Bernese GPS Software Version 5.0 - Bernese GNSS Software

8. Initial Phase Ambiguities and Ambiguity Resolution
in the case of pair of differences b1i1 − b1i2 , b2j1 − b2j2 . We sort the ambiguity pairs in
ascending order of their σ-values. For the ambiguity pair (or pair of the differences) with
the smallest σ (if this σ is lower than the specified σmax, option “Maximal sigma of resolvable NL
ambiguities” in panel “GPSEST 3.2.3: Quasi-Ionosphere-Free (QIF) Ambiguity Resolution Strategy”,
Figure 8.9) we define the search ranges (option “Search width for pairs of L1 and L2 ambiguities”)
ñ1 = NINT(b1) ± i , i = 0;1;... ;imax
ñ5 = NINT(b1 − b2) ± k , k = 0;1;... ;kmax (8.29)
ñ2 = ñ1 − ñ5
and for each pair ñ1,ñ2 of integers within the search range we compute the test value (8.23)
d3 = |β1 (b1 − ñ1) + β2 (b2 − ñ2)| . (8.30)
The pair associated with the smallest value d3 is accepted as a solution, unless
d3 ≥ dmax , (8.31)
where dmax is a user-defined maximum value (option “Maximal fractional part of resolvable NL
ambiguities”). If no ambiguity set passed the test we proceed to the next pair of ambiguities
associated with the second smallest σ. After having accepted one pair the entire leastsquares
adjustment and the procedure described above are repeated. The ambiguities are
thus resolved iteratively. All or only a subset of ambiguity pairs may be resolved in the
iteration process.
8.4 Resolution Strategies
Let us now give comments and recommendations concerning the selection of the appropriate
ambiguity resolution strategy. All algorithms described in the previous section may be used
either in the baseline mode or in the session mode. However, for the sake of efficiency, we
recommend to resolve the ambiguities in the baseline mode (processing each baseline separately)
and then introduce the resolved ambiguities as known quantities into the subsequent
session processing. There are several aspects determining the optimal ambiguity resolution
strategy. Before selecting the strategy the following questions should be answered:
(1) Are phase measurements available on both carriers? If yes, are there high quality code
measurements on both carriers, too? (This is often not true under the A/S regime.)
(2) How long is the baseline?
(3) How long is the session?
If only single frequency data are processed, there are not many possibilities how to resolve
the ambiguities. Either the SEARCH algorithm (for short sessions) or the SIGMA algorithm
(for long sessions) must be used. Only short (several kilometers) baselines should be processed.
If both frequencies are available, we have the following options:
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