Satellite-based augmentation systems (SBAS), such as EGNOS, complement existing global navigation satellite systems (GNSS). SBAS compensate for certain disadvantages of GNSS in terms of accuracy, integrity, continuity and availability.
For example, neither the USA’s GPS nor Russia’s GLONASS meet the operational requirements set by the International Civil Aviation Organisation (ICAO) for use during the most critical phases of aircraft flight, in particular landing. To solve it, ICAO decided to standardise several GNSS augmentation systems including SBAS.
The SBAS concept is based on the transmission of differential corrections and integrity messages for navigation satellites that are within sight of a network of reference stations deployed across an entire continent. SBAS messages are broadcast via geostationary satellites able to cover vast areas.
Several countries have implemented their own satellite-based augmentation system. Europe has the European Geostationary Navigation Overlay Service (EGNOS) which covers Western Europe and beyond. The USA has its Wide Area Augmentation System (WAAS). Japan is covered by its Multi-functional Satellite Augmentation System (MSAS). India has launched its own SBAS programme named GPS and GEO Augmented Navigation (GAGAN) to cover the Indian subcontinent.
All of the systems comply with a common global standard and are therefore all compatible (do not interfere with each other) and interoperable (a user with a standard receiver can benefit from the same level of service and performance whether located in the EGNOS or WAAS coverage area).
In addition to their use in the aviation sector, SBAS systems are essential for applications where accuracy and integrity are critical. In particular, they are indispensable for all applications where people’s lives are at stake or for which some form of legal or commercial guarantee is required.
For example, SBAS make it possible to improve and extend the scope of applications for GPS in areas such as precision farming, the guidance of agricultural machinery, on-road vehicle fleet management, oil exploration for the positioning of platforms at sea or for scientific applications such as geodesy.