In addition to RTK and PPP correction data, NovAtel CORRECT can utilize corrections generated by SBAS and DGPS.

Spaced Based Augmentation Systems (SBAS)

SBAS systems are geosynchronous satellite systems that provide services for improving the accuracy, integrity and availability of basic GNSS signals. Positioning accuracy is enhanced through the transmission of wide-area corrections for GNSS range errors. Integrity is enhanced by the quick detection of satellite signal errors and the sending of alerts to receivers that they should not track the failed satellite. Signal availability can be improved if the SBAS transmits ranging signals from its satellites.

A SBAS includes reference stations, master stations, uplink stations and geosynchronous satellites.

Reference stations, which are geographically distributed throughout the SBAS service area, receive GNSS signals and forward them to the master station. Since the locations of the reference stations are accurately known, the master station can accurately calculate wide-area corrections. Corrections are uplinked to the SBAS satellite then broadcast to the GNSS receivers throughout the SBAS coverage area.  User equipment receives the corrections and applies them to range calculations.

Examples of SBAS include:

  • Wide Area Augmentation System (WAAS). The US Federal Aviation Administration (FAA) established the WAAS to provide GPS corrections and a certified level of integrity to the aviation industry, to enable aircraft to conduct precision approaches to airports.
  • European Geostationary Navigation Overlay Service (EGNOS). The European Space Agency, in cooperation with the European Commission (EC) and EUROCONTROL (European Organization for the Safety of Air Navigation) developed EGNOS to improve the accuracy of positions derived from GPS signals and alerts users about the reliability of the GPS signal.
  • MTSAT Satellite Based Augmentation System (MSAS). Uses two Multifunctional Transport Satellites and a network of ground stations to augment GPS signals in Japan.
  • GPS-Aided GEO Augmented Navigation System (GAGAN). Supports flight navigation over Indian airspace. The system is based on three geostationary satellites, 15 reference stations installed throughout India, three uplink stations and two control centers.
  • System for Differential Corrections and Monitoring (SDCM). The Russian Federation is developing SDCM to provide Russia with accuracy improvements and integrity monitoring for both the GLONASS and GPS navigation systems.

Differential GPS (DGPS)

With DGPS, the position of a fixed GNSS receiver, referred to as a base station, is determined to a high degree of accuracy using conventional surveying techniques. Then, the base station determines ranges to the GNSS satellites in view using a code-based positioning technique and the location of the satellites determined from the precisely known orbit ephemerides and satellite time.

The base station compares the surveyed position to the position calculated from the satellite ranges. Differences between the positions can be attributed to satellite ephemeris and clock errors, but mostly to errors associated with atmospheric delay. The base station sends these errors to other receivers (rovers), which incorporate the corrections into their position calculations.