ASA 125th Meeting Ottawa 1993 May

5pUW7. PE modal decomposition of VLA data.

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.