境界平面における音の拡散反射

抄録

In outdoor propagation of sound, the ground surface and other obstacles such as buildings have complex scattering characteristics to the incident wave especially in high frequency region. As an ideal limit of this complex scattering, the obstacle is supposed to absorb a part of incident sound energy and reflect the remaining part of energy equally in all probable directions. The scattered field of sound intensity around the obstacle is shown to be the same as those fields associated with black body radiation of heat and diffuse reflection of light at the surface of the obstacle. As an application of this theory, it is carried out to investigate the scattered sound fields above the plane boundary which diffusely reflects the incident waves. The simple closed forms of the scattered fields are derived for the incident plane, spherical and cylindrical waves. The results are compared with those relevant to the specular (regular) reflection of the incident sound at the boundary. For the diffuse reflection an equivalent image source is introduced which is similar to the one for the specular reflection. The directivity pattern of the image source for the diffuse reflection, however, is not omnidirectional and is proportional to directional cosine of the azimuthal angle.