Assessing Accuracy of ISO 9613-2 for Calculating Ground Effects of Stack Height and Distance Using Olive Tree Labs Suite

Ray-tracing software, which normally uses ISO 9613-2 to calculate outdoor sound propagation, is typically used to model community noise from large facilities. It is computationally practical for large-scale models. While ray-tracing has been used successfully for designing industrial facilities, the accuracy of some empirical algorithms in 9613 is questionable. It is presumed that ground effects calculated using 9613 are generally accurate for grazing incidence of a ray to the ground, but their use at large angles of incidence and taller sources is of lesser but unknown accuracy. For example, at 100 m, a 100-m high stack has an angle of incidence of 45°, which is far higher than grazing incidence. Full-wave software, such as Greens Function-Parabolic Equation calculates wave length-effects, and is nominally exact, but too computationally intensive for modeling large-scale industrial facilities. On the other hand, Olive Tree Labs OTL Suite software provides the wave-length effects needed to accurately calculate and model ground reflections, and is computationally practical to model large industrial facilities. The accuracy of excess attenuations of ground effects calculated using 9613 are assessed. Conclusions on the accuracy of 9613 for use in design are made.