The characterization of clock behavior with the dynamic Allan variance

We introduce the dynamic Allan variance, a quantity that characterizes the variation in time of the stability of an atomic clock. We connect the dynamic Allan variance to the Wigner spectrum, a time-frequency representation that can reveal the time-varying frequencies generally present in the clock error noise under nonstationary conditions. We also propose a practical implementation of the dynamic Allan variance for quasi-stationary clock noises, and we show numerical results that prove the validity of our approach, both on simulated and real data.