Underwater communication
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Underwater communication primarily uses acoustic waves to transmit messages, complicated by challenges like multi-path propagation and signal attenuation. Hydrophones, devices designed for underwater sound recording, play a vital role alongside acoustic modems that convert digital data into sound signals for remote data collection. Technologies such as sonar and autonomous underwater vehicles (AUVs) utilize these principles for various applications, including seismic event monitoring and underwater object detection.
Underwater communication
- 2. 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. 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.
- 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. PEOPLE WHO THOUGHT IT IS POSSIBLE "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.
- 8. THE MAIN INITIATIVE TO DEVELOP THE TECHNOLOGY
- 10. ACOUSTIC MODEM Converts digital data into special underwater sound signals. These signals are then received by a second acoustic modem and converted back into digital data.
- 11. 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.
- 12. HYDROPHONE • Hydrophones are designed to be used underwater for recording or listening to underwater sound. • Hydrophones are based on a piezoelectric transducer that generates electricity when subjected to a pressure change • Transducers can convert a sound signal into an electrical signal since sound is a pressure wave. • From late in World War I until the introduction of active sonar, hydrophones were the sole method for submarines to detect targets while submerged
- 13. PIEZOELECTRIC TRANSDUCER • Piezoelectricity means electricity resulting from pressure. • It is a device that transforms one type of energy to another by taking advantage of the piezoelectric properties of certain crystals or other materials. • Piezoelectric material is subjected to stress or force, it generates an electrical potential or voltage proportional to the magnitude of the force. • This type of transducer ideal as a converter of mechanical energy or force into electric potential. A piezoelectric disk generates a voltage when deformed
- 14. DIRECTIONAL HYDROPHONESFocused Transducers • Uses a single transducer element with a dish or conical-shaped sound reflector to focus the signals • Can be produced from a low-cost omnidirectional type • Must be used while stationary, as the reflector impedes its movement through water Array of Hydrophones • Multiple hydrophones can be arranged in an array • It will add the signals from the desired direction while subtracting signals from other directions. • Hydrophones are arranged in a "line array“, but may be in two- or three-dimensional arrangements
- 15. Array of Hydrophones Sound is transmitted by the ship and reflected off the submerged submarine. The reflected sound reaches hydrophone A first, then hydrophone B, and finally hydrophone C. The time-of-arrival-difference between the hydrophones in the array is used to determine the direction to the submarine.
- 16. SOSUS HYDROPHONES • The United States Navy's initial intent for the system was for tracking Soviet submarines, which had to pass through the gap to attack targets further west. • Sound Surveillance System, is a chain of underwater listening posts located around the world in places such as the Atlantic Ocean near Greenland, Iceland and the United Kingdom — the GIUK gap, and at various locations in the Pacific Ocean.
- 17. • Using the sounds made by the seismic event, scientists can tell if the event is an earthquake or a volcanic eruption. • NOAA uses the Navy's Sound Surveillance System (SOSUS) and additional hydrophones to monitor the North Pacific Ocean and the North Atlantic Ocean for seismic events. • Hydrophones located around the Pacific Ocean monitor the ocean for sounds of seismic events. The sounds made by a seismic event are also used to accurately locate the event.
- 18. • Sonar (sound navigation and ranging) is a technology that uses acoustical waves to sense the location of objects in the ocean. • The simplest sonar devices send out a sound pulse from a transducer, and then precisely measure the time it takes for the sound pulses to be reflected back to the transducer. • The distance to an object can be calculated using this time difference and the speed of sound in the water (approximately 1,500 meters per second). SONAR
- 19. More sophisticated sonar systems can provide additional direction and range information. Sonar was developed during World War I as an aid in finding both submarines and icebergs. SONAR
- 20. 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
- 21. ACOUSTIC LINKS ARE USED TO CONTROL UNDERWATER INSTRUMENTS AND ACQUIRE THE DATA REMOTELY
- 22. APPLICATIONS OF AUV’S & OTHER DEVICES USING ACOUSTIC SIGNALS
- 23. 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.
- 24. 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.
- 25. Underwater data links can be combined with satellite data links to provide data in real-time from instruments on the seafloor to scientists ashore. The AUV Designed By PIBHMC
- 26. This AUV has Been Constructed by The U.S Navy to Detect underwater proximity mines and approaching torpedo's. BlueFin -21 Also known as “Mine- Hunter”
- 27. 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
- 28. There is an increasing interest in USWN technologies and their potential applications. However, there are several open issues to solve in order to provide an efficient and reliable data transport to the applications.