A guide to marker design for long-term displacement measurement in civil infrastructure using the sampling moiré technique

Abstract The demand for continuous structural integrity assessment of civil infrastructure has increased significantly in recent years. Among various optical full-field measurement techniques, the sampling moiré (SM) method has gained attention due to its high displacement accuracy and suitability for non-contact monitoring. For long-term monitoring, however, aesthetically pleasing markers are preferred since they will remain affixed to infrastructure surfaces. This study provides a basic guide to marker design for recent advancements in image sensing related to long-term structural health monitoring of infrastructures using the SM method. Simulation and experimental results demonstrated that when the marker contrast is higher than 0.2 and the marker pitch in captured images is more than 10 pixels, submillimeter-level measurement accuracy can be achieved in evaluating the displacement of infrastructure structures. This guide provides essential requirement for designing moiré markers intended for the long-term monitoring of infrastructure, including bridges, dams, tunnels, and high-rise buildings.