Page 26 - Winter2021

AS THE WIND BLOWS
Figure 8. a: Photograph of a porous dome windscreen from Noble et al. (2014). Photograph courtesy of John Noble. b: Photograph of a wind fence (Abbott et al., 2015). Photograph courtesy of John Paul Abbott, with permission of the Acoustical Society of America.
sheet metal (Raspet et al., 2019). Cylindrical wind fences (Figure 8b) have also been investigated for a wide range of porosities, diameters from 5 to 10 meters, and heights from 3 to 6 meters (Abbott et al., 2015). These enclosures reduce intrinsic pressure sources within the sheltered inte- rior at the expense of new stagnation pressure sources on the enclosure surface. As with audio microphone wind- screens, measurements show that flow distortion around the enclosure significantly reduces near-surface correlation lengths. This leads to more efficient spatial averaging and wind noise reduction at lower frequencies than might be expected for the enclosure size (Raspet et al., 2019).
Conclusion
Within the topic of noise generated by wind, there are many other problems with a rich body of work that have not been discussed here, such as wind noise on mobile devices, noise inside vehicles in motion, and noise inside
tall buildings. Wind noise is ubiquitous in outdoor sound measurements, which has led to many indepen- dent approaches to mitigation, whether mechanically or digitally. However, a common theme in the success (or failure) of noise reduction methods is exploiting the physi- cal properties that wind noise inherits from atmospheric turbulence, most significantly its correlation structure in space and time. By recognizing that microphone wind noise is not sound, the physical and statistical tools by which it may be described and mitigated are realized.
Acknowledgments
We thank the editor of Acoustics Today, Arthur Popper, for greatly improving this article with keen advice and perspec- tive. We also thank Thomas Gabrielson for helpful discussion and insight regarding pipe arrays. Permission to publish was granted by the Director, Information Technology Laboratory, US Army Engineer Research and Development Center.
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