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High-Resolution Trans-Oceanic Distributed Acoustic Sensing Enabled by a Bi-Directional Sensor Implementation

Mikael Mazur, Nicolas K. Fontaine, Roland Ryf, Martin Karrenbach, Kristopher McBrian, Keith McLaughlin, Brian Sperry, Anuar Butler, Valey Kamalov, Lauren Dallachiesa, Ells Burrows, David Winter, Haoshuo Chen, Jeewan Naik, Kishore Padmaraju, Ajay Mistry, David Neilson

Abstract

We demonstrate continuous distributed acoustic sensing over a 4400km long undersea cable. Bi-directional operation improves the strain signal-to-noise rate by >20dB, enabling 88000 50-m-spaced measurement points at a nominal telecom launch power.

High-Resolution Trans-Oceanic Distributed Acoustic Sensing Enabled by a Bi-Directional Sensor Implementation

Abstract

We demonstrate continuous distributed acoustic sensing over a 4400km long undersea cable. Bi-directional operation improves the strain signal-to-noise rate by >20dB, enabling 88000 50-m-spaced measurement points at a nominal telecom launch power.
Paper Structure (4 sections, 2 figures)

This paper contains 4 sections, 2 figures.

Table of Contents

  1. Introduction
  2. Experimental Setup
  3. Results
  4. Conclusion

Figures (2)

  • Figure 1: (a) Experimental setup for the bi-directional implementation. The sensing signals were combined with ASE loading using 100-GHz WDM filters.(b) Map showing the 4400-km undersea cable connecting California to Hawaii, USA. (c) Cable depth profile. More than 4000 km is at depths exceeding 4000 m. (d) Estimate of the optical signal-to-noise-ratio for various launch power from both directions. Lowest power of -3 dBm equals allocating one 100-GHz WDM channel for sensing. Correspondingly, 7 dBm equals allocating half the available power for sensing. A launch power of -3dBm was used in this experiment.
  • Figure 2: (a) Received power, or corresponding SNR, from the bi-directional sensing system. The lowest SNR point is shifted to the center of each span. (b) Individual spectrograms for each direction and from the combined signals. Bi-directional operation clearly reduces the noise level, improving all spans with $>$20 dB at 100 mHz and up to 40 dB at 10 mHz. The remaining red stripes are from cable movements and not limited by noise. (c) Corresponding waterfall plot for the first 200 km, showing high SNR detection of a M4.9 earthquake about 1250 km from the cable shore. (d) Waterfall diagram for a 1-minute trace with 50-m spatial resolution 2000 km offshore California. Combining both signals overcomes the noise limitation, enabling clear tracking of seismic waves on the ocean floor, which can be used for tomographic studies of earth's structure.