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J. Perelman
"Entertaining physics". Book 1.
Chapter 10. Sound and hearing

THE ECHO FROM THE SEA BOTTOM

For a long time people did not learn from echo no good, have not yet invented was a way to measure its depth of seas and oceans. The invention is originated by chance. In 1912, sank with almost all the passengers of a huge ocean liner the Titanic - sank from accidental collision with a large ice floe. To prevent such catastrophes, tried in fog or at night to use the echo to detect the presence of ice barrier ahead of the vessel. The way to practice failed, but led to another thought: to measure the depth of the seas by sound reflections from the seabed. The idea was very successful.

In the picture you can see the setup diagram.


The scheme sonar

One the ship is placed in the hold, near the bottom, Chuck, generates ignition sharp sound. Sound waves rushing through the water column, reaching the bottom of the sea, reflected and running back, carrying the echo. It is captured sensitive instrument set, as the cartridge at the bottom of the ship. Accurate clocks to measure the time interval between the occurrence of the sound and the arrival of the echo. Knowing the speed of sound in water, it is easy to calculate the distance to the reflecting barrier, i.e., to determine the depth of the sea or ocean.

The sounder, as mentioned this installation, has made a real revolution in the practice of measuring the depths of the sea. Use globalname previous systems was only possible with a stationary vessel and demanded a lot of time. Lolling have to pull from the wheel on which it is wound, is quite slow (150 meters per minute); almost as slowly produced and reverse the rise. The measurement depth of 3 km in this way takes 3/4 hours. Using sonar same measurement can be made in a few seconds at full speed of the ship, while receiving the result, much more reliable and accurate. The error in these measurements does not exceed a quarter of a meter (which intervals are determined with an accuracy of up to 3000-th fraction of a second).

If accurate measurement of large depths is important for the science of Oceanography, the ability to quickly, reliably and accurately determine the depth in the shallow areas is significant in sailing, ensuring his safety: thanks to the sonar vessel can safely and quickly move closer to the shore.

Modern echo sounders are not normal sounds, and extremely intense “ultrasounds”, inaudible to the human ear, with a frequency of the order of several million vibrations per second. Such sounds are created by vibrations of the quartz plate (quartz), placed in a quick-variable electric field.

Entertaining physics J. Perelman

 




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