1 / 11

Tips and Tricks for analysing CDS data

Tips and Tricks for analysing CDS data. Dr Peter Young SOHO/CDS Project Scientist CCLRC Rutherford Appleton Laboratory. Overview. Photon statistics Calibration uncertainty Cosmic rays NIS1-NIS2 alignment Burn-in correction SOHO roll. Photon statistics. vds_calib yields photons/s/pixel

bette
Télécharger la présentation

Tips and Tricks for analysing CDS data

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related