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).
For this device to work as intended, it must have several qualities. Firstly, the bomb needs to detonate at the correct depth, so that it can take full advantage of the deep sound channel. The sofar bomb has to sink fast enough so that it reaches the required depth within a reasonable amount of time (usually about 5 minutes).
To determine the position of a sofar bomb that has been detonated, three or more naval stations combine their reports of when they received the signal.
Detonating the sofar bomb in the deep sound channel gives it huge benefits. The channel itself helps keep the sound waves contained within the same depth, as the rays of sound that have an upward or downward velocity are pushed back towards the deep sound channel because of refraction. Because the sound waves do not spread out vertically, the horizontal sound rays maintain far more strength than they would otherwise. This makes it far easier for the stations on shore to pick up and analyze the signal. Usually, the blasts use frequencies between 30 and 150 Hz, which also helps stop the signal from weakening too much. A side effect of this is that the slightly higher frequencies of sound waves emitted move a bit faster than the lower frequencies, making the signal that the naval stations hear have a longer duration.
Dr. Maurice Ewing, a pioneer of oceanography and geophysics, first suggested putting small hollow metal spheres in pilots' emergency kits during World War II. The spheres would implode when they sank to the sofar channel, acting as a secret homing beacon to be received by microphones on coastlines that could pinpoint downed pilots’ positions. This technology turned out to be extremely useful for the naval conflicts during World War II by providing a way for ships to accurately report their position without use of radio, or to find crashed planes and ships. During the war, the primary model of sofar bomb used by the United States was the Mk-22. It worked exceptionally well, and had an adjustable fuse length for different depth detonations. The bomb was used with a chart that detailed the depth of the deep sound channel, so that the 4 pounds (1.8 kg) of TNT would explode at the correct time for its location (as the deep sound channel's actual depth varies with areas of the ocean). Its main safety mechanism was the fact that the detonator could not begin to go off without a water pressure that corresponded to at least 750 feet (230 m).
Acoustic tags are small sound-emitting devices that allow the detection and/or remote tracking of organisms in aquatic ecosystems. Acoustic tags are commonly used to monitor the behavior of fish. Studies can be conducted in lakes, rivers, tributaries, estuaries or at sea. Acoustic tag technology allows researchers to obtain locational data of tagged fish: depending on tag and receiver array configurations, researchers can receive simple presence/absence data, 2D positional data, or even 3D fish tracks in real-time with sub-meter resolution.
Acoustic tags allow researchers to:
Conduct Survival Studies
Track Behavior in Two or Three Dimensions (2D or 3D)
Measure Bypass Effectiveness at Dams and other Passages
Observe Predator/Prey DynamicsAcoustical oceanography
Acoustical oceanography is the use of underwater sound to study the sea, its boundaries and its contents.Bahama Banks
The Bahama Banks are the submerged carbonate platforms that make up much of the Bahama Archipelago. The term is usually applied in referring to either the Great Bahama Bank around Andros Island, or the Little Bahama Bank of Grand Bahama Island and Great Abaco, which are the largest of the platforms, and the Cay Sal Bank north of Cuba. The islands of these banks are politically part of the Bahamas. Other banks are the three banks of the Turks and Caicos Islands, namely the Caicos Bank of the Caicos Islands, the bank of the Turks Islands, and wholly submerged Mouchoir Bank. Further southeast are the equally wholly submerged Silver Bank and Navidad Bank north of the Dominican Republic.Carbonate platform
A carbonate platform is a sedimentary body which possesses topographic relief, and is composed of autochthonic calcareous deposits. Platform growth is mediated by sessile organisms whose skeletons build up the reef or by organisms (usually microbes) which induce carbonate precipitation through their metabolism. Therefore, carbonate platforms can not grow up everywhere: they are not present in places where limiting factors to the life of reef-building organisms exist. Such limiting factors are, among others: light, water temperature, transparency and pH-Value. For example, carbonate sedimentation along the Atlantic South American coasts takes place everywhere but at the mouth of the Amazon River, because of the intense turbidity of the water there. Spectacular examples of present-day carbonate platforms are the Bahama Banks under which the platform is roughly 8 km thick, the Yucatan Peninsula which is up to 2 km thick, the Florida platform, the platform on which the Great Barrier Reef is growing, and the Maldive atolls. All these carbonate platforms and their associated reefs are confined to tropical latitudes. Today's reefs are built mainly by scleractinian corals, but in the distant past other organisms, like archaeocyatha (during the Cambrian) or extinct cnidaria (tabulata and rugosa) were important reef builders.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 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 biological habitat characteristics.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.
