UAV noise emission characterisation using a compact on-board measurement system

The predicted increase in UAV operations, particularly in populated areas, will result in a rise in the associated noise pollution. This requires the availability of accurate noise models for exposure mapping, but also for psychoacoustic experiments and sensitisation. Such a model must account for rotor noise and interactions between the individual rotors, the UAV body and the airflow under various flight conditions. Suitable acoustic measurement methods are required to assess these phenomena in-situ under realistic flight and atmospheric conditions. At present, ground-based microphones are usually used for this purpose. This approach, however, entails problems such as disturbance by ambient sounds or the difficulty of accurately inverting propagation effects such as the Doppler effect or ground reflections. We have therefore developed a lightweight, portable measurement system deploying MEMS microphones. This allows us to conduct on-board noise emission measurements using microphones attached to the UAV with sufficient distance to the acoustic sources. The system contains an on-board data processing device that also incorporates sensors for precise position tracking with differential GPS and for recording of the individual propeller rotational speeds. We present the measurement system and show preliminary results to demonstrate the potential of our approach to investigate noise emissions from small UAV.