If nowadays everyone uses a GPS relatively regularly and in general gets from it the required information, certain effects continue to demand particular attention and are the focus of new strategies for future satellite navigation applications. The most important of these effects is due to the density of free electrons in the ionosphere. If this is not taken into account errors can throw out the calculated position by up to dozens of metres. This is a phenomenon which is being studied by Benoît Bidaine, a FNRS researcher at the University of Liège’s Geomatics Unit.

Who today has not already used a GPS in their car? This acronym, used in an improper way to designate the receiver operated by the user, designates the Global Positioning System, the American satellite navigation system which allows us to determine our geographical position in real time. Its nominal precision is 20m for a simple car GPS. This tool, whose use has become an everyday affair, is entirely controlled by the United States Department of Defense (DoD). This monopoly will not last as Europe is preparing to provide itself with its own geo-localisation system, and which will be reserved for civilian use. Its name? Galileo, after the famous Italian astronomer.

The GPS functions on the basis of a retinue of twenty-four satellites, orbiting at an average altitude of 23,000 km. Why twenty-four? It is the minimal constellation required to enable four satellites to be permanently visible from (just about) anywhere on Earth. The Galileo system, with its 30 satellites, will allow an increase in the precision of a GNSS (Global Navigation Satellite System) receiver, this new acronym designating no matter what satellite navigation system, and will also raise its dependability in terms of a better availability of the signal for its users, amongst other things. For single frequency receivers such as are used in cars, Galileo will use the same frequency band as the GPS. We are thus moving towards interoperable systems, which could use the GPS and Galileo and its combined 54 satellites at the same time.