| The Global Positioning System (GPS), when fully deployed, will make possible an entirely new, geometric, method of precise orbit determination. The geometric approach requires continuous collection of pseudorange measurements from at least four GPS satellites, and simultaneous acquisition of carrier phase data for pseudorange smoothing. While the GPS satellite orbits are determined utilizing the classical technique, within the geometric framework, no force model representation for the user satellite is required. However, in spite of the dynamic modeling related benefits of geometric tracking, this non-dynamic technique has its own measurement liabilities. The geometrically determined orbit is extremely sensitive to the observing geometry, clock errors, accuracy of the GPS ephemerides, and other measurement error sources such as signal multipath. Therefore, a hybrid, reduced-dynamic, method has been formulated which utilizes both measurement and dynamic information for the low satellite and weights the dynamic information relative to the geometric by compensating for process noise in the user satellite force model. For {dollar}sigmasb{lcub}i{rcub}to 0{dollar} and {dollar}sigmasb{lcub}i{rcub}toinfty,{dollar} where {dollar}sigmasb{lcub}i{rcub}{dollar} is the steady state uncertainty in the process noise for the {dollar}isp{lcub}th{rcub}{dollar} batch interval, the state of the user satellite with respect to a reference dynamic orbit is estimated purely dynamically or purely kinematically, respectively.; The focus of this work is the determination of realistic orbit errors for GPS-based reduced-dynamic tracking of remote sensing satellites including the Earth Observing System (E scOS), and the Ocean Topography Experiment (T scOPEX). Comprehensive error models were developed for GPS-based tracking of T scOPEX and E scOS, and the Orbit Analysis SImulation Software (OASIS) was modified to simulate reduced-dynamic tracking of these satellites. The orbits of both the GPS and user satellites were estimated by processing undifferenced pseudorange and carrier phase information. Each transmitter and receiver clock was estimated as a white noise process noise parameter, and constant phase biases were computed for each transmitter-receiver pair per pass. Simulations were combined with consider covariance analysis to determine realistic T scOPEX and E scOS orbit errors. The reduced-dynamic tracking technique is examined from a dynamic perspective. The benefits of estimating clock parameters rather than eliminating them is discussed, especially as it relates to science support and intercontinental time transfer. Comparisons between dynamic, kinematic, and reduced-dynamic tracking and their associated performance are presented along with recommendations for future research. |
