A full-disk image standardization of the chromosphere observation at Huairou Solar Observing Station

Observations of local features in the solar chromosphere began in 1992 at Huairou Solar Observing Station, while the full-disk chromosphere observations were carried out since 2000. In order to facilitate researchers to use full-disk chromosphere observation, algorithms have been developed to standardize the full-disk images. The algorithms include the determination of the center of the image and size standardization, geometric correction and intensity normalization. The solar limb of each image is determined from a histogram analysis of its intensity distribution. The center and radius are then calculated and the image is corrected for geometric distortions. Images are re-scaled to have a fixed radius of 500 pixels and centered within the 1024 x 1024 frame. Finally, large-scale variations in intensity, such as limb-darkening, are removed using a median filter. This paper provides a detailed description of these algorithms, and a summary of the properties of these chromospheric full-disk observations to be used for further scientific investigations. (C) 2019 COSPAR. Published by Elsevier Ltd. All rights reserved.