SOUND NAVIGATION AND RANGING

[SONAR]

Shudhanshu AgarwalB.tech (EC-2011)

Roll no.-1101421102

INTRODUCTION: SONAR is originally an acronym for Sound

Navigation and Ranging. It is a technique that uses sound

propagation to navigate and detect the objects located under the surface of water

The term SONAR is also used for device that generates and receives sound.

The acoustic frequencies vary from very low(infrasonic) to extremely high(ultrasonic) frequencies.

HISTORY: For millions of years , its use by

humans was initially recorded by Leonardo da Vinci in 1490.

In 19th century, it was used as an ancillary to provide warning of hazards.

Sonar was first patented by Lewis Richardson and German physicist Alexander Behm in 1913.

During world war I the need to detect submarines prompted more research into this technology.

During1930,american engineers developed their underwater sound detection technology and they began to call it SONAR coined as equivalent to RADAR

SONAR TECHNOLOGY: Sonar is a device that is used to detect

underwater objects using sound waves. In this system a sound pulse is generated

and sent underwater through a transmitter. sound waves are reflected by the underwater

object which are received at receiver. The time taken by sound wave to come back

is recorded. And by knowing the speed of sound wave in

water the distance can be easily calculated by formula.

Distance = speed x time

TYPES OF SONAR: Sonar systems are of two types:

Active Sonar

Passive sonar

ACTIVE SONAR: It operates in three modes:

Monocratic mode

Biostatic mode

Multistate mode

Most sonars are used in monostatic mode with same array often being used for transmission and reception.

Active sonar creates a pulse of sound often called as ping and then listens for echo of the pulse.

This sound is generated by sonar projector consisting of signal generator , power amplifier, electro-acoustic array.

To measure the distance of object the time from transmission of pulse to reception of pulse is measured and converted into range by knowing the sped of sound

BLOCK DIAGRAM OF ACTIVE SONAR:

The functional components are described below:

(a) Transmitter: The transmitter generates the outgoing pulse. It determines pulse width, modulation and carrier frequency.

(b)Transducer array: The individual transducers are simple elements with little or no directionality. They are arranged in an array to improve the directivity index.

The array is configured to reduce the beamwidth in vertical direction.

Vertical beamwidth of transducer array.

(c) Beamforming processors: The input/output of each transducer is put through a beamforming processor, which applies time delays or phase shifts .

Active beamforming

(e) Duplexer. The duplexer performs the same function in an active sonar as in an radar system, namely to protect the receiver from full transmitter power while the pulse is going out.

Synchronizer: perform same function as the synchronizers in radar. Provides overall coordination and timing for system reset the display for each new pulse.

Receiver. Collects the received energy the receiver compares the power level of noise with a threshold SNR (DT) .If the DT is set too low there will be many false alarms. If it is too high, some detection capability will be lost.

(h) Display: Puts all the detection information into a visual format.

PPI(plan position indicator):The sonar system must sequentially search individual beams which are displayed in their true or relative form.

The ppi display

PASSIVE SONAR: Passive sonar listens without

transmitting It has a wide variety of techniques

to identify the source of sound. It can help in findinf nationality as

most european submarines use 50hz power systems and U.S. vessels operates at 60hz a.c power systems.

Passive sonar less used due to noise generated by them

BLOCK DIAGRAM OF PASSIVE SONAR:

Hydrophone array :these are the sensitive elements which detect the acoustic energy emitted from target.

Beamforming processor: the passive system must listen to all angles at all times. This requires very wide beamwidth.at the same time, a narrow beamwidth is required .These two objectives are achieved simultaneously by the passive beamforming processor.

Beamforming processors

Broadband display: The output of the beamforming processor is displayed as a bearing time history(BTH).The beamwidth of the system determines how accurately the bearing can be measured by such a

A typical BTH display

Frequency analyzer: the frequency analyzer breaks the signal into separate frequencies. The frequencies are divided into small bands known as frequency bins. Whose width the analysis bandwidth.

Frequency analysis graph

Sound propagation:

Sonar operation is affected by variations in sound speed .The speed is determined by:

Speed = 4388 + (11.25 × temperature (in °F)) + (0.0182 × depth (in feet)) + salinity (in parts-per-thousand).

Scattering:

When active sonar is used, scattering occurs from small objects in the sea as well as from the bottom and surface. This can be a major source of interference.

USES AND APPLICATIONS: The main uses of Sonar is as ahead:

It is used to find the actual depth of the sea.

Sonar systems are used to find lost ships and submarines.

These are used in ocean surveillance systems.

They are used by navy to detect the locations of enemy submarines.

LIMITATIONS TO SONAR: It has an adverse effects on

marine animals like dolphins and whales ,that also use sound waves for their navigation.

It leads whales to painful and often fatal decompression sickness.

The sonar systems generate lot of noise

Th@nk

you