Spatial uncertainty of measurement errors in digital image correlation

Digital image correlation is a widely used optical metrology for shape, motion, and deformation measurement. Although a number of studies have been carried out on the measurement errors of digital image correlation, the spatial uncertainty of the measurement errors, which stems from the randomness of speckle patterns, is seldom researched. In this work, a theoretical model is built for the spatial uncertainty of measurement errors. Analytical formulae for the spatial variances of both the mean bias error and the standard deviation error are derived. The influences of subset size, speckle coverage, and speckle radius on the spatial uncertainty are investigated. Numerical simulations demonstrate the correctness of the proposed model.