Physics: Principles and Problems


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For use with Chapter 15

Navy SEALS and Dolphins
Posted December 10, 1998

Sonar is an essential tool of the sea. Boats and submarines use it to map the contours of the ocean floor and to detect dangerous objects in their paths. In fact, submarines can rely solely on sonar, sent out in small bursts called "pings," to navigate their way under the surface.

During wars and other military conflicts, navies around the world place mines in the ocean to protect their waters. The mines are designed to be hard to detect with sonar, and sometimes they are not found until it is too late. Sometimes mines are left in the water and forgotten about after a conflict is over. This can be very dangerous for passing ships.

The U.S. Navy has been searching for better and better ways to detect sea mines. It appears that sometimes the best tools in this high-tech search are the animals in the ocean. The use of animals to detect explosives is nothing new. It has been done on land for many years. For example, dogs have a sense of smell over 200 times more sensitive than humans, because of this keen sense of smell they are used to sniff out land mines left after conflicts on land.

The Navy has a program to detect sea mines by taking advantage of the sonar used by dolphins. Dolphins and whales emit clicks and whistles in the range of 1.5 to 11 kHz and use the echoes to locate food and navigate through the ocean. This process, called echolocation, can locate a fish 100 meters away. It is so sensitive that a dolphin can tell the difference between a swimmer that is pregnant and one that is not, simply by the nature of the echo.

In the Navy's mine detection program, trained dolphins use echolocation to detect mines floating in the water. They swim up to the mine and attach a device to it to neutralize the explosive. Then ships can pass by without being harmed.

Other animals that use echolocation have been tested by the Navy in hopes of finding the best way to detect sea mines. A study by the National Academy of Science, published in October, found that the sonar used by bats is better than any type of sonar the Navy uses today. Bats' ability to distinguish sonar sounds is almost six times better than the best Navy electronic sonar.

Use the Internet to conduct research on dolphins and other marine mammals. How do these creatures use echolocation in their daily lives?



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