地质雷达资料的偏移速度分析和叠前偏移

Migration Velocity Analysis and Prestack Migration of Ground-Penetrating Radar

地质雷达资料偏移成像的精度与地下介质介电常数分布的确定精度有直接关系。提出用全局最优化偏移速度分析方法求取介电常数分布。目标函数定义为各共成像点道集零延迟归一化互相关值之和。在假设地下介质是分块的,且每块介质的介电常数可以用有限项的与空间坐标有关的多项式函数来表示的前提下,用遗传算法由浅至深逐块确定使目标函数达到最大的多项式函数的各项系数从而确定介电常数。叠前偏移用时间域有限差分求解麦克斯韦方程组的逆时偏移方法实现。合成雷达记录的偏移速度分析和偏移叠加结果表明,全局最优化偏移速度分析有较高的精度,偏移叠加剖面与实际构造一致。

The accuracy of migration image of ground-penetrating radar data is strongly related to the accuracy of permittivity distribution determined from multi-offset data. The authors propose a migration velocity analysis method based on a global optimization. The objective function is defined as the summation of normalized zero-delay crosscorrelation of all common-image gathers. Under the assumptions that media are piece wise, and that the permittivity of each piece can be expressed as a polynomial with limited terms, all oefficients of permittivity function of each piece, which maximize the objective function, are determined by genetic algorithm piece by piece. Prestack migration is performed by reverse-time migration method based on Maxwell’s equations using time-domain finite-difference method. A synthetic example shows that the proposed migration velocity analysis method can determine accurately the distribution of permittivity and that stack migration profile fits the true model.