Equations 53 and 54 exchange the and terms. The source term is removed, and the boundary condition bc is applied every time step. This backward in time migration of seismic data is called Reverse Time Migration. The modeling finite difference equation is
The imaging finite difference equation is
The three seismic models which were generated using the exploding reflector model are migrated using Equation 55. The dipping layer, reef, and salt models have all been computed using the initial known velocity model and are shown in Figures 22, 25, and 28, respectively. Study the moving wave fields and see if the recorded reflections move into the earth in an understandable way. As you might want to compare the migration process with the modeling process, notice that waves exiting the model sides do not appear in the migration. What does this do to the image reconstruction? Would any other imaging method be more successful in reconstruction of the missing data?