Eliminating unnecessary diffractive features in ocean sound-speed models for long-range acoustic propagation

Abstract

A major focus of long-range acoustic experiments is the study of the properties of the ocean. In order to explore these properties, it is necessary to have an effective model of the ocean that is sufficient to understand the physics of the wave propagation. Large structures in the ocean cause refraction of the acoustic waves, while smaller structures cause diffraction. Since long-range time fronts are mainly due to refractive effects, adding diffractive features to a model does not significantly change the long-range wave propagation. However, such features cause important theoretical techniques based on refraction, e.g., ray methods, to be inaccurate and they also increase computational effort in the wave propagation calculations. A prescription to remove the diffractive features in an ocean sound-speed model is outlined and the effects on the time fronts is shown. This removal eliminates the ‘‘microfolds’’ in the phase space manifolds [discussed by Simmens et al. in J. Acoust. Soc. Am. 102, 239 (1997)] and improves the wave/ray correspondence. Therefore, it is necessary to remove diffractive structures from ocean models before attempting to use ray methods to understand long-range propagation. [Work supported by ONR.]