CSAMT法一维层状介质灵敏度分析

CSAMT sensitivity analysis for 1D models

为改善CSAMT一维反演的实用性,本文以电磁场数值模拟为基础,推导出偶极源激发下频率域电磁反演中的偏导数公式.并以三层水平层状地电模型为例,针对同线装置和赤道装置两种形式,利用扰动法对本文的半解析算法结果进行验证.对比结果表明无论同线还是赤道装置,本文半解析结果和扰动法计算结果拟合程度非常好,验证了偏导数公式推导及程序代码的正确性.进而,分析了CSAMT观测数据对中间薄层参数的灵敏度.灵敏度特征分析表明:CSAMT观测资料对中间低阻薄层比较敏感,对高阻薄层的分辨率较低,但对层厚度,即便是高阻薄层,仍存在较高的灵敏度.频率对层参数的灵敏度有重要影响.实际应用中,应同时考虑资料和参数加权,以提高中间层参数的求解能力.本文的算法不仅有助于CSAMT资料反演解释,同时为地下薄目标层的有效识别提供理论依据.

In order to improve the practicability of 1DCSAMT inversion,we derive the partial derivative of EM field with respect to earth parameters for a dipole transmitter.Taking a three-layer earth as example,we check the partial derivative results with those obtained from the perturbation method for both in-line and cross-line configurations.The comparison shows the good fitness,which indicates our formulas and codes are correct.Further we analyze the sensitivities of the CSAMT survey data to the parameters of a thin intermediate layer in the earth.The characteristics of the sensitivity curves show the relations between the resolution capability and the parameters of the middle layer.The sensitivities to low resistivity is higher than to high resistivity.However,the sensitivities to the thickness of the middle layer is high whether the middle layer is of low resistivity or not.Another parameter,frequencies,affect the sensitivity more in the observation.Therefore,in order to improve the stability of the solution of the middle layer,the weight techniques among data and parameters should be considered in the inversion.The study in this paper serves not only to the CSAMT data inversion,but also to the effective solution of a thin-layer target in the earth.