Quadrotors are small unmanned aircraft systems (sUAS) that generate sound characterized by a unique acoustic signature. In this research, we aim to determine the acoustic signature of a quadrotor and differentiate it from ambient noise in audio samples. Our hypothesis is that we will be able to distinguish between different quadrotors-microphone relative ranges by analyzing the frequency spectrum around the propeller blade’s rotation rate and its harmonics. The quadrotors were designed with four Cobra CM-4008 multirotor motors connected to 11inch diameter propeller blades. In our experiment, we collected multiple one minute audio recordings of the quadrotor in an outdoor environment on campus. Data was collected at varying distances, in addition to a control recording of the ambient noise. A Dayton Audio UMM-6 microphone and windscreen were mounted to a stand boom for collecting recordings. The collected audio files were analyzed in MATLAB to produce spectrograms in the 10 Hz to 1 kHz band, plotted with a common range of intensities from -150 to -90 dB/Hz. There is evidence of higher sound intensity in the 150 Hz to 250 Hz range in audio recordings with the quadrotor operating. These frequencies correspond approximately to the motor and propeller blade rotation rates. Our preliminary results suggest that detecting the quadrotor is possible at a distance of at least 5 meters. Ongoing work aims to improve the characterization of the signature and determine if relative range can be inferred from the audio signal.
