Sentinel to measure ocean height

The sixth Sentinel in Europe’s ambitious multi-billion-euro Earth-observation project has been contracted. Sentinel-6a will measure changes in the height of the oceans,a key indicator for understanding weather and climate. The European Space Agency signed the £127M deal with Airbus Defence and Space at a remote-sensing symposium in Berlin, Germany. 
Sentinel-6a should be ready for launch in 2020. It will ensure the continuity of a data-set that stretches back to 1992. This shows global sea levels have been rising by just over 3mm per year. Part of that is down to continuing warming of the oceans; part of it is the result of water run-off from melting land ice.
The time series began with a US-French mission called Topex/Poseidon, and was then subsequently renamed Jason in later iterations. The newest version, Jason-3, is due to launch in July. Sentinel-6a will now grasp the baton in five years’ time.
European nations have so far committed 7.5bn euros to the Sentinel project and the programme that exploits its data, Copernicus. The vision is for a fleet of spacecraft that can monitor the land, the oceans and the atmosphere. And the expectation is that the initiative is unending, in the sense that every Sentinel satellite will be replaced at the demise of its mission.
Consequently, there will be a Sentinel-6b in due course, although the funding for this follow-on is not yet fully in place. Sentinel-6a remains a partnership with the US. Indeed, America will again be providing instrumentation and the rocket to put the satellite in orbit.