Augmentation of a global navigation satellite system (GNSS) is a method of improving the navigation system's attributes, such as accuracy, reliability, and availability, through the integration of external information into the calculation process. There are many such systems in place and they are generally named or described based on how the GNSS sensor receives the external information. Some systems transmit additional information about sources of error (such as clock drift, ephemeris, or ionospheric delay), others provide direct measurements of how much the signal was off in the past, while a third group provide additional vehicle information to be integrated in the calculation process.
A satellite-based augmentation system (SBAS) is a system that supports wide-area or regional augmentation through the use of additional satellite-broadcast messages. Such systems are commonly composed of multiple ground stations, located at accurately-surveyed points. The ground stations take measurements of one or more of the GNSS satellites, the satellite signals, or other environmental factors which may impact the signal received by the users. Using these measurements, information messages are created and sent to one or more satellites for broadcast to the end users.
EGNOS – das Europäisches SBAS
EGNOS is developed by the European Space Agency, the European Commission and EUROCONTROL. It supplements the GPS, GLONASS and Galileo systems by reporting on the reliability and accuracy of the signals. The official start of operations was announced by the European Commission on 1 October 2009.
According to specifications, horizontal position accuracy should be better than seven meters. In most cases, the horizontal position accuracy is at the meter level. The EGNOS system consists of three geostationary satellites and a network of ground stations.
As of March 2011, the system was also certified for use in Safety of Life (SoL) applications. A commercial service is under test and will also be made available in 2011. Initial work to extend EGNOS coverage farther East and into to the Southern Africa region is currently being undertaken.
Similar service is provided in North America by the Wide Area Augmentation System (WAAS), and in Asia, notably Japan, by the Multi-functional Satellite Augmentation System (MSAS).