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SGR-ReSI Instrument Measures Maritime Winds and Waves

May lead to better weather forecasts...

We are excited about the early results from an instrument flying onboard our TechDemoSat-1 satellite, launched earlier this year. This instrument is the Space GNSS Receiver Remote Sensing Instrument (SGR-ReSI) developed by our GNSS experts, led by Dr. Martin Unwin, principal engineer at SSTL in the United Kingdom.

We designed the SGR-ReSI to collect the signals from GPS and other navigation satellites after they have reflected off the ocean surface. The instrument generates images called delay Doppler maps, which are used to interpret ocean roughness and wind speed measurements of the sea surface.

The technique works in a similar way to existing scatterometer technology; however, it eliminates the need for a transmitter and can process multiple reflections from different GPS satellites simultaneously, presenting an opportunity for collecting data more frequently, and over a greater area at a lower cost.

“This is a complementary technology to the well-proven space-based scatterometers,” said Dr. Unwin. “GNSS reflectometry uses a longer wavelength and measures the slope of the swell at the sea surface. It only needs a relatively small, low-power, and low-cost modified GPS receiver so it’s a practical payload that can be flown on multiple satellites. Measurements from many satellites will increase the available temporal and spatial resolution over today’s state of the art, and in future could lead to better global weather forecasting.”

How does it work?

The map below shows the SGR-ReSI targeting four potential reflected signals from GPS satellites around the Bay of Alaska.
The position of the TechDemoSat-1 satellite in orbit overhead is marked by the white cross, and the targeted GPS reflections are marked as yellow points

The SGR-ReSI captures the reflected GPS signals and processes the data onboard the satellite to create delay Doppler maps, which the satellites downlink to a ground station.

Graphic shows three delay Doppler maps taken simultaneously over the Gulf of Alaska from GPS satellites numbers 12, 25, and 2. The fourth reflection from GPS satellite 31 was too weak to be picked up as it was outside the view of the SGR-ReSI antenna.

Interpretation of delay Doppler maps from GPS satellites numbers 12, 25, and 2 into wind speeds and compared to Eutemsat’s ASCAT scatterometry measurements
How can we use the data?

The maritime industry depends on wave height and wind speed information for optimum ship routing, oil and gas rig operations, and undersea cable laying. Ocean vessels rely on this information to avoid high ocean swells, storms, and extreme conditions that will either slow their progress or possibly cause damage. In coastal waters, this information is routinely verified by instruments on buoys that provide regular and true reference data. In the open ocean, however, the industry mainly relies on information based on forecasts and predictions.

This is why the results provided by the SGR-ReSI are so exciting. By flying the instrument on a constellation of small satellites, the GNSS reflectometry data could be used to map all of Earth’s ocean surface with refreshed data every couple of hours. This would not only be of enormous benefit to the maritime industry, but also offers improvements to weather services and climate research.
And there’s more. The SGR-ReSI can also pick up GPS reflections off land, snow, and ice— opening up other potential new opportunities for remote sensing such as measuring the edges and possibly the thickness of sea ice, snow depth, soil moisture levels, and the classification of vegetative foliage.

What’s next for the SGR-ReSI?

With support from the European Space Agency, Surrey is now working on preparing the ground processing and Web interface that will allow users access to the measurements over the Internet with only a short delay. We’re also planning upgrades to the SGR-ReSI that will allow it to track satellite signals from Europe’s new GALILEO and other satellites, yielding additional measurements of the ocean surface.

And on the horizon, we are working with the University of Michigan and Southwest Research Institute on NASA’s eight-satellite CYGNSS mission, due for launch in 2016. The mission uses the SGR-ReSI to target tropical cyclones and hurricanes.

Surrey received funding to support the development of the SGR-ReSI and ground processing capabilities from the UK CEOI, SEEDA, Innovate UK, and the European Space Agency.

A video is available on YouTube that shows the processing and application of the SGR-ReSI data.


03 November 20140 Comments1 Comment

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