Shallow‐Water Propagation under Downward‐Refraction Conditions

Propagation‐loss results obtained in 30‐f (fathom) water under downward‐refraction conditions are interpreted in terms of ray theory, and are found to depend directly upon the velocity profile and the bottom loss. A bottom loss value of 1.3 dB per bounce was inferred from the measurements, and is shown to compare favorably with theoretical values computed from bottom‐impedance information. Observed pulse shapes are then compared with theoretical pulse shapes synthesized from the combined ray and bottom‐loss models. In addition, the computed propagation‐loss values for the various paths are presented as a function of source angle in order to illustrate the vertical directivity introduced by the environment. Finally, the effect of this vertical directivity on shallow‐water propagation measurements is demonstrated by comparing propagation loss results for directional and explosive sources.