Statistical estimates of the contribution of multiply scattered radiation to the intensity of acoustic radiation transmitted through a lower 500-m atmospheric layer

Abstract

551.596The problem of acoustic radiation propagation through a lower 500-m plane-stratified turbulent atmospheric layer has been solved by the Monte Carlo method. Statistical estimates of the contribution of multiply scattered radiation to the transmitted acoustic radiation intensity are obtained. A point omnidirectional source of monochromatic acoustic radiation was placed at a height of 35 m above the absorbing Earth's surface. Statistical estimates of the contribution of multiply scattered radiation to the transmitted radiation intensity have shown that it does not exceed 15% for the outer scale of atmospheric turbulence L 0 = 10 m and sound frequency F = 1700 Hz, reaches 30% for L 0 = 20 m, and increases to 90% for L 0 = 80 m. A comparison of the calculated results with the available experimental data demonstrates their satisfactory agreement.

Statistical estimates of the influence of the source divergence angle on the characteristics of acoustic radiation transmitted through the atmosphere

“…The outer scale of turbulence L 0 was set equal to 10, 15, 20, 40, 60, and 80 m. Acoustic radiation of the source propagated through plane-parallel layers of the atmosphere with the coefficients of classical and molecular absorption σ cl (j) and σ mol (j) and scattering on turbulent temperature and wind velocity fluctuations σ T (j) and σ V (j) being constant within these layers, where j = 1, …, 25. Formulas for calculating the corresponding coefficients and compact formulas for the phase functions of sound scattering on the turbulent temperature and wind velocity fluctuations were taken from [8]. In our calculations, the vertical profiles of the air temperature, pressure, and sound speed were taken from the standard model of the atmosphere at middle latitudes in summer [13].…”

“…In [4] it has been demonstrated that the extinction of vertically propagating sound beams is determined by their broadening due to the atmospheric turbulence. Difficulties of analytical approaches to a solution of the problem of acoustic radiation transfer through the outdoor atmosphere call for the use of numerical methods (for example, see [5,6]), from which the method of statistical simulation (Monte Carlo) is most promising [7][8][9][10][11][12]. This method allows sound scattering on the refractive index fluctuations caused by wind velocity and temperature inhomogeneities to be taken into account for the most realistic models of the atmosphere.…”

Variations of the multiple scattering contribution to the transmitted acoustic radiation intensity

“…The extinction coefficients were equal to the sum of the coefficients of classical and molecular absorption and coefficients of sound scattering by temperature and wind velocity fluctuations. Formulas for calculations of the corresponding coefficients and compact formulas for the normalized phase functions of scattering by turbulent fluctuations of the temperature and wind velocity were presented in [2].…”

“…Random trajectories of particles (phonons) were simulated with the use of both well-known algorithms [6] and algorithms constructed in [1, 2,7,8] with allowance for the specifics of sound interaction with the atmosphere. Details of the computational algorithm were discussed in [1,2].…”

“…Details of the computational algorithm were discussed in [1,2]. The Earth's surface was considered absolutely absorbing.…”