Experimental Study of the Propagation of Sound over Ground

Abstract

The attenuation of sound propagated out-of-doors is conveniently separated into attenuation due to spherical divergence and excess attenuation due to atmospheric and terrain effects. This excess attenuation is principally caused by sound absorption in the air, the refractive effects of temperature and wind gradients, by turbulence and the effects of terrain and ground cover. To investigate these effects the propagation of sound over open, level ground, through dense evergreen forests, and between hilltops was studied experimentally in the frequency range between about 300 cps and 5000 cps. Extensive micrometeorological instrumentation was utilized to measure and record the relevant micrometeorological parameters simultaneously with the acoustic data for a wide variety of weather conditions. Data on the attenuation of the mean received sound pressure level as well as on the fluctuations about the mean were obtained and correlated with the state of the atmosphere. Over open level terrain, the excess attenuation upwind was found to exceed that for downwind propagation by as much as 25–30 db for source and receiver heights of 12 and 5 ft, respectively. Temperature and wind gradients near the ground-air interface largely account for this difference. In hilltop-to-hilltop propagation, wind direction is of secondary importance, and in dense woods absorption and scattering control. Empirical functions were derived for the purpose of estimating the mean excess attenuation as a function of frequency and distance, for a given set of micrometeorological conditions. These charts have been found useful in many practical problems involving the propagation of sound over open level ground.

Noise-induced changes in calls of the Japanese quail

“…One of the most common sources of ambient noise-wind-not only increases the background noise level, but also affects the propagation of the acoustic signal itself. A gusty wind may cause peak-to-peak fluctuation in the receiving end of over 20 dB at a 100-m distance fram the source (Ingard, 1953;Wiener & Keast, 1959). "Stable" nighttime conditions may result in 5-dB differences (Wiener & Keast, 1959).…”

“…A gusty wind may cause peak-to-peak fluctuation in the receiving end of over 20 dB at a 100-m distance fram the source (Ingard, 1953;Wiener & Keast, 1959). "Stable" nighttime conditions may result in 5-dB differences (Wiener & Keast, 1959). Laboratory experiments utilizing human listeners under re I a t i vely stable propagation conditions indicate that repetition of words results in a modest improvement in their detection equivalent to that produced by raising intensity by about 3 dB (Kryter, 1970;Thwing, 1956).…”

Outdoor Warning Systems Guide

“…This attenuation appeared to be related to visibility in the Jungle. Wiener and Keast [17] found no such correlation. Nor did Embleton [18], who, in an extensive study of Canadian forests, found "edge effects" along with attenuations considerably in excess of those observed in very similar Russian forests [19].…”

“…The concluding statement about the rariability with time of distant sound levels from a steady source comes from many studies [17,31,43].…”

Comparison between dispersed nuclear power plants and a nuclear energy center at a hypothetical site on Kentucky Lake, Tennessee

“…The effect of a wind gradient is usually the more important of the two and will override the temperature gradient effect resulting in no shadow zone down wind. Wiener and Keast 13 have developed equations with which the location of the shadow zone, if one ~xists, can be approximated and with which the excess attenuation can be calculated at any distance from the source.…”