Report from New Orleans

Propagation model

I’ve just returned from a week-long conference of the Acoustical Society of America (ASA) in New Orleans. The Acoustical Society has a very broad remit, serving all professionals and academics working with sound and acoustics. This intersects the fields of architecture, engineering, medical imaging, music, speech and language, signal processing. underwater acoustics, acoustical oceanography, and of course, animal bio-acoustics.

The ASA has meetings twice a year and for various reasons – such as proximity to various institutions and/or regional characteristics, the conference will congeal around certain themes. So it wasn’t surprising that there was an Animal Bioacoustics (AB) session on the Gulf of Mexico. This day-long session was themed in memoriam to the late University of New Orleans physics professor George Ioup and was co-hosted by the Acoustical Oceanography and Underwater Acoustics groups.

This collaboration set the tone for the entire meeting. So while there we a few AB papers specifically focused on animals, there were many papers on modeling, propagation, and characterization of sound-sources and their measure. There were a number of really great papers, although most of them probably a bit dry for those reading this. But there was one paper that inferred something that stimulated my imagination.

Altan Turgut’s “Bottom characterization in the northern Gulf of Mexico using chirp sonar and ship noise data” initially set out to use opportunistic and introduced sounds to probe the layers of seafloor found in the Gulf. This is akin to sonograms used in medical imaging, except at much lower frequencies. Although in the course of his research he was noticing that the clicks of sperm whales were kicking back signatures of these same layers on his equipment.

If Altan’s equipment revealed these layers, there’s some reason to suspect that the sperm whales might also be able to read these echoes. This would infer that the whales are swimming in a more nuanced representation of their surrounding – sensing bottom composition and surface states much like we are able to see the forests, meadows, and mountains surrounding us as we wander about.

I presented a paper on modeling the propagation characteristic of high-frequency, multi-nodal communication networks. This issue has been a concern of mine ever since I started working on marine noise pollution. The time is fast arriving where these communication networks will be saturating ever greater ocean areas – much to the detriment of the critters who inhabit the sea.

The gist of my presentation is that while current regulations evaluate noise sources on a piece-by-piece basis, these networks are designed to work in clusters, so they should be evaluated – and regulated as such. And given that these sources are pretty loud, and they broadcast pretty lousy sounding noises continuously, we are unwittingly colonizing large areas of the ocean without regard to the impacts that will ensue.

I fear that we will continue advancing in this direction, and is why I have been pushing the use of signal characteristics as a metric – encouraging us to tailor our communication signals to be more like biological sounds, and less like stabbing acoustical icepicks.

If we don’t do this, the nuanced soundscapes inhabited by the sperm whales could be getting a lot more miserable for these curious and majestic creatures.