Echolocation is the use of sound waves to locate objects and barriers. Sounds are emitted into air or water, where they bounce off any objects in their path and return echoes that reveal the location and size of the objects. Certain animal species have a sophisticated physiological system that enables them to interpret these echoes with great precision. Bats and dolphins are the best known members of the animal kingdom who use echolocation, but other animals, including humans, are also able to "see" by interpreting sound waves.
Most bats emit high-pitched sounds and then interpret the returned sound waves, or echoes, to help them navigate safely in the dark and locate their prey. Toothed dolphins and whales also use echolocation. When one of these animals transmits highly focused sound waves, the sound waves bounce off any objects in the animal's path and are returned to the whale or dolphin. These returned echoes are then transformed into nerve impulses that convey size, shape, and distance of the objects to the animal's brain, enabling it to avoid obstacles, even in the darkest locations, and to easily find preferred prey. In addition to bats, whales, and dolphins, shrews and a few cave-dwelling birds use echolocation, primarily to help them navigate safely in the dark.
Humans have been able to use echolocation in several ways. The U.S. Navy, which uses sound waves for underwater object location — especially for location of underwater mines, hazards, and enemy vessels — has studied marine mammals in an effort to improve its sound navigation and ranging (SONAR) technology. In addition, the Navy Marine Mammal Program has made direct use of animal echolocation abilities. The program has trained dolphins to serve as sentries and to use their echolocation skills to find underwater mines and mark them for safe removal.
Humans are capable of echolocation even without the use of technology. People lack the acute sense of hearing and the sophisticated biological echolocation system that echolocating animals have, but some blind people have learned to "see" obstacles and navigate around them quite efficiently by making palatal clicks. Listening carefully to the returning sound waves enables these people to identify the objects that are associated with specific sound wave patterns and determine the exact location of obstacles. Some blind people use echolocation so well that they can ride bicycles safely and confidently. Several echolocation training programs for the blind are already available.