Tracking granules on the Sun's surface and reconstructing velocity fields - I. The CST algorithm
Tracking granules on the Sun's surface and reconstructing velocity fields - I. The CST algorithm
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跟踪太阳表面颗粒并重建速度场 - I. CST 算法
DOI：
10.1051/0004-6361:20066491
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发表时间：
2007
影响因子：
6.5
通讯作者：
Christophe Ducottet
中科院分区：
文献类型：
--
作者：
M. Rieutord;T. Roudier;S. Roques;Christophe Ducottet
目标。确定太阳表面的水平速度场对于理解中颗粒或超颗粒等结构的动力学或简单地了解磁场的分布至关重要。方法：研究方法。在这里，我们继续开发一种称为CST的相干结构跟踪方法，该方法确定颗粒在视场中的水平运动。结果。我们首先设计了一种推广的Stous方法用于图像分割，并表明当分割更接近颗粒的形状时，颗粒跟踪对大颗粒的效果较差，因为对颗粒破碎的敏感性增加。然后介绍了基于Daubechies小波的速度场多分辨率分析，提供了不同尺度上的速度场图像。给出了计算水平散度和垂直涡度等场导数的算法。文中还简要讨论了缺乏数据或陆地大气扭曲对图像的影响。
Aims. Determination of horizontal velocity fields on the solar surface is crucial for understanding the dynamics of structures like mesogranulation or supergranulation or simply the distribution of magnetic fields. Methods. We pursue here the development of a method called CST for coherent structure tracking, which determines the horizontal motion of granules in the field of view. Results. We first devise a generalization of Strous method for the segmentation of images and show that when segmentation follows the shape of granules more closely, granule tracking is less effective for large granules because of increased sensitivity to granule fragmentation. We then introduce the multi-resolution analysis on the velocity field, based on Daubechies wavelets, which provides a view of this field on different scales. An algorithm for computing the field derivatives, like the horizontal divergence and the vertical vorticity, is also devised. The effects from the lack of data or from terrestrial atmospheric distortion of the images are also briefly discussed.