Localization of noise sources around aircraft in flight based on time-domain beamforming technique

摘要

Acoustic models of aircraft can be used to predict aircraft noise around airports. When constructing such models, detailed aircraft sound source properties, including the positions and frequency characteristics of individual noise sources, are necessary to achieve high fidelity. We have developed a phased array microphone system to accurately locate noise sources on and around an aircraft in flight. This paper describes the measurement technique and its results, while the companion paper will discuss how to construct a prediction model from those measurements. Acoustic signals from an aircraft flying overhead are measured by a microphone array on the ground and transformed into an aircraft-fixed coordinate system to correct frequency and amplitude distortions due to Doppler effect. Then, a time-domain delay-and-sum beamforming algorithm is applied with additional methods such as weight factors for each microphone and diagonal removal from Cross-Spectral Matrix to improve resolution and quality of acoustic images. In experiments, a 30m-diameter array of 195 microphones was deployed on a temporary platform beside the runway of a regional airport. Noise measurement flights were conducted using JAXA's 'Hisho' experiment aircraft, and acoustic maps were calculated at different emission angles. The aircraft's flaps and landing gear were confirmed to be the dominant noise sources when the engines were at idle. The flaps are characterized as dipole sound sources with directivity in the direction perpendicular to the flap panel, so sound from the extended flap panels is radiated in the forward direction.