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

4aUW9. The extraction of acoustic propagation parameters in shallow water using synthetic aperture processing.

Thomas N. Lawrence

Nancy R. Bedford

Appl. Res. Labs., University of Texas at Austin, P. O. Box 8029, Austin, TX 78713

Synthetic aperture processing (SAP) is a method of extracting horizontal wave numbers from recordings on one, or on a very few hydrophones. The authors have reported results from a range-dependent experiment using an array in deep water [J. Acoust. Soc. Am. 93, 2374(A) (1993)]. In the experiment reported in this presentation SAP have been combined with the robustness of a 48-element vertical array covering most of the water column in 400 m of water. A determination was made of detailed shallow water propagation parameters using a moving cw sound source projecting 25 and 45 Hz. Estimations can be made for mode depth functions, mode attenuation, and mode eigenvalues as a function of source range. At 25 Hz almost all propagating modes are bottom interacting. So a determination of the effects of bottom properties on acoustic propagation can be made without direct measurement of bottom parameters. The environment is slightly range dependent, and experimental results will be compared with parameters obtained from an adiabatic normal mode model.