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Valley correction for wind turbine noise
The IOA GPG TO ETSU-R-97 recommends that a correction of +3 dB (or +1.5 dB if using G=0.0) should be added to the calculated noise level of a wind turbine for propagation “across a valley”. The following criterion of application is recommended: hm ≥ 1.5 x (abs (hs – hr) /2). In this criterion hm is the mean height above the ground of the direct line of sight from the receiver to the source (as defined in ISO 9613-2, figure 3).
Although the formula is simple enough, the criterion when to apply the valley correction is not. Because there is no exact and unambiguous definition of ‘propagation across a valley’, the consultant will have to decide ‘manually’ in which situation a valley correction is applicable.
When it is decided that a valley correction is needed, determining the mean height hm manually can be time consuming. As the calculation of hm is part of the ISO 9613 calculation method, the iNoise Free software can be helpful. In iNoise the calculated mean height above the digital terrain model for any chosen receiver – wind turbine combination can be displayed.
For more information on iNoise register for a Free Q&A Webinar at https://dgmrsoftware.com/webinars/ or visit our booth on 23-24 April at Acoustics 2018 in Cardiff.