ASA 126th Meeting Denver 1993 October 4-8

2aUW14. A normal-mode theory of shallow-water reverberation.

Renhe Zhang

State Key Lab. of Acoust., Chinese Acad. of Sci., Beijing 100080, People's Republic of China

Guoliang Jin Dinghua Guan Wenhua Li Xinfang Qiu

Shanghai Acoust. Lab., Chinese Acad. of Sci., Shanghai 200032, People's Republic of China

Shallow-water reverberation is mainly caused by bottom scattering, and is much more complicated than the deep-water one. Ray theory can be used for calculating short-range reverberation simply by ignoring the water inhomogeneity, but is not suitable for long-range reverberation due to effects of refraction and multipath transmission. Assuming that the scattering sources are homogeneously distributed on the bottom and regarded as the secondary sound sources with certain directivity, by using the WKBZ approximation a normal-mode theory suitable for long-range reverberation is developed. Because the effects of the complex eigenvalues on the mode incident field have been considered, the theory is better than the former ones. The given expressions of reverberation intensity have explicit physical meaning and concise form so that they are easily used for numerical calculation and analytical discussion. Both theory and experiment show that the reverberation in inhomogeneous shallow water has obvious depth dependence and there exists the relationship: I[sub R](r,z[sub 1],z[sub 2])=[I[sub R](r,z [sub 1],z[sub 1])xI[sub R](r,z[sub 2],z[sub 2])][sup 1/2]. Some experimental results are given that are consistent with theory.