European geostationary overlay service (GPS) (EGNOS)

European Geostationary Overlay Service (EGNOS) is a navigation system initiated by the Europeans to increase the positioning accuracy of the GPS system to within a few meters.

The Egnos system operates with three geostationary satellites that, like the 34 receiving stations, the Ranging and Integrity Monitor Station( RIMS), calculate correction signals for GPS reception. These correction signals relate to variations in GPS satellite orbits and ionospheric disturbances that affect tracking accuracy. The calculated correction signals are emitted by GEO satellites such as Inmarsat on the GPS frequency of the L1 band at 1,575.42 MHz.

The Egnos system, developed by the Europeans and operated by the European Space Agency( ESA), is one of the Satellite Based Augmentation Systems ( SBAS) and is similar to the Wide Area Augmentation System( WAAS) developed by the Americans and the Multi-Functional Satellite Augmentation System( MSAS) developed by the Asians. The three geostationary satellites of the Egnos system, Inmarsat AOR-E, Artemis and Inmarsat IOR-W, are positioned at longitudes 15.5° West, 21.3° East and 65.5° East and cover the European and African continents.

The Egnos signals can be received and used for civil purposes with appropriate receivers in the air, on land and on water. The positioning accuracy is about 1 m to 3 m in contrast to the GPS accuracy of about 10 m.