Bernese GPS Software Version 5.0 - Bernese GNSS Software

16. Antenna Phase Center Offsets and Variations
16.2.2 Satellite Antenna Phase Center
The information related to the satellite antenna phase center model is contained in two files:
• The second part of the satellite information file (description in Section 22.4.5, example
in Figure 22.7).
• The phase center eccentricity file (description in Section 22.4.4, example in Figure 22.5
and 22.6).
The mean phase center offset for the satellite antenna with respect to the center of mass
of the satellite is given in the satellite information file. The phase center eccentricity file
contains the (azimuth- and) nadir-dependent part of the antenna model. The constant offsets
in the first part of the phase center eccentricity file are not used for satellite antennas and
thus set to zero.
For a given PRN and time window the satellite name listed in column SATELLITE NAME
in the second part of the satellite information file has to match a corresponding name in
the phase center eccentricity file (column ANTENNA TYPE). This name starts with MW
TRANSM to identify a microwave transmitter followed by the GNSS block type (e.g., II or
IIR-A for GPS resp. S or S-M for GLONASS) and the SVN of the satellite (not PRN) to
allow for an unambiguous identification for the entire constellation history.
GNSS satellite antenna offsets are applied according to the nominal attitude of the satellite.
If a Block II or IIA satellite passes through the Earth’s shadow (for up to 55 minutes),
however, it cannot orient itself correctly with respect to the Sun [Bar-Sever, 1996] and the
resulting mis-orientation leads to biases in the geometrical distance (up to about 10 cm
for very long baselines). This situation may persist up to 30 minutes after reentering into
sunlight. There is also a dynamical effect caused by this mis-orientation: the solar-panelaxis
is no longer perpendicular to the direction Sun-satellite and the solar radiation pressure
force becomes very difficult to model. Both effects, the geometrical and the dynamical, are
not taken into account by the software.
To apply the antenna phase center positions from the satellite information file it is necessary
to know if the satellite positions (given in precise orbit file) represent the center of mass
(which is the normal case) or directly the positions of the antenna phase center. The user has
to specify this in the option “Apply antenna offset” in panel “ORBGEN 3.1: Options” when running
program ORBGEN (”Menu>Orbits/EOP>Create standard orbits”). CODE and IGS orbits always
refer to the center of mass of the satellite.
SLR Observations
Only the offset of the retroreflector with respect to the satellite’s center of mass needs
to be considered for ranging measurements. It is given in the satellite information file.
The SATELLITE NAME starts with SLR REFL to identify the sensor type. Entries for SLR
retroreflectors also need to be included in the phase center eccentricity file even though they
are usually zero (but may accommodate variations of the optical center).
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