Functional Beamforming applied to full scale landing aircraft

Aircraft noise is becoming an increasingly important problem for the aerospace industry and for the residents living in the vicinities of airports. For efforts aiming at reducing aircraft noise levels, it is important to know all the aircraft elements which generate noise and their relative contribution. Experimental measurements with aircraft under operational conditions provide essential information for this purpose. The use of microphone arrays and high resolution beamforming techniques are required to image the acoustic sources at the relatively large distance between the observer and the aircraft. Functional beamforming is a novel nonlinear technique which offers improved array spatial resolution and dynamic range. For an appropriately selected exponent value, most array sidelobes are substantially decreased. This method requires a similar computational time as the conventional beamforming algorithm. In this research, the performance of functional beamforming is investigated with full scale aircraft under operational conditions. The sound of 115 landing aircraft fly-overs was recorded in Amsterdam Airport Schiphol utilizing a 32 microphone array. It was found that functional beamforming provides a good performance, allowing for the identification of individual noise sources on the aircraft. The dynamic range obtained is approximately 30 times larger and its array spatial resolution is about 6 times better than the conventional beamformer.