We present a procedure which extracts bright loop features from solar EUV images. In terms of image intensities, these features are elongated ridge-like intensity maxima. To discriminate the maxima, we need information of the spatial derivatives of the image intensity. Commonly, the derivative estimates are strongly affected by image noise. We therefore use a regularized estimation of the derivative which is then used to interpolate a discrete vector field of ridge
points(ridgels) which are positioned on the ridge center and have the intrinsic orientation of the local ridge direction. A scheme is proposed to connect ridgels to smooth, spline-represented curves which fit the observed loops. Finally, a half-automated user interface allows to merge or split, eliminate or select loop fits obtained form the above procedure. In this paper we apply our tool to one of the first EUV images observed by the SECCHI instrument on board the recently launched STEREO spacecraft. We compare the extracted loops with projected field lines computed from almost simultaneously taken magnetograms measured by the MDI/SOHO Doppler imager. The field lines were calculated using a linear force-free field model. This comparison allows to verify faint and spurious loop connections produced by our segmentation tool and it also helps to prove the quality of the magnetic field model where well identified loop structures comply with field line projections. We also discuss further potential applications of our tool such as loop oscillations and stereoscopy.
Authors: Bernd Inhester, Li Feng, Thomas Wiegelmann
Publication Status: Solar Physics, in press
Last Modified: 2007-08-02 11:11
We discuss some basic principles of stereoscopy and their
relevance to the reconstruction of coronal loops. The aim of the paper is to make the solar physicsist familiar with
basic stereoscopy principles and to give hints how they may apply to the analysis of data from the forthcoming STEREO mission.
We disucss the geometry of the solar coronal stereo problem, give the basic principles of a tie-point reconstruction
algorithm and consider ambiguities and resolution errors.
Finally we mention extensions to plain stereoscopy such as
a third view, a tomography-like approach and how magnetic field information can be used to improve the reconstruction.
Authors: Bernd Inhester
Publication Status: submitted as a contribution to an ISSI publication (Intern. Space Science Institute, Bern, Switzerland)
Last Modified: 2006-12-19 10:44