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October 19, 2020 - November 10, 2020 - Two Sentinel-6 spacecraft will provide centimetre-scale measurements of global sea-level rise. The twin craft -- Sentinel-6A and Sentinel-6B -- will each carry powerful new Poseidon-4 radar altimeters.
Sentinel-6A bears the name Dr Michael Freilich -- a tireless advocate for advancing satellite measurements of the ocean -- and is the sixth mission of the European Copernicus Earth observation programme.
Sentinel-6A Michael Freilich will launch atop a SpaceX Falcon-9 rocket from Vandenberg Air Force Base at 06:31GMT (11:31PST) on November 10. Sentinel-6B will launch in 2025.
Since the early 1990s, satellite altimeters have revolutionised our understanding of sea-level change -- one of the principal concerns linked to climate change.
The Poseidon-4 radar altimeter, developed by Airbus Defence and Space, has an accuracy of 3 centimetres (1.2 inches) from low Earth orbit, about 1,330km (830 miles).
Poseidon-4 bounces radar pulses off the sea surface and measures the time it takes the signals to return to the satellite.
A microwave radiometer corrects so-called “wet-path delay” -- errors caused by water vapour in the atmosphere. The round-trip travel time calculates the distance between the spacecraft and the ocean surface.
Sentinel-6 carries a suite of instruments for Precise Orbit Determination or POD. One Doppler Orbit Radio positioning system (DORIS), a laser retro-reflector and star trackers locate the position of the satellite in orbit.
The combination of altimeter distance and Sentinel’s exact location in space, determine the height of the sea surface relative to the centre of the Earth.
During the last 25 years, the Copernicus programme has measured a global mean sea level increase of 3.3mm/year and a total global increase since 1993 of about 9.4cm (3.7 inches).
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