SONAR is the acronym for Sound Navigation and Ranging. The knowledge and understanding of underwater sound were discovered by Leonardo Da Vinci in 1490. 

The first active sonar designed in the same way was invented and developed as a direct consequence of the loss of Titanic in 1912. Where the basic requirement was to detect icebergs in 2 miles of distance. Underwater sound is used both by whales and dolphins for communication and echolocation. 

Reginald Fessenden was the inventor of SONAR. This is a method for detecting, locating and determining the speed of objects through the use of reflected sounds. This is a system transmitted along with reflected underwater sound waves for detecting and locating submerged objects. Some animals use sound as a medium of communication and object detection for years. Technologies have got the idea to make this device for detecting and locating objects underwater. 

History and Background

Though SONAR was invented with the purpose of detecting icebergs for the very first time, during World War 1, detecting submarines became a very important thing to look upon. The main idea of inventing such a device over many more things in common though such as,

• Safe diving purpose
• To detect submarines during a war
• Commercial Fishing
• To detect depth
• As a communicating system within the sea surface

Types of SONAR

SONAR is of two types. 

1. Active sonar 
2. Passive sonar

• Active SONAR: It is made of a sound transmitter as well as a receiver. And there are three modes of operation.
  • Monostatic mode: when transmitter and the receiver are at the same point
  • Bistatic mode: when the transmitter and the receiver are separated by some distance 
  • Multistate mode: when more than one transmitter is used and they are at some basic distance 

Most SONARs are incorporated mono statically in the same way and often get used for transmission as well as reception. Active sonar develops a pulse of sound which is called a “ping” as well as then listens for reflection associated with the pulse. This pulse of sound is fundamentally created electronically by the usage of a projector which consists of a single generator, power amplifier as well as an electro acoustic transducer. For measuring the distance of a specific object the stipulated time for the transmission of a pulse in reception is measured along with the conversion into a range by knowledge of the speed of sound. In order to measure the bearings different hydrophones are used. 

Functional Components

• Transmitter which creates outgoing pulse
• Transducer array improves the directivity index
• Beamforming processor create different beams
• Duplexer switch which connects transmitter and receiver 
• Synchroniser provides coordination 
• Receiver collects the received energy 
• Display puts all the detected information into a visual format 
• A-scan is the signal for a portion of the listening cycle
• Plan position indicator represents the intensity on the display

• Passive SONAR: It is a decision which listens without transmitting. This has a wide variety of techniques to identify the source of detected sounds. Passive solar system has a large sonic database but the operator classifies signals by the use of computers and uses these databases for identifying classes of ships as well as action

Functional Components:

The functional components of passive solar system are 

• Hydrophone array to detect the acoustic energy emitted from the target
• The cylindrical array of operators at a fixed vertical angle which is usually downward.  Used for bottom bound detection
• Beamforming processor which applies a unique set of time shifts to the signal to create a particular beam
• Frequency analyzer which breaks the signal into separate frequencies

Application of SONAR System

• It is used to find the actual depth of sea
• Sonar system is used to find lost ships and submarines 
• This has very usefulness in ocean surveillance systems
• They are also used by the navy to detect locations of enemy submarines 
• Used for underwater security 
• Used in fishing etc

Limitations:

The sonar system has an adverse effect on marine animals like dolphins and whales. 

This leads whales into painful and fatal decompression sickness.

A lot of noise generated by sonar systems is harmful for the ecosystem.

Sonar systems with high intensity may cause a temporary shift in hearing threshold of some fishes. 

Conclusion

SONAR is a method of detecting, locating and determining the speed of objects through the use of reflected sound waves. The acoustic frequencies used in SONAR systems vary from very low (infrasonic) to extremely high (ultrasonic). Sound waves are reflected by the underwater object which is received at the receiver. The time taken by the sound wave to come back is recorded. This device or method is very helpful to detect sound and to locate objects underwater by the wavelength measurement. This system has a wide use in commercial fishing, for the safe diving purpose, to detect submarines during war etc.