Ultrasonics and urban greening: an exploratory study on ultrasound presence in urban spaces

Abstract

Airborne ultrasound is a frequently overlooked feature of our environment as it is not audible to humans, and little is known of its health effects on humans. Presently, regulations governing noise pollution in urban areas concern only human-audible sound, and there are few regulations governing technologies that emit ultrasound as a by-product of their operation or for many devices that emit it deliberately. Moreover, developing fields of research have highlighted the role of ultrasound in non-human species communication and the deleterious consequences for some species of human-produced ultrasound. If urban spaces are to become more sustainable through urban greening—capable of sustaining significant populations of non-human species—studies must be undertaken to begin investigating the presence of ultrasound in such areas. In this paper, we present an exploratory study of urban ultrasoundscapes aimed at measuring the presence and levels of ultrasound in the Danish city of Aalborg. Our preliminary results show that there were increases in ultrasound at periods throughout the day with more or less a lower constant presence at locations that were furthest from major streets. In the urban recordings as well as one rural recording, however, the highest percentages of ultrasound occurred during the night and the lowest percentages were found during midday. Finally, the content of the ultrasound found at locations nearest to green spaces showed most commonality in spectra and levels and our location nearest to a hospital produced the highest levels and most dissimilar ultrasound spectra when compared to all other locations.