Hydroacoustics is the study and application of sound in water. Hydroacoustics, using

sonar Sonar (sound navigation and ranging or sonic navigation and ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, measure distances (ranging), communicate with or detect objects on o ...

technology, is most commonly used for monitoring of underwater physical and biological characteristics. Collecting Multibeam Sonar Data

Hydroacoustics can be used to detect the depth of a water body (

bathymetry Bathymetry (; ) is the study of underwater depth of ocean floors ('' seabed topography''), lake floors, or river floors. In other words, bathymetry is the underwater equivalent to hypsometry or topography. The first recorded evidence of water ...

), as well as the presence or absence, abundance, distribution, size, and behavior of underwater plants and animals. Hydroacoustic sensing involves " passive acoustics" (listening for sounds) or ''

active acoustics Sonar (sound navigation and ranging or sonic navigation and ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, measure distances (ranging), communicate with or detect objects on or ...

'' making a sound and listening for the echo, hence the common name for the device,

echo sounder Echo sounding or depth sounding is the use of sonar for ranging, normally to determine the depth of water (bathymetry). It involves transmitting acoustic waves into water and recording the time interval between emission and return of a pulse; ...

or echosounder. There are a number of different causes of noise from shipping. These can be subdivided into those caused by the propeller, those caused by machinery, and those caused by the movement of the hull through the water. The relative importance of these three different categories will depend, amongst other things, on the ship type One of the main causes of hydro acoustic noise from fully submerged lifting surfaces is the unsteady separated turbulent flow near the surface's trailing edge that produces pressure fluctuations on the surface and unsteady oscillatory flow in the near wake. The relative motion between the surface and the ocean creates a turbulent boundary layer (TBL) that surrounds the surface. The noise is generated by the fluctuating velocity and pressure fields within this TBL.

Acoustical oceanography

Acoustical oceanography is the use of

underwater sound 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, its contents and its boundaries. The water may be in the ocean, a lake, a river or a tank. Typ ...

to study the

sea The sea, connected as the world ocean or simply the ocean, is the body of salty water that covers approximately 71% of the Earth's surface. The word sea is also used to denote second-order sections of the sea, such as the Mediterranean Sea, ...

, its boundaries and its contents.

History

Interest in developing echo ranging systems began in earnest following the sinking of the

RMS Titanic RMS ''Titanic'' was a British passenger Ocean liner, liner, operated by the White Star Line, which Sinking of the Titanic, sank in the North Atlantic Ocean on 15 April 1912 after striking an iceberg during her maiden voyage from Southampton ...

in 1912. By sending a sound wave ahead of a ship, the theory went, a return echo bouncing off the submerged portion of an iceberg should give early warning of collisions. By directing the same type of beam downwards, the depth to the bottom of the ocean could be calculated. The first practical deep-ocean

was invented by Harvey C. Hayes, a U.S. Navy physicist. For the first time, it was possible to create a quasi-continuous profile of the ocean floor along the course of a ship. The first such profile was made by Hayes on board the U.S.S. Stewart, a Navy destroyer that sailed from Newport to Gibraltar between June 22 and 29, 1922. During that week, 900 deep-ocean soundings were made. Using a refined echo sounder, the

German survey ship Meteor ''Meteor'' was a German survey vessel, noted for her survey work in the Atlantic Ocean between 1925 and 1927. Handed over to the Soviet Union following World War II, the ship was renamed ''Ekvator''. Her ultimate fate is not known. Design and ...

made several passes across the South Atlantic from the equator to Antarctica between 1925 and 1927, taking soundings every 5 to 20 miles. Their work created the first detailed map of the Mid-Atlantic Ridge. It showed that the Ridge was a rugged mountain range, and not the smooth plateau that some scientists had envisioned. Since that time, both naval and research vessels have operated echo sounders almost continuously while at sea. Important contributions to acoustical oceanography have been made by: * Leonid Brekhovskikh *

Walter Munk Walter Heinrich Munk (October 19, 1917 – February 8, 2019) was an American physical oceanography, physical oceanographer. He was one of the first scientists to bring statistical methods to the analysis of oceanographic data. His work won award ...

* Herman Medwin * John L. Spiesberger * C.C. Leroy * David E. Weston *

D. Van Holliday Dale Vance Holliday (May 29, 1940 – February 4, 2010) was an American physicist and acoustician. Born in Ennis, Texas, Holliday attended the University of Texas at Austin. He graduated with a B.S. and M.A. in Physics and did extensive the ...

* Charles Greenlaw

Equipment used

The earliest and most widespread use of sound and

technology to study the properties of the sea is the use of a rainbow echo sounder to measure water depth. Sounders were the devices used that mapped the many miles of the Santa Barbara Harbor ocean floor until 1993.

Fathometer Echo sounding or depth sounding is the use of sonar for ranging, normally to determine the depth of water (bathymetry). It involves transmitting acoustic waves into water and recording the time interval between emission and return of a pulse; ...

s measure the depth of the waters. It works by electronically sending sounds from ships, therefore also receiving the sound waves that bounces back from the bottom of the ocean. A paper chart moves through the fathometer and is calibrated to record the depth. As technology advances, the development of high resolution sonars in the second half of the 20th century made it possible to not just detect underwater objects but to classify them and even image them. Electronic sensors are now attached to ROVs since nowadays, ships or robot submarines have Remotely Operated Vehicles (ROVs). There are cameras attached to these devices giving out accurate images. The oceanographers are able to get a clear and precise quality of pictures. The 'pictures' can also be sent from sonars by having sound reflected off ocean surroundings. Oftentimes sound waves reflect off animals, giving information which can be documented into deeper animal behaviour studies.

Applications

Applications of acoustical oceanography include: * fish population surveys * classification of fish species and other biota * rain rate measurement * wind speed measurement * water depth measurement * seabed classification *

ocean acoustic tomography Ocean acoustic tomography is a technique used to measure temperatures and currents over large regions of the ocean. On ocean basin scales, this technique is also known as acoustic thermometry. The technique relies on precisely measuring the ti ...

* global thermometry * monitoring of ocean-atmospheric gas exchange *

Surveillance Towed Array Sensor System The AN/UQQ-2 Surveillance Towed Array Sensor System (SURTASS), colloquially referred to as the ship's "Tail", is a towed array sonar system of the United States Navy. SURTASS Twin-Line consists of either the long passive SURTASS array or the Twi ...

Fisheries acoustics Fisheries acoustics includes a range of research and practical application topics using acoustical devices as sensors in aquatic environments. Acoustical techniques can be applied to sensing aquatic animals, zooplankton, and physical and biolog ...

Acoustic Doppler current profiler An acoustic Doppler current profiler (ADCP) is a hydroacoustic current meter similar to a sonar, used to measure water current velocities over a depth range using the Doppler effect of sound waves scattered back from particles within the water ...

for water speed measurement *

Acoustic camera An acoustic camera is an imaging device used to locate sound sources and to characterize them. It consists of a group of microphones, also called a microphone array, from which signals are simultaneously collected and processed to form a representa ...

Passive acoustic monitoring Passive may refer to: * Passive voice, a grammatical voice common in many languages, see also Pseudopassive * Passive language, a language from which an interpreter works * Passivity (behavior), the condition of submitting to the influence of on ...

Notes

References

Works cited

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