2022 Volume 33 Issue 4 Pages 87-94
A shipboard plume survey, using a high-frequency multibeam echo sounders (frequency 70-100 kHz) mounted on R/V"Kaimei", was conducted in the seafloor hydrothermal activity area of the Higashi-Aogashima knoll caldera. The high-resolution multiple acoustic scattering data of the water column were acquired. A voxel model with scattering intensity as an element was created by the Inverse Distance Weighting method for three-dimensional visualization and quantification of acoustic scattering. As a result, the specific acoustic scattering was found to be around chimneys and mounds at the base, and the scattering intensity structure was about 20 dB at the base and about 9 dB at the boundary with the water mass. The scattering shape was a conical shape with a base of 80 m in width and a height of 190 m, and the disappearing water depth of the scattering was approximately 560 m. From the similarities with the acoustic scattering of the Okinawa Trough, it was determined that the acoustic scattering detected this time was due to CO2 droplets derived from seafloor hydrothermal activity. The result shows the effectiveness of the shipboard plume survey using a highfrequency multibeam echo sounders and analysis method using voxel models in the Izu-Ogasawara arc.
