Bernese GPS Software Version 5.0 - Bernese GNSS Software

8.4 Resolution Strategies
(1) For very short baselines (up to several kilometers) the ambiguities may be resolved
independently on L1 and L2 using the SIGMA algorithm (it is possible to do that in
one program run, if both carriers are processed). This case is similar to processing
single frequency data.
(2) For longer baselines (up to approximately 2000 km) it is possible to process both
carriers together and to try to resolve both (L1 and L2) ambiguities in the same
run. The recommended strategies are QIF for long sessions and baselines of almost
arbitrary length and SEARCH for short sessions and short baselines.
(3) Using the so-called wide-laning technique case each baseline is processed twice. First
the L5 or Melbourne-Wübbena linear combination is processed, the wide-lane (L5)
ambiguities are resolved and stored in the observation header file. In the subsequent
run the L3 linear combination is processed, the wide-lane ambiguities are introduced
as known, and the narrow-lane (L1) ambiguities are resolved.
It was stated above that in the first step of the third strategy (wide-laning technique)
either the L5 or the Melbourne-Wübbena linear combination is processed. Using L5 (phase
observations only) gets satisfactory results up to baseline lengths of about 100 km (or longer
if a good a priori ionosphere model is used). In this case the processing steps are:
• Ambiguity-free L3 solution saving the coordinate results to get good a priori coordinates
for the next step.
• Wide-lane (L5) ambiguity resolution fixing all coordinates on the values obtained in
the previous step.
• L3 solution introducing the resolved L5 ambiguities and solving for the narrow-lane
ambiguities. In this third step the estimation of station-specific troposphere parameters
is highly recommended (see Chapter 11 because the geometrical term ρ (including
the tropospheric refraction) has to be accurately known – considering the small wavelength.
Note that the estimation of troposphere parameters is always recommended
for long baselines when doing narrow-lane ambiguity resolution or when using the QIF
strategy.
The approach given above (using phase observations only) does not seem to have advantages
over the QIF strategy.
Resolving wide-lane ambiguities using the Melbourne-Wübbena linear combination is very
reliable and almost baseline-length independent. However, the quality of the code measurement
is crucial. The use of smoothed code generated by the program RNXSMT may
help.
The recommended strategies are summarized in Table 8.1.
The ambiguity resolution for GLONASS is only possible with the SIGMA strategy in a
phase–only mode because inter-frequency code biases (caused by the FDMA technology of
GLONASS, see, e.g., [Dach et al., 2006a]) are not handled in the Bernese GPS Software. The
so-called single difference bias term for GLONASS was derived in Section 2.3.7. It is usually
quite small and not explicitly handled in the software. For that reason we recommend to
use the ambiguity resolution for GLONASS for test purposes, only. However, in the case of
a combined GPS/GLONASS analysis you have to make sure that no ambiguities between
the different GNSS are resolved.
Bernese GPS Software Version 5.0 Page 181