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Do satellite systems need a backup?
June 2005
Satellite navigation technologies are set to play an increasingly crucial role in road and transport management. Road pricing and collision avoidance systems have all been mooted as GPS services of the future. But such dependence will bring risks...
In June, 1995 a cruise ship en route from Bermuda to Boston ran aground near Nantucket Island off Massachusetts. There were 1509 people aboard and because the tide and weather conditions were unfavourable, it was 24 hours before they could be evacuated and taken to safety. Although no one was hurt, damage to the vessel and losses to the shipping line were estimated at $US 7 million. The incident is highlighted in a dissertation by Swedish doctoral student Rickard Karlsson, as one of the most dramatic examples of a navigational failure using the global positioning system (GPS).
He says an official enquiry determined the causes to include: "lack of adequate training, over-reliance on a single navigation system, failure to recognise that the primary (GPS) system was not working properly, system design deficiencies, and failure to check information by using any one of several working supplementary systems".
With the growing use of global navigation satellite systems - and the expected upsurge when Europe's GPS rival Galileo comes online - Mr Karlsson believes it is time to adopt a robust backup system not only for ships but also land transport.
His thesis, for Sweden's Linkoping University, describes how it would be possible to link into other monitoring devices already installed in a ship and create an entirely new navigational system. According to Mr Karlsson, the new system would require no external infrastructure and unlike GPS would not be susceptible to interference.
"Instead, the vessel's own radar is used to measure the distance to surrounding shores, and this data is then compared with a digital sea chart," he says.
"In combination with data about the movement of the vessel, the correct position can be calculated. The method is based on a mathematical algorithm, the particle filter, which is installed as a program in the vessel's computer system.
"There is no need for any further hardware to be installed beyond what is already on board."
Mr Karlsson said preliminary trials of his system had shown that the method worked "just as well as GPS" in navigating an archipelago. It could also be applied to aircraft and cars and trucks to track other vehicles to avoid collisions.
He says his new system is a back up for satellite navigation - not a replacement. He believes there are too many vulnerabilities in satellite systems for anyone to become totally reliant on it.
"GPS can be jammed, either unintentionally or intentionally," Mr Karlsson said. "Signals from the satellites can be interfered with by other communications equipment, or by physical obstacles."
In fact he says it is now even possible to buy electronic "GPS jammers".
