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From Wikipedia, the free encyclopedia

In oceanography, a sofar bomb (Sound Fixing And Ranging bomb), occasionally referred to as a sofar disc,[1] 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).

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Transcription

Hi, this is Kate from MinuteEarth. NUCLEAR APOCALYPSE… would be pretty bad... so in the 1990s, most of the world’s governments formally agreed to a deal to outlaw tests of nuclear weapons. To hold each other accountable, they set up a global network of sensors that pick up the low-frequency waves that nuclear explosions send over long distances. With a few notable exceptions, most countries adhere to the rules, so nuclear tests are pretty rare and the network mostly picks up signals from other sources, like volcanoes...rocket explosions...ship engines...and even the vibrations of icebergs. This background noise is a headache for the people listening for nuclear explosions, but it’s a boon for lots of other listeners, who can also access the data, with permission. For instance, instead of chasing down whales and attaching tracking devices to them, scientists can use their songs to estimate their locations. By listening to all the meteoroids that travel through Earth’s atmosphere, we’ve learned that there are way more out there than what we can see, suggesting that the risk of a city-destroying meteorite is as much as ten times higher than we earlier believed. By monitoring active volcanoes, or even setting off controlled explosions, and measuring how little of the energy boomerangs back to the sensors, scientists have found that the winds way above Earth’s surface are faster and more variable than we thought, which is part of the reason our current weather forecasts aren’t that great. And speaking of forecasts, data from the network’s sensors also help us locate earthquake epicenters to provide better warnings about potential tsunamis. The system may have been built to detect nuclear tests, but it’s led to an explosion of knowledge about our planet. And to a lot more questions - like what is responsible for all of the sound waves that we haven’t identified yet. This video was sponsored by the Preparatory Commission For The Nuclear-Test-Ban Treaty Organization, or CTBTO, with financial support from the European Union. CTBTO has been mandated by 183 nations to monitor for illegal nuclear tests. If you’re a researcher interested in using data from CTBTO’s monitoring system to further expand our knowledge about the world, contact the organization at ctbto.org. Thanks to CTBTO for their sponsorship - and for helping keep the world safe from nuclear weapons. And thanks to our friend Jesse Agar of This Place for illustrating this video.

Contents

Design

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).[2]

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.

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 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.

History

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.[3] 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.[4] It worked exceptionally well[clarification needed], 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).[5]

References

  1. ^ https://www.youtube.com/watch?v=EuhccACOd1U&feature=channel
  2. ^ United States. Bureau of Naval Personnel (1953), "SOFAR, Harbor Defense, and other Sonar Systems", Naval Sonar, NAVPERS 10884, Washington, DC: U.S. Government Printing Office, p. 284 
  3. ^ "Sound Channel, SOFAR, and SOSUS". Robert A. Muller. Archived from the original on 16 May 2007. Retrieved 14 April 2007. 
  4. ^ United States. Bureau of Naval Personnel (1953), "SOFAR, Harbor Defense, and other Sonar Systems", Naval Sonar, NAVPERS 10884, Washington, DC: U.S. Government Printing Office, pp. 284–286 
  5. ^ United States. Bureau of Naval Personnel (1953), "SOFAR, Harbor Defense, and other Sonar Systems", Naval Sonar, NAVPERS 10884, Washington, DC: U.S. Government Printing Office, pp. 285–286 

This page was last edited on 28 August 2018, at 12:24
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