跨孔电波衰减成像初始振幅估算方法比较

跨孔电磁法衰减层析成像是一种利用电磁波振幅信息的方法,通过发射端到接收端电磁波的振幅变化来反演介质衰减常数分布。发射端振幅也就是初始振幅,一般情况下是未知的,它的精度很大程度上影响到层析成像结果,需要在反演前得到或者通过特殊反演方法来处理。本文总结了4种初始振幅处理方法——线性拟合法、矩阵反演法、双频电磁波法以及相邻道比值法,通过合成数据验证了这四种方法的可行性,并且指出了每种方法的优缺点:线性拟合法适合物性变化不大的情况;矩阵反演法对物性情况要求不高,但计算量较大;双频电磁波法能直接得到电导率分布,但只适合良导体情况;相邻道比值法适用情况最广,但容易受干扰影响。

Comparison of initial amplitude estimation methods for cross-hole electromagnetic wave attenuation tomography

Cross-hole electromagnetic attenuation tomography is a method that uses the amplitude information of electromagnetic waves to invert the distribution of the attenuation constant of the medium by the amplitude change of the electromagnetic wave from the transmitting to the receiving. Transmitter amplitude is also called the initial amplitude, which is generally unknown. Its accuracy largely affects the tomographic results and it needs to be obtained before inversion or by special inversion methods. This paper summarizes four initial amplitude processing methods, i.e., linear fitting method, matrix inversion method, dual-frequency electromagnetic wave method and neighboring traces method. The feasibility of these four methods is verified by synthetic data, and the advantages and disadvantages of each method are pointed out: Linear fitting method is suitable for the case where the physical property changes little;matrix inversion has low requirements for physical condition, but the amount of calculation is relatively large.;dual-frequency electromagnetic wave method can directly obtain the conductivity distribution, but only for the good conductor case;the applicable situation of neighboring traces method is the most extensive, but it is susceptible to interference.