An inter-model comparison of parabolic equation methods for sound propagation from wind turbines

The modeling of sound propagation for land-based wind turbines is a complex task that takes various parameters into account. Not only do the wind speed and wind direction affect the noise received at a certain position by changing the refraction of the sound, but also the terrain complexity, ground impedance, and receiver position relative to the source and ground all affect propagation. These effects are seen by the reflections of the sound at the ground surface causing interference of sound waves, or by the receiver being positioned in and out of noise shadow zones in the upwind far field position, or in steep terrain irregularities. Several sound propagation models with different levels of fidelity have been developed through time to account for these effects. This paper will focus on two different parabolic equation models, the Beilis-Tappert Parabolic Equation and the Generalized Terrain Parabolic Equation, through theoretical studies of varying terrain complexity, ground impedance, and sound speed profiles (upwind, downwind, and no wind). In addition, the propagation models are validated through spectral comparisons to noise measurements from two different campaigns considering loudspeaker noise and wind turbine noise, respectively.