REFRACTOR VELOCITY DETERMINATION—CAUSE AND NATURE OF SOME ERRORS*

Abstract

AbstractFor detailed determination of refractor velocities of in‐line reversed profiles, two principally different systems have been employed, the ABC method and Hales's method. The two systems differ in the travel‐path arrangements used. The more conventional approach to the problem, the ABC method, makes use of critically refracted rays converging on a common surface position, while Hales's method deals with the common position on the refractor surface from which critically refracted rays diverge towards the ground surface.Because of the travel‐path system used, Hales's method has proved to be particularly applicable to high‐relief structures and to cases where the refractor lies at considerable depth. Some of the ambiguities in more commonly used interpretation techniques can be solved by Hales's method.Some attention has also been paid to errors caused by non‐critical refractions and to the diffraction problem.