Effect of wind speed and wind direction on amplitude modulation of wind turbine noise

Amplitude modulation of wind turbine noise occurs intermittently at the location of the receiver who is at a considerable distance from the turbine. This phenomenon could be because the weather conditions affect the noise source and the propagation of noise between the source and the receiver. Hence it becomes necessary to understand how amplitude modulation of wind turbine noise depends on the weather conditions. In order to understand this relationship, this paper utilizes the algorithm made by the Amplitude Modulation Work Group (AMWG) of the Institute of Acoustics (IOA) to detect amplitude modulation of wind turbine noise. Further analysis will find out how the speed and direction of the wind affects the amplitude modulated sound pressure levels (SPL). Long term measurement of wind speed (WS), wind direction (WD) and sound pressure time series recording has been done for 12 months during 2016 at Honkajoki wind park in Finland. The data used in this paper is collected approximately 1 kilometer from the nearest wind turbine. Periodic amplitude modulation within a certain frequency range is assumed to come only from wind turbines. The accuracy of amplitude modulation detection methods are uncertain, as demonstrated by Larsson and Öhlund (2014). Hence, AMWG's algorithm will also be tested on noise data which were collected on days when wind turbines were not running and on the data which are collected from places far away from the influence of wind turbine noise.