Results of a Automated GPS Tracking System in Support of Topex/Poseidon and GPSMet

Ronald Muellerschoen, Stephen Lichten, Ulf Lindqwister, and Willy Bertiger

Abstract:	A fully automated near real-time GPS tracking system has been developed around JPL’s GIPSY/OASIS I1 software. The system produces < 25 cm (3D rms) GPS orbits and one-half nanosecond (15 cm) clock estimates. The process starts automatically when a favorable global distribution of ground data from the IGS network (International GPS Service for Geodynamics) becomes available. Ionospherically corrected phase and pseudorange data are optimally combined to remove satellite and ground receiver clock errors, including selective availability. After the GPS orbits are determined within the data arc, they are then propagated with empirically determined dynamic force models. Real-time < 2 meter (3D rms) GPS orbits are always available. As a by-product of this process, other calibration estimates such as station clocks, troposphere estimates, and earth orientation parameters are also produced. For 27-hour daily arc fits, the process requires 6-7 hours of CPU time on an HP9000/735 workstation. Additionally, a second process has been developed that automatically starts when data from the Topefloseidon GPS receiver and a favorable distribution of ground stations becomes available. An optimal selection of ground stations is determined and data from these sites are then used to solve for the GPS clocks as well as the Topex/Poseidon orbit. This process makes use of the previously determined predicted GPS orbits. The Topex/Poseidon orbits determined within the data arc are precise to 5 cm radial (rms) and 18 cm 3D (rms). Real- time predicted orbits are also produced precise to 15 meters 3D (rms). This process has been adopted to also support the precise orbit determination of the GPSMet experiment.
Published in:	Proceedings of the 8th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1995) September 12 - 15, 1995 Palm Springs, CA
Pages:	183 - 193
Cite this article:	Muellerschoen, Ronald, Lichten, Stephen, Lindqwister, Ulf, Bertiger, Willy, "Results of a Automated GPS Tracking System in Support of Topex/Poseidon and GPSMet," Proceedings of the 8th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1995), Palm Springs, CA, September 1995, pp. 183-193.
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