电磁探测盲区中位移电流效应的关键问题研究

The region of near surface and underground 20m is extremely close to human activities, but it is also called the detection blind area for traditional electromagnetic methods. When applying the transient electromagnetic method (TEM) or the high-frequency electromagnetic method into such region, the displacement current effect becomes a key issue and must be considered. At present, the research on displacement current effect was rarely involved in TEM and also very limited in the high-frequency electromagnetic method. So we proposed the following systematic research topics as theory of displacement current effect, shallow probing application of TEM when the displacement current is considered, the displacement current effect experimental verification and engineering applications. At the basis of displacement current effect research, we hope to establish the forward and data interpretation theory for shallow electromagnetic detection in blind area. And at the same time we hope to provide a theoretical basis for instrument development and application. We also adopt the nonlinear optimization and Gramian method in stratification parameters inversion when considering the displacement current. And then we can achieve a shallow multi-parameter cross-sectional imaging. The research on displacement current effect will not only expand and improve the applications for electromagnetic detection, but also achieve a very good result as joint inversion because it can provide the conductivity and dielectric coefficient at the same time. The method is expected to be applied to the ground corrosion diagnosis and geology for water and other engineering. So the project has important theoretical significance and application value.

地下近地表20m范围与人类活动极为密切，却又是传统电磁方法的探测盲区，而将瞬变电磁法或高频电磁法应用到盲区，位移电流效应就成为一个必须考虑的关键问题。目前，位移电流效应研究在瞬变电磁法极少涉及、在高频电磁法方面的国内研究也非常有限，因此项目提出系统研究位移电流效应理论、计及位移电流的瞬变电磁法浅层探测应用、位移电流效应实验验证及工程应用等内容。希望通过位移电流效应的研究建立浅层电磁探测盲区正演和资料解释的理论依据，同时为仪器研发和应用提供理论基础。并在考虑位移电流效应下采用非线性优化和Gramian方法反演分层参数，进而实现浅层多参数剖面成像。计及位移电流效应的研究将拓展和完善电磁探测的应用领域，而且相对传统电磁法又能同时提供电导率和介电系数信息，获得类似联合反演的效果，并有望应用于接地腐蚀诊断和地质找水等工程中。因此，开展位移电流效应研究具有重要的理论意义和应用价值。

地下近地表20m范围与人类活动极为密切，却又是传统电磁方法的探测盲区，而将瞬变电磁法或高频电磁法应用到盲区，位移电流效应就成为一个必须考虑的关键问题。目前，位移电流效应研究在瞬变电磁法极少涉及、在高频电磁法方面的国内研究也非常有限，因此项目提出计及位移电流效应的研究课题。主要开展了以下工作：.(1) 系统推导典型激励源、典型结构模型下的频域和时域在计及位移电流下的理论解，探讨似波现象及时域(瞬变早期)瞬变电磁场的传播机理；推导斜坡和指数关断下、计及位移电流的瞬态电磁场理论解，分析媒质地电参数及结构与瞬变电磁响应的关系；进一步研究复介电系数对位移电流效应的影响。.(2) 构建高频电磁法实验平台，同时开展理论仿真和实验实测并与实测结果进行对比分析；开展位移电流效应验证的实验设计，准备不同电导率、介电系数和结构参数下的实验对象；瞬变电磁系统的关断效应、收发线圈的直接耦合以及接收线圈过渡过程研究；开展位移电流效应的瞬变电磁法实验和理论仿真并对比分析。.(3) 在分层媒质模型下，研究非线性优化算法并结合Gramian方法，开展对媒质电导率、介电系数和层厚参数的反演；在单点分层参数反演基础上，结合多点测量方式，开展浅层多参数二维剖面成像研究。.项目研究工作基本按照计划正常进行，完成了计划的研究内容，给出计及位移电流的理论解、考虑关断效应的理论解、完成位移电流效应的频域实验验证、给出改进的浅层参数非线性反演方法并实现浅层成像。