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角度域共成像点道集(ADCIGS)是偏移速度分析和振幅随角度变化分析(AVA)的基础数据。传统Kirchhoff叠前深度偏移(KPSDM)按偏移距组织数据,能方便的输出偏移距域共成像点道集(ODCIGS),其高效的角度道集输出是有挑战的。本文提出基于旅行时梯度场的KPSDM角道集输出方法。其核心步骤为:(1)利用任意介质中的动态规划法旅行时计算方法提供炮点和检波点的旅行时场;(2)根据旅行时场的梯度方向计算反射张角;(3)在偏移过程中抽取ADCIGS。由于本文旅行时计算方法没有射线阴影区,也没有对速度光滑性的要求,其角度道集输出在阴影区比传统射线追踪更有优势。基于该角度道集输出方法,本文发展了一种适合大规模三维地震数据的KPSDM及角道集输出的并行实现方案。其基本思想是:(1)按照炮数据来组织输入数据;(2)旅行时场的输入与单炮覆盖范围相联系以节省内存;(3)多炮数据间采用MPI并行处理,单炮深度切片之间采用OpenMp并行处理,可进一步提高内存利用率和并行力度。数值试验结果证明本文角度道集生成方法的优越性和本文实现方案的有效性。
Angle Domain Total Imaging Dot Gathering (ADCIGS) is the basis for migration velocity analysis and amplitude versus angle variation analysis (AVA). The traditional Kirchhoff prestack depth migration (KPSDM) organizes data by offset to facilitate the output of offset region common imaging point gathers (ODCIGS), and its efficient angular gathers output is challenging. In this paper, a KPSDM gathers output method based on the gradient of travel time is proposed. The core steps are as follows: (1) Traveling time field of shots and checkpoints is provided by using the dynamic programming method in any medium; (2) Reflected opening angle is calculated according to the gradient direction of the travel time field; (3) ADCIGS is extracted during the offset. Since the calculation method in this paper does not have the shadow area or the speed smoothness requirement, the angle gathers output has more advantages than the traditional ray tracing in the shaded area. Based on this angular gathers output method, this paper develops a parallel implementation of KPSDM and gathers output suitable for large-scale three-dimensional seismic data. The basic idea is: (1) According to the gun data to organize the input data; (2) Travel time field input and single gun coverage to save memory; (3) Multi-gun data using MPI parallel processing, single gun depth OpenMp parallel processing between slices can further improve memory utilization and parallelism. The results of numerical experiments prove the superiority of this method and the effectiveness of the proposed scheme.