New Satellite to Track Changes in Sea Levels Caused by Global Warming

This satellite will tell us more about the world's oceans.

Sentinel-6 Michael Freilich, to give it its full name, is due to be launched from Vandenberg Air Force Base in California later this month.

It will measure sea-surface height, wave-height and windspeed using radar altimetry.

This will allow scientists to monitor changes in sea levels caused by climate change.

"The main instruments on board include a dual frequency radar altimeter. This is the primary instrument of the mission. And that's the one that's measuring sea surface height, significant wave height and wind speed over the ocean," says Craig Donlon, Sentinel-6 Mission Scientist.

"And from those measurements, we can actually have the superb measurements that we expect of sea level rise, but also the waves, the significant wave height, which is the top one third of the waves if you were to look at them in time."

The new radar altimeter is called Poseidon-4 and offers very precise measurements.

Data gathered from Sentinel-6 will be used alongside information from other satellites to build as complete picture of the oceans as possible.

"Sentinel-3 is providing the sea surface temperature and the ocean biology measurements. Sentinel-1 is providing radar imaging measurements of ocean swell waves, of sea ice. Sentinel-2 provides high resolution measurements in the coastal zone. And when these are used together, a wonderful view of the Earth's oceans can be achieved. It's almost like a painting," says Donlon.

"As you add more colour, you get a brilliant view of our wonderful planet. And that's just not possible if you only have a few spacecraft. So diversity is really important. And that's what Copernicus is all about, is making sure we have the right spacecraft, the right instruments to paint that wonderful picture of planet Earth."

Sentinel-6 is just the latest in more than three decades of radar altimetry.

It will replace the Jason-3 satellite. To begin with, they will fly in tandem just 30 seconds apart, so that any differences in data can recorded to allow measurements in this long-term study of the oceans to remain stable.

"We now have a nearly 30 year long sea level record, and Sentinel-6 will ensure continuity of this altimetry based sea level record. This is very important," explains Anny Cazenave, Senior Scientist, Laboratoire d'Etudes en Géophysique et Océanographie Spatiales.

"With a long record we can precisely measure the acceleration, we eventually can detect new regime, tipping points. For example if there is runaway in the melting of Greenland or Antarctica, sea levels will record this runaway change because it is an integrator of all change that are occurring in the climate system. So we will be able to see some some change, big change in the global climate."

Understanding how quickly sea levels are rising and what locations are most at risk from the phenomenon is crucial.

Ten percent of world's population live in coastal zones less than 10 metres above sea level. A large rise puts those communities in danger,

"Sea level rise is accelerating. And it is not geographically uniform. In some regions the rate of rise is two to three times faster than the global mean. This means that in these regions the elevation since the beginning of the 90s, these are now nearly 30 centimeter, which is not negligible," says Cazenave.

The information gathered by Sentinel-6 will have far reaching significance.

It could be used for weather forecasts, mapping the topography of the seafloor and even by insurance companies to calculate flood risks.

"Eleven of the fifteen largest megacities are located at the coast. And this number will double, I mean, the number of people living in coastal area will double by 2060. Knowing how much the level is rising at the coast and how much it will rise in the future in coastal areas is of use, it's a useful measurable for human beings," adds Cazenave.

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