Acoustic and visual survey of manganese crusts using an underwater vehicle at #5 Takuyo seamount

This paper describes acoustic and visual instruments developed to perform high resolution surveys of manganese crusts. The instruments consist of an acoustic device developed to perform in situ measurements of manganese crust thickness at depths of up to 3000m, and a vision based mapping system that generates three-dimensional colour reconstructions of the sea floor. The developed systems operate at low altitudes, using an underwater platform such as an autonomous underwater vehicle (AUV) or remotely operated vehicle (ROV) to maintain a close range to the sea floor. In this communication, the authors describe the acoustic probe and vision based mapping system together with the algorithms that have been implemented to process the data they obtain, and present some results from sea trials performed using the ROV Hyper-Dolphin of JAMSTEC during the NT10-11 cruise of the R/V Natsushima at #5 Takuyo seamount. During the survey, the ROV was operated at depths of between 1000 and 3000 m at low altitudes of <;1.0m, with surge velocities of between 0.4 to 0.6 knots to survey the area both acoustically and visually. The results are the first time in situ measurements of manganese crust thickness have been successfully performed, and demonstrate that the proposed instruments are useful tools to enable more efficient surveys of manganese crusts.