Uncrewed Aerial Vehicle (UAV)

Uncrewed (or unmanned) Aerial Vehicles (UAVs) (i.e., drones) can be used as a tool for scientific research. Compared to vessels as platforms for research, UAVs are considered relatively unobtrusive.

UAVs produce a buzzing sound that can propagate below the water surface. They produce sound mostly at low frequencies (approximately 100–1000 Hz) but also in the mid frequency range (1–17 kHz). Some drones (e.g., the DJI Inspire 1) additionally produce sound at higher frequencies (approximately 28–36 kHz), a range not audible to humans but potentially to animals, including toothed whales.

To reduce the amplitude of the UAV sound underwater and therefore the potential impact on the observed animals, UAV pilots usually increase the UAV’s distance from the animal. This is effective, since larger distances to the receiver result in quieter sound. A drone pilot may increase the drone’s altitude, but interestingly, the drone sound decreases even more quickly if the horizontal distance to the receiver is increased, i.e., if the pilot flies the drone to the side of the animal, rather than higher. This is due to the way sound propagates from air to water. Increasing horizontal distance to the animal under observation is therefore a great way to reduce noise impacts and decrease the risk of potential disturbance and behavioral changes.

Additional Links on DOSITS

• Hot Topic: Using Drones to Deploy Digital Acoustic Tags 
• Science > How does sound propagate from air into water? 

References

• Laute, A., Glarou, M., Dodds, F., Gomez Røsand, S. C., Grove, T. J., Stoller, A., … & Fournet, M. E. (2023). Underwater sound of three unoccupied aerial vehicles at varying altitudes and horizontal distances. The Journal of the Acoustical Society of America, 153(6), 3419-3419.
• Christiansen, F., Rojano-Doñate, L., Madsen, P. T., & 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, 277.
• Erbe, C., Parsons, M., Duncan, A., Osterrieder, S. K., & Allen, K. (2017). Aerial and underwater sound of unmanned aerial vehicles (UAV). Journal of Unmanned Vehicle Systems, 5(3), 92-101.