page_title: Challenger Deep
section_title: Surveys and bathymetry
hierarchical_section_title: Challenger Deep / Surveys and bathymetry
caption_attribution_description: R/V Melville (1967) – originally built as the USNS Melville (T-AGOR-14) -- is a research vessel operated by Scripps Institution of Oceanography for oceanographic research. The R/V Melville is the oldest active vessel in the academic research fleet, collectively known as the University-National Oceanographic Laboratory System. Wikipedia Naval Base San Diego USS Essex (LHD-2) Family Reunion 2016 Photo: TDelCoro March 4, 2016
context_page_description: The Challenger Deep is the deepest known point in the Earth's seabed hydrosphere, with a depth of 10,902 to 10,929 m by direct measurement from deep-diving submersibles, remotely operated vehicles and benthic landers and slightly more by sonar bathymetry.
  The Challenger Deep is located in the Western Pacific Ocean, at the southern end of the Mariana Trench near the Mariana Islands group. According to the August 2011 version of the GEBCO Gazetteer of Undersea Feature Names, the Challenger Deep is 10,920 m ±10 m deep at 11°22.4′N 142°35.5′E.
  This location is in the ocean territory of the Federated States of Micronesia.
  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. The high water pressure at this depth makes designing and operating exploratory craft difficult. The first descent by any vehicle was by the manned bathyscaphe Trieste in January 1960; unmanned visits followed in 1996, 1998 and 2009. In March 2012 a manned solo descent was made by film director James Cameron in the deep-submergence vehicle Deepsea Challenger.
context_section_description: Over many years, the search for, and investigation of, the location of the maximum depth of the world's oceans has involved many different vessels, and continues into the twenty-first century.
  The accuracy of determining geographical location, and the beamwidth of (multibeam) echosounder systems, limits the horizontal and vertical bathymetric sensor resolution hydrographers can obtain from onsite data. This is especially important when sounding in deep water, as the resulting footprint of an acoustic pulse gets large once it reaches a distant sea floor. Further, sonar operation is affected by variations in sound speed, particularly in the vertical plane. The speed is determined by the water's bulk modulus, mass, and density. The bulk modulus is affected by temperature, pressure, and dissolved impurities (usually salinity).
  1875 – HMS Challenger –– In 1875, during her transit from the Admiralty Islands to Yokohama, the three-masted sailing corvette HMS Challenger attempted to make landfall at Guam, but was set to the west by "baffling winds" preventing them from "visiting either the Carolines or the Ladrones." These winds pushed her track to the west, across the 35-mile-long depression which, 85-years later, would achieve prominence as the Challenger Deep. Even more amazing, one of her thirteen sampling stations on that 2,300 nm track to Japan was within fifteen miles of the deepest depression in the world’s oceans. 
  On 23 March 1875, at sample station number #225, HMS Challenger recorded the bottom at 4,475 fathoms (26,850 ft; 8,184 m) deep, (the deepest sounding of her three-plus-year eastward circumnavigation of the Earth) at 11°24′N 143°16′E—and confirmed it with a second sounding at the same location. Depth soundings were by Baillie-weighted marked rope, and geographical locations were determined by celestial navigation (to an estimated accuracy of two nautical miles).
  The serendipitous discovery of Earth’s deepest depression by history’s first major scientific expedition devoted entirely to the emerging science of oceanography, was incredibly good fortune, and especially notable when compared to the Earth’s third deepest site (the Sirena Deep only 150 nautical miles east of the Challenger Deep), which would remain undiscovered for another 122 years.
  1951 – SV HMS Challenger II –– Seventy-five years later, the 1,140-ton British survey vessel HMS Challenger II, on her three-year westward circumnavigation of Earth, investigated the extreme depths southwest of Guam reported in 1875 by her predecessor, HMS Challenger. On her southbound track from Japan to New Zealand (May–July 1951), Challenger II conducted a survey of "the Marianas Trench between Guam and Ulithi  [sic]," using seismic-sized bomb-soundings and recorded a maximum depth of 5,663 fathoms (33,978 ft; 10,356 m). The depth was beyond Challenger II's echo sounder capability to verify, so they resorted to using a taut wire with "140-lbs of scrap iron", and documented a depth of 5,899 fathoms (35,394 ft; 10,788 m).
  In New Zealand, the Challenger II team gained the assistance of the Royal New Zealand Dockyard, "who managed to boost the echo sounder to record at the greatest depths." They returned to the "Marianas Deep" (sic) in October 1951. Using their newly improved echo sounder, they ran survey lines at right angles to the axis of the trench and discovered "a considerable area of a depth greater than 5,900 fathoms (35,400 ft; 10,790 m)"—later identified as the Challenger Deep’s western basin. The greatest depth recorded was 5,940 fathoms (35,640 ft; 10,863 m), at 11°19′N 142°15′E. Navigational accuracy of several hundred meters was attained by celestial navigation and LORAN-A. Note that the term "Challenger Deep" came into use after this 1951-52 Challenger circumnavigation, and commemorates both British ships of that name involved with the discovery of the deepest basin of the world’s oceans.
  1957–1958 – RV Vityaz –– In August 1957, the 3,248-ton Vernadsky Institute of Geochemistry research vessel Vityaz recorded a maximum depth of 11,034 metres (36,201 ft)±50 
caption: The RV Melville was operated by the Scripps Institution of Oceanography
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