Error analysis of real-time and post-processed orbit determination for the Geosat Follow-On altimetric satellite using GPS tracking.

摘要

The Global Positioning System (GPS) has the capability to supply real-time and post-processed positioning of unprecedented accuracy for low Earth orbiting (LEO) satellites. This thesis has evaluated the expected orbit accuracy of the U.S. Navy's Geosat Follow-On (GFO) altimetric satellite for real-time and post-processed modes of operation when using GPS tracking.; There is an interest in using orbit solutions that are generated by an on-board GPS navigation processor to compute altimetric ocean surface heights for near real-time mesoscale studies. Numerical simulations were performed to evaluate the on-board GFO radial orbit error, and demonstrated that the spectral content of the orbit error contained significant power at mesoscale frequencies. However, it was demonstrated that a fitting process utilizing analytical J2 orbit theory can remove this mesoscale frequency content and provide an ephemeris adequate for real-time mesoscale oceanographic studies. This fitting procedure was verified by processing on-board GPS orbit and altimeter data from the TOPEX/POSEIDON mission.; Processing GPS pseudorange and carrier phase measurements in a post-processed mode will allow precise orbit determination based on dynamics, kinematics, and a combination of the two. However, when the Department of Defense (DoD) enables their policy of Selective Availability/Anti-Spoof (SA/A-S), this positioning precision will be degraded for non SA/A-S capable receivers because they will no longer be able to use a dual frequency mode of ionospheric calibration. There does exist a less precise single frequency mode of ionospheric calibration called Differenced Range Versus Integrated Doppler (DRVID). The DRVID technique has been studied through equation development and data analysis. The method of covariance analysis was used to determine the expected radial orbit accuracy of GFO for both dual and single frequency (DRVID) GPS receiver configurations when using dynamic, kinematic and reduced dynamic tracking. These analyses showed that the GFO orbit can be determined to an accuracy below the decimeter level in the radial direction if a dual frequency GPS receiver is used with reduced dynamic tracking. A single frequency (DRVID) low data noise receiver configuration also showed the potential to reach decimeter level tracking of the radial height of GFO when reduced dynamic tracking is employed.