Tall Urban Tree Canopies May Amplify Low-Altitude UAV Noise: Evidence from Field Measurements and Psychoacoustic Assessment

The rapid growth of UAV use in urban logistics, infrastructure inspection, emergency response, and campus services has made low-altitude flights more common in residential environments. Previous studies have mainly examined aircraft acoustics, flight conditions, building transmission, or listener responses. Repeated field evidence on UAV noise under contrasting canopy-site configurations remains limited. This study compared UAV noise under low-canopy (<8 m) and tall-canopy (>15 m) conditions at a six-storey campus residential area with a regular row-type layout. The two focal sites had similar building layouts, façade conditions, measurement positions, flight altitudes, and source–receiver geometry. They differed mainly in tree height and canopy density. We tested a DJI Mavic 2 Pro and a DJI Matrice 200 V2 in three independent hovering trials for each condition. We measured sound levels using Class 1 sound level meters. We also compared indoor and outdoor exposure. The analysis included one-third-octave-band spectra from representative recordings, descriptive psychoacoustic indicators, 118 valid questionnaires, principal component analysis, and exploratory empirical Bayesian kriging based on 15 measurement points. At the outdoor focal sites, the Matrice 200 showed a LASmax 10.0 dB higher under the tall-canopy condition. Its LAeq was 2.7 dB higher, whereas its L90 was 10.5 dB lower. This pattern indicates a wider, more intermittent sound-level distribution rather than a uniform increase. The Mavic 2 outdoor LAeq was 5.0 dB higher under the tall-canopy condition. Indoor differences varied by UAV model, window condition, and acoustic indicator. Higher transient sound levels and stronger psychoacoustic responses were associated with greater annoyance. EBK interpolation was used to visualize spatial heterogeneity. The assessment framework may also support studies in campus dormitory areas and row-layout multi-storey residential compounds with similar spatial features. The findings suggest that canopy-site configuration, building enclosure, UAV characteristics, and flight geometry should be assessed together.