SBAS
The receiver supports SBAS (Satellite Based Augmentation Systems) that conform to RTCA/DO‑229C, such as WAAS, EGNOS, or MSAS. The receiver can use the WAAS (Wide Area Augmentation System) set up by the FAA (Federal Aviation Administration). WAAS was established for flight and approach navigation for civil aviation. WAAS improves the accuracy, integrity, and availability of the basic GPS signals over its coverage area, which includes the continental United States and outlying parts of Canada and Mexico.
SBAS can be used in surveying applications to improve single-point positioning when starting a reference station, or when an RTK radio corrections link is down. SBAS corrections should be used to obtain greater accuracy than autonomous positioning, not as an alternative to RTK positioning.
The SBAS system provides correction data for visible satellites. Corrections are computed from ground station observations and then uploaded to two geostationary satellites. This data is then broadcast on the L1 frequency, and is tracked using a channel on the receiver, exactly like a GPS satellite.
For more information on WAAS, refer to the FAA home page at http://gps.faa.gov.
The receiver also contains an SBAS+ mode which allows it to use pseudoranges of satellites for which SBAS corrections are present as well as pseudoranges from uncorrected satellites in the position solution. The SBAS+ solution can minimize occurrences of the solution mode switching back and forth between SBAS and Autonomous solution modes; however, the SBAS+ position solution may perform more poorly at times because uncorrected satellites have an influence in the position solution.
To receive SBAS corrections, you must be within the official service volume of that SBAS service. Receiver manufacturers often set SBAS correction volumes to be slightly larger than the ones specified by the respective SBAS service but this may depend on each receiver manufacturer. For example, Trimble receivers situated in the MSAS correction zones can use MSAS corrections between the latitudes 20 and 60 degrees North and between longitudes 110 and 150 degrees East. Hence, receivers situated within this window will track and use MSAS while a receiver situated outside this window may track but not use MSAS corrections.
