DAS vs. Interferometric Monitoring on an Urban Fiber Network: Field Validation in the Tuff Cliff of Pitigliano

The widespread deployment of optical fiber networks in urban areas by telecommunications operators opens a significant opportunity to transform existing metropolitan area network (MAN) infrastructures into large-scale distributed sensing systems. Beyond their primary communication function, buried fiber-optic cables can act as pervasive sensors for monitoring human activities, natural events, and geoscience-related processes, enabling a cost-effective and non-invasive approach to urban and environmental surveillance. In this context, Distributed Acoustic Sensing (DAS) has emerged as a highly promising technology for detecting and localizing perturbations with high resolution. Despite its remarkable potential, DAS also presents important limitations that can hinder large-scale and long-term deployment in real operational MAN scenarios. In particular, the DAS cost remains relatively high, and the technology requires significant expertise for system configuration, signal interpretation, and maintenance. Moreover, DAS generates an enormous amount of data, creating substantial challenges in terms of storage and data management, especially when continuous monitoring is required. In contrast, interferometric fiber sensing approaches represent an attractive alternative. Although they do not provide the spatial localization capability typical of DAS, they can achieve comparable sensitivity while offering major advantages in terms of reduced system complexity, lower cost, and significantly lighter data handling requirements. These characteristics make interferometric solutions particularly suitable for practical deployments where early warning is more important than precise distributed localization. Their simplified architecture can therefore facilitate the exploitation of in-service urban fiber networks as sensing assets, extending monitoring capabilities to a broader range of users and use cases.

This work presents a direct comparison between these two sensing paradigms through a real field trial carried out on an operational MAN fiber network deployed by the Italian operator OPEN FIBER in the town of Pitigliano, Italy. Pitigliano is an ancient medieval village built on a tuff cliff, a geomorphological setting of high historical and environmental value but also potentially exposed to instability phenomena. In the experiment, an already installed telecom fiber-optic cable buried beneath an unpaved road running along the tuff ridge was exploited as a sensing element to monitor both anthropogenic activities, such as pedestrians and passing vehicles, and potentially dangerous events, such as falling rocks or trees. In perspective, the same sensing infrastructure may also support the observation of possible variations affecting the stability of the tuff cliff itself, thus contributing to geoscientific monitoring and risk mitigation. The entire monitoring system was remotely operated from a service room located at the Municipality of Pitigliano, demonstrating the feasibility of centralized and fully remote management of urban fiber sensing infrastructures. Several comparative measurements obtained with both DAS and a low-cost interferometric system provided by COHAERENTIA (www.cohaerentia.com) are presented and discussed. The results show useful insight into the capabilities of sensing technologies for future smart-city, civil protection, and geoscience applications based on existing telecom fiber networks.