Broad-bandwidth distributed acoustic sensor with phase offset and phase sensitivity fading compensation

The phase offset and phase sensitivity fading effect is a major concern in broad-bandwidth distributed acoustic sensor (DAS) or frequency-division multiplexed phase-sensitive optical time-domain reflectometry (FDM Φ-OTDR). In this work, we improve the fading compensation approach one step further, from employing single reference frequency component, to using two FDM pulse trains whose frequency component numbers are different. Correspondingly, the solution method of offset and sensitivity coefficients is changed from linear fitting to solving matrix equation. This compensation approach can effectively suppress the spurious frequencies in FDM Φ-OTDR measurement results.