Dave, UR - Analysis continues...

Array with 0-degree collectors, the night before the dive

So last Tuesday, I finally got my design into the water.  The speaker we had selected to project tone in the water was supposed to be rated for a half hour in the water, at the depth of one meter. I had even opted to suspend the array on a stand, and made modifications to the target area, all with the intent of compensating for the speaker's depth limitations. The speaker made it for about a minute in the water before it was entirely inoperable. Needless to say, it is presently on its way back as a return.

In order not to waste the opportunity to test in the water, we opted to strike overflow gutter of the pool with a metal hook, in order to produce recordings for analysis.  I stood behind the target stand in each position that the speaker would have been, and rapped the overflow gutter ten times sequentially, to make sure that the recorded samples would have a reasonable degree of uniformity between iterations.  While this constituted a major deviation from the original experiment design, we determined that it could still provide for a proof of concept, and possibly still give us an indication of collector performance.

Carrying the target stand to the pool

For the things that went wrong, many more things went right, making the initial dive all the more worthwhile. All of the major structural components of the array and the associated stands all performed as they should, even despite a last minute change from 2" PVC to 1" PVC.  Stands submerged and recovered with ease, and all three collector shapes that were fabricated were tested. The 15-degree shape was removed from the dive plan the weekend prior due to maintenance downtime of 3D printers.

The Sparton PHOD-1 hydrophones were cabled with regular XLR microphone connectors and attached to digital audio recorders on loan from WDSC TV, and operated by DSC's own Jessie Guthrie. Thanks for the help Jessie!  All three hydrophones worked without problems, and stayed fixed in the array throughout the duration of the dive.

Array with 25-degree collectors mounted

All told, 45 raw audio samples were collected on Tuesday morning, and I sat down on Wednesday to perform an initial analysis of the recordings.  I used Raven Pro, and audio analysis tool from Cornell's Ornithology Lab to perform 30 different correlative analyses. I compared each 25 and 90-degree recording from each position to its corresponding 0-degree recording.

Through these comparisons, I found out a lot more than I expected with all of the changes and pitfalls considered.  First, the collectors did demonstrate an ability to enhance the collection quality of the hydrophones.  Second, initial assessments show that an increase in collector volume could result in an increase in performance, so that is being assessed as a possibility for more testing over the summer.  Moreover, it appears as though the 25 degree collectors performed optimally overall, so variance between shapes was demonstrated, satisfying the proof of concept.  More analysis is being done presently, to show how all three hydrophones performed in concert. Results of this analysis will be discussed here before I present on Friday, so keep your eyes peeled.

Array with 90-degree collectors mounted

Now I will answer some questions that were submitted by readers.
The first question comes from Aleecia, who writes, "So my question: dolphins (i think) travel in groups. When dolphins make their sounds (clicks, whistles) can you see the specific dolphin making these sounds? In other words, I can make sounds without opening my mouth. If i was in a crowded room and made this sound, how are you going to be able to tell it's me and then relate that to any obvious behavior? So what does a dolphin look like when they make these sounds? Is it obvious enough to know which specific dolphin made it?"
Aleecia, I am going to answer all of those as one, and say that there is a bit of body language that can be associated with some of the more aggressive buzzes, but otherwise visual indicators are limited. Dolphins have their auditory projection tissue back at the base of their blowhole canal, and that sound gets pushed forward through their forehead, that biologists refer to as their melon. As Dr. Herzing pointed out in her last presentation (which I included the YouTube of in a previous post), dolphins also have the ability to use their melon to point their audible projection 20-degrees to the left or right, since turning their heads suddenly in the water carries more consequence than turning ours in the air. This further complicates the task of researchers, but hopefully this tool will help, when fully developed.

The second question comes from William, who writes, "I have read articles where architects and some engineers are now creating buildings and various structures based on shapes found in nature. Have you considered looking at the shape of the dolphin's 'dish' and using that as your shape?"
William, there is much wisdom in following the designs of thousands of years worth of evolution, but in this case, I am not even sure how I would go about approaching the idea from an engineering perspective.  You see, dolphins lack an outer ear altogether, as it becomes problematic when constantly submerged, and even more problematic as depth increases.  Instead of using an outer ear, dolphins use their lower mandible for general sound collection. The jawbone is filled with extra fatty tissue to help capture and transfer sound vibrations, which are then transferred to a cochlea at the back of the mandible. Just like our cochlea, the sound vibrations are then safely transferred to nerve ganglia which get interpreted by their brains. Once those vibrations hit the ganglia, that is where our understanding of their sound interpretation stops, meaning that we have absolutely no idea what things actually sound like to them, nor do we have firm comprehension of their brain function.  It is for these reasons that I opted to start with something more traditional, though I will ponder the notion of emulating nature as I carry forward with my research. Great question!

Research presented at DSC's STEM Community Scholars Undergraduate Symposium, 29 APR 16