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 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
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.List of submarine volcanoes
A list of active and extinct submarine volcanoes and seamounts located under the world's oceans. There are estimated to be 40,000 to 55,000 seamounts in the global oceans. Almost all are not well-mapped and many may not have been identified at all. Most are unnamed and unexplored. This list is therefore confined to seamounts that are notable enough to have been named and/or explored.Maurice Ewing
William Maurice "Doc" Ewing (May 12, 1906 – May 4, 1974) was an American geophysicist and oceanographer.Ewing has been described as a pioneering geophysicist who worked on the research of seismic reflection and refraction in ocean basins, ocean bottom photography, submarine sound transmission (including the SOFAR channel), deep sea coring of the ocean bottom, theory and observation of earthquake surface waves, fluidity of the Earth's core, generation and propagation of microseisms, submarine explosion seismology, marine gravity surveys, bathymetry and sedimentation, natural radioactivity of ocean waters and sediments, study of abyssal plains and submarine canyons.Mercury-Redstone 4
Mercury-Redstone 4 was the second United States human spaceflight, on July 21, 1961. The suborbital Project Mercury flight was launched with a Mercury-Redstone Launch Vehicle, MRLV-8. The spacecraft, Mercury capsule #11, was nicknamed the Liberty Bell 7, and it was piloted by the astronaut Virgil "Gus" Grissom.
The spaceflight lasted 15 minutes 30 seconds, it reached an altitude of more than 102.8 nautical miles (190.4 km), and it flew 262.5 nautical miles (486.2 km) downrange, landing in the Atlantic Ocean. The flight went as expected until just after splashdown, when the hatch cover, designed to release explosively in the event of an emergency, accidentally blew. Grissom was at risk of drowning, but he was recovered safely via a U.S. Navy helicopter. The spacecraft sank into the Atlantic, and it was not recovered until 1999.Mercury-Redstone BD
Mercury-Redstone BD was an unmanned booster development flight in the U.S. Mercury program. It was launched on March 24, 1961 from Launch Complex 5 at Cape Canaveral, Florida. The mission used a boilerplate Mercury spacecraft and Redstone MRLV-5.After the problems that developed during the MR-2 mission carrying the chimpanzee Ham, it was apparent that the Redstone needed further development before it could be trusted to carry a human passenger.
Dr. Wernher von Braun added Mercury-Redstone BD (Booster Development) to the launch schedule between the MR-2 and MR-3 missions. This went over the protests of some, including astronaut Alan Shepard, who argued that the problems on MR-2 had been quickly identified and easily fixed. Von Braun was adamant that the Redstone could not be considered man-rated until a completely perfect test flight and that the launch vehicle performance on MR-1A and MR-2 had not met acceptable standards for carrying a human passenger.
The cause of previous Redstone rocket over-accelerations was a servo valve that did not properly regulate the flow of hydrogen peroxide to the steam generator. This in turn overpowered the fuel pumps. The thrust regulator and velocity integrator were modified on the MR-BD and later Mercury-Redstone rockets to prevent them from exceeding the speed limit again. Other modifications were made to prevent engine cutoff from propellant depletion rather than a programmed signal, which had led to an inadvertent abort and LES activation on MR-2.
Another problem encountered in previous Mercury-Redstone flights were harmonic vibrations induced by aerodynamic stress in the topmost section of the elongated Redstone. To fix this problem, four stiffeners were added to the ballast section and 210 pounds (95 kg) of insulation was applied to the inner skin of the upper part of the Mercury Redstone instrument compartment.
The mission used a boilerplate Mercury spacecraft with an inert escape rocket. The spacecraft also did not have a retro package or posigrade rockets.
The MR-BD mission lasted eight minutes and 23 seconds. It reached an apogee of 113.5 miles (183 km) and a range of 307 miles (494 km). The peak velocity was 5,123 mph (8,245 km/h).
The spacecraft experienced a peak load of 11 g (108 m/s²). There was no intention to separate the Redstone rocket and boilerplate Mercury spacecraft and they impacted together 307 miles (494 km) downrange, 5 miles (8 km) short of the plan. They sank to the bottom of the Atlantic Ocean, exploding a sofar bomb en route. Booster performance was excellent other than some vibration issues in the adapter area.
