July 5, 2004
During my time off watch today, I spent a few hours in the acoustics lab with experts Shannon Rankin and Julie Oswald to learn a bit about acoustical techniques in general and their current research in particular. The acoustics team uses two primary tools in their work. A hydrophone array is a larger apparatus towed off the fan-tail of the McArthur II, when conditions permit. Another tool that they occasionally employ are smaller sono-buoys that can be deployed off the McArthur II directly or deployed by the smaller boats AR-1 or AR-2. Both tools perform the same function, allowing the acoustics team to record sounds of the various cetacean species within range of the ship. The continuous click of the sperm whale, or the squeak of a dolphin, or the whistle of an orca, can be used as another indicator of the species encountered, in collaboration with the visual observations.
Shannon and Julie are currently running a "double-blind" study to determine whether sperm whales are best detected by visual efforts from the flying bridge or acoustically via the array. What this means in practical terms is that acoustics team is physically isolated from the flying bridge, located in the windowless dry lab midships and therefore cannot see or hear unless alerted via radio. Marine mammal observers do not inform the acoustics department of any tentative sperm whale sightings until after they have passed the 90 degree mark on either the port or starboard beam. The acoustical array is therefore their only means of detection of a sperm whale. Similarly, the acoustics department does not alert the flying bridge of any sperm whale sounds. The constant "clicking" of the sperm whale means that they are in fact often heard but not seen!
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