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Sound Bytes: Passive Acoustics Starts with the Right Equipment

October 21, 2021

What is a drifting recorder and why do we love them?

Photograph of a drifting acoustic spar buoy recorder (DASBR) deployed during the ACCESS 2021 cruise. Credit: Shannon Rankin. A drifting recorder deployed during the ACCESS 2021 cruise. Credit: NOAA Fisheries/Shannon Rankin

No one ever told me that I would need to learn how to solder to become a marine biologist. Well, here I am soldering connective wire to a 9v battery pack. Why? You may ask. Well, because in our field the first part of collecting acoustic data is building your own equipment.

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Photograph of acoustician soldering wires for equipment.
Soldering wires together for our drifting recorders. Credit: NOAA Fisheries/Shannon Rankin

My name is Cory Hom-Weaver, and I work as a passive acoustic technician contractor for Southwest Fisheries Science Center, and today I am in the process of putting together a few drifting recorders. Unfortunately there is no store I can stop by to pick one of these up, so here I am building equipment that was specially designed by the center to collect acoustic data.

Previously, you could find our acoustics team on NOAA research vessels towing hydrophone arrays in a line transect pattern across large swaths of the ocean. Occasionally we still do this, but the problem with towed array surveys is that ships are expensive and often the recordings we collect from this platform have vessel noise in them. This is not ideal if you are trying to study the soundscape of our ocean basins, or you are looking for baleen whale calls, which can be drown out by low frequency ship noise. So in 2012, Jay Barlow developed drifting recorders to help us eliminate the need for long, expensive surveys, and to help us capture quiet recordings without impacting animal behavior.

The fun thing about these buoys is that they float and drift along with the ocean currents! A pair of hydrophones dangle deep in the water column (approx. 150 meters down) so that we can record both dolphins (which tend to stay in the upper water column) and deep-diving beaked whale species. These hydrophones are plugged into a SoundTrap ST4300 recording unit. In order to extend the available memory onboard, we only record half of the time (6 minutes on, then 6 minutes off until the SD cards are full or the battery life of the recorder runs out). At the very bottom of the drifting recorder is a 30 pound weight to help keep the entire unit vertical. At the top, you will find a vacuum sealed plastic buoy with two Spot GPS units inside that transmit its location every 30 minutes. I knew you were wondering how we find these things again! And finally, to help keep them out of harm’s way, there is a 3 meter mast with a radar reflector on top to make it visible to vessels. 

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Photograph of Cory Hom-Weaver organizing wire for acoustic operations into tubs to go on the ships.
Cory Hom-Weaver organizing buoy line into a tote for transport. Credit: NOAA Fisheries/Shannon Rankin

Did I mention that the drifting recorders are also modular? This is incredibly useful when needing to transport them from one place to another. Currently we are assembling equipment for the Acoustic Ecology Lab’s ADRIFT project. This multi-year project, funded by the Bureau of Ocean Energy Management (BOEM), consists of opportunistic and directed deployments of the recorders between Point Conception and the California/Oregon border. An area of the ocean that is not easy to survey due to inclement weather and rough seas. But that’s a story for another time—until then, it’s back to soldering. Thanks for stopping by.

 

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Last updated by Southwest Fisheries Science Center on November 22, 2021

Acoustics