The number of operations of Unmanned Aerial Vehicles (UAV), commonly referred to as “drones”, has strongly increased in the past and is likely to further grow in the future. Therefore, drones are becoming a growing new source of environmental noise pollution, and annoyance reactions to drone noise are likely to occur in an increasing share of the population. To date, research on drone noise emission characteristics, and in particular also on health impacts, seems scarce, but systematic overviews on these topics are missing. The objective of this study was to establish a systematic literature review on drone noise emissions and noise effects on humans. The paper presents the methodology of the systematic reviews performed separately for noise emission and noise effects, assembles current literature, gives an overview on the state of knowledge, and identifies research gaps. Current literature suggests that drone noise is substantially more annoying than road traffic or aircraft noise due to special acoustic characteristics such as pure tones and high-frequency broadband noise. A range of open questions remains to be tackled by future studies.

Drone Noise Emission Characteristics and Noise Effects on Humans-A Systematic Review.

Utilizing autonomous unmanned aerial vehicles (drones) in the last-mile delivery of parcels is regarded as the ultimate disruptive technology that might significantly reduce the GHG emissions in the freight sector. This study estimates the CO2e emissions for UAVs under different policies compared to diesel and electric ground delivery modes. First, the international UAV flight regulations are synthesized and classified into three groups representing varying degrees of policy strictness. Second, utilizing real-word delivery demand data, full-day parcel-delivery operations of a three-digit postal code area in both urban and rural contexts are simulated for UAVs and ground delivery modes. The results show that in general, UAVs produce significantly lower emissions compared to ground delivery per parcel-km and up to 35% compared to electric vehicles. However, UAV emissions are highly dependent on the fuel mix used in electricity generation. In urban contexts, UAV policy strictness can increase GHG emissions by up to 400%.

The impact of airspace regulations on unmanned aerial vehicles in last-mile operation

In about 15 years, there is likely to be urban air mobility (UAM) in larger cities across the globe. Air taxis will provide on-demand transportation for individual needs. They will also connect important transportation nodes, such as airports and city centers, as well as providing quick transfers between train stations or a convenient option for crossing rivers and lakes. It is hoped that UAM will help meet today’s political targets of sustainability and decarbonization. However, there are certain threats that could impede the sustainable and thus successful introduction of UAM to our cities, with noise being a prominent limitation. This paper argues that citizens have to be viewed as stakeholders in urban air transportation, regardless of whether they or not intend to use it, and that a concept of resident participatory noise sensing (PNS) will be beneficial to the implementation of UAM. Web-based services and smartphones facilitate the access and updating of current information about local noise distributions, thus enabling them to be used to foster UAM in smart cities.

https://www.mdpi.com/2071-1050/12/8/3320/pdf

Sustainable Urban Air Mobility Supported with Participatory Noise Sensing

We are on the cusp of a revolution in the aviation sector, driven by the significant progress in electric power and battery technologies, and autonomous systems. Several industry leaders and governmental agencies are currently investigating the use of Unmanned Aerial Vehicles (UAVs), or “drones” as commonly known, for an ever-growing number of applications—from blue light services to parcel delivery and urban mobility. Undoubtedly, the operation of UAVs will lead to noise exposure, which has the potential to become a significant public health issue. This paper first describes the main acoustic and operational characteristics of UAVs, as an unconventional noise source compared to conventional civil aircraft. Gaps in the literature and the regulations on the noise metrics and acceptable noise levels are identified and discussed. The state-of-the-art evidence on human response to aircraft and other environmental noise sources is reviewed and its application for UAVs discussed. A methodological framework is proposed for building psychoacoustic knowledge, to inform systems and operations development to limit the noise impact on communities.

https://www.mdpi.com/1660-4601/18/2/682/pdf

A Psychoacoustic Approach to Building Knowledge about Human Response to Noise of Unmanned Aerial Vehicles.

Urban Air Mobility (UAM), recently envisioned as faster and flexible mean of transportation in large urban centers, faces considerable challenges inherent in its operation in densely populated cities and related environmental issues such as pollutant and noise emissions. To address the environmental challenges, the proposed concepts are either hybrid-electric or all-electric vehicles enabled with propellers that rotate at lower speeds than conventional rotorcraft configurations, such as helicopters. However, the feasibility of UAM in the near future requires significant progress on the all-electric propulsion systems since current battery technology still falls short when compared with fossil fuel in terms of specific energy density. In this work, a methodology is proposed to evaluate the environmental footprint of Vertical Take-Off and Landing (VTOL) aircraft for the UAM market. This methodology is applied to existing concepts for exploratory studies on mission critical performance and environmental parameters. All-electric aircraft were found to be feasible for the UAM segment from the performance perspective. However, further improvements in battery technology and electricity generation from renewable sources are required. Sustainable aviation fuels, such as Alcohol-To-Jet (ATJ) obtained from wheat straw, present a substantially lower environmental impact than conventional fuels while providing the same performance. These biofuels also contribute less to global warming and climate changes than batteries which: (i) are recharged from electric grids still dependable on non-renewable sources; and (ii) have a low number of recharge–discharge cycles.

