Session P1a: Activities at National Metrology Institutes

Improving the Stability of UTC(NIST) by Using Data From the NIST Cesium Fountains
Judah Levine and Gregory W. Hoth, Time and Frequency Division, NIST, Boulder
Location: Seaview A/B
Date/Time: Tuesday, Jan. 28, 1:50 p.m.

The long-term accuracy of UTC(NIST) is validated by comparing the time of UTC(NIST) with the UTC time scale computed by the BIPM, and the comparisons are published periodically in BIPM Circular T. The UTC(NIST) time scale is derived from an ensemble of cesium clocks and hydrogen masers. The algorithm that realizes the ensemble time is AT1, and UTC(NIST) is related to AT1 by offsets in time and in frequency. The stability of UTC(NIST) is limited by the short-term stability of AT1, and this stability has been improved by adjusting the frequency of AT1 based on data from the NIST fountains, f3 and f4. The method is challenging because cesium fountains normally prioritize longer-term accuracy over shorter-term stability. The steering algorithm that estimates these adjustments will be presented and the improved stability of AT1 and UTC(NIST) will be demonstrated. The algorithm could be adapted to steer the time scale by using data from optical reference devices, which have very good short-term stability so that the intermittent operation is not a limitation.