Statistical approach is utilised to analyse the formation of displacement gradient fringes created by shearing speckle interferometry in this paper. We calculated the impulse response function and studied the spectrum of shearing specklegram in detail. Then the optical filtering system of shearography is analysed and we found that the cosine fringes are related to the displacement gradient upon condition that the displacement component along the X-axis, can be negleected, and the fringe visibility depends on the size of filtering holes and the in-plane displacement components.
F. P. Chiang,
"Fringe Formation Of Shearing Speckle Interferometry", Proc. SPIE 0814, Photomechanics and Speckle Metrology, (17 February 1987); doi: 10.1117/12.941684; https://doi.org/10.1117/12.941684