More on SBAS and PPP
Satellite-based augmentation systems (SBAS) and precise point positioning (PPP) are technologies that improve the accuracy, integrity, and reliability of global navigation satellite system (GNSS) signals. The main objective of SBAS and PPP is to provide an accurate and reliable positioning solution that can be used in various applications such as aviation, maritime, land surveying, and location-based services.
SBAS
SBAS is a technology that uses a network of ground reference stations, satellite links, and processing facilities to determine GNSS errors caused by various atmospheric and environmental factors. The calculated errors are then broadcast to users via a geostationary satellite, allowing users to apply the necessary GNSS correction factors and improve system accuracy. SBAS’s are designed to provide a range of services, including accuracy, integrity, availability, and continuity, to meet the needs of various applications, predominantly aircraft. SBAS also provides warnings to users if GNSS signals are not reliable. This is particularly important in safety-critical applications such as aviation and maritime.
The most widely used SBAS systems are the “wide area augmentation system” (WAAS) in the United States, the “European geostationary navigation overlay service” (EGNOS) in Europe, and the “multi-functional satellite augmentation system” (MSAS) in Japan.The main limitation of SBAS is that the individual systems only cover specific areas and global coverage is not available.
PPP
PPP is a technique that can achieve centimetre-level accuracy without the need for a local reference station or real-time corrections. It uses a network of ground-based reference stations equipped with high-precision GNSS receivers and antennas that continuously track the signals from the GNSS satellites. The data collected by these reference stations is then processed using a technique known as “integer ambiguity resolution” to determine the precise orbit and clock information for each satellite.
Once precise orbit and clock information has been calculated, it is broadcast to PPP users via various means, such as the internet or satellite links. Requiring this additional communications channel is the main limitation of using PPP.
PPP is particularly useful in applications where a local reference station is not available or practical, such as surveying, precision agriculture, and geodesy. PPP can also be used in conjunction with SBAS to further improve the accuracy of GNSS signals.
PPP and SBAS integration
PPP and SBAS can be used together to provide high-accuracy positioning solutions. PPP can provide a baseline solution that is then refined using SBAS correction information. This is known as PPP-RTK, or Real-Time Kinematic, which combines the high accuracy of PPP with the real-time correction information provided by SBAS. PPP-RTK is particularly useful in applications where high-accuracy positioning is required in real-time but a local reference station is not available or practical, making it suitable for applications such as precision agriculture, construction, and machine control.
