In this paper a modified analysis method for analyzing time-average defocused speckle photographs is presented. Resolved surface slope components along the examining line can be found by measuring fringe distances from a certain point. Then amplitude changes and bending moments can be calculated. The method has been verified experimentally by examining vibrations of a rectangular glass fiber multilayer plate.
V. V. K. Karppinen,
"Virtual Fringe Analysis Method In Time-Average Defocused Speckle Photography," Optical Engineering 21(1), 210160 (1 February 1982). https://doi.org/10.1117/12.7972859