Marine submerged buoys can effectively obtain various parameters of seawater, which plays an important role in the research of marine physical phenomena, marine environmental changes, and climate change. However, traditional self-contained submerged buoys usually work underwater at a depth of about 100 m, and the observation data cannot be obtained before their recovery, which cannot satisfy the needs of real-time data acquisition for marine scientific research. To solve this problem, this paper proposes a real-time communication subsurface mooring system that consists of a satellite communication buoy (SCB), conductivity–temperature–depth sensors (CTD), and an inductive coupling mooring cable. The underwater inductive coupling link collects the data from the underwater sensors and transmit it to the SCB. Then, the data will be transmitted to the station receiver via satellite communication module integrated into the SCB. In order to ensure a high success rate of data recovery, the stress analysis and hydrodynamic simulation of the SCB were carried out in this paper. The results show that the SCB maintained a relatively stable attitude in the 3–4 sea state. The attitude data obtained from the subsequent sea trial was consistent with the simulation results, and the success rate of satellite communication during this period was more than 95%. In this paper, a modular embedded hardware circuit was designed to meet the functional requirements of the subsurface mooring system. An efficient data recovery strategy was also developed, which ensured that the average power consumption of the system was low and the success rate of data recovery is not less than 90% when operating in the severe sea state for a long time. The system underwent sea trials in the South China Sea for more than 3 months from the end of 2021 to the beginning of 2022. It transmitted more than 2034 sets of seawater profile temperature, salinity, and depth data in real-time, with a success rate of over 91% of the total sample data. The CTD data returned in real-time from our system is consistent with the data of the HYCOM and World Ocean Atlas (WOA), and a cyclonic mesoscale eddy was detected in the operation area.

The ocean represents the cradle of life on Earth, making it essential to comprehend the complex interactions between marine animal behaviors and the physical microstructure of their environments in order to study their behavioral ecology. Due to the vastness of the ocean, traditional observational techniques are constrained by distance, which poses significant challenges for conducting extended and continuous research on marine animal behavior and ecology. To overcome these challenges, this paper introduces a behavior recording tag system incorporating temperature, pressure, and miniature inertial measurement unit (MIMU) sensors as data collection modules. These sensors are integrated with a main control module and a data storage module to gather and archive behavioral and environmental information. A combined positioning recovery method is proposed, developed, and validated to address the issue of retrieving the tag system post data collection. The behavior recording tag system’s performance was assessed through laboratory and pool tests. The findings show that the accuracy of temperature sensor is about 0.01 °C, the accuracy of pressure sensor is approximately 0.5% of full scale, the continuous data collection duration can extend to 3 days, and the recovery window time after surfacing exceeds 7 days, underscoring its viability as a marine animal behavior recorder.

To address the challenge in real-time communication mooring systems where clock synchronization and data transmission are difficult to achieve simultaneously over a single jacketed steel cable loop, this paper develops a dual-carrier inductively coupled communication (ICC) scheme based on the design concept of frequency division multiplexing (FDM). Two carrier signals with distinct frequencies and modulation schemes are loaded in parallel onto the same cable loop, using binary differential phase-shift keying (2DPSK) to carry minute-level data communication and binary phase-shift keying (2PSK) to carry microsecond-level clock synchronization broadcasts. To resolve inter-carrier crosstalk and channel attenuation, a single-stage multiple feedback (MFB) narrow bandpass filter and a three-stage analog front-end consisting of “passive high-impedance filtering, differential-to-single-ended conversion, and multistage active high-gain amplification” are designed in hardware, achieving efficient separation of hybrid signals and suppression of noise. In software, a combined demodulation architecture based on digital delay differential and zero-crossing decision, along with a digital Costas loop, is constructed to accomplish data demodulation and high-precision pulse-per-second (PPS) clock recovery. Laboratory and 300 m nearshore sea trial results demonstrate that the system achieves a packet reception ratio of over 89.60%, an error-free packet delivery ratio exceeding 83.24% with a bit error ratio below 0.22%, and maintains a clock synchronization error within 200 µs.