Ch 13. Satellite‐Based Augmentation Systems (SBASs)

Todd Walter


The concept of an SBAS has its roots in the 1980s. The GPS constellation was not yet complete, but people immediately began to consider how it could be used for aviation. The main problem was that since GPS was not designed as a safety‐of‐life system, it occasionally provides misleading information. A network of monitoring stations was envisioned to send flags to the user when a satellite’s ranging information was not correct. Then it was realized that this network could differentially correct the errors, leading to better accuracy and availability. Finally, the idea of broadcasting the corrections and flags from a geostationary satellite was incorporated. The signal from this satellite would be similar to the GPS satellites and be able to provide ranging as well as data. These three ideas together are what make up an SBAS.