Nonlocal Tops and Equivalent Bottoms for Sound Propagation in Air Problems


  1. Thomson, D.J.
Corporate Authors
Defence Research Establishment Atlantic, Dartmouth NS (CAN)
One-way wave equations derived from parabolic equation (PE) approximation are widely used to model underwater and atmospheric sound propagation. Finitie-difference PE solvers based on Pade series expansions provide accurate and efficient solutions to these one-way fields for range-varying geoacoustic environments. For layered media, alternative approaches based on normal mode, multipath expansion or wavenumber integration representations are available. Since proper analysis of acoustic field behaviour often relies on using more than one propagation model, it is desirable to obtain numerical agreement between models in situations where different models apply. To solve a PE numerically, the computational grid must be terminated top and bottom. In outdoor sound applications, the acoustic field is usually assumed to satisfy a locally-reacting (constant impedance) boundary condition along the ground plane. This condition is easily incorporated into finite-difference PE models. On the other hand, wavenumber integration codes such as SAFARI, that were developed specifically for underwater sound propagation applications, do not incorporate this locally-reacting condition directly. In the first part of this paper, we design and equivalent fluid whose reflection response is numerically equivalent to that produced by a constant impedance surface. TRUNCATED
Non-local boundary condiction (NLBC);Numerical implementation;Pade approximants;One-way approximations
Report Number
DREA-SL-1999-119 — Reprint
Date of publication
19 Aug 1999
Number of Pages
Reprinted from
Canadian Acoustic, vol 27, no 3, 1999, p 18-19
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