Bernese GPS Software Version 5.0 - Bernese GNSS Software

17. Data Simulation Tool GPSSIM
The random number generator is initialized with the random seed selectable in option “Initial
integer random number”. If the same number is used in consecutive runs of GPSSIM together
with unchanged sigmas, the same “random” errors result. This offers the possibility to create
exactly the same observations several times if need be.
If low-elevation data (below 15deg) is simulated elevation-dependent sigmas may be applied.
The afore mentioned a priori sigmas then refer to an observation in zenith direction. The
a priori sigma of observations at a zenith angle z will then be computed related to the
factor 1/cos z.
17.8 Cycle Slips
If simulated data should be used for preprocessing purposes or if a high level of realism is
intended, cycle slips may be introduced. It is then quite difficult to distinguish simulated
from real observations.
The number of introduced cycle slips can be specified with “Introduce cycle slips per file” in
panel “GPSSIM 3.4: Simulation Options” (Figure 17.3). The program assumes that a slip may
occur with the same probability at each epoch and for each satellite and that its size is
uniformly distributed in the interval I = 〈−slipmax,+slipmax〉 (“Maximum size of slip”).
You may wish to apply “Same cycle slips in L1 and L2”. These slips are particularly hard to
discover because they are not accompanied by a wide-lane cycle slip.
Figure 17.3: Statistical and cycle slip options for GPSSIM.
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