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目前国内瞬变电磁数据处理与解释主要停留在一维阶段,但实际数据均来自地下三维结构.针对这一现状,本文采用三维有限差分正演程序生成三维模型的瞬变电磁数据,然后利用Levenberg-Marquardt(LM)方法对数据进行一维反演,以探讨三维模型数据的一维反演效果.大定源回线数据的一维反演结果表明,当水平尺度足够大时,在测点范围内能获取异常体的准确信息,而随着异常体水平尺度的减小,所获取的异常响应会逐渐减小,测点范围内的异常体结构恢复程度也会逐渐降低,尤其当异常体水平尺度明显小于大定源尺度时,所获得的异常响应比较微弱,且单纯增加异常体的垂直尺度并不能增强异常响应.而由异常体三维效应引起的反向异常则会随着异常体水平尺度的减小而先增大,而后随着总体异常响应的减小而减小.中心回线与大定源回线一维反演结果对比表明,中心回线反演可能得到更强烈的异常响应,但对于削弱三维异常体所引起的反向异常可能没有效果,反而可能在获取更强异常响应的同时进一步放大这种反向异常.要使一维LM方法获取与真实异常体比较接近而反向异常比较弱的一维反演结果,可能需要异常体水平尺度相对异常体垂直尺度、异常体的埋深、发射线框的尺寸均比较大.
At present, the processing and interpretation of transient electromagnetic data mainly stay in the one-dimensional stage, but the actual data are from the underground three-dimensional structure.According to the current situation, this paper uses three-dimensional finite difference forward program to generate three-dimensional model of transient electromagnetic data, and then use Levenberg -Marquardt (LM) method to investigate the one-dimensional inversion results of 3D model data.The one-dimensional inversion results of the large-bound source return data show that when the horizontal scale is large enough, The accurate information of anomalous body can be obtained. With the reduction of the horizontal scale of anomalous body, the abnormal response obtained will be gradually reduced, and the degree of abnormal body structure recovery will decrease gradually, especially when the abnormal body When the horizontal scale is obviously smaller than the large source scale, the abnormal response obtained is relatively weak, and simply increasing the vertical scale of the abnormal body can not enhance the abnormal response, while the reverse abnormality caused by the abnormal body three-dimensional effect will increase with the abnormal body level Scale decreases first and then decreases with the decrease of the overall anomalous response.The comparison of the one-dimensional inversion results of the central return line and the large fixed return line shows that the central return line However, it may not be effective to weaken the reverse anomalies caused by the three-dimensional anomaly, but may amplify the reverse anomaly even when obtaining a stronger anomalous response. To make the one-dimensional LM method obtain The one-dimensional inversion results that are close to the true anomalies and weak in the opposite anomalies may require the vertical scales of the anomaly bodies relative to the anomaly bodies, the depth of the anomalous bodies, and the size of the emitting wireframes.