Glossary
Augmentation System (SBAS) for the GNSS, consisting of three geosynchronous
satellites over Japan.
real-time differential
GNSS
Also known as real-time differential correction or DGNSS. Real-time differential GNSS is
the process of correcting GNSS data as you collect it. Corrections are calculated at a
base station and then sent to the receiver through a radio link. As the rover receives
the position it applies the corrections to give you a very accurate position in the field.
Most real-time differential correction methods apply corrections to code phase
positions.
While DGNSS is a generic term, its common interpretation is that it entails the use of
single-frequency code phase data sent from a GNSS base station to a rover GNSS
receiver to provide sub-meter position accuracy. The rover receiver can be at a long
range (greater than 100 kms (62 miles)) from the base station.
RTX
Real-time extended. A real-time differential GNSS method that uses carrier phase
measurements for greater accuracy.
SBAS
Satellite-Based Augmentation System. SBAS is based on differential GPS, but applies to
wide area (WAAS/EGNOS/MSAS) networks of reference stations. Corrections and
additional information are broadcast using geostationary satellites.
SDCM
System for Differential Correction and Monitoring (Russian SBAS system, similar to
WAAS and EGNOS)
VRS
Virtual Reference Station. A VRS system consists of GNSS hardware, software, and
communication links. It uses data from a network of base stations to provide
corrections to each rover that are more accurate than corrections from a single base
station.
To start using VRS corrections, the rover sends its position to the VRS server. The VRS
server uses the base station data to model systematic errors (such as ionospheric noise)
at the rover position. It then sends RTCM correction messages back to the rover.
WAAS
Wide Area Augmentation System. WAAS was established by the Federal Aviation
Administration (FAA) for flight and approach navigation for civil aviation. WAAS
improves the accuracy and availability of the basic GNSS signals over its coverage area,
which includes the continental United States and outlying parts of Canada and Mexico.
The WAAS 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 GNSS receiver, exactly like a GNSS satellite.
Use WAAS when other correction sources are unavailable, to obtain greater accuracy
than autonomous positions. For more information on WAAS, refer to the FAA website
at http://gps.faa.gov.
The EGNOS service is the European equivalent and MSAS is the Japanese equivalent of
WAAS.
Trimble R1 GNSS Receiver User Guide 23
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