基于互相关成像条件的保幅高斯束逆时偏移

Amplitude-preserved reverse time migration with Gaussian beam based on crosscorrelation imaging conditions

常规的逆时偏移算法都是基于双程波动方程的数值解法,实际上利用Kirchhoff积分进行波场延拓,也可以实现逆时偏移。以Kirchhoff积分为基础,采用高斯束叠加积分表示的格林函数来表示正反向延拓波场,将正反向延拓波场进行保幅的互相关得到地下成像。保幅高斯束逆时偏移方法结合了射线类偏移方法的高计算效率和逆时波动方程偏移的高精度,能很好地处理焦散点、陡倾角等问题,并且具有面向目标成像的能力,并消除了偏移过程中的几何扩散效应和入射角变化引起的振幅误差。

Conventional reverse -time migration is based on the two - way wave equation. Actually we can rely on Kirch- hoff integral for propagated wave - fields to realize reverse -time migration. Our method relies on the calculation of the Green functions for the classical wave equation by performing a summation of Gaussian beams for the direct and back propagated wave -fields. The subsurface image is obtained by calculating the amplitude preserved coherence between the direct and back propa-gated wave - fields. This method combines the advantages of the high computational speed of ray -based migration with the high accuracy of reverse -time wave -equation migration because it can overcome problems with caustics, yield good images of steep flanks,and is readily extendible to target -oriented implementation. It also can eliminate the geometric diffusion effect and amplitude error caused by the incident angle changes in the process of migration.