From England's University of Southampton - The National Oceanography Centre
Sea level mapped from space with GPS reflections
The GPS signal used for ‘sat-navs’ could help improve understanding of ocean currents, according to new research published in Geophysical Research Letters by National Oceanography Centre (NOC) scientists, alongside colleagues from the University of Michigan and Jet Propulsion Laboratory.
As part of this research, sea surface height has been measured from space using GPS signals reflected off the sea surface for the first time. Information from these GPS signal reflections can be potentially used by scientists to monitor ocean currents by measuring the slopes currents cause in the ocean’s surface.
Ocean surface height measurements are routinely made from space by radar altimeters, but this new study is the first that uses the GPS reflections. The data for this research was acquired from the TechDemoSat-1 satellite, launched in 2014 by Surrey Satellite Technology Ltd.
Dr Paolo Cipollini from NOC, who co-authored this research, said “the sea surface is not flat at all, especially when looked at over long distances. The largest ‘bulges’ are due to variations in the Earth’s gravity field. On top of those there are smaller, shorter variations due to sea surface currents. We are really encouraged by our results since it demonstrates for the first time that we are able to map the overall sea surface height from space using the GPS-reflections technique. This leads us to think that in the near future we should be able to map currents from space by detecting even smaller variations in sea surface height.”
GNSS-Reflectometry (GNSS-R) is the general term for reflectometry using navigation signals, including GPS as well as the European equivalent Galileo. The advantage of using GNSS-R is that it uses the GNSS transmitters already in orbit, and the lightweight, low-power receivers can be launched into space relatively cost-effectively. Existing satellite altimeters, although very accurate, are not in enough number to sample the ocean well at scales below 100 km. A constellation of GNSS-Reflectometry receivers would provide a thirty-fold improvement on the amount of data that could be gathered. Such a constellation will be launched in late 2016 as part of the NASA CYGNSS mission, to watch an animation of this follow this link https://youtu.be/sbQ0m5lxLD8.
No mention of the resolution but it will be interesting to see what they are able to see. I remember when the TOPEX/Poseidon system went live 1992 - one of the observations were long wake-like ripples. These were discovered to be tracks from submerged submarines and the high resolution data was subsequently 'edited' for content. It did great work during the 1987-1988 El Niño season. Unfortunately, the satellite died in January 2006. More at Wikipedia
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