Real-Time GPS Monitoring of Atomic Frequency Standards in the Canadian Active Control System (CACS)

F. Lahaye, M. Caissy, J. Popelar, R. Douglas

Abstract:	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 as 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^-I4 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.
Published in:	Proceedings of the 30th Annual Precise Time and Time Interval Systems and Applications Meeting December 1 - 3, 1998 Hyatt Regency Reston Town Center Reston, Virginia
Pages:	187 - 200
Cite this article:	Lahaye, F., Caissy, M., Popelar, J., Douglas, R., "Real-Time GPS Monitoring of Atomic Frequency Standards in the Canadian Active Control System (CACS)," Proceedings of the 30th Annual Precise Time and Time Interval Systems and Applications Meeting, Reston, Virginia, December 1998, pp. 187-200.
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