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Tips and Tricks for Analyzing CDS Data: A Comprehensive Guide by Dr. Peter Young

This guide, presented by Dr. Peter Young from the CCLRC/RAL, covers essential techniques for analyzing CDS data. Key topics include understanding photon statistics, addressing calibration uncertainties, implementing cosmic ray removal, aligning NIS1 and NIS2 images, adjusting for burn-in effects, and managing SOHO roll adjustments. Learn about various routines in software, best practices for handling cosmic rays, and the importance of appropriate calibration strategies to ensure accurate data analysis in solar observations.

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Tips and Tricks for Analyzing CDS Data: A Comprehensive Guide by Dr. Peter Young

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  1. Tips and Tricks for analysing CDS data Dr Peter Young SOHO/CDS Project Scientist CCLRC Rutherford Appleton Laboratory Dr Peter Young, CCLRC/RAL

  2. Overview • Photon statistics • Calibration uncertainty • Cosmic rays • NIS1-NIS2 alignment • Burn-in correction • SOHO roll Dr Peter Young, CCLRC/RAL

  3. Photon statistics • vds_calib yields photons/s/pixel • use Bill’s expression to yield fractional noise (fN) • √(2N + n)/N • proceed with calibration to yield intensity units • apply fNto yield error on intensity Dr Peter Young, CCLRC/RAL

  4. Calibration uncertainties • For large counts, calibration uncertainties dominate over photon statistic errors • Difference between relative and absolute calibration uncertainties (e.g., line ratios vs. DEM) • Relative uncertainty is λ dependent and varies from 12 to 29% • For absolute uncertainty, additional contribution of 13% • See Sect. 3.3 of Lanzafame et al. (2005, A&A, 432, 1063) for more details Dr Peter Young, CCLRC/RAL

  5. Cosmic Ray Removal • Three routines available in software • cds_new_spike • cds_clean_exp • cds_clean • Make sure to set $CDS_EXTERNAL for routines to run quickly Dr Peter Young, CCLRC/RAL

  6. Fill or not to fill? • The cosmic ray routines allow two options for dealing with CRs • fill with median value of surrounding pixels • flag as missing data • The latter is best option for preserving statistics Dr Peter Young, CCLRC/RAL

  7. NIS1-NIS2 alignment • NIS1 and NIS2 images are not spatially coincident IDL> gt_nis_alignment, qlds, x, y • Pre-loss: X~1”, Y~2” • Post-loss: X~1”, Y~3-7” • Depends on Y-location! Dr Peter Young, CCLRC/RAL

  8. Burn-in Correction • Narrow slit burn-in is not fully corrected for in the CDS software • Affects both line width and intensity IDL> result=get_width_corr(’22-sep-2005’,629.7) • Currently 20% for O V λ629.7 Dr Peter Young, CCLRC/RAL

  9. SOHO Roll • To find out SOHO roll angle on a particular date: IDL> angle=get_soho_roll(’22-sep-2005’) • To make CDS images appear in the usual format, use IDL> data=gt_windata(a,0,/invert) Dr Peter Young, CCLRC/RAL

  10. Dr Peter Young, CCLRC/RAL

  11. User Routines • Do you have IDL routines for your CDS analysis that you’d like to share? • Are there any new IDL routines that you’d like to see? • Routines can be added to CDS branch of Solarsoft • Requirements: • provide header in standard format • check that obvious errors are caught Dr Peter Young, CCLRC/RAL

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