Evaluation of image-shift measurement algorithms for solar Shack-Hartmann wavefront sensors
TLDR
In this article, the inherent accuracy of the methods and the effects of various sources of error, such as noise, bias mismatch, and blurring, were evaluated and the best methods for shift measurements were based on the square difference function and the absolute difference function squared, with subpixel accuracy accomplished by use of two-dimensional quadratic interpolation.Abstract:
Context. Solar Shack–Hartmann wavefront sensors measure differential wavefront tilts as the relative shift between images from different subapertures. There are several methods in use for measuring these shifts. Aims. We evaluate the inherent accuracy of the methods and the effects of various sources of error, such as noise, bias mismatch, and blurring. We investigate whether Z-tilts or G-tilts are measured. Methods. We test the algorithms on two kinds of artificial data sets, one corresponding to images with known shifts and one corresponding to seeing with different r0. Results. Our results show that the best methods for shift measurements are based on the square difference function and the absolute difference function squared, with subpixel accuracy accomplished by use of two-dimensional quadratic interpolation. These methods measure Z-tilts rather than G-tilts.read more
Citations
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Solar Adaptive Optics
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Horizontal flow fields observed in Hinode G-band images - I. Methods
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Is the sky the limit?. Performance of the revamped Swedish 1-m Solar Telescope and its blue- and red-beam reimaging systems
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Precise Proper-Motion Measurement of Solar Granulation
L. J. November,George W. Simon +1 more
TL;DR: In this paper, a cross-correlation technique for the precise measurement of the proper motion of tracers seen on successive images of a time series of solar granulation is described, defined as a function of position within a spatially localized apodization window.
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Probability of getting a lucky short-exposure image through turbulence*
TL;DR: In this article, it was shown that the probability of obtaining a good short-exposure image corresponds to a hyperspace integral in which the spatial dimensions are the independent random coefficients in the orthonormal series expansion.
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From Differential Image Motion to Seeing
TL;DR: The theory of the differential image motion monitor (DIMM) is reviewed and extended in this paper. But the contribution of CCD readout noise to image motion variance is modeled, and it can substantially bias DIMM results if left unsubtracted.
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