Bernese GPS Software Version 5.0 - Bernese GNSS Software

6.2 Preprocessing on the RINEX Level
(1) GPSEST to store normalized residuals (from a zero-difference or double-difference
solution),
(2) RESRMS to detect outliers in the residuals to write an edit information file, and to
generate a summary file,
(3) RESCHK to detect misbehaving stations in the RESRMS summary file (restart the
processing without the corrupted station), and
(4) SATMRK to mark outliers in observation files according to the content of the edit
information file.
6.2 Preprocessing on the RINEX Level (RNXSMT)
The program RNXSMT (”Menu>RINEX>RINEX utilities>Clean/smooth observation files”), which stands
for RINEX SMooThing, is the RINEX preprocessing tool in the Bernese GPS Software.
It processes a single RINEX file without using any geometry information. The program
requires dual frequency code and phase observations. The output is again a RINEX file
which should be free of outliers and cycle slips and contains smoothed code measurements.
RNXSMT is normally only used to clean RINEX files for zero-difference processing.
The actions taken by the program are summarized in the output. Each RINEX file is
processed arc by arc where an arc usually is a satellite pass. The observations of each
satellite arc are processed in four steps:
(1) Screening of the Melbourne-Wübbena linear combination, Eqn. (2.50), for outliers and
cycle slips.
(2) If cycle slips are detected, the geometry-free linear combination, Eqn. (2.46), is checked
in order to determine the size of the cycle slips on both frequencies. This information
can be used to connect the observations before and after the cycle slip. Currently only
the smoothed code data pieces (arcs) may be “connected”. Phase cycle slips are not
repaired, but a new ambiguity is set up at the corresponding epoch.
(3) Screening of the difference between the ionosphere-free linear combinations of code
and phase, Eqns. (2.41) and (2.42), i.e., L3 − P3, to remove bad observations which
were not detected during the Melbourne-Wübbena based screening (step 1).
(4) Smoothing the code observations using code and carrier phase data of the clean observation
arcs.
In the following, each of these steps is discussed in detail. Additional information may also
be found in [Springer, 2000].
6.2.1 Data Screening Based on Melbourne-Wübbena Linear Combination
The Melbourne-Wübbena combination eliminates the effects of the ionosphere, geometry,
clocks, and the troposphere (see Eqn. (2.50)). Apart from the wide-lane ambiguity the
remaining signal should be pure noise, with a RMS error of approximately 0.7 times the
RMS of the code observations on the L1 frequency. If the noise of the Melbourne-Wübbena
combination has an RMS below 0.5 wide-lane cycles (43 cm) it is almost trivial to detect
Bernese GPS Software Version 5.0 Page 103