Wind noise measured at the ground surface

Abstract

Measurements of the wind noise measured at the ground surface outdoors are analyzed using the mirror flow model of anisotropic turbulence by Kraichnan [J. Acoust. Soc. Am. 28(3), 378-390 (1956)]. Predictions of the resulting behavior of the turbulence spectrum with height are developed, as well as predictions of the turbulence-shear interaction pressure at the surface for different wind velocity profiles and microphone mounting geometries are developed. The theoretical results of the behavior of the velocity spectra with height are compared to measurements to demonstrate the applicability of the mirror flow model to outdoor turbulence. The use of a logarithmic wind velocity profile for analysis is tested using meteorological models for wind velocity profiles under different stability conditions. Next, calculations of the turbulence-shear interaction pressure are compared to flush microphone measurements at the surface and microphone measurements with a foam covering flush with the surface. The measurements underneath the thin layers of foam agree closely with the predictions, indicating that the turbulence-shear interaction pressure is the dominant source of wind noise at the surface. The flush microphones measurements are intermittently larger than the predictions which may indicate other contributions not accounted for by the turbulence-shear interaction pressure.

Infrasonic wind noise under a deciduous tree canopy

“…At low frequencies, the turbulence-shear interaction above the canopy is quite large and is comparable to levels measured on level grassy ground. 6 The wind noise levels in the deciduous forest with leaves are comparable to the wind noise levels measured under the similar height pine forest of Ref. 1.…”

“…3 Deviations are expected since the logarithmic form is only correct for meteorologically neutral conditions. 5 Yu et al 6 investigated the effect of using the Businger-Dyer formula for wind velocity profile as a function of Monin-Obukov length in calculations of the turbulence-shear interaction wind noise over a grassy surface. The difference in the result for the logarithmic form versus the Businger-Dyer form were small for the range of estimated Monin-Obukov lengths for similar measurement conditions to those reported herein.…”

Wind noise under a pine tree canopy

“…2 The actual mechanism for this noise reduction has not been investigated, however, and it would be useful to develop a methodology to measure and predict the effects of trees on infrasonic wind noise. Recent research [3][4][5] has developed quantitative calculations of wind noise generation by atmospheric turbulence based on fluid dynamic theory. 6,7 In this paper we develop a calculation of the infrasonic wind noise in a pine forest from the measured turbulence spectra and wind velocity profiles in and above the tree canopy.…”

Wind Noise Suppression for Infrasound Sensors

“…For low frequency acoustics, the wind noise contributions due to turbulence have been shown to be divided into turbulence-sensor, turbulence-turbulence, and turbulence-mean shear interactions (6). Recently, these models have been extended to include contributions in the source region of the turbulence spectrum (7)(8)(9). The stagnation pressure is a result of the pressure imparted on an object due to the deflection of the wind around the object.…”

“…Based on work by Raspet et al (8), Yu et al (7,9,10), and Abbott et al (11)(12)(13), a model was developed to determine the pressure at the center of a wind barrier or wind screen. The pressure (Pc) can be calculated by summing the pressure contributions due to atmospheric turbulence from each of the three regions of the wind screen: inside (P1), boundary (P2), and outside (P3).…”