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.
Flood frequency analysis using partial series data has been shown to provide better estimates of small to medium magnitude flood events than the annual series, but the annual series is more often employed due to its simplicity. Where partial series average recurrence intervals are required, annual series values are often "converted" to partial series values using the Langbein equation, regardless of whether the statistical assumptions behind the equation are fulfilled. This study uses data from Northern Tasmanian stream-gauging stations to make empirical comparisons between annual series and partial flood frequency estimates and values provided by the Langbein equation. At T = 1.1 years annual series estimates were found to be one third the magnitude of partial series estimates, while Langbein adjusted estimates were three quarters the magnitude of partial series estimates. The three methods converged as average recurrence interval increased until there was no significant difference between the different methods at T = 5 years. These results suggest that while the Langbein equation reduces the differences between the quantile estimates of annual maxima derived from annual maxima series and partial duration series flood frequency estimates, it does not provide a suitable alternative method to using partial series data. These results have significance for the practical estimation of the magnitude-frequency of small floods.
Insertion loss in octave bands was measured for 14 residences in upstate New York using a carefully developed procedure similar to ASTM E336-71 A1.2. Although other dwelling attenuation data are available [e.g., House Noise-Reduction Measurements for Use in Studies of Aircraft Flyover Noise, Soc. Automative Engrs., AIR 1081; Oct. 1971] none was clearly applicable to rural areas of upstate New York and to sources of noise located near the ground. The source was simulated by a three-speaker array using broadband noise. Attenuation of transmission line noise was derived mathematically by applying the measured octave-band attenuations to a typical broadband transmission line noise spectrum and converting to A-weighted and sound levels. Average attenuation was about 15 dBA with windows open 2 ft2, and about 30 dBA with windows closed. [The study was conducted by Rochester Gas and Electric Corporation and their consultant Bolt Beranek and Newman in consultation with the New York State Departments of Public Service and Environmental Conservation.]
NOTICE , This report was prepared as an account of work sponsored by the United States G'overnment. Neither the United States nor the Udited States Department of Energy (DOE), nor any of their employees, , nor any of their contrdctors, subcontractors, or theit employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any information, apparatus, product or process disclosed, or rspresents that its use would not infringe privately owned rights.
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