Deformation measurements of dragonfly's wings in free flight by using Windowed Fourier Transform

Grating Projection method was used to measure the height distribution of dragonfly's wings in free flight. Then the fringe patterns on the dragonfly were recorded by a high-speed CCD camera. Since the fringe patterns recorded in such a way have poor contrast and brightness, Windowed Fourier Transform (WFT), which is insensitive to noise and fringe amplitude, was used to process the fringe patterns to extract the phase. Finally, the height distributions of dragonfly's wings in free flight were obtained by using the Weighted Least-Squares Phase Unwrapping method. The choice of integration limits and the size of the window of WFT are briefly discussed here