations obtained by space geodesy techniques (GNSS and DORIS positioning systems, laser telemetry on artificial satellites and on the Moon, and very long baseline radio interferometry on extra-galactic radiosources (VLBI)), partly within the framework of the Earth Rotation Service and IERS (International Earth rotation and Reference systems Service) and the VLBI Data and Analysis Center, component of the IVS (International VLBI Service for geodesy and astrometry).
On November 21, 2020, the first of the Sentinel-6 satellites (Michael Freilich) was launched, a series of satellites dedicated to the continuity of altimetry and climate measurements, taking over from the iconic Topex/Jason series of altimetry satellites. After the calibration and validation phase, which is expected to last 12 months, Sentinel-6 will become the new altimetry reference mission in place of Jason-3, and will extend its mission to serve the scientific community and operational applications on a new orbit to be selected during 2021.
Sentinel-6 Michael Freilich will measure sea level with increased accuracy, aiming for millimeter over one year to meet the reorders of GCOS (Global Climate Observing System) and thus guarantee a stability, at the global level, better than 0.3 mm/year over 10 years. This level of accuracy will be used to observe coastal areas, areas with a very high concentration of people and particularly vulnerable to the devastating effects of rising water and extreme weather events.
For more information:
Researcher : Pascal Bonnefond
The link to the article published in the magazine La météorologie
A video on DORIS
A video on Jason
The CNES press release
The video of the launch on the ESA website
Credits:
Thumbnail: "Sentinel-6 carries a radar altimeter to provide high-precision and timely observations of the topography of the global ocean," © ESA, https://earth.esa.int/web/guest/missions/esa-future-missions/sentinel-6
Figure: Altimeter series and mean sea level rise in centimeters since 1992. NASA, CNES, LEGOS, CLS