Techniques to establish accurate background noise levels in areas affected by operational wind turbine noise

Abstract

During the planning process for an onshore wind farm, the establishment of accurate background noise levels at nearby noise sensitive receptors is vital in determining the allowable noise limits at these locations. This is typically achieved through background noise monitoring at a selection of representative noise sensitive receptors. As onshore windfarms have become more prevalent, areas suitable for wind farm development are increasingly within the vicinity of operational wind farms. The result of this is background noise monitoring at receptors is now often influenced by nearby operational wind farms and is not a true representation of the unaffected noise levels at these locations. Current good UK practice (as set out in the Institute of Acoustics document 'A good practice guide to the application of ETSU-R-97 for the assessment and rating of wind turbine noise') proposes a number of solutions to account for this additional wind farm noise. One solution is to consider directional filtering or the subtraction of the predicted noise levels from the measured baseline data. Whilst both approaches are valid, it can often be unclear which approach is most appropriate for a particular scenario. Within this paper, the limitations of current good practice are discussed, and an alternative methodology is proposed which combines both approaches to establish the unaffected background noise levels. Specific examples of where this alternative approach has been used are presented within the paper as validation.