Distributed Acoustic Sensing in the Marine Environment—Where Are We Now and Where Are We Going?

Abstract Distributed acoustic sensing (DAS) senses changes in a fiber-optic (FO) waveguide by “interrogating” FO cables with laser pulses and measuring how backscattered energy is modulated by the stressed waveguide. The core ideas are not new, dating back some 30 years, but recent advances have enabled a rapidly expanding range of applications spanning seismology, ocean acoustics, oceanography and now, opto-acoustic communication, which are attracting a great deal of attention. Data are available in real time and provide information over large distances (~150 km without repeaters) with enviable spatial resolution (as little as ~1 m). DAS can generate ~1 Gb/s of data, but each virtual sensor is currently relatively “noisy” and of lower quality than a ceramic hydrophone or seismometer. There are also key physical mechanisms that play a role in the cable’s strain response to stress. Existing telecommunication fibers are encapsulated with power cables, wire armoring, plastic sheathing, and so forth that modulate the mechanical strain response to stress. There is also an inherent directivity of each virtual sensor due to the finite length of the laser pulse and spatial averaging applied to reduce system noise. Finally, the response is modified by interaction with the seabed, whether the cable is laid over hard rock or entrenched in soft sediment. DAS already offers unique capabilities, but it is not a “silver bullet” and successful future development of its considerable potential will require improved understanding of the stress-strain physics, coupling and noise statistics, optimal signal processing, and how to deal efficiently with the high data rate.