基于全区视电阻率的中心回线瞬变电磁快速成像研究

Research on Fast Imaging for Central-loop TEM Data Based on All-time Apparent Resistivity

基于中心回线瞬变电磁正演理论和全区视电阻率定义,通过数值计算的方法求取了全区视电阻率。为避开感应电动势求解早晚期视电阻率的跳跃性,采用瞬变电磁场求解全区视电阻率得到精度较高且连续的全区视电阻率。快速成像采用烟圈反演和快速一阶与二阶近似成像两种反演方法,进一步对比分析了这两种方法各自的优缺点,尤其二阶近似成像能很好地反映地下深度和电导率,这对瞬变电磁正确研究地下一维电性的垂向变化特征具有重要参考意义。

Based on the forward theory of central-loop TEM and the apparent resistivity algorithm,the all-time apparent resistivity is obtained by numerical calculation.In order to avoid the jumping which is yielded in the process of using induced electromotive force to solve the early-late apparent resistivity,this paper adopts transient electromagnetic field to solve the all-time apparent resistivity,and obtains the values with higher precision and continuous curve.As for fast imaging,the paper uses two kinds of inversion methods,i.e.smoke-rings and fast imaging which has first and second order approximate.According to the analysis of the advantages of the two methods,it is found that the second order approximate imaging can reflect underground depth and conductivity better,which provides an important guidance for the research on the characteristics of underground 1-D electrical vertical variation for TEM.