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The Challenger Deep is the deepest known point in the Earth's seabed hydrosphere, with a depth of by direct measurement from submersibles, and slightly more by sonar bathymetry (see below). It is in the Pacific Ocean, at the southern end of the Mariana Trench near the Mariana Islands group. The Challenger Deep is a relatively small slot-shaped depression in the bottom of a considerably larger crescent-shaped oceanic trench, which itself is an unusually deep feature in the ocean floor. Its bottom is about long and wide, with gently sloping sides. The closest land to the Challenger Deep is Fais Island (one of the outer islands of Yap), southwest, and Guam, to the northeast. It is located in the ocean territory of the Federated States of Micronesia, from its border with ocean territory associated with Guam.〔The Colbert Report, airdate: 2012 April 12, interview with James Cameron〕 The depression is named after the British Royal Navy survey ship HMS ''Challenger'', whose expedition of 1872–1876 made the first recordings of its depth. According to the August 2011 version of the GEBCO Gazetteer of Undersea Feature Names, the location and depth of the Challenger Deep are and ±. June 2009 sonar mapping of the Challenger Deep by the Simrad EM120 (sonar multibeam bathymetry system for 300–11,000 m deep water mapping) aboard the RV ''Kilo Moana'' indicated a depth of . The sonar system uses phase and amplitude bottom detection, with a precision of 0.2% to 0.5% of water depth; this is an error of about at this depth.〔 Further soundings made by the US Center for Coastal & Ocean Mapping in October 2010 are in agreement with this figure, preliminarily placing the deepest part of the Challenger Deep at , with an estimated vertical uncertainty of ±. A 2014 study concludes that with the best of 2010 multibeam echosounder technologies a depth uncertainty of ± (95% confidence level) on 9 degrees of freedom and a positional uncertainty of ± (2drms) remain and the location of the deepest depth recorded in the 2010 mapping is at ().〔 Only four descents have ever been achieved. The first descent by any vehicle was by the manned bathyscaphe ''Trieste'' in 1960. This was followed by the unmanned ROVs ''Kaikō'' in 1995 and ''Nereus'' in 2009. In March 2012 a manned solo descent was made by the deep-submergence vehicle ''Deepsea Challenger''. These expeditions measured very similar depths of . ==History of depth mapping from the surface== Over the years the search for the point of maximum depth has involved many vessels. *The HMS ''Challenger'' expedition (December 1872 – May 1876) first sounded the depths now known as the Challenger Deep. This first sounding was made on 23 March 1875 at station 225.〔(【引用サイトリンク】title=Report on the scientific results of the voyage of H.M.S. Challenger during the years of 1872-76 (page 877) )〕 The reported depth was at , based on two separate soundings. *A 1912 book, ''The Depths of the Ocean'' by Sir John Murray, records the depth of the Challenger Deep as , reporting the sounding taken by the converted navy collier USS ''Nero'' in 1899. Murray was one of the expedition scientists.〔(Page 131 ) of Murray's book refers to the Challenger Deep.〕 *In 1951, about 75 years after its original discovery, the entire Mariana Trench was surveyed by a second Royal Navy vessel, captained by George Stephen Ritchie (later Rear Admiral Ritchie); this vessel was also named HMS ''Challenger'', after the original expedition ship. This survey recorded the deepest part of the trench using echo sounding, a more precise and easier way to measure depth than the sounding equipment and drag lines used in the original expedition. A depth of was measured at . *The maximum surveyed depth of the Challenger Deep was reported in 1957 by the Soviet vessel ''Vityaz'' recording a spot ± deep at .〔 It was dubbed the ''Mariana Hollow'' and is listed in many reference sources, including the ''Encyclopædia Britannica'', articles in ''National Geographic''〔("Life Is Found Thriving at Ocean's Deepest Point" ), National Geographic News, 3 February 2005〕 and on maps. The pressure at this depth is approximately 1,099 times that at the surface, or . *In 1959 the US Navy research vessel ''RV Stranger'' using bomb-sounding surveyed a maximum depth of ± at .〔〔 *In 1962 the US Navy research vessel ''RV Spencer F. Baird'' using a frequency-controlled depth recorder surveyed a maximum depth of ± at .〔 *In 1975 and 1980 the US Navy research vessel ''RV Thomas Washington'' using a precision depth recorder with satellite positioning surveyed a maximum depth of ± at .〔 *In 1984, the survey vessel ''Takuyo'' from the Hydrographic Department of Japan, used a narrow, multibeam echo sounder to take a measurement of ± at .