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)
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
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
developed their underwater
sound detection technology and
they began to call it SONAR
coined as equivalent to RADAR
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
And by knowing the speed of sound wave in
water the distance can be easily calculated
Distance = speed x time
Sonar systems are of two
It operates in three modes:
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
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
The functional components are described
(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
(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
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
(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
Passive sonar listens without
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
Hydrophone array :these are the
sensitive elements which detect the
acoustic energy emitted from
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
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.
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-
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
The main uses of Sonar is as ahead:
It is used to find the actual depth of
Sonar systems are used to find lost
ships and submarines.
These are used in ocean surveillance
They are used by navy to detect the
locations of enemy submarines.
It has an adverse effects on marine
animals like dolphins and whales
,that also use sound waves for their
It leads whales to painful and often
fatal decompression sickness.
The sonar systems generate lot of
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