Sonar navigation (deriving from the hydrophone listening principal that is shared with whales and dolphins) is commercially used to navigate water craft, communicating with or detecting objects below or on the water’s surface. The detection of other vessels within a given vicinity is a typical example of use. There are 2 basic types that share the sonar name.
ACTIVE Sonar: emits pulses of sounds and listens back for echoes.
PASSIVE Sonar: listens for the sound made by surface vessels.
Sonar navigation can be used for acoustic location and measurement of echoes to locate ‘targets’ in the water. Acoustic location was also used for airborne detection well before the introduction of radar by the R.A.F. Sonar can still be used in open air for robot and machine navigation. SODAR is used for atmospheric weather study and also for the equipment used to generate and receive the sound. The scope of the acoustics used in sonar vary from extremely high to very low frequencies.
The study of underwater sound is better known as hydroacoustics. Underwater acoustics all use a form of hydrophone pick-up transducers or ultrasonic sensors to receive the signal.
How does sonar navigation work?
Sonar, in the simplest terms, makes use of an echo. When a machine or animal makes a noise, it produces a sound wave into a space around it. The soundwaves that are produced then bounce off nearby objects, resulting in some reflecting back to the object that created the noise. It is these reflected sound waves that can be heard just the same as when your own voice echoes back to you from a mountain.
Whales and dolphins share the same ability as a sonar machine – they use the reflected waves in order to locate distant objects and sense their shape and movement.
The potential range of low-frequency sonar is completely remarkable. Whales and dolphins are able to detect the difference between objects as small as a pearl from fifteen meters away. They prefer to use sonar more than their sight in finding food, members of their group, and navigational direction.
Low frequency sonar is also being put through exhaustive tests by the military. It has the ability to travel thousands of miles and could potentially cover three quarters of Earth’s oceans by broadcasting from only four way-points. The registered frequency that whales and the military are using is between 100 and 500 Hz. Whales typically output signals between 160 and 190 Db range, whereas naval tests have utilised signals up to 230db.