Behavior of the correction factor for aircraft noise faade measurements

ISO 1996-2 standard has an appendix called Annex B which specifies the reference position of the microphone to undertake the measurement, and a simplified correction factor to use in case that the measurement must be located near a reflecting surface (3dB). Aircraft noise behaves as an extended noise source and its source-receiver geometry differs to that of other extended sources as it has an altitude. The altitude and the slant distance form a slant angle which modifies noise incidence on faade. Measurements in the reference and faade positions were performed in places with exposure to aircraft noise. Different slant angles were obtained with all aircraft noise events measured. The correction factor near a reflecting surface (3 dB) was tested through a model. With this model a relationship among the noise level in the reference position, the level in the faade position, the slant angle and the flight type was calculated. The model was tested for different scenarios and it was determined that the slant angle along with the flight type are variables that modify the ISO 1996-2's Annex B correction factor significantly.