Improving satellite orbit solution using double-differenced GPS carrier phase in kinematic mode

The limit of orbit accuracy associated with processing the ionospheric-free double-differenced (DD) GPS carrier phase observable in pure kinematic mode is investigated. The kinematic orbit determination problem becomes unobservable when the satellite positions at all epochs and all of the DD ambiguities are estimated simultaneously without any constraints. Although searching for some of the DD ambiguities can make the problem observable, this is not practical when the DD ambiguities are not integers. However, if a reasonably accurate a priori satellite orbit solution is available, epoch-by-epoch satellite positions and the DD ambiguities can be estimated by constraining a geometrically strong DD pass. The technique was demonstrated with TOPEX GPS data, which gave a final radial RMS orbit accuracy of 4 cm with respect to a fully dynamic solution.