Salomons E.

In many practical outdoor situations, the direct sound path between a noise source and a receiver is screened by an obstacle. In these situations indirect sound paths become important, in particular reflections of sound waves. Reflections may occur at man-made objects such as a vertical wall, but also at the edge of a wood. In this paper a method is described for the calculation of: i) specular reflection from a vertical wall, and ii) diffuse reflection from the edge of a wood. The method is derived from numerical computations and scattering theory, but the resulting formulas are simple enough for implementation in engineering models for outdoor noise. For a reflection from a vertical wall, the height and width of the wall are taken into account, based on Babinet's principle and results of computations with the Parabolic Equation method for atmospheric sound propagation. The reflection depends on wind and temperature profiles in the atmosphere. A diffuse reflection from the edge of a wood is modeled as a reflection from a single row of trees, with an effective spacing between the trees that represents the reflection contribution of trees behind this row. The reflection is calculated by incoherent summation of the reflected fields of all the trees in the single row. The calculation of the reflected field of a single tree is based on the theory of scattering of spherical waves by a cylinder. The model takes into account the height, the average diameter, and the spacing of the trees in the wood.