Time-frequency analysis of atomic clock anomalies

Atomic clocks are key elements in several applications, such as global navigation satellite systems. Monitoring their behavior is therefore fundamental. Since during an anomaly the frequency spectrum of the signal made by the clock frequency measurements changes with time, we transform this signal into the time-frequency domain by computing the spectrogram. In the time-frequency domain, the spectrogram localizes and separates the anomalies, and it can be hence used to reveal the nonstationary structure of the clock signal, such as, for instance, the presence of time-varying sinusoidal terms.