Influence of Real Atmospheric Conditions on Free Propagation of Aircraft Noise

Kurzfassung

The propagation of sound in the atmosphere is influenced by meteorological conditions. During computation a detailed description of meteorological conditions takes a lot of time but principally the needed meteorological data are not available in most cases. That is why the sound propagation calculation of common tools, like the German AzB or the Integrated Noise Model, is based on standardised meteorological conditions. The main objective of this study is to quantify the noise level differences between common propagation and propagation considering real weather conditions. Therefore the two important sound propagation effects for free sound propagation (atmospheric attenuation and geometrical spreading) are investigated for sources in higher altitudes. A ray-tracing algorithm is used to model the refractions of sound due to wind, wind gradients, and temperature gradients. The atmospheric attenuation is calculated by ISO 9613-1. The used meteorological conditions based on the parameters, i.e. temperature, wind, and relative humidity, from one year radiosonde measurements taken at the meteorological observatory Lindenberg in Germany. All in all, for long-term periods all these calculated average sound pressure levels and the levels calculated for standardised atmospheric conditions are similar in size. Furthermore, common noise calculations overestimate the meteorological influence on sound propagation slightly.