Editing Challenger Deep (section)

===1992 – RV ''Hakuhō Maru''===
The 3,987-ton Japanese research vessel ''Hakuhō Maru'', an Ocean Research Institute – University of Tokyo sponsored ship, on cruise KH-92-5 cast three Sea-Bird SBE-9 ultra-deep [[CTD (instrument)|CTD]] (conductivity-temperature-depth) profilers in a transverse line across the Challenger Deep on 1 December 1992. The center CTD was located at {{Coord|11|22.78|N|142|34.95|E}}, in the eastern basin, at {{convert|10989|m|ft}} by the SeaBeam depth recorder and {{convert|10884|m|ft}} by the CTD. The other two CTDs were cast 19.9&nbsp;km to the north and 16.1&nbsp;km to the south. ''Hakuhō Maru'' was equipped with a narrow beam SeaBeam 500 multi-beam echosounder for depth determination, and had an Auto-Nav system with inputs from [[Satellite Transit System|NAVSAT/NNSS]], GPS, Doppler Log, EM log and track display, with a [[Geodetic datum|geodetic positioning]] accuracy approaching {{convert|100|m|ft}}.<ref>{{cite web |url=https://www.aori.u-tokyo.ac.jp/english/coop/hakuhomaru.html |title=Research Vessel Hakuho Maru |publisher=Atmosphere and Ocean Research Institute, The University of Tokyo |access-date=21 January 2020 |archive-date=27 July 2020 |archive-url=https://web.archive.org/web/20200727192321/https://www.aori.u-tokyo.ac.jp/english/coop/hakuhomaru.html |url-status=live }}</ref> When conducting CTD operations in the Challenger deep, they used the SeaBeam as a single beam depth recorder. At {{Coord|11|22.6|N|142|35.0|E}} the corrected depth was {{convert|10989|m|ft}}, and at {{Coord|11|22.0|N|142|34.0|E}} the depth was {{convert|10927|m|ft}}; both in the ''eastern'' basin. This may demonstrate that the basins might not be flat [[Sedimentary basin|sedimentary pools]] but rather undulate with a difference of {{convert|50|m|ft}} or more. Taira revealed, "We considered that a [[Trough (geology)|trough]] deeper that ''Vitiaz''{{'s}} record by {{convert|5|m|ft}} was detected. There is a possibility that a depth exceeding {{convert|11000|m|ft|0}} with a horizontal scale less than the [[beam width]] of measurements exists in the Challenger Deep.<ref>Keisuke Taira, Daigo Yanagimoto and Shoji Kitagawa, [https://www.terrapub.co.jp/journals/JO/pdf/6103/61030447.pdf "Deep CTD Casts in the Challenger Deep, Mariana Trench"] {{Webarchive|url=https://web.archive.org/web/20200919101822/https://www.terrapub.co.jp/journals/JO/pdf/6103/61030447.pdf |date=19 September 2020 }}, 447 ''Journal of Oceanography'', Vol. 61, pp. 447–454, 2005</ref> Since each SeaBeam 2.7-degree beam width sonar ping expands to cover a circular area about {{convert|500|m|ft|0}} in diameter at {{convert|11000|m|ft|0}} depth, dips in the bottom that are less than that size would be difficult to detect from a sonar-emitting platform seven miles above.

[[File:JAMSTEC Yokosuka P5123676.jpg|thumb|RV ''Yokosuka'' was used as the support ship for ROV ''Kaikō''.]]