Sokkia Axis 3, Operation Manual

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14 Axis
3™
Chapter 2 Introduction
2.5 Radio Beacon Position Accuracy
Many factors affect the positioning accuracy that a user may
expect from a DGPS system. The most significant of these
influences include:
• Proximity of the remote user to the reference station
• Age of the received differential corrections
• Atmospheric conditions at the beacon and remote user
locations
• Satellite geometry, often expressed as a Dilution of
Precision (DOP)
• Magnitude of multipath present at the remote station
• Quality of the GPS receiver being used at both the reference
and remote stations
2.5.1 Proximity
The distance between a remote user and the reference station is
often considerable when using 300 kHz DGPS radiobeacons.
Broadcast ranges may be as great as 450 km (280 miles) or more,
depending primarily upon transmission power and surface
conductivity. Consequently, some of the errors associated with
GPS at the base station differ somewhat from those at the
remote user’s location. This spatial decorrelation of errors can
result in a relative position offset from the absolute coordinates
of the remote receiver. This offset may be as much as one meter
for every 100 km (62 miles) between the base station and remote
receiver.
*
Note: The OmniSTAR DGPS service is not susceptible to
this error because this system uses a wide-area correction
format and VBS processing.