This paper demonstrates by theoretical and numerical examples that in the calculation of ray‐theory intensities in an underwater sound field the use of constant gradient layers can introduce spurious caustics and in some cases can omit real caustics. The theoretical intensity is discontinuous and becomes zero for a ray which is horizontal at any layer interface where the slope of the velocity‐depth function is discontinuous, not only for constant gradient layers but for any function which might be used to approximate the profile. If the slopes as well as velocities are continuous at a layer interface, the intensity will generally be continuous. The use of curved line segments preserving both velocity and slope continuity in the profile approximation is suggested.

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