In order to perform long-term predictions of aircraft noise propagation more accurately, it is necessary to examine the temporal fluctuation of atmospheric absorption which depends strongly on air temperature and humidity. Large variations occur according to the time and place in actual meteorological conditions. The variability of atmospheric absorption is usually neglected in outdoor noise assessment work. The authors have calculated the attenuation coefficients for atmospheric absorption at high altitudes from meteorological data obtained at several aerological observatories throughout the world during a year, using the calculation described in ISO 9613-1. To examine the effects of atmospheric absorption on aircraft noise propagation, the aircraft noises heard on the ground were calculated from the attenuation coefficients at altitudes up to 3500m. Results show that the temporal fluctuations of the attenuation coefficients tend to increase with increasing the altitude, and sound exposure levels of aircraft noise near the ground in the winter are highly variable as compared with those in the summer. In this study, it has been found that the sound exposure levels and sound spectra of aircraft noise vary strongly because of the changes in atmospheric absorption, which depend on actual meteorological conditions.
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