Effect of randomly varying impedance on the interference of the direct and ground-reflected waves

Ostashev, Vladimir E.; Wilson, D. Keith; Vecherin, Sergey N.

doi:10.1121/1.3624817

Cited by 6 publications

(7 citation statements)

References 11 publications

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“…The relationships between some of these parameters follows from Ref. 33. The static flow resistivity and porosity are chosen for the fermentation/humus layer in a forest: 34 / ¼ 52 kPa s m À2 and X ¼ 0.763.…”

Section: Numerical Resultsmentioning

confidence: 99%

Correspondence between sound propagation in discrete and continuous random media with application to forest acoustics

Ostashev

Wilson

Muhlestein

et al. 2018

The Journal of the Acoustical Society of America

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Although sound propagation in a forest is important in several applications, there are currently no rigorous yet computationally tractable prediction methods. Due to the complexity of sound scattering in a forest, it is natural to formulate the problem stochastically. In this paper, it is demonstrated that the equations for the statistical moments of the sound field propagating in a forest have the same form as those for sound propagation in a turbulent atmosphere if the scattering properties of the two media are expressed in terms of the differential scattering and total cross sections. Using the existing theories for sound propagation in a turbulent atmosphere, this analogy enables the derivation of several results for predicting forest acoustics. In particular, the second-moment parabolic equation is formulated for the spatial correlation function of the sound field propagating above an impedance ground in a forest with micrometeorology. Effective numerical techniques for solving this equation have been developed in atmospheric acoustics. In another example, formulas are obtained that describe the effect of a forest on the interference between the direct and ground-reflected waves. The formulated correspondence between wave propagation in discrete and continuous random media can also be used in other fields of physics.

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Section: Numerical Resultsmentioning

confidence: 99%

Correspondence between sound propagation in discrete and continuous random media with application to forest acoustics

Ostashev

Wilson

Muhlestein

et al. 2018

The Journal of the Acoustical Society of America

Self Cite

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“…One practically important example is urban environments, for which acoustic and RF energy may reflect from buildings and other surfaces before reaching the receiver. Even in a flat, open environment, there may be direct-and ground-reflected ray paths, for which it is important to consider uncertainties in modeling the interference between the ray paths (e.g., Ostashev et al 2011).…”

Section: Gamma (Weak Scattering Approximation and Strong Scattering)mentioning

confidence: 99%

Impact of Parametric Uncertainties on Scattered Signal Distributions and Receiver Operating Characteristics

Wilson¹,

Breton²,

Hart³

et al. 2018

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Many different distributions are used to model statistics of waves that have been randomly scattered in atmospheric and terrain environments. These distributions have varying analytical advantages and ranges of physical applicability. This report reviews several basic distributions and discusses how they can be extended to include spatial and temporal variability in the scattering process. For this purpose, a compound probability density function (pdf) can be introduced in which a basic pdf describing the underlying scattering process is modulated by a second pdf describing parametric uncertainties in the scattering. We describe some useful new formulations based on the compound pdf, including strong and Rytov (lognormal) scattering processes modulated by the environment. These new formulations lead to relatively simple marginalized signal power distributions (Lomax and lognormal, respectively). Furthermore, we show how the conditional scattered signal pdf may be viewed as a likelihood function in which the modulating pdf is the Bayesian conjugate prior. The parameters of the modulating process can thus be refined by simple sequential Bayesian updating. Finally, the impact of the parametric uncertainties on signal detection and receiver operating characteristic curves is discussed and shown to be a very important consideration in practical applications. DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents.

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“…Consequence of the uncertainties in the ground properties on the SPL predictions has been partly investigated. Ostashev et al 14 have treated the case of a homogeneous admittance plane with random properties. After prescribing probability density functions for the flow resistivity, tortuosity, and porosity of the ground surface, the statistics of the sound pressure at long range were computed using the analytical solution for a homogeneous plane.…”

Section: Andmentioning

confidence: 99%

Sound propagation over the ground with a random spatially-varying surface admittance

Dragna

Blanc‐Benon

2017

The Journal of the Acoustical Society of America

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Sound propagation over the ground with a random spatially-varying surface admittance is investigated. Starting from the Green's theorem, a Dyson equation is derived for the coherent acoustic pressure. Under the Bourret approximation, an explicit expression is deduced and an effective admittance that depends on the correlation function of the admittance fluctuations is exhibited. An asymptotic expression at long range is then obtained. Influence of the randomness on the amplitude of the reflection coefficient and on the wavenumbers of the surface wave component is analyzed. Afterwards, numerical simulations of the linearized Euler equations are carried out and the coherent pressure obtained by an ensemble-averaging over 200 realizations of the admittance is found to be in good agreement with the analytical solution. In the considered examples of grounds, the mean intensity is shown to be similar to the intensity in the non-random case, except near interferences that are smoothened out due to randomness. It is however exemplified that the intensity fluctuations can be large, especially near destructive interferences.

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Effect of randomly varying impedance on the interference of the direct and ground-reflected waves

Cited by 6 publications

References 11 publications

Correspondence between sound propagation in discrete and continuous random media with application to forest acoustics

Correspondence between sound propagation in discrete and continuous random media with application to forest acoustics

Impact of Parametric Uncertainties on Scattered Signal Distributions and Receiver Operating Characteristics

Sound propagation over the ground with a random spatially-varying surface admittance

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