### ASA 126th Meeting Denver 1993 October 4-8

## 5aUW1. Implementation of generalized impedance boundary condition in the
split-step Fourier 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, and when the solution
decays sufficiently with depth. This allows use of fast Fourier transform (FFT)
methods to implement the SSFPE algorithm. Typically the infinite domain
radiation condition is approximated on a finite calculation grid by employing
an artificial absorber or sponge. In some cases involving strong bottom
interaction, however, the required absorber region may be quite large. This
results in an increased computational load. A new method for truncating the
absorber region will be described that is based upon splitting the PE field
into two components that are in turn propagated on different vertical
wave-number grids. Illustrative examples that use this new method will be
shown. [Work supported by NRaD IR program.]