Studies of NPL's Clock Ensemble Algorithm

In the last few years the National Physical Laboratory (NPL) has been investigating a Kalman-filter based atomic clock ensemble algorithm as part of its long-term strategy for improving the stability of the UK’s national time scale UTC(NPL). To achieve this, Flicker Frequency Modulation (FFM) clock noise has been modeled within the algorithm, using integrated Markov noise processes. Recent results have indicated the performance of the composite time scale generated for a 150-day data-set using an ensemble of two 5071A cesium clocks together with three active hydrogen masers. Here we firstly investigate the performance of the algorithm using a longer data-set of 846 days. We then investigate its performance by comparison against UTC and NPL’s cesium fountain, NPL-CsF2. We also consider how data from NPL-CsF2 can be exploited within the algorithm to improve the stability of the generated composite. Finally, we briefly discuss the potential application of such an algorithm for improving the stability of the UK’s national time scale UTC(NPL).