f Extrapolation operators by beam tracing

The key process in seismic imaging is given by migration. The accuracy and efficiency of the migration process is directly determined by the involved downward extrapolation operators. Taking into account that a downward extrapolation operator equals the response at the surface due to a point source in a subsurface grid point of a macro model, the computation of point source responses in macro models is of vital importance for the seismic method.