Lateral attenuation of aircraft noise

Abstract

Lateral attenuation of aircraft noise comprises all of the losses in addition to spherical spreading and at- mospheric absorption. The phenomenon is primarily due to ground interference effects and is often regarded as a function of source-receiv er distance and elevation angle. In this paper, theoretical predictions are made in order to examine the consistency of existing empirical data on lateral noise attenuation. The results indicate that the effects of source spectrum shape and meteorological conditions must also be considered in any model for predicting lateral noise attenuation. F great importance to the control of community noise around airports is an accurate knowledge of the locations of equal noise load contours. In turn, the noise load at a given position is strongly dependent on the noise levels received from the individual aircraft at that place. To obtain the noise levels at arbitrary positions, ex- trapolations are usually made from noise data measured beneath the flight path. Although the noise level decay rate with increasing distance from the source is due primarily to spherical spreading and atmospheric absorption, other phenomena also produce attenuations. In particular, excess attenuations are caused by the effects of ground reflection. In addition, at low elevation .angles, shielding effects of the aircraft on emitted noise might alter the observed noise levels. The latter influences give rise to the so-called lateral noise attenuation. By definition, this quantity is the difference in time-integrat ed or maximum noise levels during flyover between that received on the flight track and that received at a sideline position, at a distance from the aircraft equal to the distance to the position on the flight track. The SAE-A21 Aircraft Noise Committee has developed an interim empirical prediction method for lateral attenuation of aircraft noise.1 The method uses the effective perceived noise level as a measure of the noise. The recommended curves for