Propagation of Environmental Noise: More theoretical and experimental work could permit the prediction and subsequent control of environmental noise.

Although the basic processes associated with the propagation of environmental noise, such as reflection, scattering, and spreading are well known, numerous theoretical problems remain. The propagation processes that are significant in different situations have yet to be identified, and criteria for evaluating their relative importance in each situation must be developed. In evaluating the noise of aircraft, for example, attenuation caused by the spreading of energy may exceed 60 dB, with atmospheric attenuation accounting for another 10 dB or so. In the propagation of highway noise, on the other hand, spreading may account for only 10 dB of attenuation, air absorption for 1 dB, and absorption by ground may account for 10 to 15 dB of attenuation. If those problems are approached systematically, we should be able to predict accurately the effects of noise sources and barriers and thus control the distribution of noise levels in cities and suburban areas.