Design and Offshore Testing of the Nodal Deep Sea Seismic–Electromagnetic Joint Acquisition System

Abstract This paper presents the design, development, and offshore validation of OBSEM, a pioneering marine seismic-electromagnetic joint acquisition system aimed at enhancing comprehensive underwater observation capabilities. The system integrates the functionalities of ocean bottom seismometers (OBS) and ocean bottom electro-magnetometers (OBEM), enabling synchronous collection of seismic and electromagnetic signals. Detailed are the structural components, including sensors, data acquisition unit, power supply, clock synchronization system, and signal conditioning techniques employed to augment the signal-to-noise ratio of low-frequency electromagnetic signals. Noteworthy is the clock synchronization methodology employing a hybrid GPS and atomic clock configuration for precise temporal alignment. Furthermore, an automatic leveling system is engineered to maintain the seismometer’s horizontal orientation, crucial for ensuring data fidelity. The integration of seismic and electromagnetic data offers a significant advancement in marine geophysical surveys, promising heightened exploration efficacy and inversion accuracy. Offshore trials conducted in the South China Sea affirm the efficacy of OBSEM, with future endeavors aimed at deep-sea validation.