Underwater Acoustic Communication is a technique of sending and receiving message below water. There are several ways of employing such communication but the most common is using hydrophones. Underwater communication is difficult due to factors like multi-path propagation, time variations of the channel, small available bandwidth and strong signal attenuation, especially over long ranges. In Underwater Communication there are low data rates compared to terrestrial communication, since underwater communication uses acoustic waves instead of electromagnetic waves.

Underwater Acoustics is the study of the propagation of sound in water and the interaction of the mechanical waves that constitute sound with the water and its boundaries. Underwater acoustics is sometimes known as Hydroacoustics. The water may be in the ocean, a lake or a tank. A sound wave propagating underwater consists of alternating compressions and rarefactions of the water. These compressions and rarefactions are detected by a receiver, such as the human ear or a hydrophone, as changes in pressure.

Typical frequencies associated with underwater acoustics are between 10 Hz and 1 MHz. Absorption of low frequency sound is weak. The main cause of sound attenuation in fresh water, and at high frequency in sea water (above 100 kHz) is viscosity. Important additional contributions at lower frequency in seawater are associated with the ionic relaxation of boric acid (up to c. 10 kHz) and magnesium sulfate (c. 10 kHz-500 kHz). Ambient noise is another problem of Underwater Acoustic Communication.

Technologies & Applications of Underwater Acoustic Communication

  • Underwater Sonar Communication – Sonar is the name given to the acoustic equivalent of Radar. Pulses of sound are used to probe the sea, and the echoes are then processed to extract information about the sea, its boundaries and submerged objects. Passive Sonar is the listening to the sounds radiated by underwater objects.
  • Underwater Acoustic Telemetry – The need for underwater acoustic telemetry exists in applications such as data harvesting for environmental monitoring, communication with and between manned and unmanned underwater vehicles, transmission of diver speech, etc. A related application is underwater remote control, in which acoustic telemetry is used to remotely actuate a switch or trigger an event.
  • Underwater Navigation and TrackingUnderwater Navigation and Tracking is an Underwater Acoustic Positioning System for exploration and work by divers, ROV, autonomous underwater vehicles (AUV), manned submersibles and submarines alike. Unlike most radio signals which are quickly absorbed, sound propagates far underwater and at a rate that can be precisely measured or estimated.
  • Underwater Weather and Climate ObservationUnderwater Acoustic Sensors Transducers can be used to monitor the sound made by wind and precipitation. Lightning strikes can also be detected. Acoustic thermometry of ocean climate (ATOC) uses low frequency sound to measure the global ocean temperature. Underwater Seismic Exploration is another example of ocean weather monitoring.
  • Oceanography & Marine Biology – Large scale ocean features can be detected by ocean acoustic tomography. Bottom characteristics can be measured by side-scan sonar and sub-bottom profiling. Echo sounders are often used to provide data on marine life abundance, distribution, and behavior information. Echo sounders, also referred to as hydroacoustics is also used for fish location, quantity, size, and biomass.