Operation 37
Operation
Sources of Error
The major sources of error affecting the accuracy of GPS range measurements
are satellite orbit estimation, satellite clock estimation, ionosphere, troposphere,
multipath, and receiver noise in measuring range. The first four sources of error
are almost totally removed by differential corrections. The residual error is in the
order of one millimeter for every kilometer of separation between base and remote
receivers.
Receiver noise is not correlated between the base and the remote receiver and is
not canceled by differential GPS. However, in the G12, integrated doppler
measurements are used to smooth the range measurements and reduce the
errors resulting from receiver noise.
At the instant an satellite is locked, there is also RMS noise affecting the range
measurement. RMS noise is reduced over time by the square root of the number
of measurements computed by the receiver. For example, after 100 seconds of
locking to a satellite, the rms noise in range measurement is reduced by a factor
Figure 3.2. RTCM Remote System
G12RevD.book Page 37 Tuesday, April 2, 2002 4:33 PM
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