Astronomy and Astrophysics – Astronomy
Scientific paper
May 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009iau...261.0404f&link_type=abstract
American Astronomical Society, IAU Symposium #261. Relativity in Fundamental Astronomy: Dynamics, Reference Frames, and Data Ana
Astronomy and Astrophysics
Astronomy
Scientific paper
Time metrology provides references for experiments in the vicinity of a clock and also for applications in astro-geodetic sciences on extended environments, where time constitutes a coordinate in a space-time coordinate system.
Only a coordinate time scale can be the basis of a world-time reference. We adopt a rotating geocentric reference system where the time-coordinate is the geocentric coordinate time. Such a time scale is constructed from a clock ensemble with an appropriate algorithm. The choice of the algorithm will depend on the interval over which the frequency stability is to be assured, on the compromise between frequency stability and accuracy, and should be adapted to the type of standards and the techniques used for their comparison. This algorithm should produce a time scale more stable and accurate than any of the individual participating clocks. To profit at best the quality of the time and frequency standards, algorithms should be in the framework of general relativity.
International atomic time (TAI) is a realization of terrestrial time maintained at the Bureau International des Poids et Mesures from data of industrial atomic clocks and primary frequency standards in time metrology laboratories. TAI is calculated from thirty-day data sets and is published monthly with adelay of about 15 days after the last date of data. The frequency stability of TAI at one month is better than 0.4 ×10-15, and its frequency accuracy is of order 10-15. However, long term drifts limit the stability of TAI making it inadequate for some applications. Another atomic time scale is calculated under the acronym TT(BIPMYY) using an algorithm that eliminates the instabilities of TAI.
This presentation describes TAI and TT(BIPMYY) and tries to predict their features in view of the progress in atomic physics and technology.
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