### ASA 124th Meeting New Orleans 1992 October

## 4pPA8. Implementation of surface impedance boundary conditions in the
split-step parabolic equation.

**F. J. Ryan
**

**
**
*Ocean and Atmospheric Sci. Div., Code 541, NRaD, San Diego, CA 92152-5000
*

*
*
The parabolic wave equation (PE) is a powerful numerical method for
computing the full-wave complex acoustic pressure field in range-dependent
environments. The split-step Fourier PE algorithm (SSFPE) of Hardin and Tappert
provides a very efficient computational implementation of PE when the surface
boundary condition is of the Dirichlet or Neumann form. This allows use of fast
Fourier transform (FFT) methods to implement the SSFPE algorithm. In many
cases, however, the surface boundary condition is of the mixed or impedance
type which precludes use of simple FFTs. In this talk, generalizations of the
SSFPE algorithm will be discussed that use a novel fast radiation transform
(FRT). The FRT allows explicit incorporation of complex surface impedance
boundary conditions into the SSFPE algorithm, while still retaining
computational efficiency. Illustrative examples that use this new method will
be shown.

Posters will be on display from 1:30 to 4:30 p.m. To allow contributors an
opportunity to see other posters, contributors of odd-numbered papers will be
at their posters from 1:30 to 3:00 p.m. and contributors of even-numbered
papers will be at their posters from 3:00 to 4:30 p.m.