sonar

1. SONAR
Presented by: Mike Puato & Neil Corpuz

2. Abstract
 Sonar is a modern technology which helps us to
track submarines, fish, ship wrecks, map the seabed
and for other navigational purposes.The four main
factors that affect the performance of a sonar
system are a high power transmitter, an efficient
transducer, a sensitive receiver and an acoustic
communication system.Although the present day
sonar systems have only a limited number of
features such as a 2-dimensional screen and a view
of less than 360 degrees of the surrounding, we are
most likely to see better sonar systems with a 3-
dimensional screen, attached to new computer
systems along with a 360 degree view of the
surrounding in the near future.

3. What is SONAR?
SOund Navigation and Ranging
A sensor that is used to detect objects
through the use of high or low
frequency sound waves.

4. HISTORY
 Although some animals (dolphins and bats) have used
sound for communication and object detection for
millions of years, use by humans in the water is initially
recorded by Leonardo Da Vinci in 1490: a tube inserted
into the water was said to be used to detect vessels by
placing an ear to the tube.
 In the 19th century an underwater bell was used as an
ancillary to lighthouses to provide warning of hazards.
 The use of sound to 'echo locate' underwater in the same
way as bats use sound for aerial navigation seems to have
been prompted by the Titanic disaster of 1912. The world's
first patent for an underwater echo ranging device was
filed at the British Patent Office by English meteorologist
Lewis Richardson a month after the sinking of the Titanic,
and a German physicist Alexander Behm obtained a
patent for an echo sounder in 1913.

5.  The Canadian engineer Reginald Fessenden, while
working for the Submarine Signal Company in
Boston, built an experimental system beginning in
1912, a system later tested in Boston Harbor, and
finally in 1914 from the U.S. Revenue (now Coast
Guard) Cutter Miami on the Grand Banks off
Newfoundland Canada. In that test, Fessenden
demonstrated depth sounding, underwater
communications (Morse Code) and echo ranging
(detecting an iceberg at two miles (3 km) range). The
so-called Fessenden oscillator, at ca. 500 Hz
frequency, was unable to determine the bearing of
the berg due to the 3 meter wavelength and the small
dimension of the transducer's radiating face (less than
1 meter in diameter). The ten Montreal-built British H
class submarines launched in 1915 were equipped
with a Fessenden oscillator.

6.  ASDIC
In 1916, under the British Board of Invention and Research,
Canadian physicist Robert William Boyle took on the active
sound detection project with A B Wood, producing a
prototype for testing in mid 1917. This work, for the Anti-
Submarine Division of the British Naval Staff, was
undertaken in utmost secrecy, and used quartz
piezoelectric crystals to produce the world's first practical
underwater active sound detection apparatus. To maintain
secrecy no mention of sound experimentation or quartz
was made - the word used to describe the early work
('supersonics') was changed to 'ASD'ics, and the quartz
material to 'ASD'ivite: hence the British acronym ASDIC. In
1939, in response to a question from the Oxford English
Dictionary, the Admiralty made up the story that it stood
for 'Allied Submarine Detection Investigation Committee',
and this is still widely believed, though no committee
bearing this name has been found in the Admiralty
archives.

7. At the start of World War II, British ASDIC technology
was transferred for free to the United States.
Research on ASDIC and underwater sound was
expanded in the UK and in the US. Many new types
of military sound detection were developed. These
included sonobuoys, first developed by the British in
1944 under the codename High Tea, dipping/dunking
sonar and mine detection sonar. This work formed
the basis for post war developments related to
countering the nuclear submarine. Work on sonar
had also been carried out in the Axis countries,
notably in Germany, which included
countermeasures. At the end of World War II this
German work was assimilated by Britain and the US.
Sonars have continued to be developed by many
countries, including Russia, for both military and civil
uses. In recent years the major military development
has been the increasing interest in low frequency
active systems.

8.  During the 1930s American engineers developed their
own underwater sound detection technology and
important discoveries were made, such as
thermoclines, that would help future development.[8]
After technical information was exchanged between
the two countries during the Second World War,
Americans began to use the term SONAR for their
systems, coined as the equivalent of RADAR.

9. Frequency
192 kHz 50 kHz
Shallower depths
Narrow cone angle
Better definition and
target separation
Less noise
susceptibility
Deeper depths
Wide cone angle
Less definition and
target separation
More noise
susceptibility

10. Types of SONAR system
Active sonar systems
Generally an acoustic projector is used in
these systems to generate a sound wave that
spreads outwards, which is reflected back by
the target object.The projector may be
placed on a floating sonobuoy, attached to a
vessel’s hull, or suspended in the sea by a line
lowered from a helicopter.

