Bernese GPS Software Version 5.0 - Bernese GNSS Software

6.3 Receiver Clock Synchronization and Preprocessing of Code Observations
The procedure requires satellite clock corrections. These may be obtained from broadcast
navigation messages or, better, from precise IGS orbit files or combined IGS clock files (see
Section 5.5). Specify the clock file in option “Satellite clocks” in panel “CODSPP 1: Filenames”.
The user may also estimate the coordinates of the receivers. The model used in the program
is represented by Eqns. (2.34c,d). The unknown parameter δk appears implicitly in the term
̺i k , too. Therefore, CODSPP estimates the parameters iteratively (using a least-squares
adjustment). The second reason for the iterations is, that the a priori coordinates may not
be accurate enough. In fact, if you do not have any a priori coordinates for your new points,
you might simply start with “0/0/0”.
If GPS and GLONASS data are processed simultaneously, one additional parameter for
each station and session is estimated by program CODSPP, namely the difference between
GPS and GLONASS system time. An additional section appears in the CODSPP program
output listing this estimated system time difference and its RMS value for the combined
receivers:
************************************************************************
GLONASS/GPS TIME OFFSETS
************************************************************************
FILE STATION NAME TIME OFFSET (NS) RMS ERROR (NS)
-----------------------------------------------------------
1 WHIT 40136M001 NO RESULTS AVAILABLE
2 WTZR 14201M010 NO RESULTS AVAILABLE
3 WTZZ 14201M014 -149.403 0.356
4 YELL 40127M003B NO RESULTS AVAILABLE
5 YIBL 25001M001 NO RESULTS AVAILABLE
6 YSSK 12329M003 NO RESULTS AVAILABLE
7 ZAMB 34601M001 NO RESULTS AVAILABLE
8 ZIMJ 14001M006 -150.042 0.371
9 ZIMM 14001M004 NO RESULTS AVAILABLE
-----------------------------------------------------------
2 TOTAL -149.709 0.257
-----------------------------------------------------------
From the nine stations in this program run only two are combined GPS/GLONASS receivers
(WTZZ and ZIMJ). Therefore, the time offset is only available for these two receivers.
During the IGEX campaign (International GLONASS Experiment) it became clear, however,
that we do not have direct access to the pure difference between GPS and GLONASS
system time, but that receiver specific measurement biases influence the results. Processing
data of different receivers leads to different estimated time offsets for each individual receiver
[Ineichen et al., 2000]. In addition these biases depend on the individual GLONASS
frequency of the received signal [Dach et al., 2006a]. It is important to note, however, that
for all relevant receiver types the estimated system time difference does not exceed 1 µs. Using
the estimated GPS receiver clocks for subsequent processing steps is therefore sufficient
and results in a GLONASS orbit error smaller than 1 mm.
Bernese GPS Software Version 5.0 Page 109