How to Handle a Satellite Change in an Operational TWSTFT Network

Kun Liang, Thorsten Feldmann, Andreas Bauch, and Dirk Piester

Abstract:	Two-way satellite time and frequency transfer (TWSTFT) is a powerful technique because of its real-time capabilities. In principle, the time difference between remote clocks is almost instantaneously known after a measurement session. Long-term TWSTFT operations have required changes between satellites, but also of ground hardware. We analyzed how well and how fast an accompanying step in the time series following a gap in the data can be determined. We used data collected during about 3 months during 2009 in links of the USA-Europe TWSTFT network connecting to PTB. The results are applicable under the current constraints of operations, i.e. nominally 12 measurements per day with typical performance. We found that a time step can be determined with sufficient accuracy by extrapolating the time scale differences involved over the data gap and comparing to one or two data points immediately after the gap. The maximum deviation and the standard deviation between prediction and measurement result increase with the gap width and increase with the instability of the time scale. The largest deviations after a 1-day gap were found below 6 ns, the standard deviation between 1.5 ns and 2.5 ns. The best results were obtained when comparing time scales generated from frequency steered hydrogen masers or from direct comparison of masers. Our findings confirm that the use of TWSTFT in operational systems, such as the ground segment of a GNSS, remains a valuable option despite of the occasional interruption of operations.
Published in:	Proceedings of the 42nd Annual Precise Time and Time Interval Systems and Applications Meeting November 15 - 18, 2010 Hyatt Regency Reston Town Center Reston, Virginia
Pages:	285 - 294
Cite this article:	Liang, Kun, Feldmann, Thorsten, Bauch, Andreas, Piester, Dirk, "How to Handle a Satellite Change in an Operational TWSTFT Network," Proceedings of the 42nd Annual Precise Time and Time Interval Systems and Applications Meeting, Reston, Virginia, November 2010, pp. 285-294.
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