Real-Time GPS Monitoring of Atomic Frequency Standards in the Canadian Active Control System (CACS)
NATURAL RESOURCES CANADA OTTAWA (ONTARIO)
Pagination or Media Count:
Ten Real-Time Active Control Points RTACP across Canada continuously monitor all GPS satellites in view and generate wide area GPS corrections with an update rate of 2 s. Dual frequency high precision geodetic GPS receivers using free running atomic frequency standards masers, Cs and Rb provide pseudorange and phase measurements at 1 s intervals. Ionosphere-free, carrier-phase-filtered pseudorange data are combined with rapid GPS satellite orbit predictions and RTACP coordinates in a least-squares adjustment to determine satellite and station clock offsets with respect to a virtual reference clock VRC. The VRC is maintained us a weighted mean of RTACP long-term clock models. The VRC is related to the mean GPS system time using a long-term linear clock model with correlation time of a few days and it is traceable to UTC TVRC. This approach mitigates the effects of instabilities of individual RTACP clocks, eliminates clock discontinuities, and provides VRC stability better than 10-14 for time intervals greater than 1 day. The system provides continuous RTACP clock synchronization with RMS residuals in the range of 0.1-0.5 ns and real-time GPS satellite clock corrections with RMS residuals in the range of 0.3-0.8 ns. The quality of the real-time results are presented and discussed.
- Test Facilities, Equipment and Methods
- Navigation and Guidance
- Human Factors Engineering and Man Machine Systems