European Geostationary Navigation Overlay Service

The European Geostationary Navigation Overlay Service is a satellite-based augmentation system developed by the European Space Agency and Eurocontrol on behalf of the European Commission. It currently supplements GPS by monitoring the reliability and accuracy of its positioning signals and broadcasting correction data, and is intended to also supplement the Galileo system in a future version. The system consists of forty ranging integrity monitoring stations, two mission control centres, six navigation land earth stations, a wide area ground network, and three geostationary satellites, with ground stations determining signal accuracy and relaying it through the satellites to any receiver equipped to use it. Aviation is one of its principal uses, and its specified horizontal accuracy of better than seven metres is exceeded in practice, reaching roughly one metre.