Perturbation approximations for bathymetrically controlled ocean acoustic mode coupling

A perturbation approximation of mode coupling equations for acoustic propagation in a submarine canyon environment is presented. The vertical modes and mode coefficients are represented by nearly adiabatic dominant mode functions and correction terms that are sensitive to the horizontal gradient of the variable bathymetry. This approach allows for a more accurate representation of the bottom boundary condition, and eliminates computationally expensive implicit equations for the mode coefficients, replacing them with explicit equations for the nearly adiabatic contributions and the bathymetrically sensitive corrections. The presented method is applied to sloping bottom environments based on real bathymetric data to examine in detail the role of bottom variations in coupled mode propagation scenarios. [Work supported by the ONR.]