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Application of the Beilis–Tappert parabolic equation method to sound propagation over irregular terrain

J. Acoust. Soc. Am. Volume 131, Issue 2, pp. 1039-1046 (2012); (8 pages)

Santosh Parakkal, Kenneth E. Gilbert, and Xiao Di

National Center for Physical Acoustics, University of Mississippi, University, Mississippi 38677

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The Beilis–Tappert (1979) parabolic equation method is attractive for irregular terrain because it treats surface variations in terms of a simple multiplicative factor (“phase screen”). However, implementing the exact sloping-surface impedance condition is problematic if one wants the computational efficiency of a Fourier parabolic equation algorithm. This article investigates an approximate flat-ground impedance condition that allows the Beilis–Tappert phase screen method to be used with a Fourier algorithm without any added complications. The exact sloping-surface impedance condition is derived and applied to propagation predictions over hills with maximum slopes from 5° to 22°. The predictions with the exact impedance condition are compared to predictions using the approximate flat-ground impedance condition. It is found that for slopes less than 15°–20°, the flat-ground impedance condition is sufficiently accurate. For slopes greater than approximately 20°, the limiting factor on numerical accuracy is not the flat-ground impedance approximation, but rather the narrow-angle approximation required by the Beilis–Tappert method. Thus, within the 20° limitation and using the flat-ground impedance condition with a Fourier parabolic equation, sound propagation over irregular terrain can be computed simply, efficiently, and accurately.

© 2012 Acoustical Society of America

ACKNOWLEDGMENT

The authors gratefully acknowledge funding from the U. S. Army TACOM-ARDEC at Picatinny Arsenal, New Jersey.

Article Outline

  1. INTRODUCTION
  2. THE PHYSICAL PROBLEM
  3. THE BEILIS–TAPPERT PARABOLIC EQUATION FOR SOUND PROPAGATION OVER IRREGULAR TERRAIN
    1. Coordinate transformation
    2. Wave function transformation
    3. Split-step solution
    4. Operator commutivity and the split-step approximation
  4. IMPEDANCE BOUNDARY CONDITION ON A SLOPE
    1. Impedance boundary condition on a sloping ground surface
    2. Sloping-surface impedance condition with a coordinate transformation and the Beilis–Tappert wave function transformation
      1. Coordinate transformation
      2. Wave function transformation
    3. Numerical implementation of the impedance boundary condition on a slope
      1. Finite difference parabolic equation
      2. Fourier parabolic equation
  5. COMPARISON OF THE BEILIS–TAPPERT METHOD WITH BENCHMARK CALCULATIONS AND WITH EXPERIMENTAL MEASUREMENTS
    1. Benchmark calculations
    2. Comparison with experiment
  6. CONCLUSIONS AND DISCUSSION

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KEYWORDS and PACS

PACS

  • 43.28.En

    Interaction of sound with ground surfaces, ground cover and topography, acoustic impedance of outdoor surfaces

  • 43.28.Js

    Numerical models for outdoor propagation

  • 43.28.Fp

    Outdoor sound propagation through a stationary atmosphere, meteorological factors

ARTICLE DATA

History
Received 26 Aug 2011
Accepted 21 Dec 2011
Revised 16 Dec 2011

PUBLICATION DATA

ISSN

0001-4966 (print)  

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