Top: California Sea lion hears in at least three ways
Below: Snapping Shrimp cavitation bubble – one of the more ubiquitous natural sounds in coastal waters
Last week was in an International Standards Organization (ISO) meeting working on reconciling ISO 18405 – Underwater Acoustical Terminology, and ISO 30207 – Underwater Internet of Things.
I got involved in standards definitions back in 2006 we were doing a literature review on hearing thresholds of marine mammals and fishes – ostensibly to bolster my hypothesis that marine animal hearing thresholds were correlated to naturally occurring noise levels in the sea. This would give us an easy way to estimate how anthropogenic noises that exceeded the natural noise curves (called the “Wenz curves” after the classic GM Wenz 1962 paper), and what impacts that noise might have on marine animals.
My hypothesis was correct, and easy to determine with marine mammals, although it wasn’t quite as clear with the fishes, because the Wenz curves were calibrated using acoustical-pressure-sensing hydrophones, and fishes also sense “particle motion” acoustical energy which is not reflected in the curves.
But what got me off into the “standards jag” was that in the ~150 papers each we reviewed for fishes and marine mammals, there were no less than nine different metric expressions of sound exposure levels.* Some were expressions of instantaneous exposure, some were expressions of accumulated exposure over time (typically 1 second), some were “average,” some were “peak,” and quite a number were just nonsense (these were all from “peer reviewed” scientific papers, by the way).
I realized that if I was going to contribute to the regulatory discussion about ocean noise impacts, that scientists, regulators, the Navy, conservationists, and industry would need to be drinking out of the same tap. So OCR joined the American National Standards Institute (ANSI) which naturally fed into me being an ANSI delegate to the ISO. This led to me jumping into the ISO 18405 fray, sitting in rooms with physicists and biologists much more qualified than I to hammer out metric definitions to things like “Acoustical Field and Power Quantities,” “Terms related to propagation and scattering of underwater sound,” and “Source waveforms and factors.”
These definitions are built upon physical properties, and based on measurable units, so we just needed to determine the necessary terms and plow through them. This only took 5 years of annual and sometimes semi-annual meetings. (Thanks to Zoom we can now have these meetings more frequently – even if I need to get up a 4am for a meeting hosted in Korea).
Last week’s meeting was a bit different; what one might think would be the starting point of this whole discussion has become the sealing of the envelope: the biological definitions of sound perception and sound creation.
These run amok because they juggle the elements of purpose, intent, and incidence in the making and perceiving of sound. We had two guest experts joining us; Dr. Arthur Popper, who has been exploring the hearing modalities of fishes since the 1960s, and Dr. Darlene Ketten, a neuroanatomist with WHOI, who among other feats, has been mapping the auditory physiology of the hearing of baleen whales through the mathematical modeling of their cochlea and the neurological transmission of the sounds they perceive into the brain.
I really enjoy being in the room with smart folks like Art and Darlene.
So where did we get? The easy one for me is sound creation. There are three terms which I see as nesting terms: “Sonation” – which is a sound as a consequence of an activity, “Phonation,” which is an intentional creation of sound through any number of mechanisms, and “Vocalization,” which is a sound created through the passage of air through larynx (in primates) or syrinx (in birds).
Sound perception is a bit more complicated. Terrestrial animals have “ears” that collect sounds and transfer the acoustical energy through a bunch of different mechanisms into neural impulses to the brain. In marine animals there are a lot more mechanisms, which I’ve realized at this point are too complicated to detail in a newsletter which I try to keep at around a minute read.
So I guess our next newsletter we’ll roll up our sleeves on the details of “Hearing,” and the nested terms of “Sonation.”
* This spreadsheet has a lot of pages, including the graphical output