ASA 124th Meeting New Orleans 1992 October

3aUW8. Predictability of low-frequency acoustic propagation in shallow, sloping bottom channels.

R. J. Cederberg

W. L. Siegmann

M. J. Jacobson

Rensselaer Polytechnic Inst., Troy, NY 12180-3590

W. M. Carey

Defense Adv. Res. Project Agency, Arlington, VA 22202

The accuracy of PE model predictions for frequencies below 100 Hz in shallow-water channels with sloping bottoms is investigated. Comparisons are made among adiabatic approximations of analytic solutions to the Helmholtz equation and a wide-angle PE for two-layer isospeed sloping channels, an exact solution to the Helmholtz equation in a wedge, and predictions from the IFD implementation of the wide-angle PE. Inaccuracies due to the parabolic and adiabatic approximations are shown to be generally small for cases considered. Accuracy restrictions imposed by uncertainties of environmental and acoustic parameters are determined by observing changes in intensity and horizontal wave numbers caused by parameter variations in one adiabatic model. Range dependence of wave numbers is determined and methods for comparing these wave numbers are considered. Sensitivities of parameters such as sound speeds and bottom density are found to be similar to those from an earlier investigation of a flat bottom model [J. Acoust. Soc. Am. 89, 1896 (A) (1991)]. Parameter values and magnitudes of variations are selected consistent with a recent New Jersey shelf experiment. Comparisons of the experimental results with model predictions are discussed. [Work supported by ONR.]