The European Geostationary Navigation Overlay Service (EGNOS) is Europe’s first venture into satellite navigation. It will augment the two military satellite navigation systems now operating, the US GPS and Russian GLONASS systems, and make them suitable for safety critical applications such as flying aircraft or navigating ships through narrow channels.
Consisting of three geostationary satellites and a network of ground stations, EGNOS will achieve its aim by transmitting a signal containing information on the reliability and accuracy of the positioning signals sent out by the Global Positioning System (GPS) and the Global Orbiting Navigation Satellite System (GLONASS). It will allow users in Europe and beyond to determine their position to within 5 m compared with about 20 m at present.
EGNOS is a joint project of the European Space Agency (ESA), the European Commission (EC), and Eurocontrol, the European Organisation for the Safety of Air Navigation. It is Europe’s contribution to the first stage of the global navigation satellite system (GNSS) and is a precursor to Galileo, the full global satellite navigation system under development in Europe.
[source: European Space Agency]