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Huw Morgan, Shadia Habbal, Richard Woo

This research focuses on processing white light images of the solar corona to accurately depict its structure. The study compares results with standard LASCO images and introduces a new method using Normalizing Radial Graded Filter (NRGF) for improved visualization. The processing technique helps in avoiding saturation and allows for finer details to be observed at different coronal heights. Application of NRGF to both solar minimum and maximum observations is discussed, highlighting the method's effectiveness. The research also touches upon the challenges of processing WL and pB observations and stresses the importance of using the NRGF for unbiased image enhancement.

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Huw Morgan, Shadia Habbal, Richard Woo

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  1. Coronal Image ProcessingThe Accurate Depiction of Structure in Qualitative Images of the White Light Corona Huw Morgan, Shadia Habbal, Richard Woo

  2. Outline • Finding an unbiased radial graded filter using a model pB corona • Apply to pB observations • Compare results with standard LASCO images (made using division by a long term minimum method) • Processing of white light images

  3. Current sheet width pB at pole pB at equator Synthetic Solar Minimum Corona w is constant so RADIAL corona LOG pB pB at equator pB at pole

  4. Simple Radial Graded Filter (RGF) Processed intensity Original intensity Intensity averaged over all latitudes at r r height  latitude WHY NOT RADIAL ????

  5. DATA WHY NOT RADIAL? Sol. min • Large change in relative contrast between high and low intensity regions with height • RGF neglects the change in contrast so processed corona is distorted Sol. max MODEL Average Std. dev. Average Std. deviation 

  6. Processed Original Average Normalizing Radial Graded Filter (NRGF) Std. dev. RGF equator NRGF equator RGF pole NRGF pole

  7. Application to pB observations - Solar Minimum January 18 1997 • MLSO MKIII & MKIV coronameters - 1.15-2.28 Rs • LASCO (SOHO) C2 coronagraph - 2.28-6.2 Rs NRGF ‘Standard’ LASCO & MKIII

  8. Application to pB observations - Solar Maximum (June 21 2000) NRGF ‘Standard’ LASCO & MKIII

  9. LASCO ‘standard’ images or the NRGF - which gives the true picture? Latitudinal profiles at 3 heights Solar min Solar max LOG Standard NRGF

  10. How we do it... • Calculate WL-pB for many days surrounding observation, and average. • Subtract this average from desired observation • This method provides excellent qualitative images of coronal structure after final processing with NRGF Application to white light (WL)... • Easy to apply NRGF to pB observations since pB does not contain F corona and stray light. Why bother with WL? • LASCO makes ~30 WL obs./day, compared with ~2 pB. • LASCO WL observations have 12” resolution (1024x1024 pix). LASCO pB have half this resolution. White light processed White light pB Minimum Maximum

  11. Application to WL - comparison with LASCO standard images

  12. Application to WL - CME

  13. Conclusions • The NRGF is a correct method for removing radial gradient from coronal images • Division by a long term minimum almost invariably leads to a misleading depiction of structure • A new method for processing white light images provides good results with LASCO C2 observations (C3 needs more work - due to polarization of F corona?) • Using the NRGF, we can avoid saturating the image to see structure, and finer detail can be seen at all heights in the corona.

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