为了使Kirchhoff型反偏移的输出结果与数值模拟结果相等,提出了一种旨在消除Kirchhoff型反偏移中所出现的振幅畸变现象的高保真反偏移方法.与常规的Kirchhoff型反偏移不同,高保真反偏移是一种与反射面有关的反射地震成像方法.因此,在高保真反偏移中首先要确定反射面的位置,其次要确定振幅畸变因子的数值,最后要根据在反射点上振幅畸变因子恒等于1这一事实进行振幅畸变校正.在具体实施过程中,为了求出反射点的空间位置和振幅畸变因子的具体数值,采用四重加权叠加法,即在一次反偏移运算中同时采用一个单位加权函数和三个非单位加权函数.其中,非单位加权函数由常规的真振幅加权函数和用于建立Kircohhoff型反偏移算子的全局坐标系中的水平坐标组成.通过在四个反偏移场之间进行比值运算,可以达到提取反射点坐标和振幅畸变因子的目的.一旦得到反射点坐标和振幅畸变因子的具体数值,就可以通过简单的除法消除掉振幅畸变因子对反偏移像场振幅的影响.%For making the output of Kirchhoff-type demigration equal to the output of numerical modeling,we present a demigration method called high fidelity demigration, which is able to eliminate the amplitude distortion effect in Kirchhoff-type demigration. Different from the conventional Kirchhoff-type demigration, the high fidelity demigration is reflector-dependent. As a result,in high fidelity demigration we first need to determine the position of the reflector, then to determine the amplitude distortion factor, and finally to correct the demigration amplitude according to the fact that the amplitude distortion factor in demigration is equal to one at a reflection point. In practical implementation of high fidelity demigration, we use four weighting functions in a single weighted isocheone stack, namely the unit weighting function, the conventional true amplitude weighting function, and the two horizontal coordinates of the global coordinate system that is used for establishing the Kirchhoff-type demigration operator. By performing division operations among the four dimigrated images, we can extract the position of the reflection point and the amplitude distortion factor. Once the position of the reflection point and the amplitude distortion factor are obtained, the amplitude distortion effect in demigration can be corrected by a simple division.
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