Back in 1992, physical oceanographer Walter Munk was advancing a program called “Acoustic Tomography of Ocean Climate” or ATOC. The stated objective was to project coherent sound across ocean basins with the understanding that distortions in the sound received at the receiving end would reveal distorting factors between the signal and receiver transducers.
Given that there are correlations between water temperature, water density, and sound speed, what could be inferred from the distortions was the aggregate temperature of the ocean. But as there would be other distorting factors, like ocean currents and thermal layers, other properties could be read. And like the tomography used to view babies in the womb, density variables in the ocean could be read. This would include upwellings like the “El Niño” and La Niña” current events which have such profound effects on global weather.
But what can also be extracted out of the data would be the presence of large things moving underwater – like submarines – wherein the movement would create a doppler frequency shift in the originating signal. So while physical oceanographers could surmise oceanic climate conditions using ATOC, military intelligence could track submarines – foreign and domestic.
Getting coherent signals across ocean basins is actually useful for a lot of things, and the ATOC program came along just in the nick of time for the submariners. Submarines are all about stealth, but they need to get assignments from somewhere – and at depth they couldn’t just pick up the phone.
Prior to 1990, communicating with submarines involved them coming close to the surface and dragging 2km radio antennas across the water surface, receiving long-wavelength radio waves broadcast from shore. But this communication strategy was instantly made obsolete in the early 1990s, when satellites fixed with magnetometers could spot these antennas from space.
So while nobody is saying anything, in addition to measuring ocean climates, the ATOC program advanced the feasibility of conveying instructions to the submarines – inaugurating the age of underwater acoustical communication – and the resumption of surreptitious submarine communication.
This was about the time I dipped into the water on ocean noise. The physical oceanographers, while brilliant in their own field, were not considering the fact that marine animals – particularly the great whales, had worked this acoustical communication channel out millions of years before. And because the ATOC (or other) communication signals sounded relatively benign, nobody thought the whales would mind.
This was the flashing red light in my dashboard; it would only be a matter of time before some less benign signals started hitting the whales.
The first evidence of this was the notorious Bahamas Beaked Whale strandings – which happened while the public was commenting on “Low Frequency Active Sonar (LFAS), another underwater signal that the Navy was proposing. LFAS was also relatively benign, but the Bahamas stranding was using a very nasty sounding mid-frequency sonar (which we in the public didn’t get to comment on…). Think ‘icepicks into the eardrums.’
I mention this because a couple of weeks ago, when I was in an Animal Bioacoustics Committee meeting at the Acoustical Society conference, our committee was visited by Timothy Schoechle, a member from the Acoustical Society Underwater Communications Standards committee. Their committee was drawing up a “Smart Ocean” proposal which included transmission and coding standards for an “Underwater Internet of Things” (UIoT).
At face value, this sounds like a really lousy idea; having all equipment we humans deploy underwater with their own acoustical communication modems – tapped into a global acoustical Global Positioning System (GPS). Given the propagation characteristics of sound in the ocean, and the need to address both transmission distance and accuracy, the signal frequencies would predominantly be in the 9kHz – 15kHz range. This is well within the hearing and communication ranges of porpoises, dolphins, seals, and sealions – and likely within the perceptual range on many fishes.
Tim reasoned that before they drew up communication signal standards in this biological auditory range, it would be wise to confer with the folks who know the animals.
I couldn’t agree more, and will expand on this in the next blog. Stay tuned!