基于共轭梯度再加权优化的时间域海洋CSEM 1D各向异性反演研究

The marine controlled source electromagnetic method (CSEM) is a technology to determine the electrical structure under the seafoor by electromagnetic (EM) wave propagation. In this method, the EM signals are transmitted by the dipole souce (electrical /magnetic dipole-dipole ) located (or towed) in the ocean nearby the seafloor (or sea surface) into the seafloor, and then detected and recorded by the recievers deployed (towed) in the seafoor (or nearby the sea surface). The distributions of the conductivity under the seabed are obtained through analysing and interpreting the recorded EM signal. The responses of the time domain EM method is broadband signal, which is benefit to obtain more information about the subsurface structure. The transient EM method has been applied to achieve a great success in the terrestrial environment (such as mineral prospecting, etc.) , while it hasn’t been sufficiently applied and developed in the marine environment. The fact that the crust and the upper mantle are anisotropic determines that anisotropy must be considered in the marine EM survey. The research on the inversion of time domain marine CSEM data in anisotropy conductivity structure will be conducted in this application. Based on the inversion of frequency domain CSEM data in electrical isotropic structure and magnetotelluric data in anisotropic conductivity sructure, the target function which is suitable for the inversion of the time domain marine CSEM 1D data in anisotropic structure, is presented. Then the conjugate gradient reweighted optimization，whose convergence and stability have been found reliable in practical tests, will be applied to solve the inversion equations. The inversion of time domain marine CSEM 1D data in anisotropic structure will be finally achieved. The application will provide new data interpretation techniques and theoretical methods for the marine CSEM surveys.

海洋可控源电磁法（CSEM）是利用拖曳在海底（或海面）附近海水中的偶极源（电/磁偶极）发射随时间不断变化的电磁波，经海底反射之后被布置在海底（或拖曳在海面附近）的接收器探测和记录下来。通过对记录的电磁场特征分析进而获得海底下方的电性构造分布。时间域电磁法采用的频谱宽，有助于获得更多的地下构造的信息，它在陆地环境下（如探矿等）已取得了巨大的成功，而海洋环境下的应用及发展尚不足。地壳和上地幔是各向异性的事实决定了在海洋电磁探测中必须考虑各向异性的影响。本申请拟开展时间域海洋CSEM 1D各向异性反演研究，在借鉴频率域海洋CSEM各向同性反演以及大地电磁各向异性反演的基础上，提出适合于时间域海洋CSEM 1D各向异性反演的目标函数，在反演过程中采用收敛性和稳定性高的共轭梯度再加权优化方法求解反演方程，最终实现时间域海洋CSEM 1D各向异性反演，为海洋电磁探测提供新的数据解释手段和理论方法技术。