Abstract
In addition to air pollution, environmental noise has become one of the major hazards for citizens, being Road Traffic Noise (RTN) as its main source in urban areas. Recently, low-cost Wireless Acoustic Sensor Networks (WASNs) have become an alternative to traditional strategic noise mapping in cities. In order to monitor RTN solely, WASN-based approaches should automatize the off-line removal of those events unrelated to regular road traffic (e.g., sirens, airplanes, trams, etc.). Within the LIFE DYNAMAP project, 15 urban Anomalous Noise Events (ANEs) were described through an expert-based recording campaign. However, that work only focused on the overall analysis of the events gathered during non-sequential diurnal periods. As a step forward to characterize the temporal and local particularities of urban ANEs in real acoustic environments, this work analyses their distribution between day (06:00–22:00) and night (22:00–06:00) in narrow (1 lane) and wide (more than 1 lane) streets. The study is developed on a manually-labelled 151-h acoustic database obtained from the 24-nodes WASN deployed across DYNAMAP’s Milan pilot area during a weekday and a weekend day. Results confirm the unbalanced nature of the problem (RTN represents 83.5% of the data), while identifying 26 ANE subcategories mainly derived from pedestrians, animals, transports and industry. Their presence depends more significantly on the time period than on the street type, as most events have been observed in the day-time during the weekday, despite being especially present in narrow streets. Moreover, although ANEs show quite similar median durations regardless of time and location in general terms, they usually present higher median signal-to-noise ratios at night, mainly on the weekend, which becomes especially relevant for the WASN-based computation of equivalent RTN levels.
Highlights
Nowadays, 55% of people is living in urban areas, a percentage that is expected to grow to around 70% by 2050 according to the United Nations [1]
We have advanced in the characterization of anomalous noise events in real urban environments, extending previous analyses by studying their presence and individual features according to their evolution throughout the day and night, together with their local particularities found in narrow and wide streets during a weekday and a weekend day
A Wireless Acoustic Sensor Networks (WASNs)-based database of 151 h has been designed and developed to have enough representative samples of this kind of acoustic events in real-life urban environments through the 24-nodes WASN of the DYNAMAP project deployed across District 9 of Milan pilot area
Summary
55% of people is living in urban areas, a percentage that is expected to grow to around 70% by 2050 according to the United Nations [1]. They have to inform citizens about their exposure to noise levels—typically differentiating day and night periods [10], besides defining and developing the corresponding action plans to mitigate the noise levels every five years where necessary These strategic noise maps have been hitherto developed from representative acoustic data collected by experts using certified devices, taking into account the urban spatial characteristics of their location for the proper simulation of sound propagation [13,14,15], among which the canyon effect in narrow streets becomes an important parameter to consider [16,17].
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