海洋CSEM是低频电磁探测方法，扩散电磁场满足似稳态麦克斯韦方程组，以随机运动为特征，存在频散。传统正演模拟方法需同时考虑电磁场的几何与物理衰减规律，对网格剖分要求极高。低频电磁场无波动性，没有明确的传播方向，故传统方法仅能静态地描述电磁场的分布特征，却难以动态地分析电磁场的传播规律。针对以上问题，本课题拟开展基于虚拟波动域的三维海洋CSEM正演和低频电磁场传播规律的分析。根据对应原理，把模拟低频扩散电磁场过程分解为模拟“虚拟电磁波”时间序列和计算“虚拟电磁波”随时间衰减的积分两个部分。“虚拟电磁波”仅有几何衰减，无频散，正演离散网格大小仅依赖于波长，再利用自适应亚网格技术精细剖分复杂地电模型，并根据“虚拟电磁波”传播特征动态地优化网格，提高计算精度和效率。“虚拟电磁波”有明确的速度和传播方向，存在反射、折射和绕射等现象，可结合波的运动学和动力学定量地动态分析海洋CSEM电磁场的传播规律。

Marine CSEM is a low-frequency electromagnetic survey method, the motion of the diffusive EM field, which satisfies quasi-static Maxwell's equations, is random and the EM propagation velocity is frequency dispersion. The traditional marine CSEM modeling methods require extremely excellent division mesh because they have to consider both the geometric and physical attenuation of the diffusive EM field. As the low frequency diffusive EM field is not a wave and has no clear propagation direction, the traditional method can only describe the distribution characteristics of the EM field statically without propagation analyzing dynamically. To address these problems, this project intends to carry out a three-dimensional marine CSEM modelling and field propagation analyzing based on the fictitious wave domain. According to the corresponding principle, the process of simulating the low-frequency diffusive EM field is decomposed into two parts: simulating the ‘fictitious EM wave’ time series and calculating the time attenuation integral of the ‘fictitious EM wave’. The velocity of the ‘fictitious EM wave’, which attenuate only geometrically, is not frequency dispersion, so the size of the modelling discrete grid depends only on the wavelength. By using the adaptive refinement mesh technology, the complex conductivity model can be finely dispersed and continually dynamically optimized based on the ‘fictitious EM wave’ propagation characteristics, and then the simulation accuracy and efficiency is improved. As the velocity and the propagation direction of the ‘fictitious EM wave’ is clear, the phenomena such as reflection, refraction and diffraction exists. Then the wave kinematics and dynamics can be used to analyze the propagation characteristic of marine CSEM EM field dynamically and quantitatively.