Operational modal analysis is based on data collected using a network of sensors installed on a monitored structure to measure its response to the external stimuli. As the instrumentation can be costly, sensors are placed at a limited number of locations where damage-sensitive features can hopefully be sensed. Hence, the actual ability to detect a shift from the undamaged structural state in real time might be detrimentally affected. Non-contact measurement methods relying on, e.g., digital video cameras, which have gained interest in recent years, can instead provide high-resolution and diffused measurements/information. In this study, moving from videos of a vibrating structure, a shift in its dynamic response was assessed. By means of a phase-based optical flow methodology, a linear correlation between the phase and the structural motion was customarily assumed using, e.g., the Gabor filter. Since such a correlation does not result in being always linear, linearization is necessary for all the frames. By using the blind source separation method, mode shapes and vibration frequencies were finally obtained. The performance of the proposed method is investigated to verify the accuracy in extracting the dynamic features of the considered structure using the proposed method.
