Hemisphere GPS MBX-4, User Manual

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10
1: Introduction
Factors Affecting Positioning 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.
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.