Service areas of satellite-based augmentation systems (SBAS).
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. SBAS is sometimes synonymous with WADGPS, wide-area DGPS.
For details on how various SBAS are implemented, please see the following articles:
The Wide Area Augmentation System (WAAS), operated by the United States Federal Aviation Administration (FAA).
The European Geostationary Navigation Overlay Service (EGNOS), operated by the European Space Agency.
The Multi-functional Satellite Augmentation System (MSAS) system, operated by Japan's Ministry of Land, Infrastructure and Transport Japan Civil Aviation Bureau (JCAB).
The Quasi-Zenith Satellite System (QZSS), proposed by Japan.
The GPS Aided Geo Augmented Navigation (GAGAN) system being operatlonalized by India.
The GLONASS System for Differential Correction and Monitoring (SDCM), proposed by Russia.
The Satellite Navigation Augmentation System (SNAS), proposed by China.
The Wide Area GPS Enhancement (WAGE), operated by the United States Department of Defense for use by military and authorized receivers.
The commercial StarFire navigation system, operated by John Deere.
The commercial Starfix DGPS System and OmniSTAR system, operated by Fugro.