AT2, a new time scale algorithm : AT1 plus frequency variance

The existing AT1 algorithm produces a time scale with a fractional frequency variation smaller than that of any clock in the ensemble. We are developing a modification to AT1 that includes the additional desirable features: automatic frequency-step detection, the option to run in an optimal post-processing mode and to run with minimal supervision in non-technical environments. These properties are facilitated by the inclusion of a Kalman-filter estimate of the frequency variance of each clock in the scale. Results are reported from both simulated and real clock data to demonstrate automatic frequency-step detection.