Hemisphere GPS MBX-4, Руководство пользователя

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1: Introduction
Differential GPS
The purpose of differential GPS (DGPS) is to remove the effects of SA (if
present), atmospheric errors, timing errors, and satellite orbit errors,
while enhancing system integrity.
How it Works
DGPS involves setting up a reference GPS receiver at a point of known
coordinates. This receiver makes distance measurements, in real-time,
to each of the GPS satellites. The measured ranges include the errors
present in the system. The base station receiver calculates what the true
range should be without errors, knowing its coordinates and those of
each satellite. The difference between the known and measured range
for each satellite is the range error. This error is the amount that needs
to be removed from each satellite distance measurement in order to
correct for errors present in the system.
Real-Time DGPS
The base station transmits the range error corrections to remote
receivers in real-time. The remote receiver corrects its satellite range
measurements using these differential corrections, yielding a much
more accurate position. This is the predominant DGPS strategy used for
a majority of real-time applications. Positioning using corrections
generated by DGPS radiobeacons will provide a horizontal accuracy of 1
to 5 meters with a 95% confidence. More sophisticated, short-range
DGPS systems (10 to 15 km) can achieve centimeter-level accuracy, but
are very expensive and often limited to precise survey applications due
to technical constraints on their use.