〔〔 *In 1998 a regional bathymetric survey of the Challenger Deep was conducted by the Deep Sea Research Vessel ''RV Kairei'', from the Japan Agency for Marine-Earth Science and Technology, using a SeaBeam 2112 multibeam echosounder. The regional bathymetric map made from the data obtained in 1998 shows that the greatest depths in the eastern, central, and western depressions are ±, ±, and ±, respectively, making the eastern depression the deepest of the three.〔 *In 1999 and 2002 the ''RV Kairei'' revisited the Challenger Deep. The cross track survey in the 1999 ''RV Kairei'' cruise shows that the greatest depths in the eastern, central, and western depressions are ±, ±, and ±, respectively, which supports the results of the 1998 survey. The detailed grid survey in 2002 showed that the deepest site is located in the eastern part of the eastern depression around , with a depth of ±, about southeast of the deepest site determined by the survey vessel ''Takuyo'' in 1984 and about east of the deepest place determined by the 1998 ''RV Kairei'' survey.〔 *On 1 June 2009 sonar mapping of the Challenger Deep by the Kongsberg Simrad EM 120 sonar multibeam bathymetry system for deep water (300 – 11,000 metres) mapping aboard the ''RV Kilo Moana'' (mothership of the ''Nereus'' underwater vehicle) indicated a depth of . The sonar system uses phase and amplitude bottom detection, which is capable of an accuracy of 0.2% to 0.5% of water depth across the entire swath.〔〔〔(EM 120 sonar multibeam bathymetry system brochure )〕 In 2014 the multibeam bathymetry data of this sonar mapping have yet to be publicly released, so the data are not available for comparisons with other soundings.〔 *On 7 October 2010 further sonar mapping of the Challenger Deep area was conducted by the US Center for Coastal & Ocean Mapping/Joint Hydrographic Center (CCOM/JHC) aboard the ''USNS Sumner (T-AGS-61)''. The results were reported in December 2011 at the annual American Geophysical Union fall meeting. Using a Kongsberg Maritime EM 122 multibeam echosounder system coupled to positioning equipment that can determine latitude and longitude up to accuracy, from thousands of individual soundings around the deepest part the CCOM/JHC team preliminary determined that the Challenger Deep has a maximum depth of at , with an estimated vertical uncertainty of ± at 2 standard deviations (≈ 95.4%) confidence level.〔 A secondary deep with a depth of was located at approximately to the east at in the Mariana Trench.〔〔(EM 122 Multibeam echosounder )〕〔(EM 122 sonar multibeam bathymetry system brochure )〕〔(Instruction manual EM Series (EM 120 & EM 122) Multibeam echo sounders )〕 In 2014 a study was conducted regarding the determination of the depth and location of the Challenger Deep based on data collected previous to and during the 2010 sonar mapping of the Mariana Trench with a Kongsberg Maritime EM 122 multibeam echosounder system aboard the USNS Sumner (T-AGS-61). This study by James. V. Gardner et al. of the Center for Coastal & Ocean Mapping-Joint Hydrographic Center (CCOM/JHC), Chase Ocean Engineering Laboratory of the University of New Hampshire splits the measurement attempt history into three main groups: early single-beam echo sounders (1950s - 1970's), early multibeam echo sounders (1980s - 21st century), and modern (i.e., post-GPS, high-resolution) multibeam echo sounders. Taking uncertainties in depth measurements and position estimation into account the raw data of the 2010 bathymetry of the Challenger Deep vicinity consisting of 2,051,371 soundings from eight survey lines was analyzed. The study concludes that with the best of 2010 multibeam echosounder technologies after the analysis a depth uncertainty of ± (95% confidence level) on 9 degrees of freedom and a positional uncertainty of ± (2drms) remain and the location of the deepest depth recorded in the 2010 mapping is at . The depth measurement uncertainty is a composite of measured uncertainties in the spatial variations in sound-speed through the water volume, the ray-tracing and bottom-detection algorithms of the multibeam system, the accuracies and calibration of the motion sensor and navigation systems, estimates of spherical spreading, attenuation throughout the water volume, and so forth. The 2009 and 2010 maximal depths were not confirmed by the series of dives ''Nereus'' made to the bottom during an expedition in May–June 2009. The direct descent measurements by the four expeditions which have reported from the bottom, have fixed depths in a narrow range from 10,916 m (''Trieste'') to 10,911 m (''Kaikō''), to 10,902 m (''Nereus'') to 10,898 m (''Deepsea Challenger'') Although an attempt was made to correlate locations, it could not be absolutely certain that Nereus (or the other descents) reached exactly the same points found to be maximally deep by the sonar/echo sounders of previous mapping expeditions, even though one of these echo soundings was made by ''Nereus'' mothership. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Challenger Deep」の詳細全文を読む スポンサード リンク
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