11. Passive sonar systems
These are usually mounted on a ship’s hull,
deployed from a sonobuoy, towed behind a
ship or laid on the ocean floor to monitor
sound continuously. Passive sonar systems
consists of a receiver that pick up the noise
produced by an object such as ship or a
submarine.The sound waves are analysed to
identify the type of ship and to determine its
direction, speed and distance.

12. Acoustic communication systems
Acoustic communication systems require a
projector and a receiver at both ends of
the acoustic path.These systems enable
ships to communicate with submarines or
divers.
The same principle allows dolphins to
communicate among their own species.

13. Applications
 Submarine and mine detection
 Commercial fishing
 Diving safety
 Communication at sea
 Used to detect icebergs
 Water depth
 Locate sunken ships/or other historical objects
 Locate fish or track animals that are being
studied
 Mapping underwater features

14. Who else uses sonar
 Actually nobody but animals use echolocation
and that is actually where we learned the
technique
 Bats, whales, and dolphins are some of the best
known animals to use echolocation

15. How does SONAR work

16. Sound Properties
Sound travels (slower than EMR) at 4,800 fps or
1460 meters per second – we will use 1500
mps.
(in elastic mediums - air, water, or earth NOT
in a vacuum)
Sound waves are measured in hertz (Hz). The
human ear can detect frequencies ranging
from 20 Hz to 20,000 Hz.

17. Sonar Noise
 The sound-listening problem for the
operator consists primarily of learning
to distinguish between :
 (1) sounds emitted by another ship's machinery
through the hull and from the propeller
 (2) the multitude of other sounds that exist in the
ocean.

18. Sonar Noise

19. Sound wave sent outward: Animals – noises
made with their bodies, seismic – explosions
or impact plates, ultrasound – transducer
converts sound to electricity and back, ships
– “ping” or emit a burst of acoustic energy.
Sound waves returned: Animals – waves
sensed through ears (bats) or teeth and
bones (whales), seismic – waves sensed
through geo-phones, ships – waves sensed
by hydrophones or….

20.  Any listening system that consist of
(1) a hydrophone
(2) an electronic receiver
(3) a bearing indicator
(4) a speaker or headphones.

21. Theoretical equation
 d = s x (t/2)
Time – it takes half of the time to go
down and half to return
Speed – approximately 1500 m/s
through seawater at 13°c
Distance

22. Navigation and Ranging
Issues
 Depth is determined by dividing travel time of sound by 2
and then multiplying by 1500 mps
12 seconds travel time
12/2 = 6X1500 = 9000 meters deep
 The Doppler principle applicable to all wave motion was
developed by the Austrian physicist, Christian Doppler
(1803-1853).
 Frequency of sound appears to increase when an
observer moves toward a source and appears to decrease
when he moves away from it. Similarly, if the source is
moving toward the observer, the frequency is higher; if
the source is moving away from the observer, it is lower.

26. How a map is made
 A Sonar echo recorder is dragged behind a ship
and is called a towfish
 It sends out a ping … sound travels to the
bottom and is reflected back to the hydrophone
 An instrument on the ship collects and analyzes
the data
 These points of data are combined to create a
picture of the seafloor
 A ship must travel over the area that is being
studied multiple times this is called mowing the
grass

28. Sea floor off of L.A. A mosaic map

29. Types of Imaging Sonar
 Side-Scan Sonar Systems
 Used for mapping the sea
floor for nautical charts,
bathymetric maps, maritime
archeology, and surveys.
 The intensity of the acoustic
reflections from the seafloor
of this fan-shaped beam is
recorded in a series of cross-track
slices. When stitched together along the direction of
motion, these slices form an image of the sea bottom
within the swath (coverage width) of the beam.

30. Side-Scan Sonar Systems
 The sound frequencies used in side-scan sonar usually
range from 100 to 500 kHz; higher frequencies yield better
resolution but less range.
 Notice that the volcano casts a shadow to the left, and the slope
facing to the right is very bright. Smaller bumps also cast small
shadows making the topography look lumpy. Each image is 3 km
(1.8 miles) wide.

31. Single-beam Sonar Systems
 Single beam sonar data are collected along transect lines
and typically cannot provide continuous coverage of the
seafloor.The output resolution of the data are determined
by the footprint size, sampling interval, sampling speed, and
distance between transects.
 Used primarily for mapping channels and bathymetry for
hydrologic and engineering applications.

32. Multi-beam Sonar Systems
 Instead of just one transducer pointing down, “multibeam
bathymetry systems” have arrays of 12 kHz transducers,
sometimes up to 120 of them, arranged in a precise
geometric pattern on ships’ hulls.
 The swath of sound they send out covers a distance on either
side of the ship that is equal to about two times the water
depth.The sound bounces off the seafloor at different angles
and is received by the ship at slightly different times.
the signals are then processed by computers
on board the ship, converted into water depths, and
automatically plotted as a bathymetric map
with an accuracy of about 5 meters to less than
a meter with differential GPS.

33. Multi-beam Sonar Systems