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Pubic froortm,.q oraen for th.% collecton of info'matlorn Ii etimate• to lc'.qc o • o r '* cioom.e ncwolr, TI~ ,,me for o rev, nq intrucions ,earc q ea.ftlnfi (a2. vour'ie oath e'rng and maintaining the data needed. and cOmpleting and r•viewinq the colection of intorSmtion %vnd comMrent regardritn this burden Ortjf'itC 0' al•ft "nher # ecC of This cOllection 01 ,nformetfto. including sugg~t,•ttot fo, redu(cPig thi Ouleto Wathohngton rPf4Oduaftfr% SiptC1. e )cej O ft•!Ot 12b. DISTRIBUTION CODEApproved for public release; distribution is unlimited. ABSTRACT (Maximum 200 words)The impact of refraction, attenuation, and scattering due to a near-surface bubbly layer on acoustic propagation modeling can be significant in sensitive surface duct and shallow water environments.Hall (J. Acoustic. Soc. Am. 86(3), September 1989) presents a semi-empirical acoustic model to determine the propagation effects of the bubbly layer on one-way horizontal transmission in a surface duct. Expressions for the depth-dependent complex sound speed and attenuation are used to extend the Hall model to the general near-surface acoustic interaction problem. The rough surface scattering at the air-sea interface and the propagation through the subsurface bubbly layer are treated independently in a simplified approach toward examining the impact of bubbles on modeled surface duct and shallow water transmission loss. The dependence of the "effective" surface loss on grazing angle and wind speed is analyzed in the frequency band of approximately 0.5-5 kHz. interactions (e.g., shallow water and surface duct) is particularly affected by propagation loss at the near-surface boundary. Thus, the inclusion of near-surface bubbles in the acoustic propagation problem is seen as a necessary requirement in ensuring that all mechanisms at the surface boundary are properly addressed. This study will examine the impact of the bubbly layer on acoustic propagation in the 0.5-to 5-kHz frequency regime.VIEWGRAPH 2 BACKGROUND

New London, ConnecticutApproved for public release; distribution Is unlimited. 92-0683492 r 1l r15