Benefits of Satellite-Based Augmentation Systems

• Satellite-Based Augmentation (SBAS) provides accurate location data relative to standard GPS

• SBAS uses ground stations and satellites together

• SBAS is likely to have enhanced economic and navigational benefits this decade

Satellite-Based augmentation system (SBAS) services provide capabilities to improve location data for normal and more developed global positioning system (GPS) devices. The global navigation satellite system (GNSS) signals received in normal GPS devices can be improved from several meters accuracy to sub-meter accuracy, making it closer in accuracy as some GPS methods such as differential GPS (DGPS).

In this geospatial podcast, Chris Marshall, a positioning engineer at a company called FrontierSI, discussed how SBAS technology works.^[1] 

In addition to satellite signals, the technology leverages a network of reference stations that continuously operate. In particular, the governments of Australia and New Zealand have seen SBAS as a great national benefit and have invested in the system.

The countries have developed a network of continuously operating reference stations (CORS) that integrate different measurements from ground stations that then compute corrections for a region. Once the data are corrected, that location data are sent to a processing center. The data are then uploaded to a satellite with a downlink from a satellite given to the end-users.

For the system to operate, the computer determined position at each core site is corrected versus a known location from an entire network. The system allows the determination of how much error is being brought into the system — that is error connecting from the satellite to the ground stations. Stations generally correct for ionospheric errors with signals sent to a ground processing station. This processing station can take all the data and display corrections for the entire SBAS region.

Having more ground stations improves accuracy, with some parts of the world not having sufficient SBAS coverage due to a lack of stations. The system does not replace real time kinematics (RTK), although it can provide up to 10 cm accuracy. In fact, unlike RTK, which decreases in accuracy as you go further away from a base station, SBAS accuracy does not decrease within the network.^[2]

What all this means is that end-users will see the location data without having to have other devices, such as a base and rover, to correct location data. Effectively, this makes SBAS work like a DGPS in the sky, with a satellite used as a sky base station. One can, in fact, use RTK corrections to improve signals received and get even more precise location data. However, one other disadvantage of kinematic ground-based systems is that they depend on mobile coverage and 3D and 4D coverage do not allow uplink or downlink information in two directions. The advantage of SBAS is that you do not need mobile data coverage; the visibility of the satellite is all that is required, enabling location data to be obtained in remote areas.

Another benefit of SBAS systems is they likely do not need specialized software or hardware. In the basic implementation of SBAS, the same frequency as standard GPS satellites can be used.

For users, SBAS satellites operate as any other GPS satellite and signal data are given albeit at a much higher accuracy level than standard GPS. While many existing GPS receivers are SBAS compatible, more advanced uses of SBAS may require new hardware and software.

Standard mobile phones can also work with this technology. Benefits include GPS signals that are more reliable and signals will likely be more correct than other augmented GPS signals. For mapping purposes, benefits include seeing one’s location on the correct side of a road or a person’s location on roads that are closely parallel to each other can be determined properly. We can think of the service as an extra, rather than a stronger, signal to enable a more accurate position. It is still possible in urban regions or large canyons that signals are blocked and accuracy could be compromised. However, if you can correct for common error sources in such cases, it is possible to get a more reliable service even with fewer available satellites in given limited areas. Current uses of SBAS has included its application with agriculture, where enhanced pasture utilization has been applied by developing virtual fencing for animals where animals graze along specific defined areas without needing fences. Additionally, SBAS has been used in aviation, with civil aviation standards adapting to use the system. 

In the United States, SBAS has existed for about ten years. For the US system, the Wide Area Augmentation System (WAAS) has been operational and was the first SBAS used for North America. Other systems being developed include those by European, Russian, Indian, and South Korean efforts. For now, SBAS has provided high levels of accuracy but it may not always be appropriate for all use cases, as RTK and enhancement techniques for signals could provide even more accurate location data. For the future, dual-frequency multi-constellation SBAS is being envisioned, which would use two major satellite constellations with corrections providing slightly higher accuracy than the standard service. 

Currently, SBAS is down in Australia and New Zealand, but the systems should be operational in 2021 and 2025 in aviation. The service is free and as SBAS expands to other countries we will likely see more use of this service in coming years, including in many different industries, with economic forecasts estimating billions of dollars in benefits by integrating this system in different industries. 

References

^[1]    For more on this MapScaping podcast on SBAS, see: https://mapscaping.com/blogs/the-mapscaping-podcast/satellite-based-augmentation-system-a-base-station-in-the-sky.

^[2]    For more on SBAS and satellite and ground-based systems used, see:  Rao, G.S., 2010. Global navigation satellite systems: with essentials of satellite communications (affiliated link). Tata McGraw Hill, New Delhi.

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