Noise levels of multi-rotor unmanned aerial vehicles with implications for potential underwater impacts on marine mammals
Full Citation: Christiansen, F., Rojano-Doñate, L., Madsen P.T. and Bejder, L. 2016. Noise Levels of Multi-Rotor Unmanned Aerial Vehicles with Implications for Potential Underwater Impacts on Marine Mammals. Frontiers in Marine Science 3 doi: 0.3389/fmars.2016.00277
Despite the rapid increase in the use of unmanned aerial vehicles (UAVs) in marine mammal research, knowledge of the effects of UAVs on study animals is very limited. We recorded the in-air and in-water noise from two commonly used multi-rotor UAVs, the SwellPro Splashdrone and the DJI Inspire 1 Pro, to assess the potential for negative noise effects of UAV use (Figure 1). The Splashdrone and Inspire UAVs produced broad-band in-air source levels of 80 dB re 20 μPa and 81 dB re 20 μPa (rms), with fundamental frequencies centered at 60 Hz and 150 Hz. The noise of the UAVs coupled poorly into the water, and could only be quantified above background noise of the recording sites at 1 m depth when flying at altitudes of 5 and 10 m, resulting in broad-band received levels around 95 dB re μPa rms for the Splashdrone and around 101 dB re μPa rms for the Inspire (Figure 2). The third octave levels of the underwater UAV noise profiles are (i) close to ambient noise levels in many shallow water habitats, (ii) largely below the hearing thresholds at low frequencies of toothed whales, but (iii) likely above the hearing thresholds of baleen whales and pinnipeds (Figure 2, Figure 3). So while UAV noise may be heard by some marine mammals underwater, it is implied that the underwater noise effect is small, even for animals close to the water surface. Our findings will be valuable for wildlife managers and regulators when issuing permits and setting guidelines for UAV operations. Further, our experimental setup can be used by others to evaluate noise effects of larger sized UAVs on marine mammals.
Please note: We want to emphasize that this study was carried out under strict permitting conditions and that the pilot (F Christiansen) was trained and licensed to use UAVs for scientific purposes. With the use of recreational UAVs increasing rapidly around the world, regulators need to take a precautionary approach when setting up guidelines and regulations for the public, to minimize potential negative impacts from inexperienced and irresponsible operators.
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Acknowledgements: We thank M. L. K. Nielsen, K. R. Sprogis, J. Totterdell (Marine Information and Research Group, Australia) and J. A. Tyne for assisting during the field trials. We thank J. N. Smith for technical assistance with the SoundTrap. We thank Global Unmanned Systems (http://www.gus-uav.com) and Victorian UAS Training (http://www.victorianuastraining.com.au) for UAV technical support and training. We thank Associate Editor R. Harcourt and two reviewers for their constructive comments which helped to improve this manuscript. The UAVs in this study were operated under a Remotely Piloted Aircraft System License (ARN: 837589) and two UAV Operator Certificates (CASA.UOC.0136 and CASA.UOC.1-YC6NP-03), in accordance with regulations by the Australian Civil Aviation Safety Authority (CASA).