A three-dimension propagation model using stepwise coupled modes

Abstract

A propagation model has been developed that is applicable to shallow-water waveguides characterized by three-dimensional inhomogeneities which induce horizontal refraction and mode coupling. A normal-mode approach is chosen for this work because the field decomposition into modal amplitudes provides insight into the effects of the environment on the acoustic field. The model is based on the stepwise coupled-mode technique implemented with the single-scatter approximation [R. B. Evans, J. Acoust. Soc. Am. 74, 188–195 (1983)]. The stepwise technique discretizes a range-dependent environment into a series of range-independent segments. The single-scatter solution is obtained by treating each pair of segments as an independent problem, thus neglecting the higher-order terms resulting from multiple scattering at other interfaces. The field is propagated using the parabolic equation in cylindrical coordinates. Thus, at each range step, horizontal refraction is accounted for in the angular direction and mode coupling is included in the radial direction. Examples illustrating the effects of horizontal refraction and mode coupling will be presented. [Work supported by ONR.]