Evaluation of image-shift measurement algorithms for solar Shack-Hartmann wavefront sensors

摘要

Context. Solar Shack-Hartmann wavefront sensors measure differentialwavefront tilts as the relative shift between images from differentsubapertures. There are several methods in use for measuring these shifts.Aims. We evaluate the inherent accuracy of the methods and the effects ofvarious sources of error, such as noise, bias mismatch, and blurring. Weinvestigate whether Z-tilts or G-tilts are measured. Methods. We test thealgorithms on two kinds of artificial data sets, one corresponding to imageswith known shifts and one corresponding to seeing with different r_0. Results.Our results show that the best methods for shift measurements are based on thesquare difference function and the absolute difference function squared, withsubpixel accuracy accomplished by use of two-dimensional quadraticinterpolation. These methods measure Z-tilts rather than G-tilts.