关于深度偏移的几个相关概念

Several associated conceptions of depth migration.

本文仅对深度偏移和时间偏移的关系 ,叠前深度偏移和叠后深度偏移的关系 ,法向射线与成像射线、射线偏移、相干反演等相关概念进行了分析。明确了所有的偏移公式都是在深度域定义的 ;只有当前层以上所有各层的速度都正确时 ,修改速度模型使其共成像点道集上同相轴达到平直 ,方可认为该速度和深度接近于真实值。论述了射线偏移在建立速度一深度模型过程中的重要作用 ,它可以把时间域层位转化为深度域层位 ;进一步明确了法向射线与成像射线的概念 ,利用法向射线可以将叠加时间剖面上层位转换为深度域层位 ;利用成像射线可以把时间偏移剖面的层位转化为深度域层位 ;提出了利用相干反演建立初始速度一深度模型的优缺点及克服其缺点的办法。只有深入地理解这些概念才能提高利用深度偏移方法解决问题的能力。

The paper only analyzed the following concep tions concerning to relation between depth rnigra tion and time migration,relation between prestack depth migration and poststack depth migration,normal ray and imaging ray, ray migration and co-herent inversion etc ;made clear that the all migra-tion formula are defined in depth domain,the veloc-ities and the depths can be known as approaching to true values when the velocities of the each layer above current layer are correct and the events on common-image-gathers are aligned after updating velocity model;expounded the importance of ray migration in a process of building velocity-depth model, which can converse the layers in time do-main into that in depth domain;further defined the conceptions of normal ray and imaging ray, using normal rays can converse the layers on stack time sections into the layers in depth domain and using imaging rays can converse the layers on time-mi-grated sections into the layers in depth domain;showed the advantages and disadvantages using co-herent inversion to build the initial velocity depth model and the methods reducing the disadvan-tages. Only deeply understanding these conceptions can the ability of solving the problems by using depth migration method be improved.