浅水环境海洋大地电磁资料噪声压制方法研究

The stratigraphic structure and deep complex geological structure of the marine remnant basins in the Yellow Sea and Bohai Sea are the focus of research on marine geosciences in China. Although a large number of seismic exploration work has been carried out in this area, however, due to the existence of underground high-speed shielding layer, the seismic imaging quality below it is limited, making it difficult to obtain a clear deep stratum structure by seismic method. The marine magnetotelluric method (MT) is not affected by the carbonate layer and can be used to detect the electrical structure of the deep formation beneath it. However, the depth of the Yellow Sea and the Bohai Sea are very shallow (average water depth is about 44 meters), the sea water movement is intense, the electromagnetic interference energy is strong, and the frequency band is mixed with the ocean MT signal band, which greatly reduces the signal-to-noise ratio of the MT data. If the existing marine MT data preprocessing method is applied to the processing of marine MT data in shallow waters, the special environment of electromagnetic detection in shallow waters should be considered. This project combines ocean dynamics and ocean electromagnetics to establish a geoelectric model in a marine dynamic environment. Numerical simulation is used to study the characteristics of seawater electromagnetic noise, using wavelet threshold denoising method and integrated mean empirical mode decomposition threshold denoising method. The electromagnetic interference of seawater movement is suppressed, and the vibration interference of magnetic field sensor is suppressed by adaptive filtering method, and applied to the processing of measured MT data in the South Yellow Sea.The development of this project can provide important technical support for the application research of China's marine magnetotelluric method, and it is an urgent research work.

黄海、渤海海相残留盆地地层结构和深部复杂地质构造研究是我国海洋地球科学的研究重点，该海域虽已开展了大量的地震勘探工作，但上覆高速屏蔽层的存在导致其下方地震成像质量受限，仅依靠地震方法难以获得清晰的深部地层结构。海洋大地电磁法（MT）不受高速屏蔽层的影响，可用于探测黄渤海深部地层电性结构。然而，黄海、渤海水深浅（平均水深约44米），海水运动剧烈，电磁干扰能量强且频带与海洋MT信号频带混叠，极大地降低了MT资料的信噪比。若将现有的海洋MT数据预处理方法应用于浅水区海洋MT资料处理，需考虑浅水区电磁探测的特殊环境。本项目拟将海洋动力学和海洋电磁学相结合，建立海洋动力环境下的地电模型，通过数值模拟方法研究海水运动电磁噪声特征，利用小波阈值去噪和集成平均经验模式分解阈值去噪等方法压制海水运动引起的电磁干扰，并应用于南黄海实测海洋MT资料处理。本研究能为浅水区海洋MT探测提出一种有效的数据处理方法。

黄海、渤海水深浅（平均水深约44米），海水运动剧烈，电磁干扰能量强且频带与海洋大地电磁（MT）信号频带混叠，极大地降低了MT资料的信噪比。若将现有的海洋MT数据预处理方法应用于浅水区海洋MT资料处理，需考虑浅水区电磁探测的特殊环境。本项目结合海洋动力学和海洋电磁学，提出了海浪感应电磁场数值模拟方法；建立了海浪动力模型和海洋地电模型，通过模拟不同海水运动速度及幅值等海洋环境模型的海浪感应电磁场，分析了海浪感应电磁场的电磁场特征和影响因素；基于浅水区大地电磁数据中海浪感应电磁噪声的特征，根据水平电场和水平磁场在频率域的导纳张量关系，提出了用基于导纳张量的复自适应滤波方法，并应用于合成数据和南黄海实测大地电磁资料，试验表明，所提出方法能够有效压制噪声，并有效提高海洋大地电磁数据信噪比。针对海浪感应磁噪声的特征及影响的频率范围，总结了一套适用于浅水区大地电磁数据的处理方法。