Preliminary results from NPL'S clock ensemble algorithm using hydrogen masers and caesium clocks

In recent years the National Physical Laboratory (NPL) has been developing a Kalman filter-based atomic clock ensemble algorithm. The algorithm is being used to form a composite time scale which will ultimately be employed to improve the stability of the UK's national time scale UTC(NPL) and its robustness to hardware failures. The algorithm has been optimised for both short-term and long-term stability. Flicker Frequency Modulation (FFM) clock noise is modelled using a linear combination of integrated Markov noise processes. We present here recent results obtained for the composite time scale using data from an ensemble of three active hydrogen maser clocks and two caesium clocks. An initial assessment of the ensemble algorithm is carried out using a 150-day period of data and two subsets of the data. The results show that the output of the composite is consistent between different periods of clock data and also different lengths of clock data. Initial indications are that the composite is performing well.