Bernese GPS Software Version 5.0 - Bernese GNSS Software

17. Data Simulation Tool GPSSIM
17.1 Introduction
The Bernese GPS Software provides the simulation tool GPSSIM (”Menu>Service>Generate
simulated observation data”). It generates synthetic GNSS (i.e., GPS and GLONASS) observations
for terrestrial stations and for Low Earth Orbiters. Code as well as phase zero-difference
observation files may be created which can be processed by all standard Bernese programs.
SLR observations are not yet supported.
The use of GPSSIM is quite straight forward. The scope of the observation scenario is defined
by basically two files, namely
(1) a standard orbit containing the available satellites and
(2) a coordinate file defining the set of stations for which observations can be simulated.
Several additional files may be introduced to be considered for the simulating process, such
as satellite clock corrections, differential code biases, and many more. Troposphere and
ionosphere is modeled, observation noise and cycle slips can be added. Utilizing all GPSSIM
options, it is quite challenging to distinguish simulated from real observation data.
Although GNSS observations for terrestrial receivers and LEOs can be simulated even in
the same program run we will focus on ground stations throughout this chapter. The arising
differences when generating LEO observations are addressed in Section 17.9.
17.2 Underlying Principles
The models applied in GPSSIM are identical to those used in the main parameter estimation
program GPSEST. So-called “zero tests” are thus possible if exactly the same geometry and
options were used in the simulation and processing part. However, this is only true if the
data were simulated without random errors.
To retrieve more realistic data, normal distributed noise may be added during the simulation
process. Only white noise can be added, colored noise models are not implemented.
Furthermore it is not possible to inflict errors on satellite orbits or station coordinates.
One GPSSIM run produces files for one session. A complete observation campaign can be
simulated by executing the program several times in series.
Bernese GPS Software Version 5.0 Page 347