Taking apart beam migration

The years 2000–2001 sparked a flurry of activity on various flavors of beam migration. GEOPHYSICS papers by Yonghe Sun et al. on slant-stack Kirchhoff migration and Ross Hill on Gaussian-beam migration showed the potential of migration methods that combine aspects of Kirchhoff migration with some novel preprocessing. As a result, a number of variant beam-migration methods have arisen in the last few years, some promising great efficiency and some promising great imaging fidelity. On the other hand, because of beam migration's extra preprocessing, a simple interpretation of beam migration, analogous to that of Kirchhoff migration, has been hard to pin down. In this article, we try to add some intuition to the discussion of beam-migration methods. Our task is challenging since, for the most part, we will describe Gaussian-beam migration, which is possibly the most complicated of the slant-stack migrations. Of course, a successful understanding—even a partial understanding—of this important method will make it easier to understand the entire family of newly emerging beam-migration techniques.