By: Lisa Runt

What is Sonar? A technique that uses sound to navigate, communicate with or detect other vessels. These sonar waves are very high in frequency and are called ultrasonic. Ultrasound waves have frequencies above 20 kHz. Few animals can hear ultrasonic waves. Some of the animals that can hear them are dogs, cats, porpoises, rodents, whales, dolphins, seals, sea lions and bats.

Who uses Sonar? People and marine animals use sound in the sea to accomplish many tasks. Since light travels relatively short distances in the ocean, sound is often used by animals for such basic activities as finding food or a mate, navigating, and communicating. A number of animals use sonar. Among them are whales, dolphins, bats, shrew, and some birds.

Passive Acoustics In a very general sense, there are two ways that sound is used: passively and actively. In passive acoustics, the organism makes no sound of their own, but listens to sounds that are being made by others. The oceans, and particularly coastal environments, are very noisy places. By listening to the sounds, much can be learned about the environment.

Active Acoustics The second way to use sound is called active acoustics. In this case, sound is created by a source and then received by a receiver. Other active acoustic systems have the source and receiver located at the same place. In this case, sound goes out from the source, bounces off an object, and returns to the receiver. The sound returning to the receiver is called backscatter. By analyzing the sound received (the return echo), much information can be learned about the object, such as its distance, size, and composition.

How Dolphins use Echolocation The dolphin’s echolocation process goes like this: 1)The dolphin uses nasal passages to make a click and sends it through its forehead, which focuses the sounds together into a beam before sending it into the water. 2)When the sound hits as object in the water, it bounces back to the dolphin as an echo. 3)The dolphin absorbs this returning echo through its jaw. 4)A passage of fat from the jaw conducts the sound to the dolphin’s inner ear, which exchanges nerve impulses with its brain to interpret the object’s characteristics, such as size, shape and material.

Bats and Sonar Bats rely heavily on ultrasonic waves for echolocation. They use echolocation to navigate while flying and to track down prey. They send out ultrasonic waves with very high frequencies. When the waves return to them they are able to map out the location they are in. A bat’s sonar is so advanced that it allows them to fly in complete darkness, swoop down and snatch insects without warning and hover right above water levels to get a drink.

Frequency Ranges AnimalFrequency (hertz) LowHigh Humans2020,000 Cats10032,000 Dogs4046,000 Horses3140,000 Elephants1612,000 Cattle1640,000 Bats1,000150,000 Grasshoppers and locusts 10050,000 Rodents1,000100,000 Whales and dolphins 70150,000 Seals and sea lions20055,000