The launch of the 1,250-kg Sentinel-3A satellite from the Plesetsk Cosmodrome in Russia atop a Rockot vehicle took place on 16 February. Its twin, Sentinel-3B, joined it in the same 814-km orbit in April 2018.

The satellites’ radar altimeters will measure the surface height of oceans, major lakes and rivers, and the thickness of sea ice and glaciers. Together, their radiometers will deliver daily measurements of land surface temperatures with a ground resolution of 1 km. And their spectrometers will operate in 21 spectral bands to acquire data on ocean colour indicating concentrations of phytoplankton in the sea. All of these data will be available free of charge to users, mostly scientists and firms, on the Internet via CNES’s PEPS Sentinel Product Exploitation Platform, ushering in the era of operational oceanography.

Drawing on the heritage of the Envisat mission, Sentinel-3 is part of the European Commission’s Copernicus environmental monitoring and security programme. The European Space Agency (ESA) is responsible for developing the two satellites, their instruments and the ground segment. The spacecraft were designed and built by a consortium of 100 firms overseen by Thales Alenia Space. Under a cooperation agreement with ESA, CNES has supplied a new version of the DORIS instrument, vital for deriving ocean surface heights from the radar altimeters’ data. Besides DORIS, CNES is also contributing its expertise in many other areas of the Sentinel-3 mission.