A Deep Learning Approach for Boat Detection in the Venice Lagoon

Highlights: What are the main findings? The proposed Water Recreation Index (WRI) indicates the spatial distribution of recreational activities in the Venice lagoon, allowing the most attractive areas to be identified. Moreover, it shows how those activities are distributed over time, with peaks during summer weekends. Another index—the Water Transportation Index (WTI)—allows canal routes with higher transportation intensity to be mapped, and similarly to the WRI, shows much higher traffic intensities during summer weekends. What are the implications of the main findings? The spatial and temporal patterns of the two indexes can support improved planning instruments to protect the lagoon from the impact of intensive motorboat traffic in terms of wave-induced erosion and pollution, but also to exploit the recreational potential of the most attractive areas for sustainable water-based tourism in the Venice lagoon. The methodological approach might provide valuable insights into the application of a deep learning technique to freely available Sentinel-2 satellite images in the detection of small standing and moving boats. The Venice lagoon is the largest in the Mediterranean Sea. The historic city of Venice, located on a cluster of islands in the centre of this lagoon, is an enchanting and iconic destination for national and international tourists. The historical centre of Venice and the other islands of the lagoon, such as Burano, Murano and Torcello, attract crowds of tourists every year. Transportation is provided by boats navigating the lagoon along a network of canals. The lagoon itself attracts visitors who enjoy various outdoor recreational activities in the open air, such as fishing and sunbathing. While statistics are available for the activities targeting the islands, no information is currently available on the spatio-temporal distribution of recreational activities across the lagoon waters. This study explores the feasibility of using Sentinel-2 satellite images to assess and map the spatio-temporal distribution of boats in the Venice Lagoon. Cloud-free Level-2A images have been selected to study seasonal (summer vs. winter) and weekly (weekends vs. weekdays) variabilities in 2023, 2024, and 2025. The RGB threshold filtering and the U-Net Semantic Segmentation were applied to the Sentinel-2 images to ensure reliable results. Two spatial indices were produced: (i) a Water Recreation Index (WRI), identifying standing boats in areas attractive for recreation; and (ii) a Water Transportation Index (WTI), mapping moving boats along the canals. Multi-temporal WRI maps allow areas with recurring recreational activities—that are significantly higher in the summer compared to winter, and on weekends compared to other weekdays—to be identified. The WTI identifies canal paths with higher traffic intensity with seasonal and weekly variations. The latter should be targeted by measures for traffic control to limit wave induced erosion, while the first could be subject to protection or development strategies.