The ocean floor ( for Dr. Coakley) |
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The ocean floor ( for Dr. Coakley) |
Anthony G. |
May 25 2005, 03:37 PM
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#1
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Unregistered |
How exactly does multi-beam sonar work? What is used to send and recieve info that is used to map the ocean floor, and what is your most memorable ocean floor mapping?
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Bernie_Coakley |
May 25 2005, 10:12 PM
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#2
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TREC Researcher Group: TREC Team Posts: 19 Joined: 25-May 05 Member No.: 18 |
QUOTE(Anthony G. @ May 25 2005, 03:37 PM) How exactly does multi-beam sonar work? What is used to send and recieve info that is used to map the ocean floor, and what is your most memorable ocean floor mapping? Anthony It might be better if you started by thinking about a single-beam, which just measures the depth of water directly under the hull. A transducer is a physical device that can transmit or receive sound in the water. For a single beam bottom sounder, there are one or a few transducers on the bottom of the hull. You transmit a sound (or a "ping") in the water and wait to hear the return echo. The time from transmission to the echo return is the amount of time the sound took to travel from the hull to the seafloor and back. If you know what the velocity of sound is in water (it can vary a lot due to changes in temperature and salinity), you can then estimate the depth of water under the ship. Most ships make these measurement continuously while moving, collecting a profile of the ocean's depth along track. For a multi-beam, you have a bunch of transducers, an array. By being clever about how you transmit the sound (driving the different transducers in different ways) and about how you receive it (summing the different transducers) you can focus the transmitted energy so that instead of radiating like ripples on a pond, it is more like a flashlight, a focused beam illuminating the seafloor. The most memorable mapping I ever did was in the Mississippi River, near New Orleans, where I was living at the time. We found all sorts of interesting things, old shipwrecks, fractures, erosional features. It surprised me because you never think of it as being so variable. I hope this answers your questions. Bernie |
Ute_Kaden |
May 26 2005, 12:56 AM
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#3
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TREC Teacher Group: TREC Team Posts: 203 Joined: 27-April 05 Member No.: 10 |
Anthony,
We used this method in small scale when we did the lab " Graph Matching" with the Vernier LabPro motion detector. Our motion detector uses ultrasound to measure distance. Ultrasound is a sound frequency higher than we humans can hear, more than 20 000Hz. Ultrasonic pulses are emitted by the motion detector, reflected from the target, and than detected by the device. The time it takes for the reflected pulses to return is used to calculate position, velocity and acceleration. For TM students- ultrasonography uses 1 to 5 MHz sound pulses and the same scientific principal for mapping fluid, soft tissue and bones. |
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