大地电磁概率成像及其改进方法的成像效果评价

The probability tomography results of MT and the im- proved methods.

从理论机理角度对大地电磁(MT)概率成像方法的成像效果进行了分析。分析结果表明,MT概率成像方法不能对复杂地质体进行较高分辨率的反演成像,为此,对成像方法进行了改进。大地电磁微分场概率成像方法是基于归一化大地电磁场的微分,因此更能突出异常场分布特性,将大地电磁场概率成像的发生概率函数改进为实测电磁场值函数与相应扫描函数微分函数的归一化互相关函数,改进后的方法不再需要求背景电磁场值,而且提高了成像效果;面感应源概率成像方法是将线感应源的概率成像推广成面感应源的概率成像,能以较高的分辨率对多个水平方向或垂直方向上的电导率不连续界面进行成像。最后给出了用改进的方法对理论模型进行成像的例子,并与改进前的成像效果进行了比较。

The results of the probability tomography method of MT are analyzed in detail by theoretic mechanism at first. It is showed that the probability tomography of magnetotelluric fields, which need be improved on, can't inverse complex geologic body with high resolution. Several advices improved are sketched to enhance the effects of the tomograhy. The probability tomography of magnetotelluric field-derivative, based on the characteristic that the abnormal field can be stand out against the background field in virtue of the normalized magnetotelluric field-derivative, has improve on the occurrence probability function into the cross-correlation of the normalized observed EM field-derivative component and the derivative of corresponding normalized scanning function. The new method needn't calculate the primary field, and notably enhances the effects of the tomograhy; the probability tomography of surface induced sources can image the geological body which has the transverse and the longitudinal resistivity discontinuities surface with high resolution by calculating the probability of the surface induced sources instead of the line ones. The reliability of the proposed improved tomography means are validated by comparing the tomography effect of the improved methods with the original one.