| 词条 | SOFAR channel |
| 释义 |
The SOFAR channel (short for Sound Fixing and Ranging channel), or deep sound channel (DSC),[1] 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.[2] 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.[3] DetailsThe SOFAR channel is centred on the depth where the cumulative effect of temperature and water pressure (and, to a lesser extent, salinity) combine to create the region of minimum sound speed in the water column. Pressure in the ocean increases linearly with depth, but temperature is more variable, generally falling rapidly in the main thermocline from the surface to around a thousand metres deep, then remaining almost unchanged from there to the ocean floor in the deep sea. Near the surface, the rapidly falling temperature causes a decrease in sound speed, or a negative sound speed gradient. With increasing depth, the increasing pressure causes an increase in sound speed, or a positive sound speed gradient. The depth where the sound speed is at a minimum is called the sound channel axis. Near Bermuda, the sound channel axis occurs at a depth of around 1000 metres. In temperate waters, the axis is shallower, and at high latitudes (above about 60°N or below 60°S) it reaches the surface. Sound propagates in the channel by refraction of sound, which makes sound travel near the depth of slowest speed. If a sound wave propagates away from this horizontal channel, the part of the wave furthest from the channel axis travels faster, so the wave turns back toward the channel axis. As a result, the sound waves trace a path that oscillates across the SOFAR channel axis. This principle is similar to long distance transmission of light in an optical fibre. Mysterious low-frequency sounds, attributed to fin whales (Balaenoptera physalus), are a common occurrence in the channel. Scientists believe fin whales may dive down to this channel and "sing" to communicate with other fin whales many kilometers away.[4] During World War II, Dr. Maurice Ewing suggested that dropping into the ocean a small metal sphere (called a SOFAR bomb or SOFAR disc), specifically designed to implode at the SOFAR channel, could be used as a secret distress signal by downed pilots.[5] The novel The Hunt for Red October describes the use of the SOFAR channel in submarine detection. The conjectured existence of a similar channel in the upper atmosphere, theorized by Dr. Ewing, led to Project Mogul, carried out from 1947 until late 1948. Applications
See also
References1. ^{{cite book |title=Navy Supplement to the DOD Dictionary of Military and Associated Terms |date=August 2006 |publisher=Department Of The Navy |url=https://www.nwdc.navy.mil/Documents/NTRP_1-02.pdf |id=NTRP 1-02 }}{{dead link|date=January 2018 |bot=InternetArchiveBot |fix-attempted=yes }} 2. ^{{cite web |url=https://docs.google.com/viewer?url=http%3A%2F%2Fbrigus.physics.mun.ca%2F~zedel%2FP6317%2Fpapers%2Fheard_island.pdf |year=1994 |publisher=Acoustical Society of America |title=The Heard Island Feasibility Test}} 3. ^Citation for Leonid Maximovich Brekhovskikh ...for pioneering contributions to wave propagation and scattering {{webarchive|url=https://web.archive.org/web/20091023173108/http://rav.sio.rssi.ru/leon/brekhc.htm |date=2009-10-23 }} 4. ^Orientation by Means of Long Range Acoustic Signaling in Baleen Whales{{dead link|date=February 2019|bot=medic}}{{cbignore|bot=medic}}, R. Payne, D. Webb, in Annals NY Acad. Sci., 188: 110–41 (1971) 5. ^{{cite web| title = Sound Channel, SOFAR, and SOSUS| url = http://muller.lbl.gov/teaching/Physics10/old%20physics%2010/pages/SoundChannel.html| publisher = Robert A. Muller| accessdate = 2007-04-14| deadurl = yes| archiveurl = https://web.archive.org/web/20070516095529/http://muller.lbl.gov/teaching/Physics10/old%20physics%2010/pages/SoundChannel.html| archivedate = 2007-05-16| df = }} External links
3 : Oceanography|Anti-submarine warfare|Sonar |
| 随便看 |
|
开放百科全书收录14589846条英语、德语、日语等多语种百科知识，基本涵盖了大多数领域的百科知识，是一部内容自由、开放的电子版国际百科全书。