A SIMPLE COUPLED WEDGE MODE PROPAGATION METHOD

In this paper an efficient coupled-mode method is presented for modeli ng acoustic propagation in a multi-faceted oceanic waveguide. The meth od is based on the concept of ''wedge modes,'' which are identical to the usual normal modes of a range-invariant waveguide except that the mode functions are referenced to the are of a circle rather than a ver tical line. Within each wedge-like section of the waveguide, wedge mod es are assumed to propagate adiabatically. At junctures of waveguide f acets, the incident field from the previous wedge is coupled into the wedge modes of the following wedge, and the new set of wedge modes is again propagated adiabatically. ''Leaky modes,'' which account for ene rgy that is only partially reflected at the basement interface and whi ch are important only at shea ranges in flat waveguides, are included because conversion between leaky and trapped modes is important in man y range-variable waveguide geometries. Coupling of the two sets of wed ge modes at facet interfaces is performed using a method that does not assume mode orthogonality in the water. Agreement in the field comput ed using the coupled wedge mode method and a parabolic equation method is found to be very good.