Measuring infrasound outdoors with a focus on wind turbines: the benefits of a wind-shielding dome

Abstract

Wind-induced microphone noise complicates infrasound measurements considerably. A wind-shielding dome for signal-to-noise ratio improvement of acoustic pressure infrasound frequencies was designed and tested. The semi-spherical shape aimed at maximizing the pressure averaging of large atmospheric turbulent eddies while keeping the structure reasonably compact. The insertion loss of the dome was measured in a semi-anechoic chamber (in absence of flow) and showed nearly full transparency in the low frequency range. In an outdoor test, wind turbine infrasound was simultaneously measured with an uncovered and a dome-covered low-frequency microphone under different wind speeds and turbulence intensities. Largest improvements of the signal-to-noise ratio were measured at high mean wind speeds for frequencies down to 0.5 Hz. The dome allowed to clearly identify the infrasonic tonal components of wind turbines that were otherwise completely covered by the wind-induced microphone noise even at low mean wind speeds. The use of the dome thus opens possibilities for more accurately measuring infrasonic immissions from e.g. wind turbines.