Improved shift estimates on extended Shack-Hartmann wavefront sensor images

• Main Authors: Townson, M. J, Kellerer, A, Saunter, C. D
• Format: Journal Article
• Language: English
• Published: 20-08-2015
• Subjects: Physics - Instrumentation and Methods for Astrophysics
• DOI: 10.48550/arxiv.1508.05011

An important factor which affects performance of solar adaptive optics (AO)
systems is the accuracy of tracking an extended object in the wavefront sensor.
The accuracy of a centre-ofmass approach to image shift measurement depends on
the parameters applied in thresholding the recorded image; however, there
exists no analytical prediction for these parameters for extended objects.
Motivated by this we present a new method for exploring the parameter space of
image shift measurement algorithms, and apply this to optimize the parameters
of the algorithm. Using a thresholded, windowed centre of mass, we are able to
improve centroid accuracy compared to the typical parabolic fitting approach by
a factor of 3 in a signal-to-noise regime typical for solar AO. Exploration of
the parameters occurs after initial image crosscorrelation with a reference
image, so does not require regeneration of correlation images. The results
presented employ methods which can be used in real-time to estimate the error
on centroids, allowing the system to use real data to optimize parameters,
without needing to enter a separate calibration mode. This method can also be
applied outside of solar AO to any field which requires the tracking of an
extended object.