Generation of Ensemble Timescales for Clocks at the Naval Research Laboratory

Ken Senior, Michael J. Coleman

Abstract:	A laboratory that operates a large number and variety of clocks can often benefit from the implementation of a local ensemble timescale. When some of the best performing clocks are being evaluated, the need for a more stable reference becomes important and hence a timescale becomes desirable or even necessary. At NRL’s Advanced Space PNT Branch, a collection of approximately 18 total clocks are considered in the generation of a timescale (or timescales) to provide a stable reference for other space qualified clocks that are hosted and under life test. Timescales at NRL are produced using a Kalman filter implementation complete with a multi–state clock weighting algorithm and automatic outlier and clock break mitigation to help protect the ensemble from anomalous behavior and maintain stability. An Ensemble Timescale Filter (ETF) algorithm and associated software at NRL is already in service to provide for a number of sponsored applications. New timescales are formed by filtering local clock data through the same ETF code with various ensemble membership criteria or other filter settings. Features of the NRL filter algorithm include a model of up to eight clock states including stochastic, dynamic clock weighting, linear quadratic Gaussian (LQG) steering, automatic clock outlier and clock break detection and mitigation, as well as other miscellaneous features including ensemble membership specification, and adaptive clock parameter estimation. With these features, associates within the branch have the ability to generate timescales fromof any collection of subsets of the local clocks and alignment to external timescales via LQG steering (e.g., for alignment to UTC(NRL)). The goal of this activity is to provide a reference timescale for NRL clock evaluation purposes (e.g., GPS Clock Life Tests) that has comparable or better stability than the best local clocks and that is robustly available free of the effects caused by any single clock’s anomalous behavior.
Published in:	Proceedings of the 46th Annual Precise Time and Time Interval Systems and Applications Meeting December 1 - 4, 2014 Seaport Boston Hotel Boston, Massachusetts
Pages:	98 - 105
Cite this article:	Senior, Ken, Coleman, Michael J., "Generation of Ensemble Timescales for Clocks at the Naval Research Laboratory," Proceedings of the 46th Annual Precise Time and Time Interval Systems and Applications Meeting, Boston, Massachusetts, December 2014, pp. 98-105.
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