Nationwide field measurements of wind turbine noise in Japan

A research project entitled “Research on the evaluation of human impact of low frequency noise from wind turbine generators” has been conducted over the past 3 years from fiscal year 2010, funded by a grant from the Ministry of the Environment, Japan. In this study, noise measurements were performed in the immission areas around 34 wind farms nationwide. For the survey, measurement instrumentation was devised to cover low frequency components including infrasound, and measurement techniques were investigated in order to detect wind turbine noise in ambient environmental noises. Each field measurement was performed continuously and unattended for 120 h, and sound pressure signals were recorded on specially manufactured wide-frequency-range sound level meters. From the recordings, 1/3-octave-band and A-, C-, and G-weighted sound pressure levels were obtained during the time when the wind turbines were under a rated operation condition. Amplitude modulation sound, which is a serious problem of wind turbine noise, was also analyzed with emphasis on the sound pressure level variation and modulation period. In parallel with the measurements around wind farms, 16 control areas without wind turbine noise were chosen and the residual noise was measured for comparison.