POS MV V4 User Guide
Theory of Operation
Copyright © Applanix Corporation, 2009
B-34
approximately one hundred cycles by knowing the satellite pseudo-range, but
there remains some uncertainty in its precise determination.
Predicted position from
satellite pseudo-range
Feasible positionsFeasible positions
Measured
phase
Number of cycles in
transmission path
Figure 76: Carrier Phase Cycle Measurement
Because of the uncertainty in its knowledge of the number of integer
wavelengths in the transmission path, the receiver has a number of feasible
true positions. These all lie along the circumferences of circles, centred on the
satellite and varying in radius by the signal wavelength.
The range to any satellite is very large and so, for the purposes of this
explanation, the feasible positions lie along parallel straight lines. These lines
are 19 cm apart and are within a circle of radius ‘R’ equal to the uncertainty in
the GNSS position solution. This is represented by the shaded circle in
Figure 77.
The uncertainty in determining which line is the one on which the actual
position lies is the carrier phase ambiguity. It can be resolved by performing
the same operation using multiple satellites.
Figure 78 shows that, by performing the same operation using signals from
two satellites, the range of feasible position solutions is reduced to a number
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