Astronomy and Astrophysics – Astrophysics
Scientific paper
2007-07-13
Astronomy and Astrophysics
Astrophysics
in press in Astronomy and Astrophysics, 9 pages
Scientific paper
10.1051/0004-6361:20066491
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. 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. 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.
Ducottet C.
Rieutord Michel
Roques Sylvie
Roudier Th.
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