計量魚群探知機によるメタンプルームの観測とメタン運搬量の見積もり

摘要

During methane hydrate exploration and research, remote and on -board acoustic surveying and monitoring of methane hydrate can be easily and economically conducted using a quantita?tive echo sounder. Simultaneously, the structure and the floating -up speed of methane plumes can be obta ined from a n analysis of acoustic data. We conducted a survey of methane plumes from 2004 through 2008 at a spur situated south?west off the coast of Sado Island (tentatively called Umitaka Spur) and at the Joetsu Knoll. In 2007 and 2008, we performed experiments by releasing methane hydrate bubbles and methane hydrate, and letting them float upward. Consequently, we demonstrated that acoustical reflec?tion from the methane plumes correlates with water temperature and depth, that the floating-up speed is constant but depends on the conditions of methane hydrate, that the discharge of meth?ane hydrate bubbles changes, and that there is a wide scattering of materials below the seafloor where methane plumes are located. Furthermore, the amount of methane hydrate bubbles seep ?ing was estimated by a preliminary calculation. The method will be applied not only to basic research on methane hydrate but also to assess ?ments of the environmental impact of methane hydrate exploitation.