动态网络最短路径射线追踪

A METHOD OF SHORTEST PATH RAYTRACING WITH DYNAMIC NETWORKS

最短路径射线追踪算法 ,用预先设置的网络节点的连线表示地震波传播路径 ,当网络节点稀疏时 ,获得的射线路径呈之字形 ,计算的走时比实际走时系统偏大 .本文在波前扩展和反向确定射线路径的过程中 ,在每个矩形单元内 ,通过对某边界上的已知走时节点的走时进行线性插值 ,并利用Fermat原理即时求出从该边界到达其他边界节点的最小走时及其子震源位置和射线路径 ,发展了相应的动态网络算法 .从而克服了最短路径射线追踪算法的缺陷 ,大大提高了最小走时和射线路径的计算精度 .

The shortest path raytracing algorithm in networks is widely applied to calculate seismic ray paths and traveltimes, in which the beelines between network nodes are used to approximate the ray paths. When using a few nodes the ray usually follows a zig-zag path that is longer than the real raypath, and the calculated traveltime at a receiver is also larger than the real one. To solve this problem, we develop a shortest path raytracing method with dynamic networks based on the shortest path algorithm. In the process of expanding wavefront away from a source throughout the entire model, the wavefront times are sampled at all nodes on the cell edges. In each cell the traveltime at any point on an edge is expressed with linear interpolation between calculated traveltimes at adjacent nodes on the same cell edge, and then Fermat’s Principle is used to determine the first arrival times at the nodes on the other edges of this cell. After the first arrival times at all nodes are calculated, trace raypath from a receiver to a source in the same way as the forward sampling for all pairs of receives and sources is performed. So the drawbacks of conventional shortest path raytracing methods are overcome, and the precision of calculated minimum traveltimes and the correspondent raypaths are improved greatly.