automated detection and characterization of solar filaments and sigmoids
DESCRIPTION
Automated Detection and Characterization of Solar Filaments and Sigmoids. K. Wagstaff, D. M. Rust, B. J. LaBonte and P. N. Bernasconi Johns Hopkins University Applied Physics Laboratory Laurel, Maryland USA Solar Image Recognition Workshop Brussels October 23-24, 2003. - PowerPoint PPT PresentationTRANSCRIPT
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Automated Detection and Characterization of Solar Filaments and Sigmoids
K. Wagstaff, D. M. Rust, B. J. LaBonte and P. N. Bernasconi
Johns Hopkins University Applied Physics LaboratoryLaurel, Maryland USA
Solar Image Recognition WorkshopBrussels
October 23-24, 2003
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Objectives of Solar Filament Detection and Classification
• Report automatically on filament disappearances
• Provide warning of geomagnetic storms• Characterize magnetic flux rope chirality and
orientation of principal axis• Forecast pattern of Bz in magnetic clouds
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Filaments observed in H on 1 January 2003 at 1708 UTC (BBSO image)
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Filament Detection Method
• Identify filament pixels– Apply darkness threshold– Group dark pixels into contiguous regions– Prune out small dark regions and artifacts– Draw contours around filament boundary
• Find spines (filament centerlines)– Use simplified Kegl’s algorithm for finding the
principal curve defined by a set of points
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Detected filaments with borders outlined.
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Filaments with spines indicated.
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Find Barbs (protrusions from filament)
• Identify points farthest from the spine• Follow boundary in each direction to find
bays, i.e. local minimum distances from spine
• Establish each barb centerline by connecting the farthest point to the midpoint of left and right bays
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Barbs indicated by white lines.
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Chirality (handedness) Classification
• Calculate angle between barb centerline and spine
• Classify barbs by obtuse and acute angles• Assign filament chirality based on majority
classification: right-handed for acute angles; left-handed for obtuse angles
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Deducing filament chirality from barb counts.
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The solar disk observed in H on 30 June 2002 at 1540 UTC (BBSO image). Ten filaments identified, five filaments classified.
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Contoured filament with first approximation to spine.
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Second approximation.
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Fourth approximation.
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Sixth approximation.
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Eighth approximation.
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Final approximation to spine and classification of filament.
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Southern hemisphere filament rests in a right-handed flux rope.
Solar disk in H on 22 August 2002 at 1603 UTC (BBSO image)
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Northern hemisphere filament rests in a left-handed flux rope.
Mirror image would be associated with right-handed flux rope.
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Future Developments
• Make detection algorithm more robust• Test against man-made lists• Compare filament positions on successive
images after correcting for solar rotation• Set alarm bit if filament can’t be found• Estimate geoeffectiveness from filament
position on the disk and magnetic indices
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Sigmoid Detection
• Sigmoid = elongate structure, S or inverse-S shape = signal of enhanced CME probability
• Present method: observers watching 24 hr/day• Improved space weather forecasts require
automatic, accurate sigmoid detection
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X-ray Sigmoid
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Algorithm developed for filament detection can be used on sigmoids.
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Sigmoid Detection Problems
• Structure and intensity not well correlated• Intensity dynamic range as high as 1000• Internal structure makes detection dependent
on spatial resolution• Visibility varies with temperature. Visibility
is best at 2 - 4 x 106 K, but often only 106 K images are available
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Chart: Outline of a Sigmoid Recognition Program
contour the imageoptional: smooth/sharpen
trace out individual contoursstore contour data in a structure
compute k-curvature from data
extract curvature stats
compare curve stats to model stats
Sigmoid Decision
Curvature Stats and Measures
Curvature vs. Arc-length Plots
Structured Contour Data
Contour Map of Image
Solar Imagetaken from Yohkoh
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Image Contouring
• Threshold image at different intensity levels• Lines of equal intensity create closed contours• Closed contours have distinct shapes
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Characterizing a Shape with Curvature
• Curvature is change in tangent angle per change in arc length
• Counter-clockwise curving lines have positive curvature.
κ p =dθds
≈ φq−p + p−o
κ p ≈σ ⋅ φv u 2+ v v 2
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Interpreting the curvature-arclength plot
• Unique features: position of extrema and zeros; number of zeros; area under the curve; length of perimeter
κ ds=s2
s1
∫ dθ =s2
s1
∫ θ2 −θ1
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Sample Case 1: Non-Sigmoid
• Number of Regions between zeros: 6• Extrema at: s = 0.05, 0.18, 0.35,
0.60, 0.70, 0.93• Area under the curve in each region:
-2.88, 0.09, -2.89, 0.08, -2.60, 1.03
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Sample Case 2: Sigmoid
• Number of Regions between zeros: 4• Extrema at: s = 0.36, 0.50, 0.83, 0.94• Area under the curve in each region:
-4.36, 0.57, -4.53, 0.61
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Successes and Problems
• 8 out of 10 Sigmoids Correctly Identified– 6 false detections in 4 different images
• Reasons for False Detections– Sigmoids are not yet precisely defined– Sigmoids are often superposed on complicated
background• Recent Developments:
– Algorithm refined and tested on SXI and EIT images– Web-based implementation operates on real-time images
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Conclusions
• Developed algorithm for automatic detection and classification of H filaments
• Developed algorithm for automatic detection of sigmoids
• Test results: sigmoid detector successfully flags periods of high activity