The World of Acoustics

By Aedan Mell

Hello, I am a research technician from the Marine Ecology and Acoustics Lab at FIU under Professor Boswell. I just graduated last spring with my bachelors and now I’m taking some time to gain more experience before graduate school. I got the opportunity to come along on this trip to help out with the acoustic transect surveys. We have 4 echosounders each transmitting adifferent frequency to allow us to observe Diel Vertical Migration, the largest animal migration on Earth that happens every day. It describes the synchronized vertical movement of deep sea animals and zooplankton to the surface at night to feed on phytoplankton. With our echosounders, we can observe this phenomenon as deep scattering layers that we can track vertically over the course of a 24-hour period.

Photo: Aedan with the CTD which sends some of the acoustic equipment down into the midwater column

This is my first trip doing research this far out at sea. It's also my first time actually working with echosounders, which is exciting because it's the instrument most of our lab’s work revolves around. I'm more familiar with another type of acoustic instrument called multibeam imaging sonar. This type of sonar uses multiple beams at high frequencies to record high definition acoustic footage. Personally, this is my favorite type of hydroacoustic instrument, as it allows you to see individual organisms and observe how they move through the field of view. It's also sometimes referred to as an acoustic camera, as its footage is more representative as a video footage rather than a standard echosounder echogram.

For our trip we brought a Kongsberg M3 multibeam imaging sonar. At 500 kHz, this model runs at a relatively lower frequency for an imaging sonar, facilitating greater sampling volume and range at the cost of reduced resolution. I'm super excited to drop this in the water and see what's going on down there. Hopefully our data will help us in target classification. A big issue with the echosounders is that it can be difficult to classify what kind of organisms are in these deep scattering layers. By dropping imaging sonar into these layers we could get a better idea of their compositions based on the observed morphologies of the acoustic targets. Maybe if we’re lucky, we might be able to see some predator prey interactions at night!

Photo:  Threadfin dragonfish 

From watching sharks surround our boat at night to pulling up rare deep sea critters, there have been so many great experiences on this trip it's hard to fit everything in this post. Just this morning our boat was surrounded by a huge pod of dolphins. One of the best nights was when we had to dock at a port in Pensacola to get away from Hurricane Francine. We were all a little bit seasick so getting off the boat was a welcome development. We went out to eat and got to know each other better while in port. It's been such a great experience, not only just to learn more about marine research and get professional insight from deep sea experts, but also to make friends and get to see what life is like on a research vessel.

Photos:  Sun over Gulf of Mexico; pod of Pantropical Spotted dolphins.