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B2X: Flare recognition in Solar EUV Images Applications to EUVI

B2X: Flare recognition in Solar EUV Images Applications to EUVI. Véronique Delouille, Judith de Patoul Bogdan Nicula, Jean-François Hochedez. 5th SECCHI Consortium Meeting, 4-8 March 2007. Outline. Goal : Real-time alerts & EUV flares Catalog Method : CRH (Cosmic Ray Hit) removal

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B2X: Flare recognition in Solar EUV Images Applications to EUVI

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  1. B2X: Flare recognition in Solar EUV ImagesApplications to EUVI Véronique Delouille, Judith de Patoul Bogdan Nicula, Jean-François Hochedez 5th SECCHI Consortium Meeting, 4-8 March 2007

  2. Outline • Goal : • Real-time alerts & EUV flares Catalog • Method : • CRH (Cosmic Ray Hit) removal • Median filter, Wavelet denoising • Histogram processing • Skewness monitoring • Data set : • 24 January 2007; • Images from EUVI-A and EUVI-B

  3. Detection of brightness enhancement in EUV images SOHO-EIT, 1 May 98, 18:19 • Aim : • Process EUV images, and detect when a flare is happening. • In case of detection, give all characteristics such as localization, size, intensity, time duration. • Catalog EUV flares • Tool : • Look for increased skewness of the pixel intensity distribution Flaring or non flaring ?

  4. Sudden brightness enhancement  increased skewness in image histogram Skewness of difference image histogram  Coronal Dimmings detection Cfr NEMO-Dimming detection by Elena Podladchikova & David Berghmans Mean: Skewness : a measure of assymetry Chi 2 Gaussian distribution Skewness: Skewness > 0 Skewness = 0

  5. Goes B Flare B2X on secchi_prep’edFSFR images: raw 2k2 EUVI A - Skewness A EUVI B - Skewness

  6. Discussion of previous graphs • Pre-processing needed against Cosmic Ray Hits (CRH) • Possible strategies: • Rebinning • Median filter for CRH removal • Wavelet denoising • Exclude the far off-disc region (and hence off-disk CRH)

  7. B2X on secchi_prep’edFSHR imagesImages 2x2 rebinned  1k2 EUVI A Goes B Flare EUVI B Goes B Flare

  8. Discussion : B2X on Images 2x2 rebinned  1k2 • Still lots of unwanted increase in the skewness • CRH cleaning : remove pxl > 3 (local median) • Wavelet denoising

  9. B2X on secchi_prep’edFSHR images :Median filter pre-proc for CRH removal EUVI A Goes B Flare EUVI B Goes B Flare

  10. ‘Problematic’ images EUVI A EUVI B 24 Jan’ 07 02:21:40 Pb in image acquisition ICER 7 image 24 Jan’ 07 19:25:40 Post-flare activity

  11. Remove finest discrete detail coefficients and reconstruct (linear Wavelet denoising) Gibbs effect introduce small values near large value. It reduces the asymmetry and hence the skewness CRH attenuation via Wavelet Denoising (1/2) 24 Jan’ 07 10:05:40

  12. Remove first 2 levels of wavelet coefficients, and reconstruct (linear Wavelet denoising) Gibbs effect introduce small values near large value. It attenuates the asymmetry and hence the skewness On-disc flares less affected than off-disc Cosmic Ray Hits CRH attenuation via Wavelet Denoising(1/2) 24 Jan’ 07 05:15:40

  13. Goes B Flare Goes B Flare B2X on secchi_prep’edFSHR images :Linear Wavelet denoising

  14. Flare localisation • Once an increase in skewness has been detected: • find the flare position by finding pixel with maximum intensity • Mask the flare and re-compute skewness to find possible other flare(s) EUVI-A 24 Jan 2007 05:15:40 Mexican Hat continuous wavelet transform Scale a=10; find position of maxima

  15. B2X- Flare detection quality: minimize False Detection Rate • Correlation between flare candidate and AR position Segmentation of EUV disc -> localize Active Regions Barra, Delouille, Hochedez, ‘Segmentation of Extreme Ultraviolet Solar Images via Multichannel Fuzzy Clustering’, AdvSpRes, submitted.

  16. Conclusion : B2X Combining: • EUVI-A & EUVI-B images, • pre-processing (CR removal, wavelet denoising) • skewness measure, • localisation information allows to detect with high confidence B to X flares.

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