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Bioacoustics is the study of how animals communicates with any acoustic waves. Strickly speaking, it involves any substrates where the acoustic waves propagate: liquids (water), gas (air) and solids (e.g. plant stem, soil).

However, differences in methodologies can be found to record in each medium. For instance, people studying surface-borne acoustic-wave communication usually refers themselves as biometrologists and not as bioacousticians (see here and here), which probably highlights some differences.

I would like to focus my question on the recording techniques to pick up the diversity of acoustic waves in the different media. In particular, what are the main differences to be taken into account when recording solid-borne, water-borne and air-borne sounds?

EDIT: initially, there were multiple questions in the body text which was confusing for people answering, so I've tried to make it more focused on the main question (the one which is and was in the title) and I've created another question focused on difference between biotremology and bioacoustics

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  • $\begingroup$ The DOI for Cocroft does not seem to work? $\endgroup$
    – Shannon
    Commented Jul 1, 2022 at 22:07
  • $\begingroup$ Thanks @Shannon! The ref was wrong, this is now corrected! $\endgroup$
    – Noil
    Commented Jul 2, 2022 at 11:10

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The main difference is the coupling of the sensor to the propagating waves (sound/vibration).

For example, MEMS microphones work better in air than filled with water, piezo-ceramics are better in water, but pick up sound also in air, contact piezo pickup vibrations (e.g. from musical instruments), geophones are good to pickup seismic waves.

In general, all sensors that are capable to transform sound waves/vibrations into voltage could be used in different media, but the efficiency (sensitivity) will vary. Also the practicality is relevant. For example, geophones can easily pick up low frequency baleen whales, but require good gimbaling.

Also, gas and liquids have only pressure (longitudinal) waves, solids have also shear waves, interface waves etc., that ask for special sensors. Measuring particle motion requires dedicated sensors as discussed in other thread (particle velocity)

Edit: changed notation to reflect Noil's comment re pressure waves

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    $\begingroup$ Would it be correct and clearer to say "gas and liquids have only longitudinal waves" instead of "pressure waves"? Otherwise, one could think that there could not be any particle-velocity waves in gas or liquids. $\endgroup$
    – Noil
    Commented Jul 28, 2022 at 11:52
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    $\begingroup$ @Noi, not sure there exist something like particle velocity waves, but sensors that are sensitive to particle motion. All waves are associated with displacement of particles/atoms/molecules. However I replaced the term pressure wave in my answer $\endgroup$
    – WMXZ
    Commented Jul 28, 2022 at 18:21
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    $\begingroup$ @Noi not sure this justifies being the 'correct' answer here- The question was about biotremology as a discipline, and how we define it. The answer you have accepted is a physical explanation, that has no added biological context, so it does not answer your question. [see my answer below for a biotremologists perspective on this] $\endgroup$
    – LouR
    Commented Jul 28, 2022 at 19:13
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    $\begingroup$ That's the title yes- did you read the rest of the question though..? ; ) $\endgroup$
    – LouR
    Commented Jul 29, 2022 at 18:26
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    $\begingroup$ @LouR Sorry for the confusion, my bad, the title question and the ones in the body text did not match. The ones in the body text were to give some context, I edited the body text to have the title question again there. The best may have been to make 2 different questions.... I hope we will see more questions about surface-born acoustic communication / biotremology. $\endgroup$
    – Noil
    Commented Jul 29, 2022 at 18:27
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I'm noticing acoustic monitoring of soils is an increasingly hot topic within the passive acoustics community (rather than the physics side that you mention).

Some recent papers on that here - Lacoste, M., Ruiz, S., & Or, D. (2018). Listening to earthworms burrowing and roots growing-acoustic signatures of soil biological activity. Scientific reports, 8(1), 1-9. https://www.nature.com/articles/s41598-018-28582-9.

Maeder, M., Gossner, M. M., Keller, A., & Neukom, M. (2019). Sounding soil: An acoustic, ecological artistic investigation of soil life. Soundscape Journal, 18, 005-014. https://www.researchgate.net/publication/335826299_Sounding_Soil_An_Acoustic_Ecological_Artistic_Investigation_of_Soil_Life.

