Using Sound to "See" Underwater

When I first tell people I don't need my eyes or a video camera or even light to see under water, you can imagine the look on their faces and the numerous questions that immediately follow.  Instead, I "look" at fish using a sonar - a Dual Frequency Identification Sonar (DIDSON) to be exact.
Dual Frequency Identification Sonar
The black cord connects the underwater DIDSON (above) to a computer  on the boat.  This allows me to watch and record everything the DIDSON "sees."
Without getting into all the technical details of the DIDSON (visit the company's webpage for that), the sonar emits sound-waves that "bounce" off of objects (such as fish) and then return to the unit with information on how far the wave traveled and the "intensity" of the object it hit.  The DIDSON then uses that information to create an image.  Now it's worth noting that the image it creates does not capture information on the color of the fish it hit and it may not be detailed enough to distinguish one particular species over another, especially if the fish is very small.  However, it is useful if you want to observe fish in their natural habitat without disturbing them or scaring them away.  It's also great if you want to conduct research at night when there is little to no light available.  Below is a series of clips of the DIDSON in action.  This is a "top-down" view of a canal in the Everglades.  So imagine you were standing over the canal looking down watching all the fish swimming by.  The numbers on the side serve as a scale (in meters).  Enjoy!


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