Bernese GPS Software Version 5.0 - Bernese GNSS Software

14. Clock Estimation
to zero. All computed clock corrections are the differences to this reference clock which can
be convenient in some cases. The pre-requirement for this approach is that the reference
clock values are close enough to the GPS time (so that the receiver clock synchronization
with program CODSPP is not required) and the observation file contains measurements for
all epochs because the estimation of clock corrections gets singular for epochs without a
reference clock.
In general it is preferable to choose a zero-mean condition for the clock correction estimates
of an ensemble of reference station clocks. If an epoch is missing for a station the clock
corrections for all other receivers can be computed. If, e.g., all receiver clocks are synchronized
to the GPS time scale with program CODSPP you may select all receiver clocks as
reference independently from the performance of the receiver clocks. An alignment of the
resulting clock corrections to an optionally selected reference clock can be done later using
program CCRNXC (see Section 14.3.4). The advantage is that no station fulfilling special
requirements needs to be selected for the processing.
Instead of an ensemble of receiver clocks you may choose also the satellite clocks as reference.
Be careful in this case when a satellite clock maintenance event takes place. You may use
the program CODXTR to remove such satellites from the Bernese satellite clock files (see
Section 6.3.4).
If parts in your network are not connected to the reference clock by observations to common
satellites, the clock parameters in these parts are singular and no solution is available for
these clocks. For applying the zero-mean condition in program GPSEST it is required, too,
that no isolated parts exist in the network.
14.2.3 Program Output and Result Files
The program output of GPSEST has two sections for reporting the results of the estimation of
clock corrections: A first section is dedicated to receiver clocks, a second section to satellite
clocks. If the clocks are computed using the epoch-wise pre-elimination/backsubstitution
algorithm the clock values are ordered by time, otherwise the list is sorted by the clock
names. Figure 14.3 shows the results in the program output for the processing example
described in Section 20.4.4 for session 1390 in year 2003. Because this part of the program
output may get very large you can enable the option “Suppression of output concerning epoch
parameters” in panel “GPSEST 3.3: Extended Printing Options” to skip this part of the program
output.
The first part reports the receiver clock corrections. For each parameter one line is printed
containing the following information:
TYPE and STAT: Internal numbering in GPSEST.
EPOCH (MJD) : Epoch of the clock parameter in modified Julian date.
STATION CLOCK VALUES (USEC):
A PRIORI : A priori value of the clock from the observation file in microseconds.
CORRECTION : Estimated correction of the clock value in microseconds.
TOTAL : Total estimated clock correction in microseconds.
RMS (NSEC) : Formal error for the estimated parameter in nanoseconds.
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