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Investigation of a microphone height correction for long-range wind farm noise measurements  

Author:  | Noise, Technology

Abstract:
In the measurement of wind farm noise, it is standard practice to mount outdoor microphones at a height of 1.5 m. On the other hand, measurements at this height can be affected by wind-induced noise, which has the potential to mask the noise of interest, particularly at low and infrasonic frequencies. Therefore, to minimise wind-induced noise, it is advantageous to measure on or below the ground, where the wind speed is close to zero. However, results from measurements taken at any height other than 1.5 m must be interpreted with caution, due to different interference effects between direct and ground-reflected waves at each location. This investigation explores the feasibility of using a prediction model based on Nord2000 algorithms to correct the 1/3-octave sound pressure level measured at ground level to obtain a representative value for a height of 1.5 m. The model takes into account phase changes due to the difference in travel-time for the direct and reflected rays and finite ground impedance, multiple source contributions and incoherence due to turbulence. The focus is on propagation distances greater than 2 km, where limited validation of existing propagation models has been attempted previously. Comparison is made between the model and measurement results obtained at four locations near a wind farm, where microphones were mounted at a height of 1.5 m and at ground level. A lack of agreement between measurements and the model indicates that the efficient and practical correction method considered here is not feasible for long-range wind farm measurements. Thus, it is recommended that wind farm noise is measured at both 1.5 m (for mid- to high-frequency noise) and at ground level (for low-frequency noise, which is more affected by wind).

Kristy L. Hansen, Branko Zajamšek, College of Science and Engineering, Flinders University, Tonsley, Australia
Colin H. Hansen, School of Mechanical Engineering, University of Adelaide, Adelaide, Australia

Applied Acoustics
Volume 155, 1 December 2019, Pages 97-110
doi: 10.1016/j.apacoust.2019.05.015

Investigation of a microphone height correction for long-range wind farm noise measurements

This material is the work of the author(s) indicated. Any opinions expressed in it are not necessarily those of National Wind Watch.

The copyright of this material resides with the author(s). As part of its noncommercial effort to present the environmental, social, scientific, and economic issues of large-scale wind power development to a global audience seeking such information, National Wind Watch endeavors to observe “fair use” as provided for in section 107 of U.S. Copyright Law and similar “fair dealing” provisions of the copyright laws of other nations. Send queries to query/wind-watch.org.

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