Structural health monitoring of Au Sable Light Station using distributed fiber optic sensing and 3D point clouds

Preserving heritage structures from degradation over time is crucial due to their significant cultural, social, and economic impact. Thus, to ensure the structural integrity and performance of these structures over time, it is essential to carry out regular or periodic structural health monitoring (SHM). However, the primary challenge in implementing SHM for heritage structures lies in choosing appropriate techniques with minimum intervention to the historical and architectural value of these structures. Distributed fiber optic sensing (DFOS) is a prominent SHM technique that achieves this goal with minimal or no impact on the aesthetic appearance of the structures. In this study, the Au Sable Light station, a 150-year-old historic structure at the Pictured Rocks National Lakeshore in Michigan was equipped with multiple fiber optic sensors to acquire distributed strain (DSS), temperature (DTS), and acoustic (DAS) sensing data over a month using three different Rayleigh and Brillouin-based DFOS systems. Additionally, point cloud scanning was conducted to accurately map the locations of the fiber optic cables attached to the lighthouse. The collected data were analyzed to assess in-service strain variations in response to varying environmental conditions and to detect human movement. This analysis will aid in evaluating the necessity for continuous monitoring and inform decisions on taking necessary actions to mitigate any potential threats to the structural integrity of the light station.