Overview of distributed acoustic sensing: Theory and ocean applications

Area of Science:

• Oceanography
• Geophysics
• Acoustics

Background:

• Acoustic monitoring is crucial for oceanography, security, and Earth science.
• Distributed acoustic sensing (DAS) offers continuous, wide-coverage measurement of mechanical vibrations.
• Existing telecommunication fiber-optic cables present an opportunity for widespread underwater acoustic monitoring.

Purpose of the Study:

• To review advances in Distributed Acoustic Sensing (DAS) over the last decade.
• To explain the physics underlying DAS, from electromagnetic to acoustic quantities.
• To guide the application of DAS in oceanography by detailing the effects of acquisition parameters on signal processing.

Main Methods:

• Illuminating optical fiber with laser pulses to measure backscattered waves.
• Analyzing modulations in the backscattered signal caused by external stimuli (e.g., acoustic wavefields).
• Demonstrating DAS capabilities using data from the Ocean Observatories Initiative (OOI) Regional Cabled Array.

Main Results:

• DAS effectively measures mechanical vibrations and acoustic wavefields along deployed fiber optic cables.
• The technique allows for continuous sensing of the underwater soundscape.
• DAS successfully detected various sound sources, including whales, ships, and earthquakes, in real-world ocean data.

Conclusions:

• Distributed Acoustic Sensing (DAS) is a promising technology for monitoring the underwater soundscape using existing fiber optic infrastructure.
• Understanding DAS physics and acquisition parameters is key to optimizing its use in ocean applications.
• DAS provides a valuable tool for diverse ocean monitoring needs, from marine biology to seismic activity.