Hydroacoustics

Hydroacoustics is the study and application of sound in water. Hydroacoustics, using sonar technology, is most commonly used for monitoring of underwater physical and biological characteristics.

Collecting Multibeam Sonar Data
Collecting Multibeam Sonar Data

Hydroacoustics can be used to detect the depth of a water body (bathymetry), as well as the presence or absence, abundance, distribution, size, and behavior of underwater plants[1] and animals. Hydroacoustic sensing involves "passive acoustics" (listening for sounds) or active acoustics making a sound and listening for the echo, hence the common name for the device, echo sounder 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[2] 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.

Specific applications

Related publications

References

  1. ^ http://www.erdc.usace.army.mil/pls/erdcpub/!www_fact_sheet.product_page?ps_product_numb=112825&tmp_Main_Topic=&page=STATUS
  2. ^ reducing underwater noise pollution from large commercial vessels
Acoustical oceanography

Acoustical oceanography is the use of underwater sound to study the sea, its boundaries and its contents.

Baik Island

Baik Island (Malay: Pulau Baik) is an island located in the Celebes Sea near Lahad Datu area in Sabah, Malaysia.

Echo sounding

Echo sounding is a type of sonar used to determine the depth of water by transmitting sound waves into water. The time interval between emission and return of a pulse is recorded, which is used to determine the depth of water along with the speed of sound in water at the time. This information is then typically used for navigation purposes or in order to obtain depths for charting purposes. Echo sounding can also refer to hydroacoustic "echo sounders" defined as active sound in water (sonar) used to study fish. Hydroacoustic assessments have traditionally employed mobile surveys from boats to evaluate fish biomass and spatial distributions. Conversely, fixed-location techniques use stationary transducers to monitor passing fish.

The word sounding is used for all types of depth measurements, including those that don't use sound, and is unrelated in origin to the word sound in the sense of noise or tones. Echo sounding is a more rapid method of measuring depth than the previous technique of lowering a sounding line until it touched bottom.

Fisheries and Illinois Aquaculture Center

The Fisheries and Illinois Aquaculture Center at Southern Illinois University Carbondale (SIUC) was founded by Dr. William M. Lewis, Senior in 1950. The Center is administratively housed in the Graduate School. Faculty have joint appointments in the Center and the Department of Zoology within the College of Science or in the Department of Animal Science, Food and Nutrition in the College of Agricultural Sciences.

Research faculty in the Center have diverse capabilities including molecular genetics, aquatic toxicology, aquatic ecology, bioenergetics, fish nutrition, fish physiology, fisheries policy and management, and aquaculture technology.

Facilities include several research laboratories, an experimental pond facility (90 ponds), a large wet laboratory, research boats (including a 27-foot (8.2 m) research vessel with advanced hydroacoustics), and offices.

The Center generates many peer-reviewed publications and garners grant support from many state and federal agencies as well as foundations.

Helgoland Habitat

The Helgoland underwater laboratory (UWL) is an underwater habitat. It was built by Dräger in Lübeck, Germany in 1968 for the Biological Institute Helgoland, and was the first of its kind in the world built for use in colder waters. It is named after the island Helgoland.

The habitat allowed divers to spend several weeks under water using saturation diving techniques. The scientists and technicians would live and work in the laboratory, returning to it after every diving session. Only once they had reached the end of their stay did they decompress in the UWL itself, being able to then resurface without coming to any harm. After experience gained in the first deployment, a wet section was added.

The UWL was used in the waters of the North and Baltic Seas and, in 1975, on Jeffreys Ledge, in the Gulf of Maine along the coast of New England in the United States.

Joachim Wendler

Joachim Wendler (born June 6, 1939, Erfurt, Germany – died September 25, 1975, Rockport, Massachusetts) was a West German aquanaut who died of an air embolism while returning to the surface of the Gulf of Maine from the Helgoland underwater habitat. He was participating in a checkout mission for the First International Saturation Study of Herring and Hydroacoustics (FISSHH) project.

