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CDS Users’ Meeting, Sep 2005CDS Users’ Meeting, Sep 2005

Tips and Tricks for analysing CDS Tips and Tricks for analysing CDS datadata

Dr Peter YoungDr Peter YoungSOHO/CDS Project ScientistSOHO/CDS Project Scientist

CCLRC Rutherford Appleton LaboratoryCCLRC Rutherford Appleton Laboratory

Dr Peter Young, CCLRC/RALDr Peter Young, CCLRC/RALSO

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OverviewOverview

• Photon statisticsPhoton statistics• Calibration uncertaintyCalibration uncertainty• Cosmic raysCosmic rays• NIS1-NIS2 alignmentNIS1-NIS2 alignment• Burn-in correctionBurn-in correction• SOHO rollSOHO roll

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Photon statisticsPhoton statistics

• vds_calib yields photons/s/pixelvds_calib yields photons/s/pixel

• use Bill’s expression to yield fractional noise (use Bill’s expression to yield fractional noise (ffNN))

– √√(2N + n)/N(2N + n)/N• proceed with calibration to yield intensity unitsproceed with calibration to yield intensity units

• apply apply ffNN to yield error on intensityto yield error on intensity

Dr Peter Young, CCLRC/RALDr Peter Young, CCLRC/RALSO

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Calibration uncertaintiesCalibration uncertainties

• For large counts, calibration uncertainties dominate over For large counts, calibration uncertainties dominate over photon statistic errorsphoton statistic errors

• Difference between Difference between relativerelative and and absoluteabsolute calibration calibration uncertainties (e.g., line ratios vs. DEM)uncertainties (e.g., line ratios vs. DEM)

• Relative uncertainty is Relative uncertainty is λλ dependent and varies from 12 to 29% dependent and varies from 12 to 29%

• For absolute uncertainty, additional contribution of 13%For absolute uncertainty, additional contribution of 13%

• See Sect. 3.3 of Lanzafame et al. (2005, A&A, 432, 1063) for See Sect. 3.3 of Lanzafame et al. (2005, A&A, 432, 1063) for more detailsmore details

Dr Peter Young, CCLRC/RALDr Peter Young, CCLRC/RALSO

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Cosmic Ray RemovalCosmic Ray Removal

• Three routines available in softwareThree routines available in software

– cds_new_spikecds_new_spike– cds_clean_expcds_clean_exp– cds_cleancds_clean

• Make sure to set $CDS_EXTERNAL for routines to run quicklyMake sure to set $CDS_EXTERNAL for routines to run quickly

Dr Peter Young, CCLRC/RALDr Peter Young, CCLRC/RALSO

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CDS Users’ Meeting, Sep 2005CDS Users’ Meeting, Sep 2005

Fill or not to fill?Fill or not to fill?

• The cosmic ray routines allow two options for dealing with CRsThe cosmic ray routines allow two options for dealing with CRs

1.1. fill with median value of surrounding pixelsfill with median value of surrounding pixels

2.2. flag as missing dataflag as missing data

• The latter is best option for preserving statisticsThe latter is best option for preserving statistics

Dr Peter Young, CCLRC/RALDr Peter Young, CCLRC/RALSO

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CDS Users’ Meeting, Sep 2005CDS Users’ Meeting, Sep 2005

NIS1-NIS2 alignmentNIS1-NIS2 alignment

• NIS1 and NIS2 images are not spatially coincidentNIS1 and NIS2 images are not spatially coincident

IDL> gt_nis_alignment, qlds, x, yIDL> gt_nis_alignment, qlds, x, y

• Pre-loss: X~1”, Y~2”Pre-loss: X~1”, Y~2”• Post-loss: X~1”, Y~3-7”Post-loss: X~1”, Y~3-7”

• Depends on Y-location!Depends on Y-location!

Dr Peter Young, CCLRC/RALDr Peter Young, CCLRC/RALSO

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CDS Users’ Meeting, Sep 2005CDS Users’ Meeting, Sep 2005

Burn-in CorrectionBurn-in Correction

• Narrow slit burn-in is not fully corrected for in the CDS Narrow slit burn-in is not fully corrected for in the CDS softwaresoftware

• Affects both line width and intensityAffects both line width and intensity

IDL> result=get_width_corr(’22-sep-2005’,629.7)IDL> result=get_width_corr(’22-sep-2005’,629.7)

• Currently 20% for O V Currently 20% for O V λλ629.7629.7

Dr Peter Young, CCLRC/RALDr Peter Young, CCLRC/RALSO

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CDS Users’ Meeting, Sep 2005CDS Users’ Meeting, Sep 2005

SOHO RollSOHO Roll

• To find out SOHO roll angle on a particular date:To find out SOHO roll angle on a particular date:

IDL> angle=get_soho_roll(’22-sep-2005’)IDL> angle=get_soho_roll(’22-sep-2005’)

• To make CDS images appear in the usual format, useTo make CDS images appear in the usual format, use

IDL> data=gt_windata(a,0,/invert)IDL> data=gt_windata(a,0,/invert)

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User RoutinesUser Routines

• Do you have IDL routines for your CDS analysis that you’d like Do you have IDL routines for your CDS analysis that you’d like to share?to share?

• Are there any new IDL routines that you’d like to see?Are there any new IDL routines that you’d like to see?

• Routines can be added to CDS branch of Routines can be added to CDS branch of SolarsoftSolarsoft

• Requirements:Requirements:– provide header in standard formatprovide header in standard format– check that obvious errors are caughtcheck that obvious errors are caught