One of our interests is how does an animal's orientation (relative to the acoustic wave) affect the echo from the animal. We studied this in 1994 (but are now getting around to analyzing the data, science can sometimes be a slow business) with samples from the R/V Endeavor cruise in George's Bank (just off of Cape Cod, Massachusetts). We took video camera images of the shrimp while we pinged it acoustically so that we could know the animal's orientation, and what its acoustic echo looked like. Here are two representative examples of the different positions the animal would be in (the animal is tethered with a thin monofilament which is the vertical line running through the picture.)
| | Here the animal is broadside (perpendicular) to the acoustic wave front. Thus we would expect a large return since the cross sectional scattering area is at (or near) a maximum for this animal. |
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| Now the animal has rotated, such that it is no longer broadside to the acoustic beam. Since the cross sectional scattering area is smaller in this case, we would expect a smaller Target Strength for its echo. |
In another series of experiments we took measurements of 6 different snails (Periwinkles caught locally here in Woods Hole), these animals are similar in appearance to pelagic snails that are important scatterers in the Gulf of Maine and Georges Bank region (and elsewhere). However the pelagic snails (such as Limacina Retroversa ) are very small (lengths on the order of 1 mm) and difficult to handle. The periwinkles we used are larger and easier to use. We believe that they scale similarly to the pelagic gastropods so that we can use information collected on these animals to explain scattering by the smaller marine snails.
Hopefully I'll write up a section on BIOMAPER because its a pretty cool system as well. But until I do, here's a picture of
it coming out of the water covered in siphonophores (the pink strands are smooshed animals).
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