Precise Orbit Determination of Global Navigation Satellite System of ...

Chapter 9 Software and Simulation Results
CHAPTER 9 SOFTWARE AND SIMULATION RESULTS
9.1 Software
According to the discussions and algorithms in the previous chapters, I have written the software for IGSO and
GEO orbit determination using extended Kalman filter, called GEOKAL (GEO/IGSO orbit determination using
KALman filter). At present in the software, GEOKAL, the major perturbations such as geopotential perturbation,
solar and lunar attractions and solar radiation force are included in the satellite dynamic models. Observations
which can be processed are ranges and carrier phases. The major flow chart of software GEOKAL is as follows:
Start
Read Initial Orbit Parameters and
Observation Data File
Compute State Matrix
Predict Orbit using
Numerical Integration
Transform the Coordinates of
Tracking Stations From Earth-fixed
System to Inertial System
Create Observations with ±1 m Errors
Figure 9-1 The flowchart of Program GEOKAL
9.1.1 Coordinate System
In the software, GEOKAL, there are two coordinate systems used, i.e. the earth-fixed geocentric coordinate
WGS84 which is defined and maintained by National Imagery and Mapping Agency (NIMA), USA and inertial
coordinate FK5 in which polar axis points in the direction of the mean pole at J2000.0 as defined by the IAU
conventional models of precession and nutation.
113
Create O-C Differences
Form Design Matrix
Kalman Filter Processor
Compute the PDOP of Orbit Determination
Output the Results of Kalman Filter
Yes
Prepare for Next Processing
Check if there are
sufficient observation
Stop
No