THE ACOUSTICAL GEOMETRY OF AIRCRAFT OVERFLIGHTS

Noise perceived in the surroundings of an airport is an important cause of annoyance because aircraft are very high sound power noise sources and, as a result of the lack of obstacles, propagation conditions are fairly good. Several publications, such as ICAO's Annex 16 on aircraft noise as well as Circular No 205 of the same entity, suggest methods to predict noise levels in the surroundings of an airport, including how to compute several descriptors which have proved useful in airport environmental noise assessment. However, they require intensive use of data regarding noise emission from different aircrafts, which in practice may be difficult or expensive to obtain. In this paper we show how these data may be easily derived from field measurements performed during aircraft overflights. From an aircraft overflight noise signal, acquired with a digital audio tape (DAT) recorder, the audio signal is computer-processed to plot its spectrogram. This is used to estimate the aircraft's speed and to derive the aircraft's altitude and elevation angle. Once the geometry of the overflight has been secured, the last step involves matching the propagation-corrected measured noise at several instants with the corresponding aircraft position. This allows to draft the polar pattern of the aircraft viewed as a noise source. (A) For the covering abstract see ITRD E113232.