A Satellite Based Augmentation System (SBAS) is a wide area differential Global Navigation Satellite System signal augmentation system which uses a number of geostationary satellites, able to cover vast areas, to broadcast primary GNSS data which has been provided with ranging, integrity and correction information by a network of SBAS ground stations. While the primary purpose of SBAS is to provide integrity assurance, use of the system also increases the accuracy and reduces position errors to less than 1 meter.
The European Geostationary Navigation Overlay Service (EGNOS) is the European version of this system and the Wide Area Augmentation System (WAAS) is the United States equivalent. The latter was the first to become operational - in 2003 - and now covers the continental US plus Canada, Alaska and Mexico. In excess of a thousand North American airports now have instrument approaches which depend on WAAS. Japan has developed used its Multi-functional Satellite Augmentation System (MSAS) to provide SBAS functionality. India has launched its own SBAS programme and both Korea and China have announced plans to start their own SBAS implementation.