Study on the Algorithm of Local Atomic Time

Details Study on the Algorithm of Local Atomic Time Study on the Algorithm of Local Atomic Time

Oct 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010acasn..51..404l&link_type=abstract

Acta Astronomica Sinica, vol. 51, no. 4, p.404-411

Statistics

Computation

Time, Methods: Data Analysis

Scientific paper

It is always an endless target for all time and frequency laboratories to develop, own and keep a stable, accurate and reliable time scale. As a comparatively mature algorithm, ALGOS, which has been concerned about the long-term stability of the time scale, is widely used by the majority of time laboratories. For ALGOS, the weights are assumed on the basis of the frequencies of 12 months and the present month interval is included in the computation. This procedure uses clock measurements covering 12 months, so annual frequency variations and long-term drifts can lead to de-weight. This helps to decrease the seasonal variation of the time scale and improve its long-term stability. However, the local atomic time scale is primarily concerned with long-term stability not more than 60 days. So when the local time scale is computed with ALGOS in time laboratories, it is necessary to modify ALGOS correspondingly according to the performances of contributing clocks, the requirement of stability for local time scale and so on. There are 22 high performance atomic clocks at National Time Service Center, Chinese Academy of Sciences (NTSC). They include 18 cesium standards and 4 hydrogen masers. Because hydrogen masers behave poor, we only regard an ensemble of 18 cesium clocks in our improved algorithm. The performances of these clocks are very similar, and the number is less than 20. By analyzing and studying the noise models of atomic clocks, this paper presents a complete improved algorithm of TA(NTSC). This improved TA(NTSC) algorithm includes three aspects: the selection of the maximum weight, the selection of clocks taking part in TA(NTSC) computation and the estimation of the weights of contributing clocks. We validate the new algorithm with the annually atomic clock comparative data of NTSC taking part in TAI computation in 2008. The results show that the long-term and short-term stabilities of TA(NTSC) are all improved. This conclusion is based on the clock measurement data at NTSC. The performances of these clocks are very similar. So for those laboratories with the time-keeping system structure similar to NTSC, this new algorithm is appropriate to compute the local atomic time.

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