同时实现地质雷达数据地形校正和偏移成像的方法

Terrain correction and migration of GPR profile fulfilled simultaneously using reverse-time migration

起伏地形使地质雷达图像变得复杂、地层界面的反射同相轴畸变、绕射同相轴严重偏离双曲线形状。提出了用麦克斯韦方程逆时偏移的方法同时实现地形校正和偏移成像以消除地形的影响。该方法将等偏移距逆时记录作为在接收点位置处的电流源,用时间域有限差分法求介质中的波场,输入波场退为零时刻时的空间电场分布即为地形校正和偏移成像结果。由于地形校正也是基于波动方程实现的,因此它比基于射线理论的常规静校正方法精确。通过比较该方法与常规静校正加逆时偏移之效果可知,该方法能更准确地对起伏地形下方的金属管线等绕射体成像。

Ground-penetrating radar images collected on an undulating terrain become complicated because of the terrain. Reflections on a common-offset radar profile from interfaces are far from the true shapes of the reflectors; and diffractions are not hyperbolas anymore. This paper proposes to use reverse-time migration method for compensating the effect of the terrain and for completing migration at the same time. The reversal of common-offset radar data received on a terrain are served as incident currents at corresponding receivers' positions, the electric field in the whole space is calculated by Maxwell's equations solved by the finite-difference time-domain method. The spatial distribution of the electric field at zero time is the terrain corrected and migrated result. The terrain correction is done by the wave equation too. A synthetic radar profile is processed by using the conventional static correction method based on the ray theory plus migration and by using the reverse-time method, respectively. The numerical example demonstrates that the reverse-time migration method directly applied to the radar data can image a metallic pipe more accurately than the conventional static correction method plus migration.