Technology

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).

Coincidentally, HRH Duke Of Kent was visiting SSTL at the time and was given a whistlestop tour which touched on "bistatic radar" and "forward scatterometry" (keep reading...).

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”

Nigeria's newly appointed Minister of Science, Chief Grace Ekpiwhre, began her new role with a visit to UK space company, Surrey Satellite Technology Ltd (SSTL). The Honourable Minister was joined by Professor Robert Boroffice, Director-General, National Space Research and Development Agency, for briefing talks on a two-satellite contract currently under manufacture at SSTL for the Federal Republic of Nigeria.

A new-design SSTL-300 enhanced microsatellite, to be called N2, will boost the country's space capability with a high performance operational mission delivering the latest in high resolution Earth imaging, to join the Disaster Monitoring Constellation (DMC) when launched in 2009. The imaging system will include a high-resolution 2.5-metre panchromatic camera with two further multispectral imagers: 5-metre 4-band (20km swath) and medium resolution 22-metre 4-band (300km swath).

Mrs Ekpiwhre also met with 11 Nigerian engineers currently working alongside SSTL engineers on the development of a training satellite. The SSTL-100 satellite, to be called NX, is an integral part of a know-how transfer programme that is providing the Nigerian engineers with hands-on experience in all aspects of spacecraft analysis, build, integration and test. NX will carry a 22-metre multispectral imaging system with ultra-wide 600km swath. The engineers will fully manage the complete life-cycle of the satellite, with responsibility for the delivery of the spacecraft to full flight specification.

The Minister visited both SSTL sites in Guildford, including the manufacturing clean rooms where she saw modules for the N2 spacecraft under construction.

This latest contract is the second between SSTL and Nigeria. NigeriaSat-1 was launched into the DMC in 2003 and continues to provide the country with 32-metre resolution imaging, used by the Government to monitor pollution, manage land use and monitor medium-scale changes to the landscape. N2 will enhance that capability significantly, providing Nigeria with hundreds of valuable geographically referenced images each day, for applications in mapping, water resource management, agricultural land use, population estimation, health hazard monitoring and disaster mitigation and management.

The ESA-supported Surrey Rigid Array (SRA) development project at SSTL completed its Manufacturing Kick-Off Review at Airborne Composites in Holland on 15th May. The review followed on from a successful Critical Design Review (CDR) with ESA in February and marked the initiation of the manufacture of the full size solar array panels. Upon completion of the panel manufacture and acceptance testing, the panels will be ready for solar cell lay-down and the subsequent environmental test campaign.

The Surrey Rigid Array is precisely engineered for high energy output, and crucially, low weight. The carbon fibre / aluminium sandwich panels are produced in a clean room environment and cured in the Airborne autoclave at the Ypenburg, The Hague facility.

SRA is partially funded by ESA’s Advanced Research in TElecommunications Systems funding stream 4 (ARTES 4) initiative aimed at supporting developments within industry that are close to market. The project addresses the design, analysis, manufacture and test of a solar array suitable for small Geostationary (GEO) satellite platforms with a 7 year mission lifetime requiring 1kW minimum power generation.

Monitoring and detecting greenhouses gases is of critical importance to the future of the planet. While there are some conflicting reports that attempt to quantify the rate of climatic change, one fact that the scientific community do seem to agree on is that greenhouse gases are adversely influencing our environment today and will continue to do so in the future. The Kyoto protocol requires such harmful gases to be monitored, therefore the European Space Agency (ESA) have awarded an important contract to a UK team lead by space experts Surrey Satellite Technologies Ltd (SSTL) to provide a solution to this global problem.

The impact of climate change on the global environment is currently attracting significant global coverage. The key question requiring an answer is how human activity affects the surrounding environment is a subject generating significant debate from both ?pro? and ?anti? lobbies. A number of inter-governmental treaties have been signed (including Kyoto) which attempt to limit the amount of greenhouse gases (CO2, CH4, N2O, O3) produced around the globe. Careful monitoring of greenhouse gases is essential if we are to understand fully the impact of these elevated levels on our environment. The key gases are CO2 (carbon dioxide) and CH4 (methane), which have the biggest impact on the Earth?s atmosphere.

Levels of CO2 in the atmosphere have increased dramatically in the last 50 years to levels currently (2005) exceeding 370 ppm. This alarming trend is thought to be a significant factor in global warming.

ESA is considering using a LIDAR instrument to monitor the levels of CO2 within the atmosphere. The most effective wavelength to detect CO2 is at 2 ?m due to its deep absorption signature at this wavelength.

SSTL has been awarded a contract from ESA to develop a new detector to address this spectral region. SSTL will prime the activity with Sheffield and Heriot Watt Universities and Lidar Technologies Ltd as subcontractors. The total contract value is ?400k and will be undertaken in 18 months.