Volume acoustic scattering by internal waves causes a mismatch between the true environment and the idealized environment assumed in matched‐field processing. To assess the effect of internal waves, the performance of various matched‐field algorithms has been tested using simulations based upon the parabolic approximation. Internal wave and sound‐speed parameters appropriate to the deep ocean have been used. Using a combination of theory and simulated results, the dependence of processor performance on range, frequency, and aperture size is discussed. [Work supported by ONR.]