Prestack reverse-time migration by the grid method
格子法在起伏地表叠前逆时深度偏移中的应用

The two-way wave equation based reverse-time migration(RTM) attracts much research interest recently,because it has potential to image overturning wave and multiple reflections,canproperly hande strong lateral velocity variations and does not impose dip limitations on the images.In this work the grid method is applied to prestack RTM with surface topography.By discretizing the domain with the irregular grid,this method allows larger time steps and requires less memory storage during reverse-time migration,which enables higher efficiency.Moreover,it is easy to implement the grid method in parallel computation.By using a smoothed artificial boundary,the irregular-grid PML method can also avoid the special treatments to the corners,which lead to complex computer implementations in the conventional PML method.Owing to that the local geometrical coefficients are computed and stored in a table in advance,no extra computational costs arise when we use the irregular-grid PML method rather than the conventional PML method.A 2D acoustic case is presented here.