ASA 127th Meeting M.I.T. 1994 June 6-10

3pUW11. Range/depth dependence of long-range reverberation in shallow water.

Ji-Xun Zhou

Xue-Zhen Zhang

Peter H. Rogers

School of Mech. Eng., Georgia Inst. of Technol., Atlanta, GA 30332

Using an angular power spectrum method can greatly simplify some calculations for shallow water sound transmission, long-range reverberation, and their spatial coherence. The method is based on normal mode and ray-mode analogies and originally appeared in Chinese papers that are not available in English [J. X. Zhou, Acta Acust. Sin. 5, 86--99 (1980) and Acta Oceano. Sin. 1, 212--217 (1979)]. The average field intensity is calculated by summing the power spectrum of local plane waves for all normal modes propagating in different directions. In this presentation, analytical expressions for range/depth dependences of the propagation, long-range reverberation, and echo-reverberation ratio are given for two cases: a linear negative gradient layer and a Pekeris model. The results will be compared with some experimental data. At small grazing angles the bottom equivalent scattering coefficient is expressed as M((theta),(phi))=(mu) sin[sup m] (theta) sin[sup n] (phi). The range dependence of echo-reverberation ratio (ER) in the three-half law region (r[sup -3/2]) for the Pekeris model can be expressed as ER(r)~r[sup (m+n-2)]. It will decrease or increase with increasing distance. For Lambert's scattering law (m=n=1), ER should be independent of the distance. In a linear negative gradient shallow water, ER(r,z;z[sub 0])~F(z,z[sub 0])/r. An analytical expression of the depth distribution function F(z,z[sub 0]) will be given. [Work supported by ONR.]