Abstract Summary
Trees provide essential ecosystem services in the urban environment. From a noise pollution perspective, trees disperse and scatter sound waves in street canyons and urban courtyards. A handful of studies have been published on the sound attenuating effects of trees, or tree belts, in street canyons, none focusing on aircraft noise specifically. Compared to other environmental noise sources such as road and railway traffic noise, aircraft noise is emitted from a airborne source and enters street canyons from above. The effect of urban form and architectural design on aircraft noise is investigated at the Urban Comforti Laba full-scale, semi-controlled environment close to Schiphol airport. In three courtyards, continuous measurements of local sound pressure levels emitted by aircraft flyovers are recorded. For this experiment, 36 trees were placed in one courtyard. The sound measurements were processed to a-weighted sound exposure levels (ASEL) for each aircraft flyover. The recordings from the courtyard with trees were compared to the ASEL recorded by microphones in the same positions in a statistically similar, bare courtyard. Microphone ASEL differences between the courtyard with, and without trees were subsequently compared. For the exposed microphone in the tree courtyard, the ASEL decrease was dependent on aircraft operation. For the shielded microphone in the courtyard with trees, the mean decrease amounted to 1.1 dB(A). These differences in ASEL indicate that trees in courtyards scatter noise, both for noise entering the courtyard and for sound waves reflected by the courtyard walls. The results suggest that trees can be used as a measure for noise adaptive design in airport regions, as they scatter sound waves entering through through trunks, branches and pots.
