Comparison of Five Numerical Codes for Automated Tracing of Coronal Loops |
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Authors: | Markus J Aschwanden Jong Kwan Lee G Allen Gary Michael Smith Bernd Inhester |
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Institution: | (1) Solar and Astrophysics Laboratory, Lockheed Martin Advanced Technology Center, Department ADBS, Building 252, 3251 Hanover Street, Palo Alto, CA 94304, USA;(2) Department of Computer Science, University of Alabama in Huntsville, Huntsville, AL 35899, USA;(3) National Space Science and Technology Center, University of Alabama in Huntsville, Huntsville, AL 35899, USA;(4) Mullard Space Science Laboratory, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, UK;(5) Max-Planck Institute for Solar System Research, 37191 Katlenburg-Lindau, Germany |
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Abstract: | The three-dimensional (3D) modeling of coronal loops and filaments requires algorithms that automatically trace curvilinear
features in solar EUV or soft X-ray images. We compare five existing algorithms that have been developed and customized to
trace curvilinear features in solar images: i) the oriented-connectivity method (OCM), which is an extension of the Strous pixel-labeling algorithm (developed by Lee,
Newman, and Gary); ii) the dynamic aperture-based loop-segmentation method (developed by Lee, Newman, and Gary); iii) unbiased detection of curvilinear structures (developed by Steger, Raghupathy, and Smith); iv) the oriented-direction method (developed by Aschwanden); and v) ridge detection by automated scaling (developed by Inhester). We test the five existing numerical codes with a TRACE image
that shows a bipolar active region and contains over 100 discernable loops. We evaluate the performance of the five codes
by comparing the cumulative distribution of loop lengths, the median and maximum loop length, the completeness or detection
efficiency, the accuracy, and flux sensitivity. These algorithms are useful for the reconstruction of the 3D geometry of coronal
loops from stereoscopic observations with the STEREO spacecraft, or for quantitative comparisons of observed EUV loop geometries
with (nonlinear force-free) magnetic field extrapolation models. |
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Keywords: | Corona: structures Sun: EUV Methods: pattern recognition |
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