Underwater sound of three unoccupied aerial vehicles at varying altitudes and horizontal distances

Unoccupied aerial vehicles (UAVs), or "drones," are increasingly used as a tool for cetacean research, but knowledge about how these tools contribute to underwater sound is lacking. In this study, underwater sound levels of three commonly used UAV models (Mavic Pro Platinum, Phantom 4 Pro v2.0, Inspire 1 Pro) were recorded. For each model, three replicate flights were conducted at 36 positions at standardized horizontal (0-30 m) and vertical (2-40 m) distances from a hydrophone (1m depth). Median broadband received levels of the Inspire were highest at 96.5 dB(rms 141-17 783 Hz) re 1 mu Pa-2, followed by the Phantom (92.4 dB(rms 141-17 783 Hz) re 1 mu Pa-2) and Mavic, which was quietest (85.9 dB(rms 141-17 783 Hz) re 1 mu Pa-2). Median ambient sound levels in the absence of an UAV were 82.7 dB(rms) (141-17 783 Hz) re 1 mu Pa-2. Significant increases in ambient sound levels associated with UAV flights occurred at higher altitudes than previously reported, and received levels decreased more with increasing horizontal distance of the UAV than with altitude. To minimize potential noise impacts on sensitive marine animal subjects, we recommend increasing horizontal distance to the animal, rather than altitude, and choosing the quietest UAV feasible. VC 2023 Acoustical Society of America. https://doi.org/10.1121/10.0019805