Aerial and underwater sound of unmanned aerial vehicles (UAV, drones)

Abstract

Unmanned aerial vehicles/systems (UAV/UAS, drones) are increasingly being used for terrestrial and marine ecological surveying and research. Studies on the potential disturbance of fauna by UAVs have been sparse, with most reports on the behavioral responses of birds. Responses of marine mammals have been reported in the case of pinnipeds on land, with very limited information on marine mammals at sea. Whether the stimulus was visual (the UAV or its shadow) or acoustic (noise) is unknown. While UAV technology is developing fast, guidelines for the responsible use of UAVs around fauna are lagging behind. We recorded aerial and underwater sound from four aerial drones in different environments. Sound spectra exhibited distinct tones <2 kHz. Median broadband source levels were 77–89 dB re 20 μPa rms at 1 m in air. Under water, median broadband received levels were <100 dB re 1 μPa rms varying with drone altitude, flight mode, and recorder depth. Drone power spectral density exceeded underwater ambient levels by up to 30 dB between 100 and 10 000 Hz. Drone levels were well below those commonly considered in underwater noise regulations. Simple sound propagation and transmission calculations predicted underwater levels within −3.2 to +6.2 dB of measured levels.