Sound source characteristics of an operating polymetallic nodule mining vehicle

Experimental mining activities have begun in deep waters. These resources are present in vast quantities, and if they can be stably supplied from Exclusive Economic Zone (EEZ) or from international waters, they hold great potential for promoting industry and ensuring economic security. Deep Ocean Resources Development Co., Ltd. (DORD) has contract areas at the Clarion Clipperton Fracture Zone (CCFZ) and is developing mining vehicle for polymetallic nodule. The deep seafloor is a quiet environment, and there is growing concern about the potential impacts of noise generated by such activities on deep-sea ecosystems and biodiversity. In this study, we conducted a test operation of a mining vehicle in a shallow-water area and measured its acoustic properties. The mining vehicle was remotely operated from a vessel, and the time of its closest point of approach to the hydrophone was determined acoustically. The closest distance was directly measured by a diver based on visible track marks. As a result, the frequency range contributing most to the acoustic energy was identified as 90–110 Hz. The overall broadband source level was estimated to be 161 dB rms re 1 μPa, which is similar to the source level of a fishing boat.