Developments with Motion Magnification for Structural Modal Identification through Camera Video

Non-contact measurement of the response of vibrating structures may be achieved using several different methods including the use of video cameras that offer flexibility in use and advantage in terms of cost. Videos can provide valuable qualitative information to an informed person, but quantitative measurements obtained using computer vision techniques are essential for structural assessment. Motion Magnification in videos refers to a collection of techniques that amplify small motions in videos in specified bands of frequencies for visualization, which can also be used to determine displacements of distinct edges of structures being measured. We will present recent developments in motion magnification for the modal identification of structures. A new algorithm based on the Riesz transform has been developed allowing for real-time application of motion magnification to normal-speed videos with similar quality to the previous computationally intensive phase-based algorithm. Displacement signals are extracted from strong edges in the video as a basis for the data necessary for modal identification. Methodologies for output-only modal analysis applicable to the large number of signals and short length signals are demonstrated on example videos of vibrating structures.