Sofar bomb
Encyclopedia
In oceanography
, a sofar bomb (SOund Fixing And Ranging bomb), occasionally also referred to as a sofar disc, is a long-range position-fixing system that uses explosive sounds in the deep sound channel of the ocean to pinpoint the location of ships or crashed planes. This depth of water is ideal for the device, as the minimal speed of sound
helps with the positioning calculations and 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 3000 miles (4,828 km).
To find the position of a sofar bomb that was detonated, three or more naval stations combine their reports of when they received the signal. Using the differences in the exact time at which each base registered the sound wave and the length of the signal's sound, the location at which the sofar bomb was set off can be found with a type of trilateration
calculation.
are pushed back towards the deep sound channel because of the diffraction
properties of waves. 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. This duration, if measured precisely, can be used as another factor in calculating the location of the sofar bomb.
, 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 WWII 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 4 lbs 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 (228.6 m).
Oceanography
Oceanography , also called oceanology or marine science, is the branch of Earth science that studies the ocean...
, a sofar bomb (SOund Fixing And Ranging bomb), occasionally also referred to as a sofar disc, is a long-range position-fixing system that uses explosive sounds in the deep sound channel of the ocean to pinpoint the location of ships or crashed planes. This depth of water is ideal for the device, as the minimal speed of sound
Speed of sound
The speed of sound is the distance travelled during a unit of time by a sound wave propagating through an elastic medium. In dry air at , the speed of sound is . This is , or about one kilometer in three seconds or approximately one mile in five seconds....
helps with the positioning calculations and 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 3000 miles (4,828 km).
Design
For this invention to work as intended, it must have several necessary 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). This explosion must be of significant enough strength that its sound waves reach the microphone stations that will determine its location; however, safeguards are necessary to prevent a dangerous premature detonation.To find the position of a sofar bomb that was detonated, three or more naval stations combine their reports of when they received the signal. Using the differences in the exact time at which each base registered the sound wave and the length of the signal's sound, the location at which the sofar bomb was set off can be found with a type of trilateration
Trilateration
In geometry, trilateration is the process of determinating absolute or relative locations of points by measurement of distances, using the geometry of circles, spheres or triangles. In addition to its interest as a geometric problem, trilateration does have practical applications in surveying and...
calculation.
Benefits of the Deep Sound Channel
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 velocityVelocity
In physics, velocity is speed in a given direction. Speed describes only how fast an object is moving, whereas velocity gives both the speed and direction of the object's motion. To have a constant velocity, an object must have a constant speed and motion in a constant direction. Constant ...
are pushed back towards the deep sound channel because of the diffraction
Diffraction
Diffraction refers to various phenomena which occur when a wave encounters an obstacle. Italian scientist Francesco Maria Grimaldi coined the word "diffraction" and was the first to record accurate observations of the phenomenon in 1665...
properties of waves. 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. This duration, if measured precisely, can be used as another factor in calculating the location of the sofar bomb.
History
Dr. Maurice EwingMaurice Ewing
William Maurice "Doc" Ewing 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 , deep sea coring of the ocean...
, a pioneer of oceanography and geophysics
Geophysics
Geophysics is the physics of the Earth and its environment in space; also the study of the Earth using quantitative physical methods. The term geophysics sometimes refers only to the geological applications: Earth's shape; its gravitational and magnetic fields; its internal structure and...
, first suggested putting small hollow metal spheres in pilots' emergency kits during World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
. 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 WWII 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 4 lbs of TNT
TNT
TNT is the chemical explosive trinitrotoluene.TNT or T.N.T. may also refer to:-Television:* TNT , American cable television channel and its international offshoots* TNT , a television station in Launceston, Australia...
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
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
that corresponded to at least 750 feet (228.6 m).