Post-processing ROA data clocks for optimal stability in the ensemble timescale

In recent years, a certain correlation detected between clocks at time and frequency laboratories has been the main reason behind the development of a revised version of the classical `Three-Cornered Hat' method as a mathematical tool to estimate the frequency instability of a set of clocks. The method has been formulated keeping in mind the possibility of dependence among clocks and has been generalized to an ensemble of N clocks [1–5]. It basically consists of the minimization of an objective function, the quadratic sum of cross-correlation coefficients, with the constraint condition established by the positive definiteness of the (estimated) absolute covariance matrix related to the clocks.