A SHALLOW-WATER NORMAL-MODE REVERBERATION MODEL

A practical model to compute shallow‐water boundary reverberation is described. Normal modes are used to calculate the acoustic energy propagating from the source to the scattering area, and from the scattering area to the receiver. At the scattering patch each mode is decomposed into up‐ and down‐going waves, then ray‐mode analogies and empirical scattering functions can be used to compute the scattered energy. The method was first described by Bucker and Morris [J. Acoust. Soc. Am. 44, 827–828 (1968)], and papers which first appeared in the Chinese literature. Their work is extended here by using group velocities to obtain the travel times for each mode pair, and by further developing the ray‐mode analogy. The effects of summing the modes coherently or incoherently and of including the time spreading due to the modal group velocities are examined. This paper deals with the range‐independent monostatic case, although the technique is extendible to bistatic geometries and range‐dependent environments. Calculations show excellent agreement with some ray‐based models, and, using the Lambert bottom‐scattering coefficient as the only adjustable parameter, good agreement is obtained with some measured shallow‐water reverberation.