起伏海面对反射地震偏移成像结果的影响

Influence of undulating sea surface on the result of reflection seismic imaging

实际海面受风浪的影响是个随机起伏的复杂曲面.一个随机起伏的自由表面对地震波形成相当复杂的散射,进而影响波场在靶区的二次照明与成像结果;此外,起伏海面具有小尺度随机起伏的特性,难以用贴体网格等处理大尺度起伏地表的常规方法和技术对其进行逼近和处理.鉴于此,利用不等距有限差分法实现小尺度起伏海面的波场自由表面边界条件,以此进行正演、波场照明分析;利用逆时偏移(ReverseTimeMigration,RTM)进行起伏海面下的成像并对成像结果进行分析.不同模型的试算结果表明:起伏海面引起的复杂散射使靶区地下照明不均匀、成像界面发生弯曲和畸变,从而降低成像结果的分辨率和信噪比.

The actual sea surface affected by wind and waves is a complex surface with random fluctuations.A random undulating free surface scatters the seismic wave very complex,which affects the secondary illumination and imaging results of the wave field in the target area.In addition,the undulating sea surface has the characteristics of small-scale random undulation,and it is difficult to approximate and process the sea surface with conventional methods and techniques such as body-fitted grids,which are used to process the large-scale undulating surface.In view of this,the finite difference method with unequal distances is used to realize the free surface boundary conditions of wave field on small-scale undulating sea surface for forward modeling and wave field illumination analysis,and Reverse Time Migration(RTM)is used for imaging under undulating sea surface and the imaging results are analyzed.The experimental results of different models show that the complex scattering caused by undulating sea surface makes the illumination uneven in the target area,and the imaging interface bent and distorted,thus reducing the resolution and signal-to-noise ratio of the imaging results.