Wendler, a 36-year-old experienced diver, and two other German aquanauts began the two-day/two-night checkout mission on September 21, 1975. All three divers were employees of the German firm Gesellschaft fur Kernenergieverwertung in Schiffbau und Schiffahrt mbH (GKSS), which operated the Helgoland habitat. On September 23 the three Germans were joined by two American divers: Lieutenant Commander Laurence Bussey of the United States Navy, the head of the project for the National Oceanic and Atmospheric Administration (NOAA), and Roger Clifford, a fisheries scientist from NOAA's laboratory at Woods Hole. Wendler, Bussey, and another of the German aquanauts, Joachim Rediske, proceeded to undergo a 49-hour decompression inside Helgoland, which was completed at 6:30 p.m. on September 24. Their return to the surface was then delayed by 15 hours due to bad weather and in order to enable them to surface in daylight.At 11:30 a.m. on September 25 the three aquanauts surfaced; Wendler was hampered by gear he was carrying. It was later theorized by Captain George F. Bond, the "Father of Saturation Diving", who was participating in the project, that Wendler may have been lifted ten feet or more by a passing swell just after taking a deep breath. The change in pressure would have allowed bubbles from his lungs to enter his circulatory system. In the final 15 feet before reaching the surface, Wendler suffered a massive gas embolism.Having reached the surface, Wendler clung to a buoy and waved for help. He was brought by the diving tender boat to Rockport, Massachusetts, and received oxygen, mouth-to-mouth resuscitation and external heart massage aboard the boat. Upon arrival in Rockport, Wendler was placed in a portable recompression chamber at the project's headquarters at the Ralph Waldo Emerson Inn, where he was recompressed to 165 feet. Wendler spent two hours in the chamber, attended by GKSS medical supervisor Anthony Low, M.D., before being pronounced dead.NOAA convened a board of investigation, headed by Dr. J. Morgan Wells of NOAA's Manned Undersea Science and Technology (MUST) office. The board concluded that Wendler's death "was in no way connected with the systems in the habitat or the decompression procedures". NOAA Associate Administrator David Wallace ordered that, in order for FISSHH to continue, a recompression chamber must be made available on the dive boat.On November 21, 1975, an American aquanaut experienced either central nervous system bends or an embolism on surfacing from Helgoland; he was successfully treated but experienced some residual disability. Captain Bond later said that the FISSHH project had as many serious safety incidents as he could remember in a project of similar length. Joachim Wendler was the world's second aquanaut to die as a result of participating in an underwater habitat project, the first having been SEALAB III aquanaut Berry L. Cannon.

Kongsberg Maritime

Kongsberg Maritime (KM) is a Norwegian technology enterprise within the Kongsberg Gruppen (KOG). Kongsberg Maritime deliver systems for positioning, surveying, navigation and automation to merchant vessels and offshore installations. Their most well known products exist within dynamic positioning systems, marine automation and surveillance systems, process automation, satellite navigation and hydroacoustics.

Passive acoustics

Passive acoustics is the action of listening for sounds, often at specific frequencies or for purposes of specific analyses.

As applied to underwater acoustics, also termed hydroacoustics or sonar, passive acoustics can be used to listen for underwater explosions, earthquakes, volcanic eruptions, sounds produced by fish and other animals, vessel activity or aquatic detecting equipment (as in hydroacoustics to track fish).

Pennsylvania State University Applied Research Laboratory

The Pennsylvania State University Applied Research Laboratory (short: Penn State ARL or simply ARL), is a specialized research unit dedicated to interdisciplinary scientific research at the Penn State, University Park campus. The ARL is a DoD designated U.S. Navy University Affiliated Research Center. It is the university's largest research unit with over 1,000 faculty and staff. The Laboratory ranks 2nd in DoD and 10th in NASA funding to universities.ARL maintains a long-term relationship with the Naval Sea Systems Command and the Office of Naval Research.

Pyotr Lebedev (research vessel)

Pyotr Lebedev is a research vessel, built at Wärtsilä Crichton-Vulcan in Turku, Finland, originally as a merchant vessel Chapayev in 1957. She was subsequently acquired for the Soviet Union and refitted as a research ship. The vessel was owned and operated by the Andreev Acoustics Institute, and was used to make hydrophysical observations of the Atlantic Ocean such as during the Polygon experiment. Pyotr Lebedev possessed five on-board laboratories used to study hydroacoustics, hydrology, hydrobiology, hydrochemistry, and electronics. The ship was active as a research vessel from 1967 until 1977. She is current registered in Saint Vincent and the Grenadines.