MR-BD was highly successful and led the way to the flight of Alan Shepard aboard MR-3.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 time it takes sound signals to travel between two instruments, one an acoustic source and one a receiver, separated by ranges of 100–5000 km. If the locations of the instruments are known precisely, the measurement of time-of-flight can be used to infer the speed of sound, averaged over the acoustic path. Changes in the speed of sound are primarily caused by changes in the temperature of the ocean, hence the measurement of the travel times is equivalent to a measurement of temperature. A 1 °C change in temperature corresponds to about 4 m/s change in sound speed. An oceanographic experiment employing tomography typically uses several source-receiver pairs in a moored array that measures an area of ocean.Oceanic plateau
An oceanic or submarine plateau is a large, relatively flat elevation that is higher than the surrounding relief with one or more relatively steep sides.There are 184 oceanic plateaus covering an area of 18,486,600 km2 (7,137,700 sq mi), or about 5.11% of the oceans. The South Pacific region around Australia and New Zealand contains the greatest number of oceanic plateaus (see map).
Oceanic plateaus produced by large igneous provinces are often associated with hotspots, mantle plumes, and volcanic islands — such as Iceland, Hawaii, Cape Verde, and Kerguelen. The three largest plateaus, the Caribbean, Ontong Java, and Mid-Pacific Mountains, are located on thermal swells. Other oceanic plateaus, however, are made of rifted continental crust, for example Falkland Plateau, Lord Howe Rise, and parts of Kerguelen, Seychelles, and Arctic ridges.
Plateaus formed by large igneous provinces were formed by the equivalent of continental flood basalts such as the Deccan Traps in India and the Snake River Plain in the United States.
In contrast to continental flood basalts, most igneous oceanic plateaus erupt through young and thin (6–7 km (3.7–4.3 mi)) mafic or ultra-mafic crust and are therefore uncontaminated by felsic crust and representative for their mantle sources.
These plateaus often rise 2–3 km (1.2–1.9 mi) above the surrounding ocean floor and are more buoyant than oceanic crust. They therefore tend to withstand subduction, more-so when thick and when reaching subduction zones shortly after their formations. As a consequence, they tend to "dock" to continental margins and be preserved as accreted terranes. Such terranes are often better preserved than the exposed parts of continental flood basalts and are therefore a better record of large-scale volcanic eruptions throughout Earth's history. This "docking" also means that oceanic plateaus are important contributors to the growth of continental crust. Their formations often had a dramatic impact on global climate, such as the most recent plateaus formed, the three, large, Cretaceous oceanic plateaus in the Pacific and Indian Ocean: Ontong Java, Kerguelen, and Caribbean.Physical oceanography
Physical oceanography is the study of physical conditions and physical processes within the ocean, especially the motions and physical properties of ocean waters.
Physical oceanography is one of several sub-domains into which oceanography is divided. Others include biological, chemical and geological oceanography.
Physical oceanography may be subdivided into descriptive and dynamical physical oceanography.Descriptive physical oceanography seeks to research the ocean through observations and complex numerical models, which describe the fluid motions as precisely as possible.
Dynamical physical oceanography focuses primarily upon the processes that govern the motion of fluids with emphasis upon theoretical research and numerical models. These are part of the large field of Geophysical Fluid Dynamics (GFD) that is shared together with meteorology. GFD is a sub field of Fluid dynamics describing flows occurring on spatial and temporal scales that are greatly influenced by the Coriolis force.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.Sofar
Sofar may refer to:
Sofar bomb (SOund Fixing And Ranging bomb), a long-range position-fixing system that uses explosive sounds in the deep sound channel of the ocean
SOFAR channel (SOund Fixing And Ranging channel), a horizontal layer of water in the ocean centered on the depth at which the speed of sound is minimumUndersea mountain range
Undersea mountain ranges are mountain ranges that are mostly or entirely underwater, and specifically under the surface of an ocean. If originated from current tectonic forces, they are often referred to as a mid-ocean ridge. In contrast, if formed by past above-water volcanism, they are known as a seamount chain. The largest and best known undersea mountain range is a mid-ocean ridge, the Mid-Atlantic Ridge. It has been observed that, "similar to those on land, the undersea mountain ranges are the loci of frequent volcanic and earthquake activity".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.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.