Sonar work or sound navigation and ranging is an umbrella term for technology and methods that use sound to detect objects, usually underwater, much the same way bats rely on sound for catching food in the air. The basic principles on which sonar relies are that sound moves at a steady rate through a given medium, such as air or water, and that certain types of objects produce certain types of sounds. With this knowledge, calculations can determine the distance to an object and identify it with reasonable certainty. The Navy mainly uses sonar to detect vessels, torpedoes and mines. Commercial applications for sonar include navigation, mapping and locating fish.
Negative Effects of Sonar - One major criticism of active sonar is its effect on marine mammals, such as dolphins and whales, who also use natural sonar for their navigation. Testing of very low frequency active sonar by the U.S. Navy, because it causes damage to an animal's ability to detect sound, has been implicated in the beaching of whales. In other cases, it has been suggested that Navy sonar tests have caused whales to surface too quickly, inducing painful and often fatal decompression sickness. The U.S. Navy accepted responsibility for the deaths of seven beached whales in the Bahamas in 2000 that were found with acoustically induced hemorrhages around the ears and eyes after a test of low-frequency sonar in the area.