Ground control

Europe’s airports are to be the first to benefit from a computerised crash-prevention technology that can determine the location, speed and direction of all ground traffic.

The European Global Navigation Overlay System Terrestrial Regional Augmentation Networks technology, or EGNOS TRAN, developed by the European Space Agency, is designed to complement GPS technology.

GPS depends on a user being within the line of sight of satellites orbiting Earth’s equator. This can affect its accuracy when someone is in a built-up area or at a high latitude, and means it is only accurate to within 15m of an object.

But EGNOS TRAN, which consists of three geostationary satellites and a complex network of ground stations, can improve this to within 3m.

The three satellites send out signals similar to those transmitted by GPS satellites, and provide information about the accuracy of position measurements delivered by GPS, such as data concerning the reliability of the atomic clocks on board the satellites and disturbances within the ionosphere that might affect the accuracy of positioning measurements.

A receiver then analyses this data to give a more accurate position than is possible with GPS, as well as an estimate of the degree of GPS error. This data and inaccuracy warning is distributed by terrestrial means in areas where satellite cover is patchy, said Hans-Hermann Fromm of ESA’s Navigation Department.

‘In a city the amount of data in EGNOS is small enough to be added to FM broadcast signals or the radio data service, which allows a station’s name to be displayed on equipment as it plays. At airports it can piggyback on data link signals received by aircraft.’

The system is more reliable than the combination of eyesight and radar control currently used to co-ordinate air traffic, he said. ‘Users get their GPS signal and also EGNOS information from the ground or satellites,’ said Fromm. ‘They are then warned if they should rely on GPS data or not, which is of particular importance when a plane is taxi-ing or landing at a busy airport. Incidents such as vans colliding with planes are a lot more common than people would think. As congestion is increasing we thought it would benefit airports most.’

The first prototype of the system is helping to monitor air and ground traffic at Sweden’s Kiruna airport, which is so far north that the curve of the Earth means low-rise buildings affect GPS data.

ESA is to demonstrate EGNOS TRAN to civil aviation representatives next week and hopes that authorities across Europe will be quick to adopt the system after a fully operational version goes live next spring.

ESA is also working to develop a technology that can couple EGNOS data with 3D maps, compass and barometric information to allow firemen to navigate within unfamiliar smoke-filled buildings.

Once the Galileo satellite system is in place in 2008 fully automated train systems may be made possible by coupling Galileo GPS signals with data from EGNOS TRAN.