中心回线瞬变电磁测深全区视纵向电导解释方法

从“薄板理论”出发，利用良导薄板上磁偶极子源激发的瞬变电磁场电场分量的表达式和互换原理推导出了中心回线瞬变电磁测深法的感应电动势与纵向电导和深度的关系表达式。通过利用感应电动势及其一阶导数表达式作简单数学推导，给出了全区视纵向电导与视深度的反演算法。所求取的视纵向电导曲线不受过渡区影响和其本身固有的特点：曲线斜率大小与电导率成正比；斜率发生变化的位置对应于电性界面；对比一条剖面上相邻的曲线形态，可以连续追踪同一地层界线，形成地电断面。利用这些特征，可获得较高质量的中心回线瞬变电磁测深电性剖面。为了验证视纵向电导解释法的有效性，采用了典型的3层H型和4层HK型地电模型的正演数据方法进行检验。试验结果表明，全区视纵向电导曲线能较好地划分电性层，并能指示电性变化关系。最后，给出视纵向电导解释方法的应用实例，通过全区视纵向电导反演计算，绘制的视纵向电导剖面具有良好的分层性，与同一剖面的反演电阻率剖面有较好的一致性，说明全区视纵向电导解释方法简单易行且有效。

All-time apparent vertical conductance interpretation method for central loop transient electromagnetic sounding

Based on the transient electromagnetic theory of a thin sheet approach, the induced EMF formula as a function of vertical conductance and depth was derived by using the reciprocation law and the formula of electric component induced by a vertical magnetic dipole over a thin sheet. At the same time, the inversion algorithm of Central Loop Transient Electromagnetic Method(CLTEM) for all time apparent vertical conductance and apparent depth was proposed by using EMF and its first derivative. In the transitional area there is no distortion for the calculated curve of apparent vertical conductance. The curve features many good characters as that the conductivity is proportional to the slope of the curve, that the changing point of the slope indicates the interface of geo model, and that by tracing the similarities of curves the structure of interfaces can be figured out. With these characters a high quality of geo electric profile can be achieved. Theoretical data forwarded from a three layer model and a four layer model was used to test the validity of algorithm. The results show that the curves of all time apparent vertical conductance can identify the layers clearly, and can also indicate the magnitude of conductance of layers. Finally, an example for field data processing was given and the inverted profile of apparent vertical conductance features a good layer structure. The profile of all time apparent vertical conductance is consistent with the profile of inverted resistivity. All these show that the interpretation method of all time apparent vertical conductance is feasible and effective.