Smaller than the eye can see: Vibration analysis with video cameras

In the field of non-destructive testing the tools that we use to conduct inspections has evolved over the years. Originally, inspectors used their senses: sight, hearing, and touch to evaluate structures, but now they use equipment such as: boroscopes, dye penetrant, microphones, and ultrasonic transducers, which can augment the human senses and/or make much finer quantitative measurements beyond any human capabilities. Recent developments in computer vision have created a “motion microscope”, where small imperceptible motions in videos can be magnified and easily seen; this technique is called motion magnification. Additionally, the method enables quantitative analysis of structures from video as the information acquired for motion magnification also provides displacement signals as a basis for vibrational analysis.In this paper, we present applications of motion magnification to vibration analysis in non-destructive testing. We describe the methodology and theory behind motion magnification, the workflow from video to modal information, and discuss strategies for processing the numerous signals collected from video data. We demonstrate making video measurements of small structures and rotating machinery in controlled conditions, and in near real time, extracting displacements from video and doing simple modal and frequency analysis. We also present the results of outdoor measurements of civil infrastructure and discuss future applications for the methodology in non-destructive testing.