Beschreibung:
This paper describes a novel approach for autonomously detecting and tracking aircraft in the vicinity of a unmanned aerial vehicle (UAV). The time difference of arrival (TDOA) of acoustic tones emanating from the distant aircraft are correlated between spatially distributed microphone pairs located on the UAV. The geometry of multiple microphone pairs then allows the elevation and azimuth of the approaching aircraft to be estimated, despite the high levels of onboard narrow- and broadband noise emanating from the engine firing sequence, propeller, airflow over the microphones, and mechanical vibration. Current signal processing techniques estimate time delay when the signal level of the approaching aircraft is above the background signature of the sensing aircraft, despite subtle frequency variations in the narrowband components of the approaching aircraft’s signature. The technique described in this paper is designed to track these unpredictable frequency variations and thus extends the detection range of the approach by enabling estimation of TDOA when the signal level is 20 dB below the noise floor. Potential detection ranges in excess of 1 km are demonstrated when the signal processing is combined with careful suppression of the many noise sources onboard the UAV.