Vibration detection by energy/power cross-correlation in φ-OTDR

Abstract

Reducing false alarming of vibration and shortening data processing time are one of the key problems of phase sensitive optical time-domain reflectometer (φ-OTDR). Generally speaking, there are two demodulation methods to locate vibrations: phase demodulation and amplitude demodulation. At present, an often-used method is phase-based crosscorrelation, which shows a comparatively reliable detection performance. Compared with phase cross-correlation, energy/power cross-correlation between different positions is simpler and has certain advantages in practical applications. In this paper, we use φ-OTDR to collects periodic vibration signals (power signals) and transient vibration signals (energy signals). Amplitude differentiation is firstly calculated along slow time axis for the Rayleigh backscattering trajectories. For periodic vibration, power spectrum is then obtained at each position, and cross-correlation coefficients between any two spectrums are computed. If the vibration is transient, average energy is calculated along fast time axis and average energy cross-correlation is performed between any two locations. With the cross-correlation values, we are able to determine whether there is vibration on the optical fiber. In the experiment, periodic vibration is simulated by a sine-driven PZT and transient vibration is mimicked by pencil-break. These results demonstrate that power (energy) cross-correlation coefficients work well to locate periodic (transient) vibrations.