Feasibility Study of ROV-Towed Marine Loop Electromagnetic System through Off-Shore Experiment

We performed an off-shore experiment with a new marine small loop electromagnetic (EM) survey system, which was developed primarily for exploration of seafloor hydrothermal deposits. The system is a multi-frequency loop EM system designed to endure high pressure in deep sea up to 2000 m. In order to maintain altitude of the system from the seafloor in rough seafloor topography condition, the system was connected rigidly to ROV (Remotely Operated Vehicle) which tows the system. We performed a test with the new loop EM system by keeping altitude of ROV 2 m above from the seafloor at a depth of 300 m near Tonga off-shore. The ROV position and attitude while moving (pitch, roll, yaw) and CTD (Conductivity, Temperature, Depth) data are also recorded simultaneously with electromagnetic responses. Experimental results showed that electromagnetic anomaly was clearly identified at the location of metallic object, and the pattern of the EM responses matches well with the theoretical responses from a 3-D integral equation EM modeling code. With the test in Tonga offshore, we confirmed that the method of operation of the EM survey system by ROV was readily feasible, and the system could detect actual seafloor hydrothermal deposits in the highly conductive seafloor environment.