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Strumming is low frequency noise created by the vibration of a cable (see this question on how to identify strumming). According to The Practical Guide for Underwater Noise Measurement, strum can be mitigated through ‘mechanical fairings’ or by ‘decoupling the hydrophones from suspension cables using compliant couplings (elastic rope)’.

What are specific methods used to mitigate cable strum in underwater recordings using seafloor or drifting recorders (not towed)? What materials were used? If they were non-conventional materials, how were they acquired? How and where were they attached? Are there methods that were found to be more successful than others?

Pictures and details are encouraged!

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  • Mind to specify towed or stationary application?
    – WMXZ
    Jul 18 at 14:41
  • Thanks-- specifically interested in drifting/seafloor (not towed array). Towed arrays are a very different beast! Question edited to identify platforms of interest.
    – Shannon
    Jul 18 at 14:45

2 Answers 2

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For drifting buoys or dipping hydrophones from small boats, I've seen both ends of a short stretch of rubber hose connected to a longer rope or the hydrophone cable to absorb effects of surface energy and strum. I've also seen short flags of electrical tape added all along a cable to act as mechanical faring, but this has the unfortunate tendency to fall off over time.

Wiggins and Hildebrand 2007 describe the use of isolation rings between the hydrophone and the rope line between the float and anchor (or other mooring components) to reduce vibration transfer from the line to the hydrophone.

Wiggins, S.M., & Hildebrand, J.A. (2007). High-frequency Acoustic Recording Package (HARP) for broad-band, long-term marine mammal monitoring. In, International Symposium on Underwater Technology 2007 and International Workshop on Scientific Use of Submarine Cables & Related Technologies 2007 (pp. 551-557). Tokyo, Japan: Institute of Electrical and Electronics Engineers

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For drifting vertical array PAM surveys, we've attached a series of small buoys underneath the surface expression, so as to decouple surface movements from the array. This can be visualized in the diagram below, from this paper (An autonomous hydrophone array to study the acoustic ecology of deep-water toothed whales, Deep Sea Research Part I).

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