The Algorithm for the Generation of UTC: Latest Improvements

G. Panfilo, A. Harmegnies, L. Tisserand, F. Arias

Abstract: The computation of International Atomic Time (TAI) and Coordinated Universal Time (UTC) is based on an algorithm consisting of three parts: the clock frequency prediction, the clock weighting procedure and the accuracy algorithm. A new frequency prediction algorithm that takes into account the frequency drift of all contributing clocks has been introduced in ALGOS since September 2011 with significant effect in terms of improvement of the EAL stability. The frequency drift of EAL relative to TT of 1.3 ×10?17/day had been stopped, and no steering correction has been applied to improve the accuracy of TAI since the last months of 2012. In the classical ALGOS version the weighting algorithm is based on the stability of the clock frequency. A change in the frequency prediction does not affect the clock weighting that is fixed in an independent process. A new version of the weighting algorithm is supported on the concept of weighting the clocks according to their predictability, so that a clock showing frequency drift can be correctly used in the timescale ensemble if its frequency is well predicted. The effect of the new weighting algorithm on the stability of EAL is satisfactory, and results in a better distribution of the clock weights enhancing the role of the H-masers. The frequency accuracy of TAI is obtained from primary frequency standards (PFS) reported for the calculation of UTC each month. BIPM Circular T includes since 2012 comparisons of the TAI frequency to that of a Rubidium standard, recommended as a secondary representation of the second (SRS). With the new value of the frequency of this SRS and its uncertainty recommended by the CIPM , this standard is adequate for contributing to the accuracy of TAI.
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: 274 - 291
Cite this article: Panfilo, G., Harmegnies, A., Tisserand, L., Arias, F., "The Algorithm for the Generation of UTC: Latest Improvements," Proceedings of the 45th Annual Precise Time and Time Interval Systems and Applications Meeting, Bellevue, Washington, December 2013, pp. 274-291.
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