界面二次源波前扩展法全局最小走时射线追踪技术

以Moser方法为代表的最短路径射线追踪算法可以快速稳定地获得整个追踪区域的全局最小走时和路径，但它存在两个缺陷：一是射线大多由折线呈锯齿状相连，长度和位置偏离真实射线路径；二是在低变速区容易出现射线路径多值现象．本文提出的界面二次源波前扩展法全局最小走时射线追踪技术（以下简称界面源法）旨在解决上述两个问题．不同于Moser方法，界面源法只在物性分界面上设置子波源点，子波出射射线可以到达任何不穿越物性界面而直接到达的空间点和界面离散点，在均匀块体内或层内地震波以精确的射线路径传播．显然，界面源法的子波出射方向数远远大于传统方法，算法的追踪误差主要由界面离散引起的，因此，界面源法很好地解决了Moser法存在的问题，大大提高了追踪的精度．同时，由于界面源法的子波源点数远远小于Moser法，因而效率也很高．模型实算证实了该算法的高效性．

A global minimum traveltime raytracing algorithm of wavefront expanding with interface points as secondary sources

The shortest path raytracing presented by Moser is a kind of fast and stable method to calculate global minimum traveltimes and raypaths.But it has two drawbacks.One is that most derived zig-zag raypaths are longer than true paths and thus mispozitioned.The other is that there may be several equally short paths,especially in flat areas with low velocity variations.The wavefront expanding method with interface points as secondary sources is studied in the paper which aims to solve the problems.Different from Moser's method,this approach only sets secondary sources on interfaces between different media.Rays from a secondary source can reach nodes as long as paths don't penetrate interfaces.Waves propagate along accurate paths in homogeneous layers or blocks.Obviously,there are much more ray directions from a secondary source with this method than with Moser's method.The main tracing errors only come from interface discretization.As a result,raytracing with the method can get much more accurate results than Moser's method.At the same time,the method is efficient as there are much less secondary sources than those in Moser's.Numerical examples show the method is efficient.