Noise Levels of Multi-Rotor Unmanned Aerial Vehicles with Implications for Potential Underwater Impacts on Marine Mammals

Abstract

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. 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. 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. 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.

The Use of Unmanned Aerial Systems in Marine Mammal Research

“…Consequently, scientific best practices for the use of UAS in wildlife surveys are being developed in order to minimize the disturbance levels. That is, systematic assessment of the potential impacts on the targeted species is of paramount importance for the survey design [3,5,65]. Finally, the current low endurance of VTOL UAV still represents a limitation, requiring back-up options to be considered for long observations.…”

“…Alternatively, the implementation of laser range finders attached to the aircraft has been proposed [49]. Furthermore, Christiansen et al [3] performed tests for the underwater and airborne noise levels generated by Splashdrone flying at different heights. This procedure is a recommended practice in the assessment of noise impacts on wildlife [50,51], and should represent an essential first step in the design of marine mammal surveys involving the use of UAVs.…”

“…This procedure is a recommended practice in the assessment of noise impacts on wildlife [50,51], and should represent an essential first step in the design of marine mammal surveys involving the use of UAVs. The authors suggested that noise (95 dB re µPa rms) may be heard underwater by toothed and baleen whales when flying at 10 m AGL or lower, but the effect is likely to be small, even for animals close to the surface [3]. …”

“…In particular, UAS have been proposed as a tool for marine mammal surveys, as they allow researchers to reach remote areas and observe animals from an advantageous perspective, being less invasive than standard aircraft [3][4][5][6][7][8][9]. Despite the challenges of operating at sea [10], UAS have been used for a number of marine mammal research applications, from abundance surveys [8,[11][12][13][14][15][16][17] to the measurement of…”

Challenges of collecting blow from small cetaceans

“…The collection of biological samples is of particular interest, as drones are potentially a noninvasive tool with minimal impact on the animals (Christiansen et al. ).…”