Based on the linear traveltime interpolation (LTI) algorithm, we propose an improved LTI (referred as ILTI) algorithm for multiphase seismic ray tracing, which uses a velocity node in model parameterization and introduces secondary nodes between adjacent velocity nodes. To better fit the undulating surface model, an irregular velocity node is used in near the irregular interface, and regular velocity nodes are still used in the region far away from the irregular interface. We derive an iterative fixed-point formula for calculating traveltime. By combining multistage computational technology and wavefront narrowband expansion technology, the proposed ILTI algorithm can efficiently trace the multiphase seismic raypath and compute the corresponding traveltime field. Through comparison and analysis with the traditional LTI algorithm, its computational accuracy can be highlighted by at least one order of magnitude. Compared with the popular fast marching method (FMM) and irregular shortest-path (ISPM) algorithms, it also has the advantages in terms of computational accuracy and efficiency. Numerical simulations in the Marmousi model show that the algorithm is also suitable for tracking multiphase seismic rays in the complex velocity model.

中文翻译：

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起伏表面模型中多相光线追踪的改进LTI算法

在线性走时插值（LTI）算法的基础上，提出了一种改进的多相地震射线追踪LTI（简称ILTI）算法，该算法在模型参数化中使用了一个速度节点，在相邻的速度节点之间引入了二级节点。为了更好地拟合起伏表面模型，在不规则界面附近使用不规则速度节点，在远离不规则界面的区域仍然使用规则速度节点。我们推导出计算旅行时间的迭代定点公式。提出的ILTI算法结合多级计算技术和波前窄带扩展技术，可以有效地追踪多级地震射线路径并计算相应的走时场。通过与传统LTI算法的对比分析，它的计算精度至少可以提高一个数量级。与流行的快速行进法（FMM）和不规则最短路径（ISPM）算法相比，它在计算精度和效率方面也具有优势。Marmousi模型的数值模拟表明，该算法也适用于复杂速度模型中的多相地震射线跟踪。