Raytracing Approach to Underwater Reverberation Modeling

摘要

The effects of multiple boundary returns and non-isovelocity conditions were incorporated into a time-varying representation of underwater reverberation measured at the moving source. The research focused on the development of the time-varying power gain and frequency spectra of scattering functions, which have been shown to characterize the reverberation from an underwater environment. A sound velocity profile, which may consist of up to fifty depth-velocity point pairs, has been introduced. The ocean has been assumed to be horizontally stratified, and each stratification to be represented by a constant velocity gradient. Acoustic beam effects, backscattering coefficients, reflection loss factors, and a varying absorption coefficient have been considered. All reverberant returns have been assumed to arrive at the receiver along the same raypath that was traversed from the source to the backscattering element. Two examples are presented for comparison of the spectra and total power levels of the modified scattering function with those of the original model. One focuses on the inclusion of multiple boundary returns only. The total power curve from the revised model was observed to decay more slowly than that of the original model because of the added boundary returns. The other emphasizes the propagation effects of a non-isovelocity profile. In this scenario, the emergence of a surface shadow zone was observed, as well as the formation of a caustic near the axis of source motion. (jhd)