Deep marine controlled-source electromagnetic (CSEM) prospecting has attracted extensive interest because it enables high efficiency and high horizontal-resolution prospecting of gas hydrate and oil. However, the elimination of time errors between the transmitter and the receiver and realization of long-distance high-speed real-time data transmission (submarine towed body status information and raw electromagnetic field data stream) are worthwhile challenges that require continuous effort. We developed a novel towed CSEM system using double-vessels that have high time synchronization accuracy and real-time data transmission. The near-seafloor-towed CSEM receiver contains a deck user terminal, master node, slave nodes, tail buoy, and neutrally buoyant towed cable. The deck user terminal generated and transmitted a pulse per second to the master node through a fiber converter and optical fiber. The RS-485 transceiver then turned the pulse signal into a differential signal and transmitted it to each slave node for error-free synchronization. The time information was also transmitted from the deck user terminal to various nodes through ethernet switches, optical fibers, and serial to ethernet converters. The deck user terminal can conveniently communicate with each node cascaded by the ethernet switch through ethernet and fiber optic communication technology. During an offshore experiment involving oil and gas exploration in the South China Sea, the towed CSEM receiver continuously acquired all electromagnetic components and status information, which achieved a preliminary prospecting result. The maximum transfer rate of real-time data can reach 10 Mbps with 300 m distance between each slave node, and the time synchronization error between transmitter and receiver is less than ±3 µs.

中文翻译：

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拖曳式电磁接收机的时间同步与数据传输方法

深海控源电磁（CSEM）勘探因其能够实现天然气水合物和石油的高效率和高水平分辨率勘探而引起了广泛的兴趣。然而，消除发射机和接收机之间的时间误差，实现远距离高速实时数据传输（潜艇拖曳体状态信息和原始电磁场数据流）是值得挑战的，需要不断努力。我们开发了一种使用双船的新型拖曳 CSEM 系统，具有高时间同步精度和实时数据传输。近海底拖曳式 CSEM 接收器包含甲板用户终端、主节点、从节点、尾浮标和中性浮力拖曳电缆。卡座用户终端每秒产生一个脉冲并通过光纤转换器和光纤传输到主节点。RS-485 收发器然后将脉冲信号转换为差分信号并将其传输到每个从节点以实现无差错同步。时间信息也通过以太网交换机、光纤和串行以太网转换器从甲板用户终端传输到各个节点。卡座用户终端可以通过以太网和光纤通信技术方便地与以太网交换机级联的各个节点进行通信。在南海油气勘探的海上实验中，拖曳式CSEM接收机持续获取所有电磁成分和状态信息，取得了初步找矿效果。