In August 2005, we succeeded in operating AUV "r2D4", which was constructed in July 2003 as one of fruits of R-Two project, into Myojin-sho Underwater Caldera in full autonomous mode. The caldera is located about 800km in the south of Tokyo, and 8km in diameter. There is an active underwater volcano Myojin-sho at the Northeastern part of outer rim of caldera, which erupted repeatedly in 1952. The Kuroshio Current is usually running over the Caldera, so that current speed around it is sometimes more than 3 knots. It can be said that the diving of human occupied vehicle and remotely operated vehicle into Myojin-sho Caldera is very dangerous due to such hostile environment. The interferometry SONAR captured a clear image of the central cone in the middle of crater, and the in-situ chemical analyzer "GAMOS" detected high concentration of manganese ion which indicates hydro-thermal activity in the crater.
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