Feb 232010

22km difference - results of a jammed GPS

On the left is a picture from an experiment carried out in 2008 by Alan Grant of the UK’s General Lighthouse Authorities. A vessel’s GPS receiver is reporting its position 22km away from its true position because it has been jammed by a device almost anyone can buy off the internet.

The question is probably not will a major incident involve a GPS jammed vessel but when. It highlights the need for seafarers to be familiar with, and competent in, traditional methods of navigation.

The problem is that GPS singles are very weak. They have been likened to seeing a 25watt on a satellite in daylight. That means the signals can be swamped easily. The issue was the subject of GPS Jamming & Interference – A Clear and Present Danger, a one-day conference held at the National Physical Laboratory in Teddington. “It’s not surprising therefore that there are many phenomena – both natural and deliberate which can upset the received GPS signal. Jamming and Interference – the two main topics of this symposium represent real threats which some industrial and military GPS receivers can address and manage. How aware will new designers and users of mission and safety critical applications with low cost silicon be to the vulnerabilities of satellite based PNT services?” says the conference flyer.

It is not difficult to conceive a scenario involving GPS jamming in the Dover Straits, around Rotterdam, or other heavy traffic areas, or indeed areas used by cruise ships where charts may not be particularly accurate. Equipment such as ECDIS and AIS will be affected by the jamming. The potential for use by pirates and insurance fraudsters goes without saying.

BBC Report Sat-nav systems under increasing threat from ‘jammers’

Professor David Last – GPS Jamming and its Impact on Today’s Society