三维MCSEM海水层影响特征分析及消除方法

海洋可控源电磁法（MCSEM）是发现海底能源和研究海底地质构造的重要地球物理手段。在浅水域，这种方法具有挑战性的困难是如何消除海水层影响，空气波和海底界面反射电磁场是海水层影响的两个重要因素。本项目首先研究非均匀电导率背景分布（IBC）多网格局域拟线性（MGLQL）积分方程三维数值模拟方法，进而分析不同海水深度情况下空气波和海底反射电磁场的影响强度和特征。研究Stratton-Chu型积分性质，理论分析、推导并实现异常电磁场主部分解，论证异常场主部可以有效消除海水层影响。基于异常场主部分解解析式，构建可用于处理有限离散实际电磁数据的数值滤波器。通过分析数值滤波器的频谱特征，确定其相对异常场分解解析式的精度，并选择合理的滤波器参数，如窗口大小、采样步长、频率等。最后，利用典型海洋地质模型模拟数据，及国外MCSEM实测数据验证方法的稳定性和有效性。

Marine controlled-source electromagnetic （MCSEM）methods are a kind of important geophysical tool for surveying seabed energy sources and researching geological structure. One challanging difficuty of the method is how to remove the effect of seawater layer. Airwave and reflection from sea water-seafloor interface are two important factors of such effect. Firstly, this project studies a multigrid integral equation modeling method with inhomogeneous background conductivity (IBC) using the multigrid localized quasi-linear (MGLQL), then analysies the amplitude and characteristics of airwave and sea bottom reflection.Researching Stratton-Chu type integral properties, theoretically analyzing,deducing and achieving anamalous field main part separation, and discussing that one can uses anamalous field main part completely remove seawater layer effects. Based on above theoretical formula,constructing the digital filter to process practical finite and discrete EM data. Analyzing frequency spectrum characteristics to determine its precision and effectiveness, moreover determine reasonable filter parameters such as window size, sampling length, frequency and so on. Finally, using numerical data based on typical marine geological models and oversea practical MCSEM data to test the stability and effect of the method.