Galileo signal reflections to monitor waves and weather at sea

For the first time a signal from a Galileo satellite - the European alternative to GPS - has been captured after reflection off the ocean surface. The successful experiment carried out by Surrey Satellite Technology Ltd (SSTL) and the University of Surrey demonstrates the potential for determining the weather at sea with remote sensing satellites. The development offers the possibility of deploying a constellation of small satellites to take measurements over the oceans where there are large gaps in forecast knowledge at present. Such a system could be used to provide severe weather warnings to mariners, data for global climate change models and even the potential to detect tsunamis.

The GPS Reflectometry Experiment was launched onboard SSTL’s UK-DMC satellite in 2003 to demonstrate the use of GPS reflections in determining the roughness of the ocean, using a method called “bistatic radar” or “forward scatterometry”. GPS Reflectometry potentially offers engineers and scientists a cost effective means of remote sensing. This is because a special transmitter is not required as GPS signals are already broadcast to the Earth 24 hours a day and also because a satellite dedicated to GPS Reflectometry would only need to carry a modified miniaturized 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 UK-DMC Reflectometry Experiment had previously been used to detect GPS signals reflected off ice and also dry land, but 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 the UK-DMC satellite is not optimized for Galileo signals, enough of the reflected signal energy was captured to allow the detection and plotting 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).

Dr Martin Unwin, head of the Global Navigation Satellite Systems (GNSS) / GPS team at SSTL explained, “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”.

A future revision of the experiment, the “GNSS Reflectometry Instrument” is now being designed at Surrey specifically to receive Galileo signals as well as those from GPS, with the intention of real time processing.