Bernese GPS Software Version 5.0 - Bernese GNSS Software

17.9 Low Earth Orbiters
17.9 Low Earth Orbiters
The simulation of GNSS observations for a Low Earth Orbiter is basically the same as for
a terrestrial station. Only some input files and settings call for special attention.
The important differences for the simulation of GNSS observations for LEOs are listed
below:
(1) Although a LEO has no defined station coordinates its name must appear in the
coordinate file in panel “GPSSIM 1: Filenames” with the same name as in the “Satellite
information” file (panel “GPSSIM 1.1: General Files”). The coordinates of the LEO are of
no importance and may even be zero.
(2) The LEO must be listed in section TYPE 005 of the “Station information”-file (panel
“GPSSIM 1.1: General Files”) with marker type SPACEBORNE. If the keyword SPACE-
BORNE is missing program GPSSIM interprets the LEO as a ground based station.
(3) Option “LEO-files” in the first panel must be checked in order to display the LEOspecific
panel “GPSSIM 1.2: LEO Options”.
(4) You need either a LEO standard orbit file or a file with kinematic coordinates to define
the trajectory of the low satellite.
(5) If you have specified “Kin. input coordinates” in the first panel you may select a file
containing kinematic velocities in panel “GPSSIM 1.2: LEO Options”. This information
is used to define the local orbit frame needed to compute the satellite’s attitude.
Alternatively you can specify a “LEO attitude” file. The attitude is necessary to apply
antenna offsets.
If the LEO trajectory is obtained from a standard orbit, no velocity file is required.
An attitude file may be used, though.
(6) No troposphere model is applied for low Earth satellites. The option “ZPD model and
mapping function” in “GPSSIM 3.2: Simulation Options” is ignored.
(7) The modeling of the ionosphere should be deactivated.
(8) The a priori sigmas and the “Elevation-dependent sigmas” checkbox are separately available
for LEOs in panel “GPSSIM 3.4: Simulation Options”.
17.10 Applications for Simulated Data
Simulated data can be used in a number of different ways. Most of the applications, however,
may be assigned to one of the following three main categories:
Verifying software algorithms: A well defined set of simulated observation data can be helpful
while testing the correct implementation of software algorithms. The testing procedure
profits from the fact that, as opposed to real data, the correct results (e.g., number
of cycle slips) are known a priori.
Pre-analyses: Satellite scenario, network layout, statistical properties, and systematic errors
are known for simulated data. Thus one may study the expected quality of the results
depending on different processing strategies and option settings. A pre-analysis makes
sense, e.g., to learn what to expect from a planned campaign or how to design a new
campaign to get optimal results.
Bernese GPS Software Version 5.0 Page 353