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B2X: Flare recognition B2X: Flare recognition in Solar EUV Imagesin Solar EUV Images

Applications to EUVIApplications to EUVI

Véronique Delouille, Judith de PatoulBogdan Nicula, Jean-François Hochedez

5th SECCHI Consortium Meeting, 4-8 March 2007

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OutlineOutline

Goal : Goal : – Real-time Real-time alertsalerts & EUV flares & EUV flares CatalogCatalog

Method : Method : – CRH (Cosmic Ray Hit) removalCRH (Cosmic Ray Hit) removal

Median filter, WaveletMedian filter, Wavelet denoising denoising– Histogram processingHistogram processing

SkewnessSkewness monitoring monitoring

Data set : Data set : – 24 January 2007; 24 January 2007; – Images from Images from EUVI-A and EUVI-BEUVI-A and EUVI-B

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Detection of brightness Detection of brightness enhancement in EUV enhancement in EUV imagesimages

Aim :Aim :– Process EUV images, Process EUV images,

and detect when a flare is and detect when a flare is happening. happening.

– In case of detection, give allIn case of detection, give all characteristics such as localization,characteristics such as localization, size, intensity, time duration.size, intensity, time duration.– Catalog EUV flaresCatalog EUV flares

Tool : Tool : – Look for increased skewness of the pixel intensity Look for increased skewness of the pixel intensity

distribution distribution

Flaring or non flaring ?

SOHO-EIT, 1 May 98, 18:19

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Skewness : Skewness : a measure of a measure of assymetry assymetry

Sudden brightness enhancement Sudden brightness enhancement increased skewness in increased skewness in imageimage histogram histogram Skewness of Skewness of difference imagedifference image histogram histogram Coronal Dimmings detection Coronal Dimmings detection

– Cfr NEMO-Dimming detection by Elena Podladchikova & David BerghmansCfr NEMO-Dimming detection by Elena Podladchikova & David Berghmans

Gaussian distribution

Chi 2

Skewness = 0 Skewness > 0

Skewness:

Mean:

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B2X on B2X on secchi_prep’edsecchi_prep’ed FSFRFSFR images: raw images: raw 2k2k22

Goes

B

Flare

A

EUVI A - Skewness

EUVI B - Skewness

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Discussion of previous graphsDiscussion of previous graphs

Pre-processing needed against Pre-processing needed against Cosmic Ray Hits (CRH)Cosmic Ray Hits (CRH)

Possible strategies:Possible strategies:– RebinningRebinning– Median filter for CRH removalMedian filter for CRH removal– Wavelet denoisingWavelet denoising– Exclude the far off-disc region (and Exclude the far off-disc region (and

hence off-disk CRH)hence off-disk CRH)

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B2X on B2X on secchi_prep’edsecchi_prep’ed FSHRFSHR imagesimagesImages 2x2 rebinned Images 2x2 rebinned 1k 1k22

Goes

B

Flare

Goes

B F

lare

EUVI A

EUVI B

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Discussion : B2X on Discussion : B2X on Images 2x2 rebinned Images 2x2 rebinned 1k 1k22

Still lots of unwanted increase in the Still lots of unwanted increase in the skewnessskewness– CRH cleaning : remove pxl > 3 (local CRH cleaning : remove pxl > 3 (local

median)median)– Wavelet denoisingWavelet denoising

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B2X on B2X on secchi_prep’edsecchi_prep’ed FSHRFSHR images :images :Median filter pre-proc for CRH Median filter pre-proc for CRH removalremoval

Goes

B

Flare

Goes

B

Flare

EUVI A

EUVI B

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‘‘Problematic’ imagesProblematic’ images

24 Jan’ 0702:21:40Pb in imageacquisition

24 Jan’ 0719:25:40

Post-flareactivity

EUVI A

ICER 7 image

EUVI B

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CRH attenuation via Wavelet CRH attenuation via Wavelet Denoising Denoising (1/2)(1/2)

Remove finest discrete detail coefficients and reconstruct Remove finest discrete detail coefficients and reconstruct (linear Wavelet denoising)(linear Wavelet denoising) Gibbs effect introduce small values near large value. Gibbs effect introduce small values near large value.

– It reduces the asymmetry and hence the skewnessIt reduces the asymmetry and hence the skewness

24 Jan’ 0724 Jan’ 0710:05:4010:05:40

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Remove first 2 levels of wavelet coefficients, and reconstruct (linear Wavelet denoising) Remove first 2 levels of wavelet coefficients, and reconstruct (linear Wavelet denoising) Gibbs effect introduce small values near large value. Gibbs effect introduce small values near large value.

– It attenuates the asymmetry and hence the skewnessIt attenuates the asymmetry and hence the skewness On-disc flares On-disc flares less affectedless affected than off-disc Cosmic Ray Hits than off-disc Cosmic Ray Hits

24 Jan’ 0724 Jan’ 0705:15:4005:15:40

CRH attenuation via Wavelet DenoisingCRH attenuation via Wavelet Denoising (1/2)(1/2)

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B2X on B2X on secchi_prep’edsecchi_prep’ed FSHRFSHR imagesimages : : Linear Wavelet denoisingLinear Wavelet denoising

Goes

B

Flare

Goes

B

Flare

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Flare localisationFlare localisation

EUVI-A 24 Jan 2007 05:15:40

Mexican Hat continuous wavelet transformScale a=10; find position of maxima

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)

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B2X- Flare detection B2X- Flare detection quality: minimize False quality: minimize False Detection RateDetection Rate

Correlation between flare candidate and AR positionCorrelation between flare candidate and AR position

Barra, Delouille, Hochedez, ‘Segmentation of Extreme Ultraviolet Solar

Images via Multichannel Fuzzy Clustering’, AdvSpRes, submitted.

Segmentation of EUV disc -> localize Active Segmentation of EUV disc -> localize Active RegionsRegions

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Conclusion : B2X

Combining:Combining: EUVI-A & EUVI-B images,EUVI-A & EUVI-B images, pre-processing (CR removal, wavelet pre-processing (CR removal, wavelet

denoising)denoising) skewness measure,skewness measure, localisation informationlocalisation information

allows to detect with high allows to detect with high confidenceconfidence

B to X flares.B to X flares.