Satellite-Based Augmentation System (SBAS) is a regional augmentation technology that improves GNSS accuracy, integrity, and availability by broadcasting correction and integrity information from geostationary satellites. SBAS systems monitor GNSS signals across their coverage regions, compute corrections for satellite and atmospheric errors, and transmit this information to users on the same frequencies as GPS, requiring no additional receiver hardware beyond standard GPS capability.

The SBAS architecture includes ground reference stations that continuously monitor GNSS signals, computing corrections for satellite clock and ephemeris errors as well as ionospheric delays across the coverage region. Central processing facilities combine reference station data to generate unified correction and integrity messages. These messages are uplinked to geostationary satellites positioned over the coverage area, which broadcast them to users on GPS L1 frequency (and increasingly L5). SBAS-capable receivers apply these corrections automatically, improving position accuracy from several meters to typically 1-3 meters.

Multiple SBAS systems provide regional coverage worldwide. WAAS (Wide Area Augmentation System) covers North America and is operated by the FAA. EGNOS (European Geostationary Navigation Overlay Service) covers Europe and is operated by EUSPA. MSAS (Multi-functional Satellite Augmentation System) serves Japan. GAGAN (GPS Aided Geo Augmented Navigation) covers India. SDCM (System for Differential Corrections and Monitoring) serves Russia. KASS (Korea Augmentation Satellite System) covers Korea. Additional systems are under development for other regions.

For safety-critical applications, SBAS provides integrity monitoring, the ability to detect satellite failures or anomalies and alert users within seconds. This capability enables certified aviation approaches, giving pilots confidence that navigation information is trustworthy. While SBAS accuracy is insufficient for centimeter-level applications, its free availability, simplicity (no communication infrastructure needed beyond the receiver), and integrity monitoring make it valuable for applications including recreational navigation, maritime approaches, and general aviation where 1-3 meter accuracy meets requirements.