Keen, S. C., Wackett, A. A., Willenbring, J. K., Yoo, K., Jonsson, H., Clow, T., & Klaminder, J. (2022). Non-native species change the tune of tundra soils: Novel access to soundscapes of the Arctic earthworm invasion. Science of The Total Environment, 838, 155976. https://www.sciencedirect.com/science/article/pii/S004896972203073X.

Lata, T. D., Deymier, P. A., Runge, K., Ferrière, R., & Huettmann, F. (2022). Topological acoustic sensing of ground stiffness: Presenting a potential means of sensing warming permafrost in a forest. Cold Regions Science and Technology, 199, 103569. https://www.sciencedirect.com/science/article/abs/pii/S0165232X2200088X

I'm not sure how much the 2 sides talk but I would guess not enough, probably. Great opportunity for inter-disciplinary work here!

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    $\begingroup$ I edited the question to make it more focused on the recording technics only, following a comment from LouR. I will post another question later on biotremology. $\endgroup$
    – Noil
    Commented Jul 29, 2022 at 23:37
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great question- biotremologists do not deal with sound waves, but other types of mechanical waves that are non-compressional. Here's the distinction between the two disciplines:

Bioacoustics--- deals with "sound" (compressional/pressure) waves, particle motion is in direction of travel, these waves travel through one media e.g. a solid, a gas, a liquid. The receiving animals typically use a pressure-sensing structure.

Biotremology--- "substrate borne vibration" e.g. surface waves, particle motion is perpendicular to the direction of travel, these waves travel at the boundaries between two media e.g. water/air, solid/air. The receiving animals have specialised structures for detection, something that some could call "not an ear" (because it's not a pressure sensor).

For these reasons biotremology is somewhat separate nowadays. Before we had the technology to measure sub-borne waves, lots of research was termed "acoustic", when it was actually "vibrational" if that makes sense!

Vibrational communication is thought to be one of the most ancient communication forms, thought to be the precursor to acoustic communication.

If you're interested in this, I'd encourage you to read this awesome primer paper: Hill, P. S. M., and Wessel, A. (2016). “Primer: Biotremology,” Curr. Biol., 26, R181-191.

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    $\begingroup$ The difficulty with a strict separation lies in the fact that pressure waves that propagate inside solids (e.g. bottom) propagate partially as shear waves, interface waves, etc. and are then picked up on the hydrophone as pressure waves. IMHO, a differentiation for sensors is justified (pressure sensor, particle velocity sensor, vibration sensor) but propagation follows same laws. $\endgroup$
    – WMXZ
    Commented Jul 28, 2022 at 8:02
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    $\begingroup$ Absolutely- we get a mix of ALL mechanical wave types altogether in solids. The difference though is in biotremology we deal with animals that do not have pressure sensors, so the most relevant stimulus for them are the non-compressional motions. Any direct pressure change is undetectable to those animals. If you can justify a differentiation of sensors, you can understand a differentiation in our receiving animals, who are effectively just different sensors, if that makes sense. It's not a perfect biological definition, no definition is, and it's evolving over time as we learn! $\endgroup$
    – LouR
    Commented Jul 28, 2022 at 14:14
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    $\begingroup$ @LouR The Johnston's organ of bees, drosophilia, mosquitoes and other flies (and some fishes too?) have air-borne acoustic sensors which are not pressure sensors (they detect air-particle velocity through viscous coupling of their antennal hairs and the air particles). So the distinction between bioacoustics versus biotremology could not be between pressure versus particle-movement sensors, could it? $\endgroup$
    – Noil
    Commented Jul 29, 2022 at 18:39
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    $\begingroup$ @LouR And thanks for the paper link Hill and Wessel 2016, I've just read it, as well as Hill et al 2019 which has a section entitled "Why Can Biotremology Not Be Accommodated Within Bioacoustics?"(doi.org/10.1007/978-3-030-22293-2_2). It still raises some questions to me, that could be the pretext for a new SE question ;-) $\endgroup$
    – Noil
    Commented Jul 29, 2022 at 18:42
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    $\begingroup$ I hope we will see more "vibrationnal" questions in the site, and more generally, more questions about invertebrates. $\endgroup$
    – Noil
    Commented Jul 29, 2022 at 18:58

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