(1. 北京矿产地质研究院，北京 100012；2. 中南大学 地球科学与信息物理学院，长沙 410083)
摘 要: 提出一种在近区测量磁场垂直虚分量提取视电阻率的频率域电磁测深方法，通过分析其特性并进行数值模拟，初步建立近区频率域电磁测深理论体系，为观测系统的设计提供理论基础。通过研究线圈中心均匀大地电磁场，推导相关解析表达式并将成熟的双频和伪随机合成电流移植到本方法中。根据一定近似条件下电磁场的理论公式，深入研究载流线圈中心垂直磁场虚分量提取视电阻率的方法特性，并编写相应正演程序，对二层、三层和四层等地电模型进行数值模拟，分析其对地下电性分布变化的分辨力。最后，根据模拟结果揭示本方法的可行性及实际意义。
关键字: 垂直磁场虚分量；线圈中心；数值模拟；频域电磁法
（1. Beijing Institute of Geology for Mineral Resources, Beijing 100012, China;
2. School of Geoscience and Info-physics, Central South University, Changsha 410083, China）
Abstract:A new frequency domain electromagnetic sounding method of extracting apparent resistivity was put forward through measuring its near zone magnetic field vertical virtual component, and a theoretical system of near zone frequency domain electromagnetic sounding method was conatructed by analyzing its characteristics and conducting numerical simulation, and a theoretical foundation was provided for the design of the observing system. The method integrates the mature formula of dual and pseudorandom synthetic current by studying the coil center homogeneous magnetotelluric field and deducing the related analytical expression. According to the theoretical formula fo magnetic field under certain approximate conditions, the method characteristics on extracting apparent resistivity were studied by vertical virtual component of magnetic field at current carrying coil center, the corresponding forward programs were written and its better resolution on underground electrical distribution changes was analyzed through numerical simulation on two-layered, three-layered, four-layered geoelectric models. The feasibility and significance of the method were revealed based on the simulation results.
Key words: imaginary component vertical to magnetic field; loop center; numerical simulation; frequency domain electromagnetic sounding
