Galileo signal reflections monitor ocean weather
A pioneering experiment was launched onboard UK-DMC in 2003, that uses signals reflected from the GPS signals already in orbit to monitor the weather at sea. The joint team experiment team, comprising SSTL and the University of Surrey members has now succeeded for the first time in capturing a Galileo signal from SSTL's GIOVE-A satellite reflected off the ocean surface. Although the signal was weak, because the equipment is optimised for receiving GPS signals, this is an important achievement demonstrating the potential for determining the weather at sea with remote sensing satellites.
What's more, it seems this new development is well timed - the Partnership for Observation of the Global Oceans (POGO), a distinguished partnership of international scientists is calling for a stable network of satellites for surveying vast extents of the surface of the ocean to enable societal benefits' (see POGO release, BBC).
The pioneering GPS Reflectometry Experiment was launched onboard SSTL’s UK-DMC satellite in 2003 to demonstrate the use of GPS reflections to determine the roughness of the ocean, using a method called “bistatic radar” or “forward scatterometry”. This experiment has now successfully detected a Galileo satellite navigation signal reflected by the ocean’s surface. GIOVE-A, the first Galileo demonstration satellite, also built by SSTL, was commissioned by the European Space Agency and has been transmitting prototype Galileo signals since its launch in December 2005.
In early November, 20 seconds of data were captured in orbit above the Arafura Sea, north of Australia, and downloaded to Surrey for processing. Whilst the orbiting experiment on UK-DMC is not optimised for Galileo signals, enough of the reflected signal energy was received to allow the detection and plotting of the weak signal after processing by University of Surrey PhD student, Philip Jales. The shape of the reflection gives an indication of the sea roughness and hence the weather at that place and time, where the wind speed was around 14 mph (22 km/h).
SSTL's Global Navigation Satellite Systems (GNSS) / GPS head, Dr Martin Unwin (centre left) explained
“This is an important achievement in remote sensing and demonstrates the potential offered by Galileo for scientific purposes. A constellation of small satellites could be deployed at low cost to take measurements over the oceans where there are large gaps in forecast knowledge at present. An improved measurement system in space could be used to warn mariners of storms and to provide data for global climate change models - potentially even to detect Tsunamis.”
Dr Unwin is also enthusiastic about benefits of inter-system cooperation:
“Signals from Galileo, in conjunction with GPS and the Russian and Chinese systems, Glonass and Compass, can all be used as part of a new tool for ocean sensing. The future high bandwidth signals transmitted by Galileo, in particular, will enable higher resolution measurements of special interest to scientists, for example, in resolving wave heights”
GPS Reflectometry is of great interest to engineers and scientists as a cost effective means of remote sensing. Firstly, a special transmitter is not required because GPS signals are already broadcast to the Earth 24 hours a day. Also, a satellite dedicated to GPS reflectometry would only need to carry a modified miniaturised GPS/Galileo receiver and an antenna, which could potentially be accommodated on a tiny 10 kg satellite platform at low cost, enabling multiple satellites on a single launch.
The concept is shown in the animation shown to the left (this is freely available and can be embedded into blogs from YouTube).
The UK-DMC Reflectometry Experiment has also previously been used to detect GPS signals reflected off ice and, surprisingly, dry land. The value of these measurements has yet to be fully explored but they may be used as inputs for climate modelling.
A future revision of the experiment, the “GNSS Reflectometry Instrument” is now being designed at Surrey with a view to flight on a future satellite mission. It is being designed specifically to receive Galileo signals as well as those from GPS, with the intention of real time processing. Dr Unwin's final words on the matter, “The sooner Galileo is up and transmitting the better”
Tue, 18.11.2008 10:36
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