GC: n
CT: Sonar is an acronym (like radar, now spelled with all lower-case letters) for sound navigation and ranging. The principle involves bouncing acoustic waves off of objects, and determining their distances by measuring the time for the echoes to return. Sonar is commonly used on board ships and boats to measure the depths of bodies of water. It can also be used to locate underwater objects such as fish, submarines, and the shipwrecks of Spanish galleons.
S: SMB – https://bit.ly/2UQkRHO (last access: 17 December 2018)
N: 1. “Apparatus for detection underwater”, 1946, from first letters of sound navigation and ranging, on pattern of radar.
2. A method or device for detecting and locating objects especially underwater by means of sound waves sent out to be reflected by the objects.
3. The principle of functioning is simple. A sonar consists of a transmitter, transducer, receiver, and display. An electrical impulse from a transmitter (such as a very short burst of electrical energy generated by an electronic “power pack”) is converted into a sound wave (which is also a very short burst of high frequency sound energy) by the transducer and sent into the water. When this wave strikes an object, it rebounds. This echo strikes the transducer, which converts it back into an electric signal, which is amplified by the receiver and sent to the display. The time variation is displayed on the read out of the sonar screen device by means of flashing lights, Liquid Crystal Display (LCD) or Cathode Ray Tube (CRT or TV screen). Since the speed of sound in water is constant (approximately 1440 metres per second), the time lapse between the transmitted signal and the received echo can be measured and the distance to the object determined.
4. Sonar systems may be divided into three categories. In active sonar systems an acoustic projector generates a sound wave that spreads outward and is reflected back by a target object. A receiver picks up and analyzes the reflected signal and may determine the range, bearing, and relative motion of the target. Passive systems consist simply of receiving sensors that pick up the noise produced by the target (such as a ship, submarine, or torpedo). Waveforms thus detected may be analyzed for identifying characteristics as well as direction and distance. The third category of sonar devices is acoustic communication systems, which require a projector and receiver at both ends of the acoustic path.
5. It is important not to confuse sonar and radar, although both are remote sensing systems with important military, scientific and commercial applications. They rely on two fundamentally different types of wave transmission. Radar sends out electromagnetic waves, while active sonar transmits acoustic (i.e., sound) waves. In both systems, these waves return echoes from certain features or targets that allow the determination of important properties and attributes of the target (i.e., shape, size, speed, distance, etc.). Because electromagnetic waves are strongly attenuated (diminished) in water, radar signals are mostly used for ground or atmospheric observations. Because SONAR signals easily penetrate water, they are ideal for navigation and measurement under water.
S: 1. Etymonline – https://bit.ly/2R0w3SW (last access: 17 December 2018). 2. MW – https://bit.ly/2LmKQCq (last access: 17 December 2018). 3. ScienceABC – https://bit.ly/2BrnDKN (last access: 17 December 2018). 4. EncBrit – https://bit.ly/2DJYz0x (last access: 17 December 2018). 5. ENCY – https://bit.ly/2PNj9Dq (last access: 17 December 2018).
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