Measurement of 3-D vibration by dynamic photogrammetry using least-square image matching for sub-pixel targeting

This paper deals with a methodology to measure 3-D dynamic displacements of a structure by the digital close-range photogrammetry. Using stereo sequence images of a vibrating structure taken by two cameras, a method is proposed to accurately trace the spatial displacement of the structure in 3-dimensional space. This method combines the correlation and the least square image matching so that the sub-pixel targeting is achieved to increase the measurement accuracy. Experiments have been successfully performed to measure displacements of a beam under forced vibration in both bending and torsional modes simultaneously with multiple frequencies. The proposed method only requires inexpensive daily-use cameras, and can remotely detect the dynamic full-field displacement of a structure vibrating in a complex 3-D defection shape up to the sub-pixel accuracy. It has various potential applications, e.g., remote vibration monitoring of a non-accessible or dangerous facilities, etc.