Wavelength Dependence of Image Quality Metrics and Seeing Parameters and their Relation to Adaptive Optics Performance

Abstract

Ground-based solar observations are severely affected by Earth's turbulent atmosphere. As a consequence, observed image quality and prevailing seeing conditions are closely related. Partial correction of image degradation is nowadays provided in real-time by adaptive optics (AO) systems. In this study, different metrics of image quality are compared with parameters characterizing the prevailing seeing conditions, i.e., Median Filter Gradient Similarity (MFGS), Median Filter Laplacian Similarity (MFLS), Helmli-Scherer mean, granular rms-contrast, differential image motion, and Fried-parameter r0. The quiet-Sun observations at disk center were carried out at the Vacuum Tower Telescope (VTT), Observatorio del Teide (OT), Izana, Tenerife, Spain. In July and August 2016, time-series of short-exposure images were recorded with the High-resolution Fast Imager (HiFI) at various wavelengths in the visible and near-infrared parts of the spectrum. Correlation analysis yields the wavelength dependence of the image quality metrics and seeing parameters, and Uniform Manifold Approximation and Projection (UMAP) is employed to characterize the seeing on a particular observing day. In addition, the image quality metrics and seeing parameters are used to determine the field-dependence of the correction provided by the AO system. Management of high-resolution imaging data from large-aperture, ground-based telescopes demands reliable image quality metrics and meaningful characterization of prevailing seeing conditions and AO performance. The present study offers guidance how to retrieve such information ex post facto.

arXiv comment30 pages, 13 figure, 2 tables, accepted to be published in Solar Physics

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