Comparison of measurement data for different microphone position heights in an outdoor environment.

One of the problems present when measuring noise generated in outdoor environments is the appropriate microphone placement, and there are different approaches and techniques applied within this scope. For measurements of noise generated by wind turbines, standard EN 61400 specifies installing the microphone on a mounting board at ground level, though practical demands, especially for long-term monitoring, suggest other microphone positions, above the ground level. The consequences of different microphone placements are a key issue that should be analysed and taken into consideration. Another problem specific to measurements of noise generated in outdoor environments is the influence of wind on the obtained results and the potential correction required on account of wind speed. Studies were undertaken with those issues in mind, and a comparison of different mounting positions and methods was performed. Certain other aspects, such as the influence of wind speed and the use of different windscreens, are discussed as well. This is only a preliminary stage intended to provide a perspective on the differences that may be expected when performing measurements of infrasound noise sources, and related studies should be continued in the future. The work presented in this paper concerns three aspects: the first is the dependence of the measured noise signal on the microphone position above the ground level, the second is how wind influences the measured signal quality, and the third is related to microphone positioning on a ground board. Results for a windscreen modification are presented as well. [ABSTRACT FROM AUTHOR]