AN ADVANCED CMP RAY-TRACING

The ray‐tracing algorithm presented in this paper is based on formulae derived for the common reflecting element (CRE) stacking method. A 2D, smooth, laterally‐varying media is assumed where offset rays and traveltimes are evaluated from normal‐incidence (central) rays. The method uses a second‐order asymmetrical approximation for rays and an additional oblique spherical approximation of the central wavefronts for calculating offset traveltimes. In order to solve the two‐point ray‐tracing problem for the common midpoint (CMP) configuration of source‐receiver pairs located symmetrically around the CMP stations, the central rays are perturbed to satisfy the above‐mentioned asymmetrical distribution. Although the accuracy of the calculations is limited for far offsets, it is still good for distances of the order of the reflecting depths. Since only a few normal‐incidence rays are traced through the medium, the method is very fast and is found to be most attractive for iterative inversions in macromodel estimation. Copyright © 1990, Wiley Blackwell. All rights reserved