Experimental verification of direction estimate and microphone array configuration
Kentaro NAGATA, Soichiro TANABE, Takeshi TOI · Transactions of the JSME (in Japanese) · 2026
The rapid proliferation of unmanned aerial vehicles (drones) has made ensuring safety through non-cooperative collision avoidance an urgent priority. Acoustic sensing offers a lightweight solution; however, detecting approaching rotorcraft, such as helicopters, remains challenging due to the high levels of drone self-noise. To address this challenge, this study proposes a robust sound source detection and direction estimation method focusing on the amplitude modulation (AM) characteristics inherent in rotorcraft noise. First, utilizing the cyclostationary nature of rotorcraft noise, we adopted the Fast-Spectral Correlation (Fast-SC) algorithm. By calculating the Enhanced Envelope Spectrum (EES), we successfully separated helicopter signals, which exhibit specific low-frequency modulation, from drone noise containing high-frequency modulation. Second, we developed a direction estimation technique integrating this AM analysis with a fixed delay-and-sum beamformer (DSBF) using a linear microphone array. By scanning the beam and evaluating the spatial distribution of AM intensity, the system can accurately estimate the direction of the approaching helicopter. Furthermore, we conducted a comprehensive investigation to optimize the microphone array configuration, specifically analyzing the effects of the number of microphone elements and their spacing on AM directional characteristics. The results from numerical simulations and field verification experiments showed high consistency. Consequently, suitable design parameters maximizing detection performance were identified, demonstrating the applicability of the system to practical collision avoidance.