Distributed acoustic sensing (DAS) is a recent instrumental approach allowing the conversion of fiber-optic cables into dense arrays of acoustic sensors. This technology is attractive in marine environments where instrumentation is difficult to implement. A promising application is the monitoring of environmental and anthropic noise, leveraging existing telecommunication cables on the seafloor. We assess the ability of DAS to monitor such noise using a 41.5 km-long cable offshore of Toulon, France, focusing on a known and localized source. We analyze the noise emitted by the same tanker cruising above the cable, first 5.8 km offshore in 85 m deep bathymetry, and then 20 km offshore, where the seafloor is at a depth of 2000 m. The spectral analysis, the Doppler shift, and the apparent velocity of the acoustic waves striking the fiber allow us to separate the ship radiated noise from other noise. At 85 m water depth, the signal-to-noise ratio is high, and the trajectory of the boat is recovered with beamforming analysis. At 2000 m water depth, although the acoustic signal of the ship is more attenuated, signals below 50 Hz are detected. These results confirm the potential of DAS applied to seafloor cables for remote monitoring of acoustic noise even at intermediate depth.

中文翻译：

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光纤通信电缆上使用分布式声波传感的船舶探测和航迹评估的初步评估

分布式声学感测（DAS）是一种最新的仪器方法，可以将光纤电缆转换为密集的声学传感器阵列。该技术在难以实施仪器的海洋环境中具有吸引力。一种有前途的应用是利用海底现有的电信电缆监视环境和人类噪声。我们使用法国Toulon的一条41.5公里长的海上电缆评估DAS监测此类噪声的能力，重点是已知的本地化信号源。我们分析了同一艘油轮在电缆上方巡航产生的噪声，首先是在85 m深的测深图中离海5.8 km，然后是离岸20 km（海底深度为2000 m）。频谱分析，多普勒频移，声波撞击光纤的视在速度使我们能够将船舶辐射噪声与其他噪声分开。在85 m的水深处，信噪比很高，并且通过波束成形分析可以恢复船的轨迹。在2000 m的水深处，尽管船上的声音信号衰减得更多，但仍可检测到50 Hz以下的信号。这些结果证实了DAS应用于海底电缆的潜力，即使在中等深度，也可以用于远程监测声噪声。