一种改进的三维旅行时梯度射线追踪方法  

A modified 3D traveltime gradient ray tracing method

作　　者：张婷婷[1] 邱达[2] 张东[2] 

机构地区：[1]湖北民族学院信息工程学院,湖北恩施445000 [2]武汉大学物理科学与技术学院,湖北武汉430072

出　　处：《石油地球物理勘探》2016年第5期916-923,836,共8页Oil Geophysical Prospecting

基　　金：湖北省教育厅科学技术研究项目(B2015104)资助

摘　　要：最大旅行时梯度射线追踪(The Maximum Traveltime Gradient Ray Tracing,MTG)法利用三次B样条插值计算旅行时场的最大旅行时梯度,从而追踪初至波射线路径。但由于三次B样条插值是连续光滑的插值函数,在射线通过速度突变区域时,计算次级源点的旅行时和梯度会产生一定的误差。在分析MTG算法计算误差来源的基础上,提出了一种改进的B样条/线性联合插值的三维射线追踪(The Modified Maximum Traveltime Gradient Ray Tracing,简称MMTG)算法,即在速度均匀变化的区域采用B样条插值计算旅行时梯度确定下一个次级源点,在速度变化剧烈的区域利用线性插值法在网格界面上找出旅行时最小的入射点作为次级源点,从而保证射线在速度分界面上折射产生的不连续性。数值实验结果表明,MMTG算法在保持MTG算法优点的同时进一步提高了射线路径的计算精度,能够适应更复杂的速度介质模型。The maximum traveltime gradient (MTG) ray tracing method calculates the gradient of traveltime of cubic B-spline interpolation and traces the ray path with the gradient of travel time field. How-ever, the cubic B-spline interpolation is a smooth continuous interpolation function, so in the area with abrupt velocity change, it causes calculation error. In this study, we propose a 3D modified maximum traveltime gradient (MMTG) ray tracing method based on the analysis of the error of MTG. This MMTG method uses the B-spline/linear combined interpolation to calculate the ray path of seismic waves. In this process, we determine the next tracing point with the traveltime gradient calculated by the cubic B-spline interpolation in the area with slow-varying velocity; while in the region with an abrupt velocity change, we adopted a regional linear interpolation to find out the next secondary source to ensure only discontinuous refraction at interfaces is generated. Numerical experiment results show that the proposed MMTG ray tracing method can keep basic characteristics of the MTG method and achieve more accurate computation of traveltime in inhomogeneous and discontinuous media. © 2016, Editorial Department OIL GEOPHYSICAL PROSPECTING. All right reserved.

关 键 词：射线追踪 旅行时梯度 三次B样条 旅行时线性插值 

分 类 号：P631[天文地球—地质矿产勘探]