中文摘要：

根据频率域中感应法探测金属管线的二次磁场分布，分析了感应电流形成机理和传输特征，讨论了由管线深度变化引起的异常规律。研究结果表明，频率域电磁法探测地下金属管线时，由于信号受金属管线内部电流线场的影响，管线接口的非金属介质将导致观测信号衰减。针对这种信号衰减在探测结果中易与管线变深处异常特征混淆的问题，提出了运用比值参数对两种异常有效地加以区分的方法。

英文摘要：

Based on the secondary magnetic distribution characters in frequency domain, the formation and transmission characters of faradic current were analyzed and the abnormal regularity resulting from pipeline depth change was discussed. The results indicate that when electromagnetic method is used to detect underground metal pipelines in frequency domain, the non-metal joint of mental pipeline may cause the decay of observed signals because of the influence of the inner current of mental pipelines. This phenomenon is easy to be confused with the abnormal characters resulting from depth variation. This study demonstrates that the two kinds of abnormals can be differentiated effectively by the ratio parameter method.