On the design of environmentally sustainable aircraft for urban air mobility

Several industry leaders and governmental agencies are currently investigating the use of Unmanned Aerial Vehicles (UAVs), or ‘drones’ as commonly known, for an ever-growing number of applications from blue light services to parcel delivery. For the specific case of the delivery sector, drones can alleviate road space usage and also lead to reductions in CO2 and air pollution emissions, compared to traditional diesel-powered vehicles. However, due to their unconventional acoustic characteristics and operational manoeuvres, it is uncertain how communities will respond to drone operations. Noise has been suggested as a major barrier to public acceptance of drone operations in urban areas. In this paper, a series of audio-visual scenarios were created to investigate the effects of drone noise on the reported loudness, annoyance and pleasantness of seven different types of urban soundscapes. In soundscapes highly impacted by road traffic noise, the presence of drone noise lead to small changes in the perceived loudness, annoyance and pleasantness. In soundscapes with reduced road traffic noise, the participants reported a significantly higher perceived loudness and annoyance and a lower pleasantness with the presence of the same drone noise. For instance, the reported annoyance increased from 2.3 ± 0.8 (without drone noise) to 6.8 ± 0.3 (with drone noise), in an 11-point scale (0-not at all, 10-extremely). Based on these results, the concentration of drone operations along flight paths through busy roads might aid in the mitigation of the overall community noise impact caused by drones.

/pdf/effects-of-a-hovering-unmanned-aerial-vehicle-on-urban-z3hyqvwqy4.pdf

Effects of a hovering Unmanned Aerial Vehicle on urban soundscapes perception

Several industry leaders and governmental agencies are currently investigating the use of Unmanned Aerial Vehicles (UAVs), or drones as commonly known, for an ever-growing number of applications from blue light services to parcel delivery. For the specific case of the delivery sector, drones can alleviate road space usage and also lead to reductions in CO2 and air pollution emissions, compared to traditional diesel-powered vehicles. However, due to their unconventional acoustic characteristics and operational manoeuvres, it is uncertain how communities will respond to drone operations. Noise has been suggested as a major barrier to public acceptance of drone operations in urban areas. In this paper, a series of audio-visual scenarios were created to investigate the effects of drone noise on the reported loudness, annoyance and pleasantness of seven different types of urban soundscapes. In soundscapes highly impacted by road traffic noise, the presence of drone noise lead to small changes in the perceived loudness, annoyance and pleasantness. In soundscapes with reduced road traffic noise, the participants reported a significantly higher perceived loudness and annoyance and a lower pleasantness with the presence of the same drone noise. For instance, the reported annoyance increased from 2.3 (without drone noise) to 6.8 (with drone noise), in an 11-point scale (0-not at all, 10-extremely). Based on these results, the concentration of drone operations along flight paths through busy roads might aid in the mitigation of the overall community noise impact caused by drones.

Effects of a Hovering Unmanned Aerial Vehicle on Urban Soundscapes Perception

Unmanned aerial vehicle (UAV) technologies are rapidly advancing due to the unlimited number of applications from parcel delivery to people transportation As the UAV market expands, community noise impact will become a significant problem for public acceptance Compact drone architectures based on contra-rotating propellers bring significant benefits in terms of aerodynamic performance and redundancy to ensure vehicle control in case of component failure However, contra-rotating propellers are severely noisy if not designed appropriately In the framework of a perception-influenced design approach, this paper investigates the optimal rotor spacing distance configuration to minimise noise annoyance On the basis of a series of psychoacoustic metrics (ie, loudness, fluctuation strength, roughness, sharpness, and tonality) and psychoacoustic annoyance (PA) models, the optimal rotor axial separation distance (expressed as a function of propeller blade diameter) is at a range from 02 to 04 This paper also discusses the performance of currently available psychoacoustic models to predict propeller noise annoyance and defines further work to develop a PA model optimised for rotating systems

/pdf/psychoacoustic-analysis-of-contra-rotating-propeller-noise-2le2u6w2a2.pdf

Psychoacoustic analysis of contra-rotating propeller noise for unmanned aerial vehicles

The aviation sector is rapidly evolving with more electric propulsion systems and a variety of new technologies of vertical take-off and landing manned and unmanned aerial vehicles. Community noise impact is one of the main barriers for the wider adoption of these new vehicles. Within the framework of a perception-driven engineering approach, this paper investigates the relationship between sound quality and first order physical parameters in rotor systems to aid design. Three case studies are considered: (i) contra-rotating versus single rotor systems, (ii) varying blade diameter and thrust in both contra-rotating and single rotor systems, and (iii) varying rotor-rotor axial spacing in contra-rotating systems. The outcomes of a listening experiment, where participants assessed a series of sound stimuli with varying design parameters, allow a better understanding of the annoyance induced by rotor noise. Further to this, a psychoacoustic annoyance model optimised for rotor noise has been formulated. The model includes a novel psychoacoustic function to account for the perceptual effect of impulsiveness. The significance of the proposed model lies in the quantification of the effects of psychoacoustic factors, such as loudness as the dominant factor, and also tonality, high frequency content, temporal fluctuations, and impulsiveness on rotor noise annoyance.

http://usir.salford.ac.uk/id/eprint/63269/1/Manuscript_AcceptedVersion.pdf

Zhengguang Li

Papers

Effects of a hovering Unmanned Aerial Vehicle on urban soundscapes perception

Effects of a Hovering Unmanned Aerial Vehicle on Urban Soundscapes Perception

Psychoacoustic analysis of contra-rotating propeller noise for unmanned aerial vehicles

Psychoacoustic modelling of rotor noise.

Erratum: Psychoacoustic modelling of rotor noise [J. Acoust. Soc. Am. 151, 1804-1815 (2022)].