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The European Geostationary Navigation Overlay Service (EGNOS) is as satellite-based augmentation system (SBAS) providing vital information on the accuracy and reliability of the navigation signals sent out by the US Global Positioning System (GPS) satellites. Being a joint venture between ESA, the European Commission (EC) and the European Organisation for the Safety of Air Navigation (Eurocontrol), EGNOS is the first pan-European satellite navigation system and a precursor to Galileo, the first full Global Navigation Satellite System (GNSS) under development in Europe.


EGNOS broadcasts differential corrections (with respect to the GPS satellite orbits and clocks) and ionospheric corrections to its users.  Taking EGNOS corrections into account, GPS positioning accuracy typically improves from 5-10 metres to approximately 1-3 metres.  In addition, EGNOS provides bounds for the errors associated with those corrections to make the system suitable in particular for safety-critical task like, for instance, vertical guidance of aircraft or navigating ships through narrow channels.


To achieve its aims, EGNOS combines geostationary satellites with a complex network of more than 40 ground stations positioned across the European Civil Aviation Conference (ECAC) area and beyond. A well-distributed set of more than 30 so-called Ranging and Integrity Monitoring Stations (RIMS) is permanently tracking the GPS satellite signals. The GPS raw data collected by the RIMS network are forwarded to the four Master Control Centres (MCCs), the core stations of the EGNOS ground segment. The MCCs are processing the measurements in order to generate the EGNOS corrections and associated integrity messages for each GPS satellite. The data stream from the MCCs is then uploaded by the six Navigation Land Earth Stations (NLES) to the three EGNOS geostationary satellites for broadcasting to all users in Europe equipped with an EGNOS-enabled GPS receiver.


The Navigation Support Office (NSO) is assisting the EGNOS Project Office (EPO) in monitoring the EGNOS performance both at system- and user-level. Moreover, we are actively involved in maintaining the existing ground  infrastructure and in the deployment of new RIMS  in order to extend the service in the Mediterranean and Middle East area.