A sensing instrument which can measure ocean parameters such as sea surface roughness has been developed by experts at Surrey Satellite Technology Ltd. (SSTL).
In its more familiar usage, GNSS (Global Navigation Satellite System – also known as GPS) pinpoints the geographic location of a user’s receiver anywhere in the world. However, in this small satellite instrument, reflected navigation signals are used to characterise sea, ice and land surfaces. It offers a significantly improved performance compared with that currently available, providing data with higher temporal and spatial resolutions.
The instrument is part of a pioneering UK-led project that aims to improve forecasting of adverse weather conditions at sea. Using satellite data to measure ocean roughness has been an area of interest for SSTL since an experimental GNSS receiver payload was launched on-board its UK-DMC satellite. Since then, the GNSS receivers team, with Principal Engineer Dr Martin Unwin, has investigated the use of GNSS reflectometry and have obtained promising results. They have built a prototype instrument, known as the SGR-ReSI, which is a multi-channel receiver of reflected GNSS signals and is currently being developed into a payload for the UK TechDemoSat-1 technology demonstration satellite to be launched in Summer 2013.
Vital Early Funding
Although the instrument development has benefited from substantial industrial funding, early seedcorn funding from the UK government and more recently from the Centre for Earth Observation Instrumentation (CEOI) has proved vital. This early funding helped get the project off the ground and, through the CEOI knowledge exchange programme, stimulated academic partnerships and other industrial relationships. Other project partners include Surrey Space Centre, who undertook antenna design work, National Oceanographic Centre, the University of Bath and Polar Imaging Limited. According to SSTL’s Martin Unwin, “the external funding from the CEOI has helped open doors by giving the idea an impetus and an importance that has successfully led on to an upcoming demonstration in space”.
Clever Technology
Global navigational systems like GPS, have been used increasingly for remote sensing as well as navigation. Signals at L-band with a 2-20 MHz bandwidth are being broadcast globally from a 20,000 km altitude and can be used to measure a number of things. In this case, the GNSS signals reflected off the Earth’s surface can be detected and used to measure geophysical parameters. The potential for GNSS reflectometry has already been demonstrated on the UK-DMC mission by SSTL and the University of Surrey in 2003. This experiment highlighted the potential that a microsatellite-compatible passive (receive-only) instrument may be able to make valuable geophysical measurements using the GPS reflectometry technique.
The SGR-ReSI instrument has numerous technical advantages over existing technology. For example it is able to store quantities of raw sampled data, can perform substantial amounts of processing in real time on board the satellite and enables a large number of reflections to be captured across the globe. Its low power and size lends itself for use on multiple satellites to increase the spatial and temporal coverage of the Earth.
Better Modelling and Forecasting for Industrial and Meteorological Applications
Marine operations such as offshore oil platforms and renewable energy projects, as well as shipping, are set to benefit from the data from this technology. These activities depend on high quality information on sea-state (wave height, period, direction, steepness) for economic and safety decision making. Measurements from the SGR-ReSI will enable more effective modelling and forecasting and reduce the need to use costly buoys to obtain information further away from the coast and shipping lanes.
The instrument will be demonstrated on TechDemoSat-1, due to be launched in Summer 2013. It has also been selected to provide measurements of cyclones (hurricanes and typhoons) on the NASA CYGNSS constellation of small satellites to be launched in 2016. Additionally, the Technology Strategy Board (TSB) has provided co-funding for the WaveSentry project. This industry partnership aims to collate and exploit wave knowledge by combining data derived from buoys, ferries/ship wave movements, GNSS-Reflectometry and other satellite wave data.
Key outputs from the project include better measurements of wave steepness and the integration of multiple data sources into a single system. This will ultimately provide better services for meteorology, marine users and scientists.
[mappress]
Press release, March 12, 2013; Image: ceoi