David J. Thomson
Gordon R. Ebbeson
Defence Res. Establishment Pacific, FMO Victoria, BC V0S 1B0, Canada
The first step in any matched-mode processing application is the decomposition of the measured acoustic field into its horizontal wave-number (modal) components. Previously, a PE-based method was described for carrying out the modal decomposition of the pressure field received on a vertical line array (VLA) [D. J. Thomson et al., J. Acoust. Soc. Am. 89, 2000 (1991)]. For that method, the VLA field was first interpolated between hydrophones and then extrapolated into the ocean bottom. This interpolation/extrapolation stage was needed to construct a suitable starting field on the fine computational grid used by the PE algorithm. In this paper, a modified PE model is presented that eliminates the computational grid in the bottom by applying an exact, nonlocal boundary condition along the ocean-bottom interface. Consequently, it is no longer necessary to extrapolate the VLA field prior to propagating it with PE. To demonstrate the effectiveness of the boundary condition, PE-based modal decomposition is carried out using simulated VLA data generated for a shallow-water environment.