基于正交激励源的极低频电磁波传播特性研究

The electromagnetic (EM) method using controlled source extremely low frequency (CSELF) wave is a new technology that is based on the large-power alternating electromagnetic field generated by an artificial procedure. The project intends to carry out the propagation characteristics study of the extremely low frequency electromagnetic waves, which generated by orthogonal horizontal electrical bipoles. First, we will establish the model for CSELF based on the orthogonal excitation source. Applied R function method for mathematical derivation, just like that in CSAMT, and we will deduce the formulas for electric and magnetic field component with horizontally layered isotropy formation model. Then we will deduce the formulas of spatial domain dyadic Green's function. Then we will apply Hankel filter with high sampling density and high order window function and continued fraction expansion technique to achieve the Sommerfeld integral. On this basis, achieve one-dimensional forward and three-dimensional forward modeling which based on the integral equation method. Calculate the electromagnetic wave distribution and radiation pattern for ELF which generated by orthogonal horizontal electrical bipoles, and study the electromagnetic wave characteristic when the phase of the two orthogonal sources changes or two orthogonal sources have different power contrasts. Plan to use decay rate find out a new and more reasonable method for near-field, far-field and wave-guide zone division. And then analysis the static effects, shadow effects of the ELF waves which generated by orthogonal horizontal electrical bipoles. Study the effect course by the ionosphere and the displacement current. In the end, we will reveal the characteristics of ELF wave which generated by orthogonal horizontal electrical bipoles. The study on the electromagnetic field characteristics ELF, can furnish the information for resolution, instrument development, data processing and measuring setting.

本项目拟开展基于正交水平激励电缆源的极低频电磁波传播特性研究。首先推导给出基于正交激励源的极低频电磁波水平分层各向同性介质的场强表达式；其次推导得到基于正交激励源的极低频电磁波水平分层空间域的并矢Green函数；然后采用高采样密度的Hankel滤波和基于高阶窗函数结合连分式展开法实现Sommerfeld积分；实现正交激励极低频电磁波一维正演和基于积分方程法三维正演。以此为基础，给出水平分层，正交激励时2个场源不同相位差、不同功率构成的组合电流激励信号条件下的场强分布，从衰减率的角度提出更为合理的近区、远区、波导区的划分方法；分析典型三维地电模型的静态效应、阴影效应等，分析电离层和位移电流对正交激励极低频电磁场的影响，阐述正交激励极低频电磁波的传播特性。项目作为"极低频探地工程"的基础研究，对该方法的推广实施，提升整体学术水平，具有重要的理论及实际意义。

大功率人工源极低频电磁技术是利用强大的人工固定源发射信号，探测地下电性细结构的新方法，是地球物理学和无线电物理学相结合的产物。其特点是信号强度大，抗干扰能力强，信号一致性好，测量误差小，覆盖范围广，是大地电磁测深法（MT）和可控源音频大地电磁法（CSAMT）的改进。将为我国地下资源和海洋资源探测、地震预报、气象预报、空间物理研究、地球圈层结构以及各圈层之间的相互作用和耦合关系等前沿科学技术研究提供一种全新的技术手段，是我国地下资源探测和地震预测方法的重大技术创新。.本项目开展基于正交水平激励电缆源的极低频电磁波传播特性研究。首先推导得到水平电偶源（HED）水平分层各向同性介质地表的场强计算公式，通过坐标转换和矢量合成给出基于正交激励源的极低频电磁波水平分层各向同性地表的场强计算公式。基于上一步得到HED的地表场强计算公式和各层间的边界条件推导出HED水平分层空间域的Green函数，通过坐标转换和矢量合成给出基于正交激励源的空间域的Green函数。.然后采用高采样密度的Hankel滤波和外插求积法展开法实现Sommerfeld积分；实现正交激励极低频电磁波一维正演和基于积分方程法三维正演。以此为基础，给出水平分层，正交激励时2个场源不同相位差、不同功率构成的组合电流激励信号条件下的场强分布。.本研究从衰减率的角度提出了更为合理的近区、远区、波导区的划分方法。分析电离层和位移电流对正交激励极低频电磁场的影响。阐述正交激励极低频电磁波的传播特性。.本项目经过三年的研究工作，完成了设计任务要求。已发表学术论文12篇，专著1本，其中SCI检索1篇，EI检索3篇。申请发明专利1项。参加国际学术会议4人次，参加国内学术会议4人次。培养研究生10人，获得硕士学位5人；培养本科生2人，获得硕士学位2人。