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The Effect of the Urban Street Canyon on the Noise from Low Flying Aircraft

The effect of urban streets on the noise from a low-flying aircraft has been investigated. The study first involved the development of a prediction method based on geometrical acoustics with the assumption of specular reflections. The effect of a variety of street configurations on the transmission gain was investigated and analysed in terms of changes in street geometry. The relative Effective Perceived Noise Level was also predicted. The predictions show that for specular reflections the relative Effective Perceived Noise Level increases in proportion to the ratio of building height to flying altitude, however, changing the street width has only a minor effect. The effect of mixed specular and diffuse reflections was investigated using a commercial acoustical modelling package and it was shown that although the effect on the transmission gain was small, the scattering of sound energy out of the street channel resulted in a decrease in the value of the relative Effective Perceived Noise Level with the ratio of building height to flying altitude resulting in a value of the relative Effective Perceived Noise Level which was negative for most street configurations examined. It can be concluded that although simple specular models can predict the transmission gain with reasonable accuracy, more complex models involving the effects of diffuse reflections are required for noise units involving integration over time.