Small Unmanned Aircraft Systems Acoustic Analysis for Noninvasive Marine Mammal Response: An Exploratory Field Study

Abstract

As in countless other fields of human endeavor, small unmanned aircraft systems (sUAS) have the potential to benefit pinniped (Pinnipedia; e.g., Phocidae [seals], Otariidae [sea lions], and Odobenidae [walruses]) response efforts. The employment of sUAS could give responders a close-up look at animals in distress in order to determine their condition as well as develop a response strategy. However, unlike other subjects that are regularly inspected by sUAS (e.g., croplands and civil infrastructure) pinnipeds may respond to the distinctive sound generated by small, multirotor sUAS. This reaction may include retreating into the water en masse, which could put the target individual out of reach of the response team. To potentially prevent this outcome, this exploratory field study established sUAS acoustic profiles through quantitative and qualitative measures for multiple aircraft across a range of distance and altitude. These data were collected in both a secluded rural environment and a coastal environment. The results indicate that sUAS sound pressure levels at least 20 dBA (re 20 µPa) below the ambient noise floor are required to completely mask the distinctive sound of the aircraft to human hearing. The results were used to create aircraft operational envelopes to potentially mitigate disturbance while optimizing visual information. To reflect the type of sUAS that would likely be available to small, non-profit marine mammal response groups working in remote locations, the aircraft studied were limited to compact models $3,000 or less.