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Here is an essay on ‘Sonar’ for class 8, 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Sonar’ especially written for school and college students.
Essay on Sonar
Essay Contents:
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- Essay on the Definition of Sonar
- Essay on the Types of Sonar
- Essay on the Range Estimated for Sonar
- Essay on the Bearing estimation in Sonar
- Essay on Imaging Sonar
- Essay on the Application of Sonar
- Essay on the Working of Sonar
- Essay on the Factors Affecting Sonar Performance
Essay # 1. Definition of Sonar:
Sonar is a technology that was designed and developed as a means of tracking enemy submarines during World War II. Although this was the main aim at that period of time this technology has taken a different shape in today’s world. Sonar, the short form for sound navigation and ranging, is helpful for exploring and mapping the ocean because sound waves travel farther in the water than radar and light waves.
We use modern sonar systems for many purposes such as detection, identification and location of submarines, in acoustic homing torpedoes, in acoustic explosive mines and in mine detection, in finding schools of fish, in depth sounding applications, to map the seabed, for navigation purposes and in locating submerged wrecks and also for echo detection to maximize the range at which submarines can be detected and tracked and for many other applications.
The idea of using sound to determine the depth of a lake or ocean was first proposed in the early nineteenth century. Interest in this technique, called underwater ranging, was renewed in 1912 when the luxury sailing vessel Titanic collided with an iceberg and sank.
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Two years later, during World War I (1914-18), a single German submarine sank three British cruisers carrying more than 1,200 men. In response, the British government funded a massive effort to create an underwater detection system.
The entire operation was conducted in complete secrecy, but the first working model was not ready until after the war ended. The project operated under the code name “asdic” (which stood for Allied Submarine Detection Investigating Committee). The device kept that name until the late 1950s, when the American term “sonar” was adopted.
Essay # 2. Types of Sonar:
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i. Active Sonar:
Mode of echo location by sending a signal and detecting the returning echo.
ii. Passive Sonar:
Sensitive listening-only mode to detect the presence of objects making noise.
iii. Ultrasound:
Acoustic vibrations with frequencies higher than the human threshold of hearing.
Most moving objects underwater make some kind of noise. Marine life, cavitation (small collapsing air pockets caused by propellers), hull popping of submarines changing depth, and engine vibration are all forms of underwater noise. In passive sonar ranging, no pulse signal is sent. Instead, the searcher listens for the characteristic sound of another boat or submarine.
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By doing so, the searcher can identify the target without revealing his own location. This method is most often used during wartime. However, since a submarine is usually completely submerged, it must use active sonar at times, generally to navigate past obstacles. In doing so, the submarine risks alerting others of its presence.
In such cases, the use of sonar has become a sophisticated military tactical exercise. Sonar devices have become standard equipment for most commercial and many recreational ships. Fishing boats use active sonar to locate schools of fish. Other applications of sonar include searching for shipwrecks, probing harbors where visibility is poor, mapping the ocean floor, and helping submerged vessels navigate under the Arctic Ocean ice sheets.
Essay # 3. Range Estimated for Sonar:
Range defined as the radial distance between the sonar and the reflector, can be estimated as follows:
i. A short pulse of duration Tp is transmitted in the direction of the reflector.
ii. The receiver records the signal until the echo from the reflector has arrived
iii. The time delay τ is estimated from this time series
The range to the target is then given as:
The sound velocity c has to be known to be able to map delay into space.
The accuracy of which the range is estimated is related to the pulse length Tp for traditional pings
This is equivalent to the range resolution defined as the minimum spacing two echoes can be separated and still detected A shorter pulse gives better range resolution. Shorter pulses has less energy in the pulse, which again gives shorter propagation range.
Essay # 4. Bearing Estimation in Sonar:
There are two key elements involved in the estimation of direction (or bearing) in sonar:
1. The electro-acoustic transducer and its size
2. The grouping of transducers into arrays
A transducer (or antenna or loudspeaker) is directive if the size of the antenna is large compared to the wavelength. The directivity pattern generally contains a main lobe, with a beam width
where D is the diameter (or length) of the antenna. This is shown in
For multiple antennas in the receiver array, multiple beams (or directions) can be calculated simultaneously
Essay # 5. Imaging Sonar:
The principle of imaging sonar is to estimate the reflectivity for all calculated ranges and in all selected directions. This is illustrated in the given fig below. The yield of view is given by the angular width of each element. The angular (or azimuth) resolution is given by the array length measured in wavelengths. The range resolution is given by the bandwidth of the system.
i. Signal Model:
The basic signal model for an active sonar contains three main components:
1. The signal which has propagated from the transmitter, through the medium to the rejecter, is back scattered, and then propagated back to the receiver. The backscattered signal contains the information about the target (or reflector) of interest. It depends on the physical structure of the target and its dimensions, as well as the angle of arrival and acoustic frequency.
2. Reverberation is unwanted echoes and paths of the transmitted signal. This is typically caused by surface and bottom scattering, and/or volume scattering.
3. Additive noise is acoustic signals from other sources than the sonar itself. The sonar equation is an equation for energy conservation for evaluation of the sonar system performance.
