Leica Geosystems GPS Basics - Manual (Page 24)

24
GPS Basics -1.0.0en How GPS works
4
3.3.4 Ambiguity and Ambiguity Resolution
1.
2.
an approximate
position. The
precise answer
must lie somewhere
within this circle.
The wavefronts from
a single satellite
strike both within
and outside of the
circle. The precise
point must lie
somewhere on one
of the lines formed
by these wavefronts
inside the circle.
Continued...
When a second
satellite is observed,
After removing the clock errors by double
differencing, the whole number of carrier
wavelengths plus a fraction of a wave-
length between the satellite and receiver
antenna can be determined. The
problem is that there are many ‘sets’ of
possible whole wavelengths to each
observed satellite. Thus the solution is
ambiguous. Statistical processes can
resolve this ambiguity and determine the
most probable solution.
The following explanation is an outline of
how the ambiguity resolution process
works. Many complicating factors are not
covered by this explanation but it does
provide a useful illustration.
Differential code can be used to obtain