GNSS augmentation

Satellite-based augmentation systems (SBAS) support wide-area or regional augmentation through the use of additional satellite-broadcast messages. ICAO material describes SBAS as a wide-coverage GNSS augmentation system in which the user receives correction and integrity information from a satellite-based transmitter, with Standards and Recommended Practices (SARPs) for SBAS included in Annex 10. This Annex describes a standard data format for use in aviation as well as their broadcast on L1 (and more recently L5). Many SBAS satellites also provide their own timing/ranging signals, acting as additional satellites for positioning. Using measurements from the ground stations, state-space correction messages are created and sent to one or more satellites for broadcast to end users as differential signal. These correction messages include separate values for location-independent corrections (satellite clock, ephemeris, health, etc.) and location-dependent corrections (ionospheric delay). as opposed to observation-space corrections consisting of location or pseudorange errors at specific stations. Current and upcoming SBAS systems implementing the aviation standard (ICAO) state-space format include: • The BeiDou Satellite-based Augmentation System (BDSBAS-B1c) operated by China. • The System for Differential Corrections and Monitoring (SDCM), operated by Russia's Roscosmos based on GLONASS. • The Southern Positioning Augmentation Network (SouthPAN), developed by Australia and New Zealand, with initial services going live in September 2022. • The Korea Augmentation Satellite System (KASS) (Republic of Korea), under development as of 2021. • The commercial StarFire navigation system, operated by John Deere and C-Nav Positioning Solutions (by Oceaneering International). • The commercial Starfix DGPS System and OmniSTAR system, operated by Fugro. • The commercial Atlas GNSS Global L-Band Correction Service system, operated by Hemisphere GNSS. • The Australian SBAS using the Inmarsat 4F1 geostationary satellite, which suffered an outage in April 2023. Defunct SBAS include: • The Wide Area GPS Enhancement (WAGE), operated by the United States Department of Defense for use by military and authorized receivers. • The GPS·C, short for GPS Correction, was a differential GPS data source for most of Canada, maintained by the Canadian Active Control System, part of Natural Resources Canada now decommissioned. Internet-based augmentation A few online services provide access to the data broadcast by SBAS satellites via the Internet, which is useful in areas of low SBAS visibility (e.g. unmanned aerial vehicles navigating urban canyons). Some services such as International GNSS Service (IGS) provide direct access to predicted orbit and clock corrections for GPS (covering a couple of hours). Networked Transport of RTCM via Internet Protocol is an internet protocol for access to such data. NASA operates the Global Differential GPS (GDGPS) system, using data from many ground stations located worldwide. GDGPS disseminates real-time orbit and clock corrections and supports a wide range of GNSS networks beyond GPS (GLONASS, BeiDou, Galileo, and QZSS). WAAS is based on correction data from GDGPS. GDGPS is commonly used to generate assisted GNSS data. Ground stations are commonly used to accumulate continuous GNSS observations to achieve post-hoc correction of data to the centimeter level. Two example systems are the US Continuously Operating Reference Stations (CORS) and the International GNSS Service (IGS). == Ground-based augmentation system ==

Ground-based augmentation system (GBAS) provides Differential GPS (DGPS) corrections and integrity verification near an airport, providing approaches e.g. for runways that do not have ILSs.{{cite web|title=FAA Global Navigation Satellite System Update, ICG-6 Beyond airports The US Nationwide Differential GPS System (NDGPS) was an augmentation system for users on U.S. land and waterways. It used a ground-based network of radiobeacons. == Aircraft-based augmentation system (ABAS) ==

The augmentation may also take the form of additional information from navigation sensors being blended into the position calculation, or internal algorithms that improve the navigation performance. Many times the additional avionics operate via separate principles from the GNSS and are not necessarily subject to the same sources of error or interference. A system such as this is referred to as an aircraft-based augmentation system (ABAS) by the ICAO. The most widely used form of ABAS is receiver autonomous integrity monitoring (RAIM), which uses redundant GPS signals to ensure the integrity of the position solution, and to detect faulty signals. Additional sensors may include: • eLORAN receivers • Automated celestial navigation systems • Inertial navigation systems • Distance measuring equipment, often multiple systems are used to create a positional fix (DME/DME). Can also be used with INS (DME/DME/INS). • Simple dead reckoning systems (composed of a gyro compass and a distance measurement) == Use in aviation and performance-based navigation ==

Satellite-based augmentation systems (SBAS) and ground-based augmentation systems (GBAS) are key enablers of performance-based navigation (PBN) in aviation. SBAS services such as WAAS, EGNOS and MSAS support area navigation (RNAV) and approaches with vertical guidance, including LPV procedures. GBAS installations at major airports provide localized corrections that enable highly accurate approach and landing operations on multiple runways from a single ground facility. Together, these augmentation systems allow aircraft to fly more precise routes with reduced separation, improved fuel efficiency, and lower environmental impact. == See also ==