This work presents a study of the determination of uncertainties in [UTC − UTC(k)] needed for publication in the Bureau Inernational des Poids et Mesures's (BIPM's) Circular T and the Key Comparison Database, as required by the Mutual Recognition Arrangement. In the first part of the paper, an analytical solution based on the law of the propagation of uncertainty is derived. In the second part, the solution is verified numerically using the software used by the BIPM for the generation of UTC.
In Poland, an accurate two-way optical fibre time transfer (TWOTT) baseline of 420 km has been developed with a standard uncertainty of 112 ps. Meanwhile, the BIPM has been engaged in a pilot project to reduce the uncertainty of UTC GNSS time transfer calibrations from 5 ns to approximately 1.5 ns, for which it has developed a standard calibration scheme, named METODE, associated with an integrated portable GNSS calibration station. The TWOTT and the METODE respectively represent the world's most advanced time transfer method and calibration facility.In July 2013, the BIPM calibrator and the TWOTT self-calibrated optical fibre transceivers were set up side by side to compare their results. This is the first time that an operational TWOTT has been used in accurate time transfer and the first time that a GNSS calibration method has been validated with a technique accurate to 200 ps. As the two systems are completely independent and the latter is one order of magnitude more accurate than the first, this comparison allowed validation of the METODE and its uncertainty. It also confirmed that any bias in the TWOTT is at most 1 ns.
We refine our estimate of the uncertainty in [UTC - UTC(k)] by taking into account the contribution of correlations between the links. Using a matrix formulation to facilitate computation, we re-analyze the link-based uncertainties and obtain the same solution as found previously. We then evaluate the site-based uncertainties and compare the results with the link-based uncertainties.
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