The Doppler effect is an important factor in predicting the noise levels caused by a fly-over aircraft. Dependent on the Doppler factor, the absolute sound pressure levels received on the ground can be increased or decreased for an approaching or a receding aircraft. The motion of the aircraft can also influence the frequency of the sound measured on the ground. This apparent change in the source frequency has an impact on the measured A-weighted noise levels because different weighting factors are applied in different frequency bands. In addition, the change in A-weighted noise levels due to Doppler shift is affected by the source spectra, its directivity and the receiver location. In this paper, numerical simulations are presented to investigate the influence of the Doppler effect on the A-weighted noise emitted from aircraft overflights. The numerical results are compared with experimental data obtained from a field trial for a series of propeller driven aircraft. It has been shown that the propeller driven aircraft are generally more sensitive to the effect of Doppler shift than aircraft with jet engines. The uncertainty due to the Doppler effect on the prediction of aircraft noise is quantified for different types of aircraft with different noise spectra.
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