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Low noise distributed acoustic sensor for seismology applications.
Applied Optics
|October 18, 2022
Summary
A novel distributed acoustic sensor (DAS) system achieves ultra-low noise for seismology by stabilizing laser frequency. This phase-sensitive OTDR configuration enhances signal-to-noise ratio for detecting faint seismic signals.
Area of Science:
- Optical Physics
- Geophysics
- Sensor Technology
Background:
- Distributed acoustic sensing (DAS) is crucial for seismic monitoring.
- Existing DAS systems face challenges with low-frequency noise and signal drift.
- Sub-hertz frequencies are critical for seismological studies, including earthquake detection.
Purpose of the Study:
- To propose and validate a phase-sensitive optical time-domain reflectometer (OTDR) configuration for distributed acoustic sensing.
- To achieve a significantly low noise level in the hertz and sub-hertz frequency ranges.
- To enhance signal-to-noise ratio for seismic applications.
Main Methods:
- Utilized a Mach-Zehnder interferometer to generate a dual-pulse probe signal.
- Implemented laser frequency stabilization using the interferometer as a frequency etalon.
- Employed optical path difference compensation for interfering backscattered fields.
Main Results:
- Demonstrated a low noise level in the hertz and sub-hertz frequency ranges.
- Achieved up to 35 dB signal/noise gain in sub-hertz frequencies through laser frequency stabilization.
- Successfully recorded teleseismic earthquakes using a seabed fiber-optic cable.
Conclusions:
- The proposed phase-sensitive OTDR configuration offers a low-noise solution for distributed acoustic sensing.
- Laser frequency stabilization is key to achieving high signal-to-noise ratios for seismological applications.
- The system's effectiveness is validated by real-world seismic event detection.
