Filtering of coherent noise

The standard reverse-time migration (RTM) image is obtained by computing the zero-lag correlation of the back-projected data with the source wavefield. The data are back-projected by a finite-difference algorithm, where each trace acts as a source-time history of a point source at the receiver location. This is a simple and easily understood migration method, but it is not easy to improve by the usual Kirchhoff filters such as obliquity factors, first-arrival restrictions, angle-dependent truncation of data aperture, or antialiasing filters. In Chapter , I have reformulated the equation of reverse-time migration so that it can be interpreted as summing data along a series of hyperbola-like curves, each one representing a different type of event such as a reflection or multiple. This formulation leads to filters that can be applied to the generalized diffraction-stack migration (GDM) operator to mitigate coherent migration artifacts due to, e.g., aliasing and crosstalk. Results with both synthetic and field data show that GDM images have less artifacts than those computed by the standard RTM algorithm. The main drawback is that GDM is much more memory intensive and I/O limited than the standard RTM method.