Bernese GPS Software Version 5.0 - Bernese GNSS Software

16. Antenna Phase Center Offsets and Variations
reference. Only elevation-dependent corrections and no azimuthal dependences have been
taken into account. Antenna radomes have not been considered for most of the antennas.
In addition, the variations of the satellite antenna phase centers have been neglected – only
a constant antenna offset vector from the center of mass of the satellite to the satellite
antenna was considered.
The IGS has switched to an absolute antenna phase center model in GPS week 1400 (2006-
Nov-05, day of year 309 – model name: IGSyy wwww, yy denotes the year and wwww the
week of the release, see IGS Mail 5272). It is based on a set of robot-calibrated receiver antenna
phase center variation models that consider also the azimuthal dependence [Wübbena
et al., 2000]. At the same time the satellite antenna phase center variations are considered
in a nadir-dependent model [Schmid and Rothacher, 2003]. These two changes correspond
to each other because the satellite antenna phase center model was determined based on
the absolute receiver antenna phase center model.
In addition, the IGS has started to consider the impact of different antenna radomes. Phase
patterns are either used directly from the robot calibration, or converted from the relative
model, or – if no corrections are available – the model for the antenna type without radome
is used instead.
Recent studies have shown small differences between receiver antenna phase center variations
for GLONASS and GPS frequencies. The number of calibrated GNSS receiver antennas
with individual GPS and GLONASS patterns is currently very limited, however. For that
reason the antenna phase center variations for GLONASS satellites – as included in the
upcoming IGS antenna model – are estimated on the assumption that all receiver antenna
phase patterns for GLONASS frequencies are equal to those of the corresponding GPS
frequencies. The differences between the GPS and GLONASS receiver antenna patterns are
small. Nevertheless, a mean pattern difference may have been mapped into the GLONASS
satellite pattern.
16.2 Antenna Phase Center Corrections in the Bernese GPS Software
16.2.1 Mathematical Representation of Antenna Phase Center Corrections
In the Bernese GPS Software we use the following mathematical representation of the
antenna phase center variation correction, that is also illustrated in Figure 16.1:
where
∆φ(α,z) = ∆φ ′ (α,z) + ∆r · e , (16.1)
∆φ(α,z) ... is the total phase center correction in direction α,z ,
α,z ... is the azimuth and the zenith angle of the satellite line of sight,
∆r ... defines the position of the mean antenna phase center with respect to the
mechanically defined antenna reference point. This vector is uniquely defined
by imposing the condition
2π
zmax
α=0 z=0
∆φ(α,z) sin z d z d α = min. (e.g. zmax = 75 o ) .
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