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Most published studies in wireless passive acoustic monitoring (PAM) report an audio acquisition duration that is relatively short, from a few hours to a few months. That's what one would get by deploying an off-the-shelf battery-powered solution like AudioMoth or SongMeter.

I am curious about wireless PAM surveys that lasted for over one year on remote (off-grid) sites. What were the benefits and the challenges encountered?

I'm trying to establish a general state of the art, so feel free to bring up studies about any taxon: birds, bats, cetaceans, fish, land mammals, you name it. But i'm only interested in wireless sensors operating autonomously off the grid, as opposed to short periodic surveys or wire-powered devices. Towing a hydrophone to a boat would be off-topic for this question.

Specifically, it would be helpful to know if the recordings were made continuously or intermittently, with what source of power, and what connectivity. How often did humans physically access those PAM devices, if at all.

(edited on August 8th to clarify that my question is about wireless autonomous sensors)

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    Can you specify whether you are talking air or water and perhaps also species group? There are very different challenges and possibilities for long-term PAM in air and water. Also, the need/gain from multi-year surveys depends heavily on the question and the biology of the target species. There are many examples of multi-year PAM for cetaceans, even multi-decade.
    – user18
    Aug 8 at 7:08
  • @JakobTougaard any taxon works for me, but my question revolves around deployment settings in which physical access to the device is infrequent. I have updated the question to clarify this.
    – lostanlen
    Aug 8 at 12:59

4 Answers 4

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The Australian Acoustic Observatory would always be one to mention: "approximately 360 continuously operating acoustic sensors collecting 2PB of sound data" over a period of 5 years. Devices are solar powered, and data stored on SD cards manually collected.

Sueur et al (2022) run a study designed to record for 15 years, using 1-minute-every-15-minutes sampling, started on July 13, 2018, with four SongMeter 4 recorders in the Jura Mountains in France. As of that paper, 2285 h had been recorded. Power source / connectivity don't seem to be noted in the paper.

I expect there are very long-duration projects in marine sound (e.g. using these MARU and Rockhopper units from Cornell which can record up to 200 days continuously while sitting on the ocean floor), but since I'm not the expert there I will leave that for someone else to answer in detail.

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In the marine realm, I believe high- frequency acoustic recording packages (HARPs) are able to collect the greatest data volumes for extended periods, with continuous recording sampling at 200 kHz for 18 months. Otherwise, I’m aware of the ocean noise reference stations (NRS buoys) that collect data continuously for 2 years, sampling at 5 kHz. These autonomous instruments must then be recovered, serviced, and redeployed to collect the data and replace batteries for additional data recording at a given site.

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Here's some info on cetacean studies using instruments I've designed (as Chelonia Ltd): In cetacean studies there are projects using C-PODs and F-PODs that exploit the specific target (cetacean clicks) for the data by running what is, in effect, the early stages of the post-processing, and selecting useful data to store in real time. This reduces data volumes by factors around 10k so the SAMBAH project
https://doi.org/10.1002/ece3.8554 processed 10k TB of data in real time from 1000 deployments at 300 sites over 2 years and brought 0.5TB back to shore. That represented 400years of continuous logging time at a sampling interval of 200ns.

A study in the Salish Sea by Aileen Jeffries used a similar approach at one site over a longer period to determine trends and is reported in https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0264289

The BlackCeTrends project is using 4month deployments of F-PODs at 25 sites around the Black Sea to assess the feasibility of a 'trend sampling' approach. These instruments sample continuously at 1m samples per sec, then upsample to 4m/s to carry out the selection process.

The 'BatBug' uses the same technology and sampling rate to select bat calls and then store the wavelength of every cycle in the call, plus other data. Because that target is so distinctive selection can be very specific and a 32GB SD card can hold years of data, and an A3 or A4 solar panel can enable continuous logging, but this device is not yet available.

This approach does not provide WAVE files, but is amenable to high-precision time-domain analysis, and we're learning more about that... Having small data volumes is a joy - easy to move around the planet and less long term carbon cost of storage.

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As @Jakob comments, multi-year PAM programmes exist to document, for example, cetaceans. I was lucky enough to join the Hebridean Whale and Dolphin Trust in 2019, who have been monitoring specifically harbour porpoise since 2002 using a towed hydrophone : https://hwdt.org/research-projects-1

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    I interpret OP as single continuous PAM deployment, not multiple deployments, as indicated by continuous vs intermittent, power source, etc
    – WMXZ
    Aug 8 at 11:44
  • @WMXZ right. i have edited my question to clarify.
    – lostanlen
    Aug 8 at 12:55

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