基于波前构建法的时间域深度偏移--del ta波包途径

作为一种基于射线的局部瞬态场,delta波包源自高斯波束,是高斯波束在时空域的对偶表示,具有高斯波束的全部优点和缺陷。基于delta波包叠加的时间域深度偏移,当射线穿过高速岩体时,受折射效应影响,密度降低,进而导致delta波包的分布密度降低,使成像质量变差,甚至无法成像。为了弥补这个缺陷,本文采用波前构建法计算射线路径。波前构建法能够以插入射线的方式保证均匀的射线分布,从而保证delta波包以均匀的分布密度覆盖整个成像靶区,进而提高成像质量。在具体实现上,采用链表结构替代以往使用的数组结构。Sigsbee 2A模型的数值试算表明,利用波前构建法可以改善高速体下方区域的成像质量,而利用链表存储波前信息要比利用数组至少节省9%的CPU耗时。

Depth Migration inTime Domain Using Wavefront Construction:Delta Packet Approach

The delta packet is the space-time domain counterpart of Gaussian beam,which is also the local transient wave propagating along a central ray,with all the advantages and disadvantage of Gaussian beam.Because of refraction effect,the algorithm has trouble with low ray density when rays pass through high velocity body,which would create an image in a lower quality,even no image.To solve this problem,the paper combines depth migration algorithm with wavefront construction,which is capable of raising the ray density along with wavefronts propagating.The numerical results of Sigsbee 2A model have proved that the increasing ray density could improve the image of regions beneath the high velocity body.In addition,the computation time can be shortened by at least 9% that the wavefront data are stored in chained list than in array.