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GPS RTK Base GPS Receiver User Guide 89

Glossary

SNR See signal-to-noise ratio.

triple frequency

GPS

A type of receiver that uses three carrier phase measurements (L1, L2, and

L5).

UTC Universal Time Coordinated. A time standard based on local solar mean

time at the Greenwich meridian.

VRS Virtual Reference Station. A VRS system consists of GPS 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 GPS

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 GPS receiver, exactly like a GPS 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.

WGS-84 World Geodetic System 1984. Since January 1987, WGS-84 has superseded

WGS-72 as the datum used by GPS.

The WGS-84 datum is based on the ellipsoid of the same name.

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RightWay GPS Navigator RW 430 Guia do Utilizador Página 91