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sonar

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sonar

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sonar

  1. 1. SONAR Presented by: Mike Puato & Neil Corpuz
  2. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 15. How does SONAR work
  16. 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. 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. 18. Sonar Noise
  19. 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. 20.  Any listening system that consist of (1) a hydrophone (2) an electronic receiver (3) a bearing indicator (4) a speaker or headphones.
  21. 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. 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.
  23. 23. 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
  24. 24. Sea floor off of L.A. A mosaic map
  25. 25. 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.
  26. 26. 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.
  27. 27. 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.
  28. 28. 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.
  29. 29. Multi-beam Sonar Systems

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