Extracting modal parameters of a cable on shaky motion pictures

• We extract a set of modal parameters from a shaky motion picture.
• The burred-image problem was resolved by the multi-template matching algorithm.
• The low accuracy problem was resolved by using the cross-correlation data.
• High accuracy has been achieved by using a system identification algorithm.

A set of modal parameters of a cable are extracted from a motion picture captured by a digital camera operated with shaking hands. It is difficult to identify the center of the targets attached to the cable surface from the blurred motion image of the cable, because of the high-speed motion of the cable, low sampling frequency of the camera, and the effect of shaking hands on the motion pictures. This paper proposes a multi-template matching algorithm to solve these difficulties. In addition, a sensitivity-based system identification algorithm is proposed for extracting the natural frequencies and the damping ratios from ambient cable vibration data. Three sets of vibration tests are performed to examine the validity of the proposed algorithms. The results show that the proposed approach of using these two algorithms is fairly feasible for extracting modal parameters from severely blurred motion pictures.