M. E. Mayfield
Dept. of Math. and Comput. Sci., Hood College, Frederick, MD 21701-8575
D. J. Thomson
Defence Res. Estab. Pacific, FMO Victoria, BC V0S 1B0, Canada
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