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Bernese GPS Software Version 5.0 - Bernese GNSS Software

Bernese GPS Software Version 5.0 - Bernese GNSS Software

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17. Data Simulation Tool <strong>GPS</strong>SIM<br />

The random number generator is initialized with the random seed selectable in option “Initial<br />

integer random number”. If the same number is used in consecutive runs of <strong>GPS</strong>SIM together<br />

with unchanged sigmas, the same “random” errors result. This offers the possibility to create<br />

exactly the same observations several times if need be.<br />

If low-elevation data (below 15deg) is simulated elevation-dependent sigmas may be applied.<br />

The afore mentioned a priori sigmas then refer to an observation in zenith direction. The<br />

a priori sigma of observations at a zenith angle z will then be computed related to the<br />

factor 1/cos z.<br />

17.8 Cycle Slips<br />

If simulated data should be used for preprocessing purposes or if a high level of realism is<br />

intended, cycle slips may be introduced. It is then quite difficult to distinguish simulated<br />

from real observations.<br />

The number of introduced cycle slips can be specified with “Introduce cycle slips per file” in<br />

panel “<strong>GPS</strong>SIM 3.4: Simulation Options” (Figure 17.3). The program assumes that a slip may<br />

occur with the same probability at each epoch and for each satellite and that its size is<br />

uniformly distributed in the interval I = 〈−slipmax,+slipmax〉 (“Maximum size of slip”).<br />

You may wish to apply “Same cycle slips in L1 and L2”. These slips are particularly hard to<br />

discover because they are not accompanied by a wide-lane cycle slip.<br />

Figure 17.3: Statistical and cycle slip options for <strong>GPS</strong>SIM.<br />

Page 352 AIUB

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