瞬变电磁法中的斜阶跃波效应及常规的几种校正方法分析

THE EFFECT DISCUSSION OF RAMP TIME AND SOME GENERAL CORRECTIVE METHODS OF TRANSIENT ELECTROMAGNETIC METHOD

关断时间校正是瞬变电磁资料处理中的一个重要方面,针对常用的中心回线法,详细分析了瞬变场的斜阶跃波效应。斜阶跃波相对阶跃波高频迅速振荡衰减,斜阶跃波效应主要影响瞬变场的早期,表现为幅值较低,关断时间越长,影响越大。同时对常规的几种关断时间校正方法进行对比分析,结果表明:对于“全期”段数据校正宜选Eaton法,对“晚期”段数据可选Eaton法,也可选坐标移动法。在选用Fitterman法时要注意是否满足使用条件,坐标移动法的“晚期”条件,可根据实际地电参数,通过模拟实验来确定。

The correction of ramp-time is an important part in TEM data procedure. The paper,aiming at the central loop transient electromagnetic method for its widely application,discusses two problems.At first,the paper analyses the effect of ramp time in detail.Comparing with step wave,the feature of slanting wave is the high frequency components with rapid attenuation and simultaneous oscillation. The effect of slanting wave mainly influences the early channel of transient electromagnetic signal and the result shows lower response.The longer the ramp time is,the lower the response is.Secondly,the paper discusses some general ramp-time corrective methods,the results shows: for the full time data,the Eaton method should be chosen,and for 'late time' data,the Eaton method or the moving coordinates method can all be chosen.Although the Fitterman method can be used as alternate,its application conditions must be considered carefully.The 'late time' condition about the moving coordinates method can be made certain by experimenting according to the local area parameters.