Academy warns on GPS unreliability

When in doubt, can YOU drag out the sextant and take a position?
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Leisure sailors and other mariners could find themselves in trouble if they rely totally on GPS systems a British Academy of Engineering has warned.

The report finds that the severity of the errors may be so large as to give noticeably suspect results which can immediately be identified by the users, but the real threat lies in 'dangerously misleading' results which may not seem obviously wrong - a ship directed slightly off course by faulty data could steer it into danger.

This is of vital importance to cruising sailors, when it is known that a large percentage of us do not take alternative methods of navigation and sometimes cannot carry out coastal or celestial navigation.


Dr Martyn Thomas CBE FREng, Chairman of the Royal Academy of Engineering's Global Navigation Satellite System (GNSS) working group, says: 'GPS and other GNSS are so useful and so cheap to build into equipment that we have become almost blindly reliant on the data they give us.

'A significant failure of GPS could cause lots of services to fail at the same time, including many that are thought to be completely independent of each other. The use of non-GNSS back ups is important across all critical uses of GNSS.'

Society in general may already be dangerously over-reliant on satellite radio navigation systems like GPS, the Academy warns in a report published 8 March 2011. The range of applications using the technology is now so broad that, without adequate independent backup, signal failure or interference could potentially affect safety systems and other critical parts of the economy.

Global Navigation Space Systems: reliance and vulnerabilities looks into the increasing use of global navigation satellite systems (GNSS) to gain accurate data for positioning, navigation and timing (PNT). The US-operated Global Positioning System (GPS) is best known as the first major implementation of this technology but other GNSS systems are being planned and built, including the Russian GLONASS and Europe's Galileo.

GPS vulnerability - so easy, so cheap
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The Academy's report focuses on our increasing reliance on GNSS and the current limited use of GNSS-independent backups for PNT data. The vulnerabilities of GNSS to deliberate or accidental interference, both man-made (such as jamming) and natural (such as solar flares) are also highlighted.

As well as the ubiquitous satnav, the signals are used by data networks, financial systems, shipping and air transport, agriculture, railways and emergency services. The European Commission, in its mid-term review of the European satellite radio navigation programmes (18 January 2011) estimated that an €800 billion chunk of the European economy is already dependent on GNSS.

All GNSS applications are vulnerable to failure, disruption and interference and the report looks at a range of possible consequences of these, from the inconvenient (such as passenger information system failures) to possible loss of life (such as interruptions to emergency services communications).

There is also a concern over the criminal use of jamming equipment to bypass GNSS systems - easily available technology can be used to block tracking of consignments of goods or to defraud systems that collect revenue using GNSS (such as toll-road charging).

The Academy's report looks at security awareness and recommends that critical services include GNSS vulnerabilities in their risk register and that these are reviewed regularly and mitigated effectively. It says the provision of a widely available PNT service as an alternative to GNSS is an essential part of the national infrastructure - a terrestrial radio navigation system called eLORAN is already in development for this purpose.

The Academy also suggests policy responses including the closing of a legal loophole which allows the import, advertisement and possession of jamming devices. The UK government could trial the deliberate jamming of signals for a limited period to allow users to evaluate the impact of the loss of PNT data and the effectiveness of their back-up plans.

Finally, the Academy advises the creation of an R&D programme focused on antenna and receiver improvements that would enhance the resilience of GNSS dependent systems against natural and man-made threats.

Dr Thomas adds: 'The deployment of Europe's Galileo system will greatly improve the resilience of the combined GPS/Galileo system, but many of the vulnerabilities we have identified in this report will remain. No-one has a complete picture of the many ways in which we have become dependent on weak signals 12,000 miles above us.'

The Academy's report, 'Global Navigation Space Systems: reliance and vulnerability' is available online at by www.raeng.org.uk/gnss!clicking_here.

Professor Martyn Thomas will present the conclusions of the Academy's report to the 2011 GNSS Interference, Detection and Monitoring Conference on Thursday 10 March.

About the Royal Academy of Engineering:
Founded in 1976, The Royal Academy of Engineering promotes the engineering and technological welfare of the country. Our fellowship - comprising the UK's most eminent engineers - provides the leadership and expertise for our activities, which focus on the relationships between engineering, technology, and the quality of life. As a national academy, we provide independent and impartial advice to Government; work to secure the next generation of engineers; and provide a voice for Britain's engineering community.