ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

2pUW2. Combined volume and surface scattering in a channel using a modal formulation.

Shimshon Frankenthal

M. J. Beran

Dept. of Elec. Eng., Catholic Univ. of America, Cardinal Station, Washington, DC 20064

In previous work, a modal approach was used to study random volume scattering in a shallow channel [M. J. Beran and S. Frankenthal, 3203--3211 (1992)]. Here, the way to include the effects of a rough channel surface in the formulation is shown. To include the effects of a rough surface, the modes are taken to be dependent on the range and transverse coordinates in addition to the depth coordinate. The propagation is studied in terms of the ensemble-averaged two-point coherence function and the equation governing the coherence function is derived. In order to insure energy conservation when the generalized modal field equations are simplified, the parabolic approximation is replaced by a method which includes both forward and backward propagating fields. The two-point coherence function is expressed as the sum over both self-modal and cross-modal coherence functions. The difference between the equations governing the self-modal coherence functions and the cross-modal coherence functions is considered. A numerical example which uses typical shallow water parameters is presented. Figures portray how the mode energies are transferred between the modes as the acoustical field propagates. [This work was partially supported by ONR.]