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Gene Pillard, the Res. Tech., attaches the ‘pinger’ to the dredge wire. The pinger is attached 200 meters above the dredge bag. It sends a 12 kHz sound pulse to the seafloor every second. That pulse is received on the ship, as is the pulse that gets bounced off the seafloor. In the lab, a recorder measures the difference between the two acoustic returns from the pinger to give us the altitude of the pinger off the seafloor. This helps us determine if the dredge is really on the bottom collecting rocks.

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