地下瞬变电磁法一维反演

The one-dimension inversion of underground transient electromagnetic data

瞬变电磁法在地下工程中得到了广泛地应用,但目前地下瞬变电磁的解释方法却仍主要沿用地面勘探的理论。为了进一步提高地下瞬变电磁法的解释精度,介绍一种带约束一维反演方法。基本思想是利用电偶极子等效方法进行地下瞬变电磁正演,并合理构建目标函数,利用阻尼最小二乘法进行带约束反演。首先将回线源看成是多个电偶极子产生的场的叠加,利用偶极子叠加的原理求取回线的电磁响应,并进行全域视电阻率定义,以此建立反演的初始地电模型,最后利用阻尼最小二乘法实现地下瞬变电磁数据的带约束反演。利用带约束反演方法进行数据测试,取得了较好的效果。

We defined the full-field apparent resistivity using the vertical component of time domain magnetic field.Firstly,the loop's transient electromagnetic full-field response was calculated using the integral method according to the full-space response of an electric dipole.The expression of apparent resistivity definition was given according to the full-space magnetic field response,and then obtained the apparent resistivity by using numerical iterative method.Calculation results show that the apparent resistivity definition method is fast and effective.Finally,we calculated and analyzed the influence of tunnel cavity and water-bearing systems on the apparent resistivity curve.