Bernese GPS Software Version 5.0 - Bernese GNSS Software

5.4 Preparation of Precise Orbit Information
Figure 5.6: Options for numerical integration in program ORBGEN.
Up to nine radiation pressure parameters may be adjusted per satellite and satellite arc.
They refer to the CODE Extended Radiation Pressure Model [Beutler et al., 1994], see
Section 2.2.2.3. The user has to select the radiation pressure model parameters that have to
be adjusted in panel “ORBGEN 4: Parameter Selection”, see Figure 5.5. We will give different
recommendations below for different types of tabular positions (broadcast or precise).
The standard options for the numerical integration of GNSS orbits are displayed in Figure
5.6 (see Section 2.2.3). In general, two iterations are sufficient. In the case of GPS and
GLONASS satellites, a subinterval length of 1 hour and a polynomial degree (or integration
order) of q = 10 results in an accumulated approximation error after three days which is still
below 1 mm in satellite position. For the integration of a LEOthe integration subinterval
length has to be reduced at least to 0.05 hours (corresponds to 3 minutes).
Program ORBGEN will always produce a summary concerning the fit of the tabular orbit
positions. If you were using tabular or precise orbit files stemming from broadcast messages,
such a summary (in the second iteration step) will look roughly as in Figure 5.7. The
table shows that the internal consistency of the broadcast orbits is around 1 meter (the
actual accuracy is around three meters). It was produced by adjusting only two radiation
pressure parameters, namely “D0” (direct) and “Y0” (y-bias) in panel “ORBGEN 4: Parameter
Selection” (see Figure 5.5) which is sufficient to accommodate broadcast orbits. Bulletin A
Earth orientation information was used.
Figure 5.8 shows that the fit is of the order of 1 cm if a precise IGS ephemerides file is
used together with the corresponding Earth orientation parameters and adjusting all nine
radiation pressure parameters to generate the standard orbit. This means that the force
Bernese GPS Software Version 5.0 Page 95