Vector Sensor Reference Manual 129
integer ambiguities quickly by with prior knowledge of the antenna separation. Data from the
supplemental sensors also decreases the time required for a solution to be computed.
Moving Base Station RTK
The technology at the heart of the GPS compass heading solution is a moving base station RTK
solution. This RTK solution relies on high quality GPS antennas, supporting GPS receiver
hardware, and sophisticated algorithms, which result in a 0.5° heading accuracy (90%).
How it Works
There are two GPS sensors inside the Vector Sensor that share the same clock. One receiver is
designated the base and the other the rover.
In conventional RTK systems where the base station is stationary and the rover positions away
from the base station, there is a relationship between the two receivers that can be described in
terms of an azimuth (a direction referenced to north) and separation from the base station to the
rover. No matter where the rover moves, the relationship of position can still be described in this
manner. Moving one step further, if the base station is also moving, the relationship of relative
position can still be described in this manner.
The Vector Sensor’s base (primary) and rover (secondary) antennas are rigidly fixed in position
relative to one another on a metallic bracket (the sum of the antennas and the bracket is referred
to as the Vector Antenna Array). In the case of the Vector Sensor being used on a marine vessel
for heading, when differencing the measurements, only the relative motion of the rover antenna
with respect to the base will remain. Since the separation between the two antennas remains
fixed with the antenna bracket, the only change is the result of the heading change.
Factors Affecting DGPS 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 (atmospheric and orbit errors)
• Age of the received differential corrections
• Atmospheric conditions at the beacon and remote user locations
• Satellite constellation geometry, often expressed as a Dilution of Precision (DOP)
• Magnitude of GPS signal multipath present at the remote station
• Quality of the GPS receiver being used at both the reference and remote stations
Proximity of the Reference Station
The distance between a remote user and the reference station can sometimes be considerable,
such as when using 300 kHz DGPS radiobeacons. 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
To Next Page
Loading...
Need help?
General
