A Full-disk Image Standardization of the Chromosphere Observation at Huairou Solar Observing Station

TL;DR

This paper presents algorithms for standardizing full-disk solar chromosphere images, including geometric correction, intensity normalization, and limb-darkening removal, to improve their usability for scientific research.

Contribution

The paper introduces a comprehensive image standardization process for full-disk chromosphere observations, enabling consistent analysis across datasets.

Findings

Algorithms successfully standardize image size and geometry.

Limb-darkening effects are effectively removed.

Standardized images facilitate further scientific investigations.

Abstract

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$\times$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 chromosheric full-disk observations to be used for further scientific investigations.