A Study of the Characteristics of Scattering Attenuation by Physical Modelling

散射特性之物理模型研究

謝昭輝(Chao-Hui Hsieh) ； 張永孚(Young-Fo Chang)

《Terrestrial, Atmospheric and Oceanic Sciences》 7卷1期 (1996/03) Pp. 31-42

並列摘要

Scattering attenuation (1/Q(subscript s)) depends not only on wave frequency but also on scatterer size. Using void holes as scatterers in a thin duralumin plate, and with the kα value (k is the wave number, α the scatterer radius) being changed systematically from 0.05 to 5, the fluctuation of direct waves between a homogeneous and a scattering medium are observed in order to calculate the scattering attenuation by 2-D physical model experiments. The experimental results show that 1/Q(subscript s)has a peak around kα=0.5. At high frequency, 1/Q(subscript s) is proportional to (kα)^(-1), whereas at low frequency the decay of 1./Q(subscript s) relative to (kα)^4 is steeper than predicted by Rayleigh scattering. The medium can be considered to be a quasi-homogeneous one, and the scattering effect can be neglected when kα＜0.05. The velocity fluctuation has a sharp change at kα=0.5. The velocity of the scattering medium doesn't change when 0.5＜kα, is less than that in a homogeneous medium and exhibits a constant fluctuation when kα＜0.5. Whether the wave length is smaller or greater than the scatterer size, the P-and S-waves have the same scattering attenuation coefficients if they have the same kα value.

並列關鍵字

Scattering attenuation ； Intrinsic attenuation ； Physical model