Drone Audition: On Measurements and Modeling of Drone-Related Transfer Functions

With growing applications of drones, there is a demand for drone audition functionality that allows microphone arrays to be embedded into or attached to the body of drones for sound source localization and signal enhancement. In practical acoustical environments, the performance of drone audition is degraded due to the free-field sound propagation assumption. In this paper, we propose (i) a method for modeling the scattering and diffraction of a drone body beyond free-field propagation as a Drone-Related Transfer Function (DRTF), and (ii) a practical method to estimate the DRTF coefficients using circular loudspeaker arrays. The method incorporates the acoustic reciprocity principle and a finite order spherical harmonic expansion by utilizing a discrete set of measurements by multiple loudspeaker placements on circular arrays. We validate our DRTF model and parameterization method on a known rigid sphere scatterer in both simulation and real measurements using the em32 Eigenmike. The proposed method offers a low reconstruction error ($\leq -30$ dB) over speech frequencies. Additionally, we investigate the DRTF reconstruction error for a real drone. The proposed approach reveals a practically viable method for DRTF measurements compared to the traditional spherical loudspeaker array, and alleviates the free-field assumption from drone audition.