Estimating UTC - UTC (APL) at the JHU Applied Physics Laboratory

Abstract : Our master clock accuracy goal at the Time and Frequency Laboratory of the Johns Hopkins University Applied Physics Laboratory (JHU/APL) is to maintain UTC (APL) within plus-or-minus 20 nanoseconds of UTC. This is a challenging goal, because it requires the estimation of the future character of UTC - UTC (APL) up to 6 weeks beyond the latest issue of Circular T from the BIPM. Furthermore, the accuracy of our timescale-based estimation is challenged by the environmental influence on our ensemble of six clocks and the statistical limits to the dynamic characterization of these sources. This paper will describe the estimation algorithm used to determine the steering of UTC (APL). We will describe how the residual drift within the JHU/APL timescale affects our ability to estimate UTC - UTC (APL) and how we have modified the algorithm to remove this drift from the timescale prior to computing the estimation.