By Jonathan Amos BBC Science Correspondent
17 January 2016
A US-European satellite that is fundamental to our understanding of the oceans has launched from California.
Jason-3 will measure the shape of the global sea surface to an accuracy of better than 4cm.
It will track currents, tides, winds, wave heights, and will help forecast the intensity of storms.
But the new mission will also maintain the reference data-set on sea-level rise. This shows the world’s oceans to be rising at more than 3mm per year.
Jason-3 was launched atop a SpaceX Falcon-9 rocket from Vandenberg Air Force base at 10:42 local time (18:42 GMT). The flight to orbit took just under the hour.
An attempt by SpaceX to recover the bottom part of the Falcon by landing it back on a sea barge came very close to success. The booster found the platform but could not remain upright because a landing leg failed to lock. As a result, it toppled over and exploded.