动态网络最短路径射线追踪
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摘要
当前广泛使用的最短路径射线追踪算法,用预先设置好的网络节点的连线表示实际波传播路径,在网络节点稀疏时,获得的射线路径呈之字形,计算出的旅行时比实际旅行时系统偏大。本文在波前扩展过程中,通过在每个矩形单元内对已知旅行时节点进行插值,并利用Fermat原理即时求出从该单元边界上到达某一节点的最小旅行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,克服了原最短路径射线追踪算法的缺陷,大大提高了最小旅行时和射线路径的计算精度。
The widly used shortest path raytracing algorithm in networks depends on the preset beelines between networknodes are used to approximate the ray paths. When using a few nodes and the ray usually following a zig-zag path thecalculated traveltime is larger than the real one. To solve this problem, we develop a shortest path raytracing methodwith dynamic networks. In the process of expanding wavefront from source, we use interpolation betweenknown traveltime nodes and Fermat's Principle to find the point at edges of the cell from which the ray reaches a nodewith the shortest path , meanwhile the subwave source location and raypaths are evaluated. So the drawbacks ofconventional methods are overcome, and the precision of calculated seismic minimal traveltime and raypaths isimproved greatly.
The widly used shortest path raytracing algorithm in networks depends on the preset beelines between networknodes are used to approximate the ray paths. When using a few nodes and the ray usually following a zig-zag path thecalculated traveltime is larger than the real one. To solve this problem, we develop a shortest path raytracing methodwith dynamic networks. In the process of expanding wavefront from source, we use interpolation betweenknown traveltime nodes and Fermat's Principle to find the point at edges of the cell from which the ray reaches a nodewith the shortest path , meanwhile the subwave source location and raypaths are evaluated. So the drawbacks ofconventional methods are overcome, and the precision of calculated seismic minimal traveltime and raypaths isimproved greatly.
引文
[1]Dijkstra E W.A note on two problems in connection with graphs.Numer.Math.,1959,1:269￣271
[2]Nakanishi I,Yamaguchi K.A numerical experiment on nonlinear image reconstruction from first-arrival times for two-dimensional island arc structure.J.Phys.Earth,1986,34:195￣201
[3]Moser T J.Shortest path calculation of seismic ray.Geophysics,1991,56(1):59￣67
[4]Klimes L,Kvasnicha M.3-D network ray tracing.Geophys.J.Int,1994,116:726￣738
[5]Fischer R,Lees J M.Shortest path ray tracing with sparse graphs.Geophysics,1993,58(7):987￣996
[6]Zhang J,Toksoz M N.Nonlinear refraction traveltime tomogra-phy.Geophysics,1998,63:1726￣1737
[7]Moser T J,Van Eck T,Nolet G.Hypocenter determination in strongly heterogeneous earth models using the shortest path method.J.Geophys.Res,1992,97:6563￣6572
[8]Van Avendonk H J A,Harding A J,Orcutt J A,et al.Hybrid shortest path and ray bending method for traveltime and raypath calculations.Geophysics,2001,66(2):648￣653
[9]Asakawa E,Kawanaka T.Seismic ray tracing using linear travel-time interpolation.Geophysical Prospecting,1993,41(1):99￣111
[10]常旭,刘伊克.地震正反演与成像.北京:华文出版社,2001:65￣84
[2]Nakanishi I,Yamaguchi K.A numerical experiment on nonlinear image reconstruction from first-arrival times for two-dimensional island arc structure.J.Phys.Earth,1986,34:195￣201
[3]Moser T J.Shortest path calculation of seismic ray.Geophysics,1991,56(1):59￣67
[4]Klimes L,Kvasnicha M.3-D network ray tracing.Geophys.J.Int,1994,116:726￣738
[5]Fischer R,Lees J M.Shortest path ray tracing with sparse graphs.Geophysics,1993,58(7):987￣996
[6]Zhang J,Toksoz M N.Nonlinear refraction traveltime tomogra-phy.Geophysics,1998,63:1726￣1737
[7]Moser T J,Van Eck T,Nolet G.Hypocenter determination in strongly heterogeneous earth models using the shortest path method.J.Geophys.Res,1992,97:6563￣6572
[8]Van Avendonk H J A,Harding A J,Orcutt J A,et al.Hybrid shortest path and ray bending method for traveltime and raypath calculations.Geophysics,2001,66(2):648￣653
[9]Asakawa E,Kawanaka T.Seismic ray tracing using linear travel-time interpolation.Geophysical Prospecting,1993,41(1):99￣111
[10]常旭,刘伊克.地震正反演与成像.北京:华文出版社,2001:65￣84
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