Finding of low-contrast formations in the solar corona using a low contrast method

Abstract

Coronal holes, bright coronal points, filaments, and prominences are among the initial factors responsible for variability of the space weather conditions. Radioheliographic data on low-contrast formations contain valuable information necessary for studying conditions of origination, peculiarities of evolution, and prediction of solar-terrestrial relations. It is important to identify these formations on the solar disk when physical properties of coronal holes are revealed. The algorithm based on the Wiener-Tikhonov filter modification with controlled parameters and a high-frequency contrast filter was developed in order to isolate low-contrast formations in the solar corona brightness distributions obtained at a wavelength of 5.2 cm from the Siberian solar radio telescope observations. In this case low-contrast sources are isolated in two main stages: (1) HF noise smoothing based on an evolutionary filter with controlled parameters and (2) contrasting of sources using an HF filter. The evolutionary filter regularization parameters and the dimensions of an HF contrast filter mask are selected depending on the signal-to-noise ratio and dimensions of the studied region based on the results of preliminary data processing. The corresponding software has been developed in order to identify low-contrast objects on the Sun’s radio images using this method. The algorithm is used to isolate filaments and coronal holes and the results of this usage are presented in this work.