Advanced Imaging‐Based Metrology for Precise Deformation Monitoring: Railway Bridge Case Study

In this article, two advanced imaging‐based metrology methods, the multipoint method and the tele‐wide‐angle method, are introduced to the field of structural health monitoring. Both provide the means to significantly improve either the measurement uncertainty or the field of view compared to classical imaging‐based methods. The multipoint method utilizes a computer‐generated hologram to replicate a single object point to a predefined spot pattern in the image. Spatial averaging of the spot positions improves the measurement uncertainty. The second method, called tele‐wide‐angle, uses a diffraction grating to considerably enlarge the field of view of a tele objective lens. Both methods are investigated regarding the achievable measurement uncertainty at distances between 34 and 50 m. The standard deviations of the error range between 0.027 and 0.034 mm for the multipoint method and 0.008 and 0.02 mm for the tele‐wide‐angle method. In the second part of the article, both measurement systems are employed in a field study, measuring the deformation of a railway bar arch bridge. An inductive displacement transducer and several accelerometers are installed to validate the measured displacements and dynamics.