Accession Number : ADA299369

Title :   Fast Parabolic Approximations for Acoustic Propagation in the Atmosphere.

Descriptive Note : Final rept.,

Corporate Author : ARMY RESEARCH LAB WHITE SANDS MISSILE RANGE NM

Personal Author(s) : Marlin, David H.

PDF Url : ADA299369

Report Date : SEP 1995

Pagination or Media Count : 68

Abstract : Parabolic equations can be used to find approximate solutions to the reduced wave equation. By reducing the equation to first order in the range derivative, the solution can be found by marching forward in range. Several numerical techniques can be applied to the solution of the parabolic equation (PE), including finite elements, finite differences, and a Fourier Transform method known as the split-step PE. The split-step solves for each range increment in two steps. First, it propagates forward through a homogenous atmosphere, using the Fourier Transform. It then applies a multiplicative phase correction for index-of-refraction variations. The split-step method leads to a computationally fast model for two reasons: the range steps are several wavelengths, and the Fourier Transform can be evaluated by a Fast Fourier Transform. One of the difficulties encountered in applying the split-step PE to outdoor sound propagation is accommodation of the complex ground impedance. The Green's function PE is a split-step PE which solves for the one-dimensional height-dependant Green's function in a homogenous atmosphere. This Green's function incorporates the complex ground impedance as a complex, angle-dependant plane-wave reflection coefficient. (AN)

Descriptors :   *ACOUSTIC WAVES, *WAVE PROPAGATION, *APPROXIMATION(MATHEMATICS), *WAVE EQUATIONS, MATHEMATICAL MODELS, GROUND LEVEL, PARAMETERS, FINITE ELEMENT ANALYSIS, REFRACTIVE INDEX, FINITE DIFFERENCE THEORY, SOUND TRANSMISSION, FAST FOURIER TRANSFORMS, NUMERICAL METHODS AND PROCEDURES, GREENS FUNCTIONS, ACOUSTIC VELOCITY, PLANE WAVES, ATMOSPHERIC REFRACTION, INTEGRAL TRANSFORMS, ACOUSTIC IMPEDANCE, ACOUSTIC REFLECTION, PHASE SHIFT, MULTIPLICATION FACTOR, SOUND RANGING.

Subject Categories : Acoustics

Distribution Statement : APPROVED FOR PUBLIC RELEASE