海底地震数据积分法叠前时间域成像方法

海底地震（OBS）采集包括海底拖缆（OBC）和海底节点（OBN）两种观测方式。采集时激发点位于海面而接收点置于海底，建立在同一基准面假设前提下的传统地震成像方法不再适应OBS数据。本文首先推导了OBS上、下行波不同深度反射点轨迹的计算公式，用图示法直观地展示了各自共接收点道集数据的覆盖范围；然后以镜像成像理论为指导，推导了下行波积分法叠前时间偏移旅行时计算公式，同时推导了相应的上行波旅行时计算公式，并给出了上、下行波成像时间校正和均方根速度的转换公式；最后描述了OBS叠前时间偏移加权函数的计算公式。二维模型和三维实际数据应用结果表明，用下行波代替上行波成像，不仅能够显著改善浅层成像效果，且成像结果的横向范围得到明显的扩展。

Kirchhoff prestack time migration for ocean bottom seismic data

The ocean bottom seismic (OBS) acquisition includes two ways of acquisition, i.e.ocean bottom cable (OBC) and ocean bottom node (OBN).Because shot points are located in the sea surface and receivers are placed in the sea bottom, the assumptions of traditional seismic imaging, which is based on the same datum, is no longer adapt to the OBS data.So we propose in the paper the Kirchhoff prestack time migration for ocean bottom seismic data.First the calculation formula of the travel of down-going and up-going waves from reflection points are derived, and graphs show directly the coverage range of their respective common-receiver-point gathers data.Then using the mirror imaging theory as a guidance, the calculation formulas of travel time of down-going and up-going waves for Kirchhoff time migration are given, and conversion methods between imaging time corrections and RMS velocity in the formulas are clearly specified.Finally, the calculation formula of OBS seismic prestack time migration weighted function is described.