CSAMT电场y方向视电阻率的定义及研究

在准静态近似条件下，利用水平电偶源在均匀半空间表面激发电磁场的计算公式，讨论了可控源音频大地电磁法（CSAMT）水平电场y分量E_y的观测范围、特点和由其定义视电阻率的应用优势；E_y与常规标量CSAMT测量的E_x、H_y幅值范围不同，采集并利用E_y数据可以扩大CSAMT野外观测扇区，减少采集成本。依据电法及电磁法勘探中视电阻率定义的基本原则，提出了E_y视电阻率的定义，说明了其具备频率测深的意义；通过几种典型层状模型（均匀半空间，两层D、G，三层H、K以及四层KH、HK型）的数值计算，对比了E_y视电阻率和E_x、H_y、Z_xy、Re(Z_xy)等对应的波区视电阻率及E_x、Z_xy等对应的全区视电阻率对地电断面电性特征的反映效果。结果表明：E_y视电阻率的求取仅需测点的坐标和一个方向的电场值，计算方便、不必迭代，并且在曲线低频端收敛于一稳定值，可以明显改善非波区的畸变效应。

A New Apparent Resistivity of CSAMT Defined by Electric Field y-Direction

Under the quasi-static conditions, the measurement sector, features and advantages of electric field y-direction (E_y) of controlled source audio-frequency magnetotelluric are discussed according to  the formula of electromagnetic field data from horizontal electric dipole. The amplitude range of electric field y-direction is different from the common scalar CSAMT measurement.  E_y component data can be gathered and uesed to expand the CSAMT field observation sector and reduce the acquisition costs. According to the basic principal for definition of apparent resistivity in electrical prospecting, a new apparent resistivity defined by E_y is put forward and the sounding significance by frequency of which is explained. Through numerical calculation of several typical layered models, such as homogeneous half-space, D, G, H, K, KH and HK typical models, E_y apparent resistivity is compared with wave-area apparent resistivities defined by E_x、H_y、Z_xy、Re(Z_xy) and full-wave apparent resistivities defined by E_x、Z_xy. The results show that the derivation of  E_y apparent resistivity only needs  the coordinate of the sounding station and one direction E-field intensity and the iterative procedures are unnecessary. The new apparent resistivity easily calculated can satisfactorily eliminate the distortion effect of the near and transient area,because it can converge to a stable value at low frequency parts.