层状介质下张量CSAMT最小收发距研究

Research on minimum transmit-receive distance of tensor CSAMT in layered media

可控源音频大地电磁法按照观测方式可分为标量CSAMT与张量CSAMT。由于施工方式与电阻率计算方法的差别,标量CSAMT中划分远区的最小收发距已不能精确地适用于张量CSAMT。因此,根据张量视电阻率与大地电磁视电阻率相对误差,分别计算了均匀大地模型、两层模型下的相对误差,并精确给出不同误差限下的最小收发距。结果表明对于两层模型来说,当首层厚度小于3倍趋肤深度时,不能直接应用均匀半空间的结果,对于G型模型引起误差较大。对于多层结果可由二层模型使用等效电阻率近似估计。研究结果对张量CSAMT野外施工有一定的意义。

According to the observation mode,Controlled Source Audio-frequency Magnetotelluric Method(CSAMT)can be divided into scalar CSAMT and tensor CSAMT.Due to the difference between the construction method and the resistivity calculation method,the minimum transmission and reception distance in the division of far-field of the scalar CSAMT cannot be accurately applied to the tensor CSAMT.According to the relative errors of tensor apparent resistivity and Magnetotelluric(MT)apparent resistivity,the relative errors of the homogeneous geodetic model and the two-layer model were calculated respectively,and the minimum transmission and reception distances under different error limits was accurately given.The results show that,for the two-layer model,when the thickness of the first layer is less than 3 times the skin depth,the result of homogeneous half space cannot be directly applied,which causes a large error for the G-type model.Multilayer results can be approximately evaluated from the two-layer model with equivalent resistivity.The research results in this paper have certain theoretical guiding significance for the tensor CSAMT field construction.