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.
Richard Seagraves
I am going to approve your comment because it represents an informed perspective – even while I don’t completely agree. I appreciate the time you have spent articulating it.
I am publishing our series on the drawbacks of offshore wind because I am building the argument that any of our power choices must be considered in terms of a “balance of harms.” And we know that fossil fuel is killing the planet. But all energy generation strategies – by nature of being a concentration of power, will exact some environmental damage, Including terrestrial-based wind. The advantages of offshore wind (over terrestrial based) include a more reliable persistence of wind. Also in some cases, the masts or other under-water structures can be used as vertical feeding space for natural marine life, or vertical structures for low-trophic level aquaculture (algae, kelp, shellfish, and other invertebrates).
I am not familiar with the current federal subsidies to wind power, but the previous administration eviscerated any incentives they could on wind to keep it from encroaching on the highly subsidized fossil fuel industry. Their strategy included putting high tariffs on turbines (and solar) imported from China, and eliminating tax incentives for wind farms.
I also know that due to the physical structures required for nuclear, that it would not survive in a market competition on $/watt with any other technology without being highly subsidized.
So as I am suggesting, all of these (and other) options come with costs. We just need to figure out which costs are acceptable.
Again, thanks for the time you took to express yourself. I would welcome any cogent literature substantiating your points.