Читать книгу Distributed Acoustic Sensing in Geophysics - Группа авторов - Страница 70

We demonstrate a real‐time distributed acoustic sensing (DAS) system based on phase‐sensitive optical time domain reflectometry (Φ‐OTDR) and phase‐generated carrier (PGC) demodulation algorithm. An unbalanced Michelson interferometer (MI) with specific phase modulation is introduced to overcome phase fading caused by initial phase shift in fiber optic interferometer sensing. Owing to its relatively low data requirement and polarization‐independent structure, PGC‐DAS system exhibits the superiorities of real‐time signal processing and Rayleigh polarization‐induced fading suppression. A proof‐of‐concept system is constructed to demonstrate feasibility and sensing performance. Corresponding to the average phase noise of ~5 × 10^‐4 rad/√Hz, a strain sensitivity of 8.5 pε/√Hz is achieved with a spatial resolution of 10 m, as well as a frequency response range of 2 Hz to 1 kHz over 10 km sensing distance. Further, a field trial of this system is presented to validate it in qualitative seismic monitoring on land.