In-flight directivity and sound power measurement of small-scale unmanned aerial systems

The sound emission characteristics of unmanned aerial systems are of interest in many contexts. For a realistic representation of the directional characteristics and the radiated sound energy, it is useful if the aircraft is operated under realistic conditions. However, deriving emission-based acoustic quantities for a typical mode of operation such as cruise flight is difficult. In this paper, the directivity and sound power of a quadcopter drone are determined using a microphone array measurement of a single flight through a predefined corridor. The recorded data are processed to both reconstruct the drone’s flight path and characterize its acoustic emission. To verify the reliability of the presented method, the signal processing is tested with simulated data from moving sources with the directivity of a monopole as well as a dipole. Using different discretizations of the radiation direction space and evaluating the frequency-dependent directivity factor, it is discussed how the sound radiation can be described as comprehensively as possible on the basis of as few quantities as possible.