逆时深度偏移成像方法及其在CPU／GPU异构平台上的实现

Reverse-time Depth Migration Imaging and Its Application at CPU/GPU Platform

逆时深度偏移的优点可以用来对全波场逆时外推，使得来自高角度反射界面的反射波。甚至来自超过90°反射界面的反射波精确成像。逆时深度偏移涉及到2个重要问题：精确且高效的逆时波场外推算法及反射波的成像条件。文中提出了修改的激励时间成像条件：在反射界面处，反射波出发时等于入射波到达时。认为用反射界面上某成像点与法线方向对称的波矢量所定义的波场进行相关成像是完善的成像条件。边界条件的处理借鉴Robert提出的随机边界，这可以提高波场外推算法的并行性。关于存储，认为牺牲一次正向波场外推，先把波场正传到最大时间，然后与观测波场同时逆时外推并成像，在GPU／CPU计算机平台上是比较合适的方案，这样就彻底抛弃了正向外推波场的存储。数值试验验证了分析的正确性。

The advantage of reverse time migration （RTM） is that it can accurately image the reflectors beyond 90° dipping angles. RTM uses the full wave equation to extrapolate the wave field. Reverse time depth migration involves two key issues： accurate and efficient reverse time wave field extrapolation algorithm and reflector imaging conditions. We give modified exciting time imaging conditions, that is, at reflection boundaries, the arriving time of the incident wave equals to the taking-off time of the reflection wave. It is stated that, it is applicable to use the wave field defined by wave vector symmetric to normal direction at an imaging point on reflection boundary for imaging. For disposal of boundary conditions, random boundary presented by Robert is used to improve concurrency of wave field extrapolation algorithm. With respect to storage, we believe that, sacrificing once forward wave field extrapolation, forward propagating wave field to the maximum time and then reverse time extrapolating the wave field together with observation wave field simultaneously and imaging at GPU/CPU computer platform is a suitable method. Therefore, the storage of forward extrapolation wave field is abandoned completely. Finally, numerical tests prove its correctness.