Abstract: The preliminary research result of electromagnetic prospecting of the near field(transition region) of long grounded wire in frequency domain is presented in this paper.And the full-region apparent resistivity is defined and calculated from some modeling results including the response of half space and the response of stratified space.From the results,we get the conclusion that the full-region apparent resistivity in the above situation defined from horizontal electric field and vertical magnetic field can yield a good outcome of underground electric structure.The full-region apparent resistivity calculated by using dichotomy after joining horizontal magnetic field and horizontal electrical field together can also reflect the change of electric structure underground.The full-region apparent resistivity defined by using a single component in the near field matches well with the single dimensional MT curve,therefore,mature MT inversion technology can be used to do the inversion of the near field,thus transforming the function with source to non-source types.It is available to prospect in the near field(transition region) with long grounded wire,even there are still some pending problems.

Key words: line source, near field(transition region), full-region apparent resistivity, stratified media

摘要： 对频率域无限长线源近区(过渡区)测深的理论基础进行了探索性研究。通过计算均匀半空间、层状介质等多个模型的线源响应,进而定义并计算全区视电阻率。结果发现,利用水平电场、垂直磁场分别计算的全区视电阻率均能较好地反映地下电性结构的变化。把水平磁场与水平电场联合通过二分搜索算法计算的全区视电阻率也能较好地反映地下电性结构的变化。在近区通过单分量定义的全区视电阻率与一维MT曲线吻合得很好,因此可以用成熟的MT反演技术来进行线源近区电磁资料的反演,从而把有源的问题转化到无源的问题。这初步表明频率域线源近区(过渡区)测深是可行的,但还有一些问题需要解决。

关键词: 线源, 近区(过渡区), 全区视电阻率, 层状介质