Rotor current meter

A rotor current meter (RCM) is a mechanical current meter, an oceanographic device deployed within an oceanographic mooring measuring the flow within the world oceans to learn more about ocean currents. Many RCMs have been replaced by instruments measuring the flow by hydroacoustics, the so-called Acoustic Doppler Current Profilers. However, for instance in Fram Strait, the Alfred Wegener Institute still uses RCMs for long-term monitoring the inflow into the Arctic Ocean.

SOFAR channel

The SOFAR channel (short for Sound Fixing and Ranging channel), or deep sound channel (DSC), is a horizontal layer of water in the ocean at which depth the speed of sound is at its minimum. The SOFAR channel acts as a waveguide for sound, and low frequency sound waves within the channel may travel thousands of miles before dissipating. This phenomenon is an important factor in submarine warfare. The deep sound channel was discovered and described independently by Maurice Ewing, Stanley Wong and Leonid Brekhovskikh in the 1940s.

Scientific echosounder

A scientific echosounder is a device which uses sonar technology for the measurement of underwater physical and biological components—this device is also known as scientific sonar. Applications include bathymetry, substrate classification, studies of aquatic vegetation, fish, and plankton, and differentation of water masses.

Sigve Tjøtta

Sigve Tjøtta (born 1 March 1930) is a Norwegian mathematician.

Sofar bomb

In oceanography, a sofar bomb (Sound Fixing And Ranging bomb), occasionally referred to as a sofar disc, is a long-range position-fixing system that uses impulsive sounds in the deep sound channel of the ocean to enable pinpointing of the location of ships or crashed planes. The deep sound channel is ideal for the device, as the minimum speed of sound at that depth improves the signal's traveling ability. A position is determined from the differences in arrival times at receiving stations of known geographic locations. The useful range from the signal sources to the receiver can exceed 3,000 miles (4,800 km).

Sonar

Sonar (originally an acronym for sound navigation ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, communicate with or detect objects on or under the surface of the water, such as other vessels. Two types of technology share the name "sonar": passive sonar is essentially listening for the sound made by vessels; active sonar is emitting pulses of sounds and listening for echoes. Sonar may be used as a means of acoustic location and of measurement of the echo characteristics of "targets" in the water. Acoustic location in air was used before the introduction of radar. Sonar may also be used for robot navigation, and SODAR (an upward-looking in-air sonar) is used for atmospheric investigations. The term sonar is also used for the equipment used to generate and receive the sound. The acoustic frequencies used in sonar systems vary from very low (infrasonic) to extremely high (ultrasonic). The study of underwater sound is known as underwater acoustics or hydroacoustics.

The first recorded use of the technique was by Leonardo da Vinci in 1490 who used a tube inserted into the water to detect vessels by ear. It was developed during World War I to counter the growing threat of submarine warfare, with an operational passive sonar system in use by 1918. Modern active sonar systems use an acoustic transponder to generate a sound wave which is reflected back from target objects.

Underwater acoustics

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. Typical frequencies associated with underwater acoustics are between 10 Hz and 1 MHz. The propagation of sound in the ocean at frequencies lower than 10 Hz is usually not possible without penetrating deep into the seabed, whereas frequencies above 1 MHz are rarely used because they are absorbed very quickly. Underwater acoustics is sometimes known as hydroacoustics.

The field of underwater acoustics is closely related to a number of other fields of acoustic study, including sonar, transduction, acoustic signal processing, acoustical oceanography, bioacoustics, and physical acoustics.

Underwater explosion

An underwater explosion (also known as an UNDEX) is a chemical or nuclear explosion that occurs under the surface of a body of water.

Wave base

The wave base, in physical oceanography, is the maximum depth at which a water wave's passage causes significant water motion. For water depths deeper than the wave base, bottom sediments and the seafloor are no longer stirred by the wave motion above.

Hydroacoustics
Sonar
Ocean acoustics
Acoustic ecology
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