Mechanism Design of Seafloor Current Meter (SCM) with Broadband OBS and Data Analysis in the Northeastern offshore Taiwan

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To achieve precise measurements of near seabed water current velocities, this study designed a mechanical device for the Aquadopp-6000m Current meter that can be paired with the Yardbird-BB Ocean Bottom Seismometer (OBS). To ensure it does not affect the sinking rate during deployment or the buoyancy during recovery at sea, the overall ballasting of the OBS with the integrated water current meter needed to be recalibrated. The Aquadopp-6000m can record multiple physical data parameters simultaneously. During instrument deployment tests, we recorded the orientation of the entire OBS, time of seabed contact, time of seismic sensor detachment from the A-frame and falling onto the seabed, as well as profiles of sound speed, temperature, and pressure during the instrument sinking process. In deployment planning, it was determined that the original battery capacity inside the Aquadopp-6000m was insufficient to sustain the power consumption required for sampling rates of one sample per second for more than three months. This paper also provides detailed calculations for battery power and methods for modifying battery packs. Data from deployments in the Okinawa Trough in 2019 and 2020 indicated that seabed water current velocities and seismic activity share similar frequency characteristics over long periods. For seismic wave amplitudes greater than 0.006 m/s, there were intermittent decreases in water flow velocity following the arrival of radial S-waves, while the tangent component remained unaffected. Before the formation of typhoons thousands of kilometers away, atmospheric pressure variations were observed to influence minor changes in seabed temperature, seabed flow velocities, and seawater pressure, thereby affecting oceanic sound speed.