Surrey Satellite Technology (SSTL) is involved in a project to better characterise sea conditions for real-time ‘nowcasting’.
The Wavesentry project will tap into the existing Global Navigation Satellite Systems (GNSS), including GPS, to gather sea-state data then integrate it with information from buoys and ships.
The impetus of the project comes from the fact that many offshore operations do not have sufficient information on existing sea states in the moments before they actually set out.
‘There are some high-spec radar satellites around made by NASA and ESA that take very good, accurate measurements, but there’s only a few of them and there are large parts of the ocean that are just not covered most of time,’ said Martin Unwin of SSTL, the principal engineer on the project. ‘If you picked an individual spot in the ocean, within two hours the sea state could be very different to what it was before and that’s just the temporal domain; likewise in the spatial domain if you move from one spot to another one 50km away, again the sea state could be very different.’
In an effort to address this paucity of data SSTL has been experimenting for several years using a technique known as GNSS reflectometry. It is based on the principle that the high-frequency radio signals sent by GNSS — normally picked up by receivers on the ground — reflect off the Earth’s surface then travel back into space providing useful topographical data.
‘The way that these measurements have been made in the past is using dedicated radar satellites which send a pulse down and you pick up the signal,’ Unwin said. ‘But in this case we don’t need the transmitter, it’s already there and [is] in fact not just one transmitter but many transmitters, so we can use those signals and it means that what we put up in space is much simpler. We just need, basically, a modified GPS receiver.’
Because of the small size of the payload the team has been able to opportunistically hitch a ride on certain satellites to hone the reflectometry technique so it can gather high-quality information on sea-state wave height, period, direction, steepness.
The latest iteration of the device is set to fly on the technology demonstration satellite Techdemosat-1 (TDS-1) which is supported by the Technology Strategy Board.
It will focus on the English Channel to test the feasibility of using the technique for ‘nowcasting’. Eventually, SSTL hopes to commercialise the technology for use in various offshore operations.