Evolution of the Uncertainty of [UTC-UTC(k)]

Z. Jiang and W. Lewandowski

Abstract:	Coordinated Universal Time (UTC) is computed at the International Bureau of Weights and Measures (BIPM). The calculation makes use of data from about four hundred atomic clocks belonging to the contributing laboratories worldwide. Numerically UTC is represented by the differences [UTC-UTC(k)] between UTC and the UTC realization of a laboratory k, to which uncertainties are associated [1]. According to the GUM or the JCGM 100:2008 [2-4] the uncertainty of a measurand consist of two parts: the Type A component (uA) which is estimated by statistical means and the Type B component (uB) estimated by other methods, e.g., the calibrations in metrology practices. In the case of UTC, the dominant contributions to both the uA and uB in [UTC-UTC(k)] relate to the time links [UTC(k)–UTC(PTB)]. The evolution, and therefore the evaluation, of the uncertainty in [UTC-UTC(k)] corresponds to that in the time-transfer techniques. The value of uA depends on the time transfer techniques which have been greatly developed since one and half decades. In consequence, the uA has being reduced an order. The value of uB depends on the calibration technique and how to maintain the ‘calibration setup’. In this paper, we first review the uA evaluations made in 2002 [11] and 2011 [18] and then using the METODE 2013 calibration experiment results [20], we assess the conventional uB applied in the Circular T, of which in the best case is of 5-7 ns for GNSS at present. Globally in all the UTC time links, more than 60% of the uA ? 1 ns vs. 93% of the uB ? 5 ns. This unbalance is the major challenge to improve the accuracy of the UTC-UTC(k). One of the solutions is to use the time link calibration which has been proven to be able to unify all types of UTC time links with uB ? 2 ns [17,19,20]. It is expected that the accuracy of the major part of the UTC time links will be within 2 ns in the coming years.
Published in:	Proceedings of the 45th Annual Precise Time and Time Interval Systems and Applications Meeting December 2 - 5, 2013 Hyatt Regency Bellevue Bellevue, Washington
Pages:	208 - 216
Cite this article:	Jiang, Z., Lewandowski, W., "Evolution of the Uncertainty of [UTC-UTC(k)]," Proceedings of the 45th Annual Precise Time and Time Interval Systems and Applications Meeting, Bellevue, Washington, December 2013, pp. 208-216.
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