Identification of low frequency wind turbine noise using secondary windshields of various geometries

To accurately characterise the noise measured in the vicinity of wind farms, outdoor microphones must be adequately protected from the wind. A standard 90 mm windshield is appropriate for measurements in light winds; however, as the wind speed increases, wind-induced pressure fluctuations contribute to the measured sound pressure level, leading to erroneous data. Three alternative secondary windshields have been developed and tested in an outdoor environment and evaluated for their ability to allow low frequency noise and infrasound measurements to be obtained in the presence of wind. Performance evaluation is facilitated through analysis of high resolution spectra as well as analysis of the coherence between microphones with different windshields under various meteorological conditions. This enables a distinction to be made between noise originating from sources such as a wind farm and wind-induced noise. The effect of the microphone location with respect to the ground surface has also been investigated for frequencies up to 100 Hz.