时间域航空电磁法激电信息提取研究

Research on the IP information extraction from time-domain airborne EM

时间域航空电磁晚期道数据中常出现符号反转现象,该现象被证明是由激电效应引起.鉴于利用传统实电阻率模型的成像和反演技术处理该类数据无法得到正确的反演结果,本文提出基于Occam理论的反演方法,对层状模型电阻率和充电率参数进行同时反演.本文首先通过正演模拟极化介质中电流密度的分布情况,对时间域航空电磁信号出现多次符号反转现象做出合理解释;然后通过链式法则和波形褶积技术计算Cole-Cole模型参数灵敏度,进而探讨不同Cole-Cole模型参数灵敏度差异及其对反演结果的影响.为了提高多参数反演的稳定性和准确性,在反演过程中对参数采取上下限约束,最后对Bz、dBz/dt响应单独反演结果和联合反演结果进行对比和分析,发现联合反演可以有效地降低反演结果的多解性.

Airborne Transient Electromagnetic(ATEM) data frequently shows sign reversal in the late-time channels,which has been shown to be caused by the IP effect. Traditional imaging or inversion algorithms based on real resistivity cannot deliver reasonable results for such kind of data,so this paper proposes a simultaneous inversion of the resistivity and chargeability parameters of layered model based on the Occam inversion theory. Firstly, through the forward modeling of the distribution of current density in the polarizable medium, a reasonable explanation is given for the occurrence of multiple sign reversal phenomena in the ATEM. Then the sensitivity of the Cole-Cole model parameters is calculated by Chain Rule and waveform convolution technique, and then the sensitivity difference of different Cole-Cole model parameters and its influence on the inversion results are discussed. In order to improve the stability and accuracy of multi-parameter inversion, appropriate upper and lower bounds are applied to different parameters during the inversion process. Finally, the inversion results of Bz and dBz/dt responses and the joint inversion results are compared and analyzed. It is found that joint inversion can effectively reduce the multiplicity of inversion results.