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The propagation of sound in the atmosphere is acomplexprocess influenced by the atmospheric conditions and earth'ssurface. Thus acomprehensive numerical computation of the propagation of aircraft noise in the vicinity of an airport needs adetailed description of the atmosphere and ground in arange of about 20-40 km around the airport. These data are usually not available in practice -a nd are obviously not available for future scenarios. So the sound propagation models of common aircraft noise calculation tools, liket he German AzBor the Integrated Noise Model from FAA, use standardised meteorological conditions. The main objective of this study is to quantify the noise leveldifferences between calculations for these standardised meteorological conditions and calculations based on real weather conditions. Furthermore the study estimates the uncertainties of the sound levels resulting from the variation of atmospheric conditions. This information can be helpful to estimate the uncertainties of common aircraft noise source models in comparison to measured sound leveldistributions. The study concentrates on the sound propagation through the atmosphere from point sources at higher altitudes. Therefore ground effects and the effect of microphone height are not considered in this investigation. Ar ay-tracing algorithm is used to model the refraction of sound due to wind, wind gradients, and temperature gradients. The atmospheric absorption is calculated according to ISO 9613-1. Data on temperature, wind and relative humidity were collected overo ne year from radiosonde measurements at the meteorological observatory Lindenbergi n Germany. The results showt hat the average sound pressure levels calculated for real atmospheric data overa period of one year and the levels calculated for standardised atmospheric conditions are similar in magnitude. Furthermore, common noise calculations result in slightly higher levels hence providing aconservative modelling of propagation effects.

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