中文摘要：

在LTI（Linear Travel-time Interpolation）射线追踪算法基础上提出的扩张收缩扫描算法能正确追踪直达波、绕射波和回波的射线路径，但其存在计算效率低、收敛速度慢的问题。采用交叉扫描方式对扩张收缩扫描算法进行改进，并由此提出了基于交叉扫描方式的扩张收缩扫描改进算法。理论分析及数值模拟结果表明：改进算法在保留了原扩张收缩扫描算法所有优点的同时，具有更高的计算效率；当模型网格尺寸划分较细时，改进算法在计算效率上的优势更为显著。

英文摘要：

The extension ＆amp; compaction scanning algorithm based on LTI （Linear Travel-time Interpo-lation）ray tracing algorithm can properly trace the ray path of the direct wave,diffraction wave and echo ＆#39;s,but it has the following problems：low computational efficiency and slow convergence speed.Aiming at these problems and using the cross-scan mode to improve the algorithm,an improved extension ＆amp;compac-tion scanning algorithm based on the cross-scan mode was presented.Theoretical analysis and the results of numerical calculation show that the improved algorithm not only maintains all the advantages of the ex-tension ＆amp; compaction scanning algorithm,but also has a higher computational efficiency.When the model is mesh more refined,the advantage of the improved algorithm is more significant in computational efficien-cy.