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Article

Application of Transfer Entropy Measure to Characterize Environmental Sounds in Urban and Wild Parks

by
Roberto Benocci
1,*,
Giorgia Guagliumi
1,
Andrea Potenza
1,
Valentina Zaffaroni-Caorsi
1,
H. Eduardo Roman
2,* and
Giovanni Zambon
1
1
Department of Earth and Environmental Sciences (DISAT), University of Milano-Bicocca, Piazza Della Scienza 1, 20126 Milano, Italy
2
Department of Physics, University of Milano-Bicocca, Piazza Della Scienza 3, 20126 Milano, Italy
*
Authors to whom correspondence should be addressed.
Sensors 2025, 25(4), 1046; https://doi.org/10.3390/s25041046
Submission received: 20 December 2024 / Revised: 30 January 2025 / Accepted: 7 February 2025 / Published: 10 February 2025

Abstract

Anthropized green zones in urban areas and their surroundings develop complex soundscapes, characterized by the presence of multiple sound sources. This makes the interpretation of the sound environment challenging. To accurately distinguish between different sound components, a combination of selective analysis techniques is necessary. Urban parks are significant and interesting examples, where the interaction between anthropogenic and biophonic sound sources persists over broad temporal and spatial scales, making them important sites for evaluating local soundscape quality. In this work, we suggest that a transfer entropy measure (TEM) may more efficiently disentangle relevant information than traditional eco-acoustic indices. The two study areas were Parco Nord in Milan, Italy, and Ticino River Park, also in Italy. For Parco Nord, we used 3.5-h (1-min interval) recordings taken over an area of about 20 hectares, employing 16 sensors. For the Ticino River Park, we used 5-day (1 min plus 5 min pause) recordings taken over an area of approximately 10 hectares, using a smaller set of eight sensors. We calculated the classical eco-acoustic indices and selected two of them: the acoustic entropy (H) and the bio-acoustic index (BI), calculated for all sites with a 1 min time resolution obtained after a principal components analysis. For these time series, we studied the TEM of all sites in both directions, i.e., from one site to another and vice-versa, resulting in asymmetric transfer entropies depending on the location and period of the day. The results suggest the existence of a network of interconnections among sites characterized by strong bio-phonic activity, whereas the interconnection network is damped at sites close to sources of traffic noise. The TEM seems to be independent of the choice of eco-acoustic index time series, and therefore can be considered a robust index of sound quality in urban and wild park environments, providing additional structural insights complementing the traditional approach based on eco-acoustic indices. Specifically, TEM provides directional information about intersite sound connectivity in the area of study, enabling a nuanced understanding of the sound flows across varying anthropogenic and natural sound sources, which is not available using conventional methods.
Keywords: eco-acoustic indices; animal vocalization; urban park; transfer entropy measure eco-acoustic indices; animal vocalization; urban park; transfer entropy measure

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MDPI and ACS Style

Benocci, R.; Guagliumi, G.; Potenza, A.; Zaffaroni-Caorsi, V.; Roman, H.E.; Zambon, G. Application of Transfer Entropy Measure to Characterize Environmental Sounds in Urban and Wild Parks. Sensors 2025, 25, 1046. https://doi.org/10.3390/s25041046

AMA Style

Benocci R, Guagliumi G, Potenza A, Zaffaroni-Caorsi V, Roman HE, Zambon G. Application of Transfer Entropy Measure to Characterize Environmental Sounds in Urban and Wild Parks. Sensors. 2025; 25(4):1046. https://doi.org/10.3390/s25041046

Chicago/Turabian Style

Benocci, Roberto, Giorgia Guagliumi, Andrea Potenza, Valentina Zaffaroni-Caorsi, H. Eduardo Roman, and Giovanni Zambon. 2025. "Application of Transfer Entropy Measure to Characterize Environmental Sounds in Urban and Wild Parks" Sensors 25, no. 4: 1046. https://doi.org/10.3390/s25041046

APA Style

Benocci, R., Guagliumi, G., Potenza, A., Zaffaroni-Caorsi, V., Roman, H. E., & Zambon, G. (2025). Application of Transfer Entropy Measure to Characterize Environmental Sounds in Urban and Wild Parks. Sensors, 25(4), 1046. https://doi.org/10.3390/s25041046

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