11 march 2010
Built for performance
Sea level is currently rising at a rate of 3.5 mm every year on average, against only 1.7 mm in 1993-1994.
In other words, the rate has doubled in 20 years and sea level has risen nearly 6 cm in total.
How did we obtain such precise measurements, which have served notably as a basis for the work of the IPCC*?
The answer is: thanks to the Topex/Poseidon (1992-2005), Jason-1 and Jason-2 (from 2001) altimetry satellites.
“Ocean altimetry, the ability to measure sea-surface height from space with extreme accuracy around the globe, was a paradigm shift,” says Eric Thouvenot, Jason-3 Programme Manager at CNES. “Before, we had to rely exclusively on imprecise local tide gauges.”
He adds: “The Jason altimetry satellites are a bit like Formula One racing cars, built for performance, combining the best altimeters we have today in an optimal orbit and minimizing interference from tidal effects.”
Indeed, their level of performance has made them the benchmark for other, less accurate, altimetry satellites.
Ocean weather forecasting
The launch of Jason-2 early in 2008 made it possible to acquire more data on coastal regions and major river estuaries.
The satellite provides near-real-time measurements to a broad range of users in the form of sea-surface height, wave height and wind speed maps, vital for weather forecasting, coastal fisheries and land planning.
“Jason-1 is approaching the end of its design life and is currently flying in tandem with Jason-2, thereby doubling ocean data coverage.” says Eric Thouvenot.
Jason-3 is a carbon copy of Jason-2 and will replace Jason-1 in the same 1,336-km orbit.
CNES signed the contract to build the satellite with Thales Alenia Space on 24 February.
For close on 20 years, these altimetry satellites have helped scientists to better understand and describe the vast system of ocean currents at the surface and deep below.
This system transfers huge amounts of energy and is one of the main drivers of climate change.
* Intergovernmental Panel on Climate Change.