Parameter selection in the Green's function parabolic equation for outdoor sound propagation over varied terrain
Abstract
There is a need for a method to predict the attenuation of sound over a varied terrain and for realistic weather conditions. Parabolic equation based propagation codes can deal successfully with a sound speed that is a function of height (as could be caused by wind or temperature gradients) as well as varying ground heights and impedances. The ability to predict the received sound levels for a set of digitized terrain and sound speed data is desired. The accuracy of the Green's function parabolic equation (GFPE) has already been confirmed for propagation over flat ground with a slowly varying sound speed profile and/or with atmospheric turbulence. The approach here will be to compare to a benchmark solution for each different kind of terrain (i.e. flat, slope, step, barrier) with constant sound speed to verify the numeric code and to define the limits of accuracy in the GFPE for these situations. The GFPE is based on a one-way wave equation, so the numerical model will not be able to accurately predict the pressure behind multiple barriers or for other situations in which backward reflections can affect the received pressure. We will define the additional limits to the applicability of this model based on many comparisons with analytical solutions for propagation beyond barriers with constant sound speed. The sloping terrain will be treated as a series of stairsteps---a digitized ground height. Buildings and steps will be merely larger stairsteps. Although the GFPE has already been documented, as well as wide angle parabolic equations (PEs) and PEs using conformal mapping or similar rudimentary stair-stepping terrain maps, a PE that works with large discontinuities has not been documented, nor has there been work on a propagation model over complicated terrain profiles (in the past most work has been done in underwater acoustics for oceans with a sloping bottom condition but no variation in the slope was presented). The main emphasis here will be on the assumptions and limitations inherent in the GFPE and the range of conditions over which it is valid.
- Publication:
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Ph.D. Thesis
- Pub Date:
- October 2003
- Bibcode:
- 2003PhDT.......167C