Identification and morphology analysis of granules using the New Vacuum Solar Telephone Observations

Abstract

Solar granulation is a plasma convective phenomenon from the solar convection zone to the photosphere, which appears as a cellular pattern on the solar surface. Morphological characteristics and evolution process of granules can help us to better understand the mechanism of the convective motion and the relationship to solar magnetic field. Therefore, an accurate identification method is crucial to study the mechanism and relationship. However, the traditional identification methods based on intensity- and gradient-threshold are very difficult to identify granules because the intensity distribution of granules is non-uniform and their boundaries appear to be blurred. In this paper, we proposed a new method based on phase congruency to identify granules and analyzed their morphological characteristics. The identification procedure includes three steps: (1) obtaining phase congruency feature from an original image; (2) obtaining binary image of phase congruency feature; (3) morphological filter to extract granule shapes. We selected two high-resolution image sequences taken from the New Vacuum Solar Telescope (NVST) at Fuxian Solar Observatory (FSO) to illustrate the identification procedure. For evaluating the accuracy of the proposed method, two traditional methods based on intensity threshold and marked watershed were compare to our method. Furthermore, we also selected three different thresholds to inspect the influence. The experiment result demonstrates that our proposed method is effective and accurate, and insensitive to those selected threshold. This demonstrates that our proposed method can be used to study granules evolution and their physical mechanism.