EGNOS - European Geostationary Navigation Overlap Service
EGNOS is the European Geostationary Navigation Overlay Service. It has been developed to work alongside existing satellite navigation systems to improve accuracy. This makes EGNOS suitable for safety-critical applications such as landing aircraft or navigating a ship through a narrow channel.
Improving the accuracy of satellite navigation
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Artist's impression of the EGNOS satellite.
In full operational service
The EGNOS service is broadcast via two Inmarsat communications satellites and a third European Space Agency (ESA) spacecraft, Artemis. The service covers the whole of Europe. EGNOS transmits a signal containing information on the reliability and accuracy of the positioning signals sent out by the American GPS global navigation system. It allows users to determine their position to within two metres and since reliability of the signal can be assured, EGNOS can be used in safety critical situations such as landing aircraft in poor weather.
EGNOS is a joint project between ESA and the European Commission. EGNOS has many duplicate systems and failsafe mechanisms so that the service can be guaranteed making it not only more accurate than GPS only signals, but also means that it can be relied upon for safety critical uses.
In future, EGNOS will also improve the accuracy of Galileo signals as well as GPS signals.
EGNOS consists of three geostationary satellites and a system of ground stations.
Ranging and Integrity Monitoring Stations (RIMS) on the ground pick up signals from GPS satellites.
This data is then processed in Master Control Centres (MCC). Here, the accuracy of the original signals is determined and other factors such as electrical disturbances in the atmosphere are taken into account.
This data is incorporated into an EGNOS signal and sent via a secure communications link to the three satellites.
These satellites then relay the signal back to users on the ground giving them a much more accurate position than would be achieved through GPS alone.
UK companies including BT, Astrium Limited, Logica and Airsys (UK) are involved in developing the EGNOS system. Find out more about EGNOS on the ESA website.