Behind the scenes
Speeding up sound sampling
August 11, 2017
Sound may be weightless, but echosounders—machines that use sonar to image the ocean— sure aren’t. To create a detailed picture of Monterey Bay’s ecology, Scientist Kelly Benoit-Bird uses an echosounder with five different transducers, which are devices that send and receive sound. Using these five different frequency echosounders together allow her to determine not only the depth of underwater organisms but also an animal’s identity. However the transducers together add 75 kilograms (165 pounds) to the underwater components of her echosounder.
Transporting, setting up, and deploying a large instrument like an echosounder can prove to be quite a challenge. Depending on the echosounder, it can take hours, especially when multiple scientists are sharing the same boat for many different purposes. Luckily, MBARI Mechanical Engineer Larry Bird (no relation to Benoit-Bird) built Benoit-Bird a personalized, one-piece mounting system.
Without having to assemble all of the parts on board and install each transducer individually, setup has gone from hours to just 30 minutes. Electro-Mechanical Technician Paul Coenen and his colleagues then built each of the transducer’s electrical systems into a single waterproof case, streamlining a bundle of cords into just a few.
Once Benoit-Bird and her echosounder are at sea, deployment requires only a couple of steps. Typically, over-the-side echosounder installations use soft-line (ropes) to hold the pole the transducers are affixed to in one place. In order to have the pole exactly perpendicular to the water, quite a bit of a back-and-forth is required in terms of adding and taking away slack from the ropes. To cut down on this adjustment time, Bird switched to neutral foil tubes made of aluminum. These lightweight tubes don’t stretch over time and require no adjustment. Once they’re clicked into place, Benoit-Bird and the crew know her transducers are pointing straight downwards. These aluminum foils have an added benefit of reducing strum, a type of vibration that occurs when soft lines move through the water, causing interference to Benoit-Bird’s acoustic data. Although the neutral foil tubes still experience some strum, it’s to a much lesser extent.
Whether tackling every day challenges like improving an echosounder or developing brand new approaches, teamwork between scientists, engineers, and the marine operations experts is a hallmark of most MBARI projects.
Article by Emma Bueren