Detection of hydroacoustic signals on a fiber-optic submarine cable

TLDR

A ship‑based seismic survey near a fiber‑optic submarine cable produced the first 50‑km distributed acoustic sensing recordings of air‑gun shots, demonstrating that DAS is sensitive to hydroacoustic signals from 0.1 Hz to several tens of Hz, comparable to hydrophones. The study aims to assess the detection capability of underwater acoustic signals using the DAS dataset together with co‑located hydrophones. The authors analyzed the DAS recordings along the cable in conjunction with hydrophone data to evaluate hydroacoustic signal detection. The DAS measurements identified hydroacoustic signals in frequency‑time space, revealed phase coherence over several kilometers along the cable—indicating suitability for correlation analysis—and mapped ocean microseismic background noise along the cable, though its self‑noise exceeds that of conventional hydrophones above a few hertz.

Abstract

Abstract A ship-based seismic survey was conducted close to a fiber-optic submarine cable, and 50 km-long distributed acoustic sensing (DAS) recordings with air-gun shots were obtained for the first time. We examine the acquired DAS dataset together with the co-located hydrophones to investigate the detection capability of underwater acoustic (hydroacoustic) signals. Here, we show the hydroacoustic signals identified by the DAS measurement characterizing in frequency-time space. The DAS measurement can be sensitive for hydroacoustic signals in a frequency range from $$10^{-1}\,\text {Hz}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> <mml:mspace/> <mml:mtext>Hz</mml:mtext> </mml:mrow> </mml:math> to a few tens of Hz which is similar to the hydrophones. The observed phases of hydroacoustic signals are coherent within a few kilometers along the submarine cable, suggesting the DAS is suitable for applying correlation analysis using hydroacoustic signals. Although our study suggests that virtual sensor’s self-noise of the present DAS measurement is relatively high compared to the conventional in-situ hydroacoustic sensors above a few Hz, the DAS identifies the ocean microseismic background noise along the entire submarine cable except for some cable sections de-coupled from the seafloor.