The downsides of offshore wind – survey noise

Sub Seafloor surveys – Chirps and Booms

It appears as though the current administration is running with the ball on wind generation. This is a fine thing, because – as I suggested in the previous blog , offshore wind generation will be one of the quickest ways to migrate off of dirty coal, oil, and gas fired power generation.

But deliberations of this magnitude need to be honestly addressed, because offshore wind is not without its own set of problems – many of which are known, some of which are still in question, and others yet unforeseen. And then there will be a raft of fabricated “liabilities” conjured up by the fossil fuel industry chop shops to throw doubt into the equation.

Probably the most fundamental problem with offshore wind is noise (right in our wheelhouse). From site surveys, to construction and installation, to chronic operating noise – are all part of the job. These will all be addressed in a series of sequential newsletters.

Site surveys are used to assess seafloor profiles and subsea geology for site suitability. Seafloor profiling use narrow aperture sonars – both “multi-beam” and “side scan” technologies. Most multi-beam sonars operate in the 190kHz – 400kHz frequency range – a bit too high for even the highest hearing range of the harbor porpoise, so not a noise problem.

But side-scan sonars can operate in the 40-80kHz range – overlapping the bio-sonar frequencies of most odontocetes (dolphins and porpoises). This could be disruptive, although with the narrow and locally focused beam, a quick and witty dolphin might easily avoid being directly hit.

The “sub-sea” geological surveys will typically use “sparkers” and/or “boomers.” Which are both electrical “capacitive discharge” devices that create, loud “POP!” or “BOOM!” that penetrate the seafloor up to a few hundred meters. Depending on the area of the survey, and the repetition rates, these can be as relentless as the airgun surveys used in the fossil fuel industry, with broad-band noise content sure to annoy most ocean animals (the firing rates can be as fast as four pops a second…).

Technically, these devices are classified as “pulsed” or “intermittent” signals, and thus at their typical amplitude levels and signal duration, would fall just under the National Marine Fisheries (NMFS) “Level B” regulatory threshold of 160dB (re: 1µPa) for impulsive noise. But I have always argued that continuously fired signals, regardless of how “impulsive” they may be, should fall under the NMFS 120dB “continuous noise” criteria, because they are continuously pulsing.

There are a number of other pulsed signal sources for subsea geological profiling, but the gist is  that they all create a “BANG!” of some sort – although all them with significantly less energy than seismic airguns used for oil and gas exploration (cool airgun movie).

And oddly, when speaking about the impacts of ocean noise sources, the vessels that deploy these noise sources are rarely brought into the equation. Although if you have a work vessel weaving and knitting transects over a survey area for an extended period of time, it constitutes concentrated noise in that area, which needs to be considered as well.

And all of this noise takes place before the masts are put in place and the wind generators are installed – which we will deal with in a subsequent blog.

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