The process of performing an Environmental Impact Assessment includes the study of noise propagation. Often, the path from a noise source to a noise sensitive location involves complicated mechanisms of sound transmission. These mechanisms may relate to diffraction & reflections from obstacles (natural or man made), ground properties, and meteorological conditions. The International Standards Organization proposes with standard ISO9613-2, methods by which to calculate these effects. While they are relatively easy to implement, they underestimate the true workings of the aforementioned mechanisms. In this paper, we present the OTL - Terrain software application, which accurately and precisely simulates outdoor sound propagation. The software application can be used for the prediction of environmental noise and the design of control measures. OTL - Terrain is an application which uses geometrical acoustics (GA) and models the propagation of sound in terms of rays. The tool makes use of the image source method (ISM) combined with visibility tracing techniques to implement a novel method of path-detection, taking both reflection and diffraction effects into account. Calculations utilize the predicted reflections from finite-sized objects with Fresnel zone corrections, an unlimited order of diffraction, and atmospheric turbulence. This paper presents a comparison of the predictions made by the OTL – Terrain application, the methods proposed by ISO, and the published results from experimental data.
Comparison of ISO 9613-2 vs Advanced Calculation Methods using Olive Tree Lab - Terrain