Discretization of a hybrid model for acoustic wave propagation in layered fluid media

The objective is to construct and discretize (to fourth-order accuracy) a hybrid model for waveguide problems, where a finite difference method for inhomogeneous layers is coupled to a boundary element method (BEM) for a set of homogeneous layers. Such a hybrid model is adequate for underwater acoustics in complicated environments. Waveguides with either plane or axial symmetry are treated, which leads to (algebraically) twodimensional problems. The main focus is on the collocated BEM.