Sea level mapped from space with GPS reflections

February 22, 2016
The GNSS-R principle. Credit: Paolo Cipollini from the NOC

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, 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 by measuring the slopes currents cause in the '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 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.

The video will load shortly

Dr Maria Paola Clarizia, a visiting scientist at NOC from University of Michigan, and the lead author of the paper, stressed that "the UK has been a pioneer in using GNSS reflectometry to measure ocean features, and the NOC has led the field in analysing the data."

Until recently we could only measure wind speed from GNSS-R data, so this new ability to also observe is a real breakthrough - provided we can retrieve accurate heights. Our paper is a first step in that direction."

NOC's long involvement with research in GNSS-R has been led by Christine Gommenginger, the head of Satellite Oceanography at the NOC. Results published by NOC scientists in 2015 have already demonstrated the capabilities of spaceborne GNSS-R for ocean surface wind speed retrieval.

Explore further: Slope on the ocean surface lowers the sea level in Europe

More information: Maria Paola Clarizia et al. First spaceborne observation of sea surface height using GPS-Reflectometry, Geophysical Research Letters (2016). DOI: 10.1002/2015GL066624

Related Stories

Slope on the ocean surface lowers the sea level in Europe

January 29, 2015

Research at the National Oceanography Centre (NOC) has discovered that a 'slope' on the ocean surface in the Strait of Gibraltar is lowering the sea level in Europe by 7cm. This research, published today in Geophysical Research ...

New tide gauge uses GPS signals to measure sea level change

May 21, 2014

A new way of measuring sea level using satellite navigation system signals, for instance GPS, has been implemented by scientists at Chalmers University of Technology in Sweden. Sea level and its variation can easily be monitored ...

EGNOS augments the U.S. GPS system for safer skies

February 15, 2016

The European Geostationary Navigation Overlay Service (EGNOS) is the first pan-European satellite navigation system. It augments the US GPS satellite navigation system and makes it suitable for safety critical applications ...

Tide gauge network to be updated after 30 years at sea

May 13, 2015

The National Oceanography Centre (NOC) has been awarded funding to upgrade the South Atlantic Tide Gauge Network. This network has now been continuously operating in some of Earth's most remote places for 30 years, including ...

The very hungry sea anemone

July 2, 2015

The surprising culinary preferences of an abyssal sea anemone have been unveiled by a team of scientists from the National Oceanography Centre (NOC).

Recommended for you

Scientists examine bacterium found 1,000 feet underground

December 8, 2016

Pioneering work being carried out in a cave in New Mexico by researchers at McMaster University and The University of Akron, Ohio, is changing the understanding of how antibiotic resistance may have emerged and how doctors ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.