### ASA 124th Meeting New Orleans 1992 October

## 4aPA8. A nonreflecting boundary condition for use in PE calculations of
sound propagation in air.

**M. E. Mayfield
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*Dept. of Math. and Comput. Sci., Hood College, Frederick, MD 21701-8575
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**D. J. Thomson
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*Defence Res. Estab. Pacific, FMO Victoria, BC V0S 1B0, Canada
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Although the parabolic equation (PE) method has long been used to model
underwater sound propagation, its applicability to outdoor sound propagation
has been realized only recently [e.g., K. E. Gilbert and M. J. White, J.
Acoust. Soc. Am. 85, 630--637 (1989)]. In ocean acoustics, an absorbing layer
is usually appended to the base of the computational grid to suppress unwanted
reflections that arise from a Dirichlet boundary condition imposed at a finite
distance below the ocean-bottom interface. For sound propagation in air,
however, this local boundary condition must be applied at the top (z=H) of an
absorbing layer that occupies the region h