A High-Responsivity Subsurface Buoy System With a Fiber-Optic Acoustic Vector Sensor for Continuous Low-Frequency Acoustic Monitoring in the Deep Ocean: Development and Sea Trials

High-responsivity hydrophones play a crucial role in monitoring ocean acoustic fields, detecting underwater targets, and conducting underwater acoustics research. To address the challenges of long-term, high-responsivity vector acoustic detection for low-frequency signals in deep-ocean environments, we have developed and evaluated an underwater acoustic subsurface buoy system capable of operating at depths of up to 2000 m. This system utilizes fiber-optic acoustic vector sensors to capture vector information of particle acceleration and acoustic pressure in the surrounding field. It offers excellent directionality and can autonomously function for six months with reliability. After undergoing various tests including laboratory tests, hydrostatic pressure tests, and pool tests, the system underwent a 9-day trial in the northern South China Sea. During the trial, ambient noise, anthropogenic noise, bioacoustics, and microseisms induced by tropical cyclone Ma-on were investigated. The system demonstrated the ability to detect signals from explosive sources up to 100 km away and pick up microseisms at frequencies as low as sub-0.1 Hz. These trials showcased the system's capability to operate effectively in deep-ocean environments for over six-month deployments and acquire high-quality target signals, with potential applications in seismology, acoustics, biology, and oceanography research.