Bernese GPS Software Version 5.0 - Bernese GNSS Software

5.2 Preparation of Earth Orientation Parameters
5.2.1 General Dataset Names
5.2 Preparation of Earth Orientation Parameters
A set of EOP is required to perform the transformation from the Earth-fixed to the celestial
system or vice versa. As described in the following sections the programs PRETAB and
BRDTAB compute a table of satellite positions in the inertial frame from the available orbit
information (usually precise orbits in an Earth-fixed frame, e.g., IGS00). Therefore, the
EOP file corresponding to the orbits used has to be specified in the appropriate input field
(option “Pole file”) of all program input panels.
If IGS precise orbits are used the corresponding EOP files are available at the global
data centers (see Section 4.12.2). The Earth rotation parameters associated with the IGS
ephemeris files are computed using a weighted average of all available center-specific ERP
files 2 . The ERP files stemming from CODE may be downloaded via anonymous ftp, too
(see Section 4.12.1). Be aware that in contrast to the naming rules of the Bernese environment
all these files contain pole information in IGS format although their extension is ERP
(see also Section 22.7.7)! The pole files in IGS or IERS format have to be transformed into
the Bernese pole format. This task is performed by program POLUPD with options to be
discussed in detail later.
If other than IGS precise orbits are used (and no specific ERP files are available), it is
recommended to use the IERS C04 pole. C04 is a continuous, slightly low pass filtered
series at daily intervals and can be interpolated linearly. Oscillations in UT1 and in the
length of day due to zonal tides for periods under 35 days, as well as the 14-day terms in dψ
and dε are present in full size in the series [Dick and Richter, 2001]. In Section 4.5 sources
for downloading EOP files are provided.
Nutation model and subdaily pole model coefficients are read from files located in the
directory ${X}/GEN. To be consistent with the IERS Conventions 2003 [McCarthy and Petit,
2004] useIAU2000 as the nutation model approved by the International Astronomical Union
(IAU) and IERS2000 for the model describing the subdaily tidal variations of the pole and
the rotation of the Earth. Specify these values in all program input panels for the options
“Nutation model” and “Subdaily pole model” respectively.
The two models must be equal in the programs generating a standard orbit (PRETAB
and ORBGEN) and in the programs using the standard orbit information. The names of
the models are written into the headers of the ERP files, the tabular orbit files, and the
standard orbit files. All programs reading standard orbit and Earth orientation information
check the consistency of the nutation and subdaily models.
5.2.2 Update of Pole Information
In order to obtain the most accurate EOP information covering the span of your GPS campaign
you are forced to update the file containing the Earth rotation parameter information,
whenever more consistent (with the precise orbit data) and/or more recent values become
2 The term Earth rotation parameters (ERP) is used for a 3-parameter subset of the EOP which comprises
polar motion (xp, yp) and UT1.
Bernese GPS Software Version 5.0 Page 85