UNDER WATER ACOUSTIC COMMUNICATION

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UNDER WATER ACOUSTIC COMMUNICATION

  1. 1. SEMINAR PRESENTATION ON UNDER WATER ACOUSTIC COMMUNICATION SUBMITTED BY JAISICA 05311503010 ICE 7th SEMESTER
  2. 2. INDEX Introduction Deficiencies of current U.W. Communications History About Basic Model Acoustic Modem Applications DART Robotic Crawler
  3. 3. INTRODUCTION Technique of sending and receiving message below water. Most commonly employed using hydrophones. Difficult due to factors like multi-path propagation, time variations of the channel, small available bandwidth and strong signal attenuation. Underwater communication uses acoustic waves instead of electromagnetic waves.
  4. 4. DEFICIENCY IN CURRENT COMMUNICATION Future ocean environment will be increasingly complicated. Radio waves propagate under water at extremely low frequencies (30Hz-300Hz) & require large antennae and high transmission power. Optical waves do not suffer much attenuation but are affected by scattering. Acoustic waves are the single best solution for communicating Under water.
  5. 5. HISTORY The science of underwater acoustics began in 1490, when Leonardo Da Vinci, stated "If you cause your ship to stop and place the head of a long tube in the water and place the outer extremity to your ear, you will hear ships at a great distance from you.“ In 1687 Isaac Newton wrote his Mathematical Principles of Natural Philosophy which included the first mathematical treatment of sound. In 1912 sinking of TITANIC and start of World War I, systems for detecting icebergs and U-boats were developed.
  6. 6. ABOUT Underwater Acoustics is the study of propagation of sound in water & interaction of mechanical waves that constitute with water & its boundaries. Typical frequencies associated with Underwater Acoustics are 10Hz to 1MHz The propagation of sound in the ocean at frequencies lower than 10 Hz is not possible. Frequencies above 1 MHz are rarely used because they are absorbed very quickly. Underwater Acoustics is also known as HYDROACOUSTICS.
  7. 7. BASIC ACOUSTIC COMMUNICATION MODEL
  8. 8. ACOUSTIC MODEM Is used to transmit data underwater, much as telephone modems are used to transmit data over phone lines. Converts digital data into special underwater sound signals. These signals are then received by a second acoustic modem and converted back into digital data. Can be used for underwater telemetry, ROV and AUV command and control, diver communications, underwater monitoring .
  9. 9. Underwater acoustic modems are relatively slow compared to telephone or cable modems on land.  this technology is important because it provides an accurate and efficient means to send and receive data underwater. Oceanographers use acoustics to control underwater instruments and acquire the data that they collect remotely. This technology can also be used to control small, unmanned submarines, called Autonomous Undersea Vehicles (AUV's), and get data back from them in real-time.
  10. 10. Autonomous vehicles working under the ice can be controlled and their data can be transmitted to a topside station using underwater acoustic links Autonomous Underwater Vehicle
  11. 11. ACOUSTIC LINKS ARE USED TO CONTROL UNDERWATER INSTRUMENTS AND ACQUIRE THE DATA REMOTELY
  12. 12. APPLICATIONS • Underwater data links can be combined with satellite data links to provide data in real-time from instruments on the seafloor to scientists ashore. • Can be used to provide early warnings of tsunamis generated by undersea earthquakes. • Pressure sensors that are deployed on the seafloor can detect tsunamis. • U.S. National Oceanic and Atmospheric Administration (NOAA) Deep-ocean Assessment and Reporting of Tsunamis (DART) program has installed bottom pressure sensors near regions with a history of tsunami generation, to measure waves as they spread.
  13. 13. UNDERWATER ACOUSTICS
  14. 14. DEEP OCEAN ASSESSMENT & REPORTING OF TSUNAMI
  15. 15. DEEP-OCEAN ASSESSMENT AND REPORTING OF TSUNAMIS (DART) • NOAA has created an expansive network of 39 DART buoy stations, with 32 located in the Pacific and 7 in the Atlantic Basin. • Pressure data are transmitted to a near-by surface buoy via an acoustic data link using underwater modems. • The data are then relayed to researchers on land in real-time via satellite. • Researchers can also request real-time data independent of the automatic detection system. The data are used to provide early warnings of a tsunami before it comes ashore.
  16. 16. CLOSE-UP OF A DART II SURFACE BUOY • An acoustic link transmits data from the bottom pressure sensor to the surface buoy. • Then satellite links relay the data to NOAA tsunami warning centres. • Real-time data about tsunamis is given to NOAA forecaster that could potentially impact coastal areas.
  17. 17. DETECTING UNDER WATER OBJECTS • A robot crawler carries a modem, a camera, and a digital signal-processing unit. • Traversing the seafloor, searches for an object. • When object found, sends an acoustic signal to a ship or shore based station • Can then be commanded to take a still frame photo, compress it and transfer the image to an acoustic signal that is sent back to the investigator
  18. 18. ROBOTIC CRAWLER • Can carry sensors into very shallow. water, or even into the surf zone. • Equipped with a camera and modem, can be controlled from substantial distances via acoustic communications.

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