Taking apart beam migration

Over the past decade, a number of beam depth migration methods have emerged. Papers by Sun et al. [2000] on slant-stack Kirchhoff migration and Hill [1990, 2001] on Gaussian beam migration showed the potential of migration methods that combine aspects of Kirchhoff migration with some novel preprocessing. Also during this period, a growing number of workers implemented beam migrations that combine efficiency and imaging fidelity. Unfortunately beam migration is complicated, so a simple interpretation of beam migration, analogous to that of Kirchhoff migration, has been hard to pin down. In this paper, I try to add some intuition to the discussion of beam migration methods. I describe Gaussian beam migration, which is possibly the most complicated of the slant-stack migrations; this makes my task challenging. However, an elementary interpretation of this method is possible, and allows an understanding of the entire family of newly-emerging beam migration techniques.