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Description
This paper presents an experimental evaluation of Distributed Acoustic Sensing (DAS) combined with rail-mounted monolithic distributed fiber optic sensing (DFOS) elements for measuring the dynamic response of railway infrastructure under high-speed operation. The study was conducted during controlled nighttime test runs on a secured track section using dedicated rolling stock, with train velocities incrementally increased to 200, 220, 240, and 250 km/h.The primary objective is to assess the wide-bandwidth capabilities of DAS in capturing complex vibration phenomena, with particular emphasis on high-frequency events occurring in inter-harmonic regions under high-amplitude excitation. Special attention is given to the influence of sensor installation methods on measurement fidelity and acoustic coupling efficiency. To enable a controlled comparison, the impact of installation techniques was evaluated based on measurements performed on a dedicated experimental test field. Furthermore, a low-invasiveness adhesive-based mounting technique for monolithic DFOS segments is introduced. This approach eliminates the need for mechanical pre-tensioning while significantly improving coupling between the sensor and the rail compared to conventional telecommunication fibers installed in conduits.Experimental results demonstrate that the integration of rail-mounted monolithic DFOS segments within a DAS system enhances sensitivity and extends the usable frequency range. The system successfully resolves complex spectral signatures, including high-frequency components associated with wheel–rail interaction and structural resonances at peak operational speeds.The findings confirm that optimized sensor installation plays a critical role in maximizing DAS performance. The proposed hybrid sensing configuration provides a robust and scalable solution for advanced railway monitoring, supporting the development of autonomous structural health monitoring systems under high-speed conditions.