How ImAFUSA is Enabling a Better Understanding of Drone Noise

With Urban Air Mobility (UAM) poised to reshape transport in our cities, one vital concern is how this will affect our soundscapes. While UAM holds great promise for the efficient movement of goods and people, policymakers must ensure that this does not come at the cost of unacceptable noise for communities on the ground.

Within the ImAFUSA project, the University of Salford (USAL) has led work to address this question, shifting the focus from simple laboratory tests to the complex reality of how drone noise is perceived under real-world conditions.

Real-World Reactions: From Egaleo to Scilly

A cornerstone of USAL's contribution has been moving research out of the lab and into the field. "The focus was trying to understand how people will respond to drone noise in a real scenario," explains Professor Antonio J. Torija Martinez of USAL’s Acoustics Research Centre.

To achieve this, the team conducted a groundbreaking study at Egaleo Park in Athens, Greece. "We went to Egaleo Park... and we arranged some flight demonstrations where the drone was operating at different distances from people and the drone was performing different manoeuvres," Torija Martinez notes.

An image from the ImAFUSA study at Egaleo Park in Athens

These "soundwalks" revealed the importance of proximity: operations performed closer to people, such as take-offs, landings, and hovering, were perceived as significantly more annoying and decreased participants' perception of "comfort" and "calmness".

Crucially, the study also highlighted how the perception of drone noise depends heavily on the background soundscape. In Athens, the drone flew in two distinct areas: one close to noisy road traffic and one isolated and quiet. "The effect of the drone is going to be significantly higher in the quiet area of the park compared to the noisy area," Torija Martinez observes. In the noisy area, the drone did not dominate the soundscape due to the "masking effect" of road traffic, whereas in the quiet area, it was dominant regardless of distance.

To capture the full spectrum of acoustic environments, USAL expanded this research to the Isles of Scilly. Their study provided a critical counterpoint to the urban tests, highlighting the stark trade-off policymakers face: flying in noisy cities affects more people but with lower individual changes in annoyance, whereas flying in quiet rural areas affects fewer people but with a significantly higher negative impact per person.

A photograph from USAL's soundwalks in Scilly, UK

Annoyance and Advanced Metrics

Why do many find drone noise more irritating than that from, say, a plane or helicopter? Torija Martinez points to how evolutionary biology has shaped the way humans perceive sound: "Our whole auditory system is designed to be very sensitive to those mid to high frequencies for communication, for alert". Because drones generate high-pitched sounds that are distinct from existing background noise, humans are easily disturbed by them.

USAL’s research confirms that standard acoustic metrics (like loudness) are insufficient for drones. They fail to account for characteristics like tonality (whine), sharpness (high-frequency content), and unsteadiness caused by wind or manoeuvres.

To accurately predict this annoyance, USAL developed a sophisticated noise assessment framework as part of the ImAFUSA project. According to Torija Martinez, this tool allows users to input specific parameters—such as drone type, operation, and payload—and provides "estimations of noise annoyance for that specific drone operation on the ground". The tool utilises a novel methodology to synthesise moving flyover sounds from recordings. This allows researchers to simulate the psychoacoustic impact of complex flight paths without the expense of conducting hundreds of test flights.

Standardising the Industry and Reality-Checking Regulations

A major challenge in UAM research has been the lack of a shared language between manufacturers, regulators, and researchers. To tackle this, USAL led the development of a formal Taxonomy for UAM Noise Assessment. This hierarchical framework classifies vehicles not just by weight, but by Nature of Task, Design Parameters, and Operations, allowing regulators to compare "apples to apples" when assessing noise emissions.

Beyond creating tools, USAL has actively tested existing regulations. The team conducted on-field measurements following EASA guidelines for drones lighter than 600kg. The findings revealed significant practical limitations: the current requirement to maintain a 15 dB difference between the drone's noise and the background noise is "challenging" or impossible to meet for small drones (under 3kg) in quiet environments. USAL has reported these findings, suggesting that current EASA guidelines may need amendment to be realistically enforceable for small size drones.

The Road Ahead

The ultimate goal of USAL’s work in ImAFUSA is to define thresholds for acceptability. Through the work feeding into the ImAFUSA Noise Assessment Framework, the team is building a better picture of how drones can coexist with communities.

While manufacturers continue to work to develop quieter aircraft designs, Torija Martinez notes that operational solutions—such as optimising trajectories to avoid noise-sensitive areas—will also be crucial to ensuring societal acceptance.

Alongside Professor Antonio J. Torija Martinez, key contributions to USAL’s work on the ImAFUSA Project have been provided by Dr Marc Green and Dr Carlos Ramos Romero.

To see the scientific publications that have emerged from this work, click here.