Bernese GPS Software Version 5.0 - Bernese GNSS Software

15. Estimation of Satellite Orbits and Earth Orientation Parameters
15.2 Orbit Prediction
Section 5.4 describes the procedure on how to prepare precise orbit information for use
within the Bernese GPS Software. The same procedure may be employed to fit a series
of precise files as well as to predict the adjusted orbit into the future (or the past). Sections
15.2.1 and 15.2.2 show how to obtain predicted orbits and predicted Earth orientation
information, respectively. Section 15.2.3 describes the procedure for converting standard
orbits into precise files, a procedure that is not only used for orbit prediction but also for
orbit estimation (see Section 15.3).
15.2.1 Fitting Precise Files and Predicting Orbits
For fitting n precise files, each of them is first converted to tabular format as described in
Section 5.4.1. In order to get the tabular orbits in consistent representations of the inertial
frame, special attention has to be paid to the Earth rotation information used because
UT1-UTC information from successive pole files may not be continuous (see Section 15.2.2).
Depending on the application you may use Earth orientation information from IERS, e.g.,
Bulletin A or C04 covering the time period for which you want to get the orbit fit and
prediction (see Section 5.2.2).
To fit the n tabular files, select them all in the field “Start with tabular orbits” in program
ORBGEN. For predicting the orbit into the future (or into the past) simply shift the right
(resp. left) boundary of the time window accordingly (panel “ORBGEN 5: Orbital Arc Definition”.
The complete radiation pressure model (nine parameters) is well suited to obtain a
good fit over several days. You get the standard orbit file adjusting the selected tabular files
and covering the specified time window as output. You may also generate a so-called LST
file (see Figure 22.59) that contains a table of the fit rms values for each satellite and each
input orbit file. This file may be used to compute accuracy information for a precise file
header (see Section 15.2.3).
Note that instead of tabular files precise files may directly be used as input for ORBGEN.
For each input precise file a corresponding pole file has to be available with the same name
as the precise file (but different extension).
15.2.2 Preparation and Extrapolation of Earth orientation Information
The UT1-UTC corrections provided with the Earth orientation information generated based
on GNSS tracking data are referenced to an external value independently for each pole file
by fixing, e.g., the first value to Bulletin A. The reason is that GNSS is insensitive to this
correction (see Section 15.4). As a consequence precise orbit files converted to the inertial
frame exhibit jumps at pole file boundaries that may reach more than 10 cm. If a series of
precise files shall be fitted, a common procedure for orbit prediction, the UT1-UTC values
from different pole files have first to be aligned to a common reference. Two programs
available in the Bernese GPS Software to perform this task: POLXTR and POLINT.
The first of the two programs, available at ”Menu>Orbits/EOP>Handle EOP files>Concatenate IERS
pole files”, allows for a sophisticated selection of the records from different input IEP files
(pole files in IERS format, see Section 4.5) to be concatenated to a single Bernese pole
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