Bernese GPS Software Version 5.0 - Bernese GNSS Software

7. Parameter Estimation
The binary scratch file may become quite large if many observations are processed (many
stations or high sampling rate). Note, that some operating systems have a limit for the
size of such a binary file of 2 Gb. By default the scratch files are saved in the user-specific
directory ${U}/WORK. Make sure that enough disk space is available. This is particularly true
for the ${T}-environment of the BPE if GPSEST is executed in parallel (see Chapter 19).
Residuals may be browsed using program REDISP or they may be used to screen the observation
files for outliers using programs RESRMS and SATMRK. For details see Section 6.6.2.
7.4.5 Correlations between Observations
If double-differenced observations are processed, mathematical correlations between the
differenced observations have to be considered because the same original observations may
occur in several observation differences. This is the case for one baseline but also for different
baselines as soon as they are connected. With the difference operator C defined in the
following way
y ′′ = Cy (7.19)
where y represents the vector of undifferenced observations and y ′′ is the vector containing
the double-differenced observations, the covariance matrix corresponding to the two
observation types is converted according to the equation
D(y ′′ ) = C D(y)C ⊤ . (7.20)
In the above equations the vector y contains all simultaneous observations of the network
being processed. This “simultaneity” can be defined with the option “SIMULTANEOUS OB-
SERVATIONS” in panel “SNGDIF 3: Options” when forming baselines with program SNGDIF
and with the option “Tolerance for simultaneity” in panel “GPSEST 3.1” for program GPSEST
(see Figure 7.1).
The option “Correlation strategy” in the same GPSEST-panel allows to modify the correlation
strategy. Naturally, mathematically and statistically correct modeling of the correlations
(selection CORRECT) is the method to use. All correlations within baselines and between
baselines as well as between different frequencies and linear combinations are handled correctly.
This strategy should, therefore, be applied for producing “final” solutions. If more
than about 30-40 sites are processed with correct correlations, however, the program resources
(memory, CPU time, etc.) might become critical. For such cases the Bernese GPS
Software allows to reduce the degree of correctness of the mathematical correlations.
A first compromise consists of processing clusters of sites with full correlations taken into
account only within each cluster in program GPSEST. The cluster results may then be
combined on the normal equation level using program ADDNEQ2 (see Chapter 9). In this
second step the observations used to process the individual clusters are considered to be
uncorrelated. Optimized clusters may be generated using a cluster definition file (description
see Section 22.8.16) with program SNGDIF or using program MKCLUS.
The correlation strategy FREQUENCY allows to neglect correlations between different frequencies
or linear combinations of frequencies (e.g., if processing L1&L2 together).
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