Abstract: The effect of turn-off current is a knotty problem in TEM method, especially for shallow soundings. Turn-off time is also a major parameter for evaluating the performance of instruments. Raiche (1984) discussed this problem and suggested a correction method using a ramp (linear) turn-off current expression. In this paper two types of turn-off current are discussed for the central loop configuration and a new correction strategy is suggested. According to this technique the accurate all-time apparent resistivity can be obtained in the case that the secondary and primary fields are recorded simultaneously.

Key words: Turn off time, Turn-off current, Linear mode, Exponential mode, Transient electromagnetic method

摘要： 关断时间是影响瞬变电磁资料处理和解释质量的一个重要因素,也是衡量TEM仪器性能的一个关键参数。提出了一种直接数值校正方案,并通过对线性和指数关断电流的校正描述了该方案的实施过程。根据文中提出的方案,只要仪器记录了一次场的衰减曲线,就可以进行较为精确的校正,并不必要假设线性衰减或指数衰减,这一结论无论是对TEM的仪器设计还是数据处理都具有重要意义。

关键词: 关断时间, 关断电流, 线性衰减, 指数衰减, 瞬变电磁