What is SONAR?

Sonar stands for Sound Navigation and Ranging. It is the use of sound waves underwater to locate objects. SONAR has been around since whales and dolphins have swum in the oceans. Many marine animals use echo location to locate food. According to Dr. Urick (1967) the first known reference to SONAR was in 1490 by Leonardo da Vinci when he wrote "If you cause your ship to stop, and place the head of a long tube in the water and place the outer extremity to your ear, you will hear ships at a great distance from you" (p. 2).

SONAR is used in both military and non-military applications. Non-military applications include drilling applications, animal research, ocean current mapping and scientific research. Military applications include Anti-Submarine Warfare (ASW), Anti-Surface Warfare, Mine applications, and ship identification.

Sonar is comprised of two types of sonar; Passive and Active.

Passive sonar is the ability to just listen. Passive sonar used a hydrophone as a receiver and boat carrying the hydrophone just listens for noise in the ocean. There are various noises that can be heard, natural (seismic, ocean animals, and wave noise) or man made (ships, engine noise, drilling, or even low flying aircraft). Advantages of passive sonar are that the ships deploying passive sonar techniques may remain undetected and passive sonar ranges may be very far depending on ocean conditions.

Active sonar is the ability to transmit a signal and listen for the returns. Active sonar systems include fathometers (bottom sounders), fish finders, mine searching sonar, and main frame military sonar systems. Active sonar requires the boat to carry a transmitter (transducer or projector) and a receiver (hydrophone). Active sonar is very good when searching for objects that do not make noise, for example mines. Active sonar does give away the location of the boat going active. A submarine transmitting active sonar may be easily located by a ship using passive sonar.