In its simplest form, the equation states the following:
Signal – Noise + Gain > Threshold
where Threshold is the value for which the signal after improvement (gain) is above the noise level detailed version for active sonar is:
SL – 2TL + TS – NL + DI + PG > RT
where SL is source level, T L is transmission loss, T S is target strength, NL is noise level, DI is directivity index, P G is processing gain, and RT is reception threshold. Note that the sonar equation describes logarithmic intensity in dB. Fig shows the received time series (orange profile) for a single ping of data with a target of interest.
ii. Signal Processing:
Active sonar signal processing can be divided into a number of different stages.
With reference to the given Fig. these are:
I. Preprocessing:
Filtering and applying time variable gain (TVG).
II. Pulse Compression:
Matched filtering in range (convert the time spread coded pulses to “delta”-functions).
III. Beam Forming:
Direction estimation (or matched filtering in azimuth). This is to convert element data in an array into directional beams (array signal processing).
IV. Detection:
Detection of potential targets (i.e., a fish, a submarine).
V. Parameter Estimation:
Estimation of position and velocity of the detected object.
VI. Classification:
Target recognition, pattern recognition.
Essay # 6. Applications of Sonar:
There are many applications but out of those here three applications of active sonar are mentioned:
1. Fish finding
2. Imaging of the seafloor
3. Mapping of the seafloor.
There are also other areas where sonar is widespread used, such as in military applications (i.e., finding submarines) and underwater navigation.
Essay # 7. Working of Sonar:
The word “sonar” is an abbreviation for “Sound, Navigation, and Ranging.” This is a technology that was developed as a means of tracking enemy submarines during World War II. A sonar consists of a transmitter, transducer, receiver, and display.
In the simplest terms, 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 meters per second), the time lapse between the transmitted signal and the received echo can be measured and the distance to the object determined.
Essay # 8. Factors Affecting Sonar Performance:
There are four factors to a good sonar unit:
I. High power transmitter
II. Efficient transducer
III. Sensitive receiver
IV. High resolution/contrast display
i. High Power Transmitter:
This enables the user to get a return echo under deep or poor water conditions and also lets the user to see a fine detail, such as baitfish and structures.
ii. Efficient Transducer:
This is a device that converts the electronic energy from the transmitter to high frequency sound, which is sent down through the water. When it strikes an object it bounces back as shown in the above illustration, (i.e., it echoes). When these echoes reach the transducer it converts them into electric signals once again, which are then amplified by the receiver and passed onto the display.
Therefore this unit is quite often referred to as the “antenna” of the sonar unit. The transducer should not only be able to withstand the high transmitter power impulses, converting as much of the impulses into sound energy as possible, but it also has to convert them with little loss in signal strength and has to be able to detect the smallest of echoes returning from deep water or tiny bait fish.
There are two basic types of transducers:
1. Magnetostrictive Transducers:
These are used with the higher powered, low frequency units. The advantage of this type is that they can take almost unlimited power and may be overloaded without damage
2. Ceramic Transducers:
These have the advantage of having a higher efficiency factor than the magnetostrictive types. With ceramic transducers, the lower the frequency the higher the cost and also if too much power is applied it can be damaged.
Some of the more common frequencies used are 38, 40, 50, 75, 107, 120, 150, 192, 200, 400 and 455kHz. It should be noted that transducer must match the sonar unit’s frequency. In other words, a 50 kHz transducer or even a 200 kHz transducer cannot be used on a sonar unit designed for 192 kHz.
iii. Sensitive Receiver:
This has an extremely wide range of signals it has to deal with. It should dampen the extremely high transmit signal and amplify the small signals returning from the transducer. During amplification the strength of the signals is increase to the point that they can be used to light a neon bulb, Light Emitting Diode, or to activate a pixel on an LCD.
The location of the flashes on a dial or the location of the pixels on the display can then be used to indicate the range, or distance, from the transducer to the object (bottom) or objects (fish) which have bounced back the echoes. It also has to separate targets that are close together into distinct and separate impulses for the display. This process repeats itself many times per second.
iv. High Resolution/Contrast Display:
This must have high resolution (vertical pixels) and good contrast to be able to show all of the detail sharply and clearly. This allows fish arches and fine details to be shown. All these facets together are called “Total System Performance”. All of the parts of this system must be designed to work together, under any weather condition and extreme temperatures.
Present day uses of sonar:
1. The military uses a large number of sonar systems to detect, identify and locate submarines
2. In acoustic homing torpedoes, in acoustic explosive mines and in mine detection
3. In finding schools of fish
4. For depth sounding applications
5. Mapping of the seabed.
6. Navigation purposes
7. Acoustic locating of submerged wrecks
8. Special sonar systems are used for sound and echo detection to maximize the range at which submarines can be detected and tracked
9. Dam Inspection
10. Marine Archaeology
11. Bridge Footing and Abutments Inspection
12. Location of the sunken logs from lumber operations
13. Oil pipe line location and inspection
14. Reef monitoring
Despite all these uses, there are several disadvantages in using sonar systems too.