SECCHI_PREP Defaults for EUVI (1)

By default, SECCHI_PREP applies a set of corrections:

• Trim non-imaging pixels
• Subtract bias
• Divide by exposure time (in seconds)
• Normalize to the "open" filter wheel position
• Convert DN to number of photons

Comments:

• The first two (trim and bias) are almost always desirable
• Exposure time correction is often useful (e.g. for movies)
• Normalizing to "open" is rather arbitrary (EIT "heritage")
• Conversion to photons is useful for photon statistics
      - Less useful with normalization to "open"

SECCHI_PREP Keyword Examples

• Example 1: basic near-raw images (just bias removed):
  /normal_off, /exptime_off, /dn2p_off
• Example 2: exposure time corrected (1 sec exp. equiv.):
  /normal_off, /dn2p_off
• Example 3: convert to number of photons per pixel:
  /normal_off, /exptime_off

Notes:

• /calfac_off is a synonym for /dn2p_off
• /precommcorrect_on should not be necessary anymore
• euvi_prep is a lower level routine (does not trim)

Despiking (Cosmic Ray Removal)

• Keyword /cosmic_on in secchi_prep does nothing yet
      - Plan to implement the procedure below
• For now, you can use despike_gen as follows
  secchi_prep,file,d,i,/normal_off,/dn2p_off,/exptime_off
  d = despike_gen(d,tn=8)
• Notes:
     - The parameter tn=8 works fairly well for images that have not been re-scaled in secchi_prep (as above)
     - In bad cases, repeat the step: d=despike_gen(d,tn=8)

Flat Fielding, "De-gridding" (1)

• Flat field at each wavelength based on 14 images taken at pseudo-random offpoint locations
• "Raw" flats:
     - Reveal shadowing by mesh in filter wheel filter
     - Faint residual solar image
     - Noisy near edge of field (due to low photon counts)

• Processed flats: Mesh-shadowing only
     - Peak-peak amplitude: 4% of signal (<< than EIT)
     - Less noisy

"Raw" Flat (EUVI-B @ 171)

Processed: Mesh-Shadowing Only

Flat Fielding, "De-gridding" (2)

• Flat fielding often not neccessary or desirable:
• CCDs have good cosmetics
• Amplitude of mesh shadow ("grid") pattern is only 4%
• Flat fielding can add noise, especially far off-disk
• SolarSoft currently has flats for 171 and 304:
• $SECCHI_CAL/20080416_*fCeu?.fts
• "Raw" (_raw*) and processed (_grd*)
• Flats for 195 and 284 are coming
• By default, secchi_prep applies a dummy flat (/calimg_off turns it off)
• To apply, e.g., a processed flat for EUVI-Behind 304:
  calfile = 'SECCHI_CAL/20080416_grd304_fCeuB.fts'
  secchi_prep,...,calimg_filename=calfile

Image Deconvolution with PSF

• SolarSoft routine euvi_psf.pro creates a best-estimate PSF for any given telescope (A or B) and wavelength
• PSF includes both a core (from lunar transit results) and extended wings (diffraction model fitted to flare observations)
• Use: psf = euvi_psf(2048,image_hdr)
• Direct deconvolution of 2k x 2k image:
  fft_psf = fft(shift(euvi_psf(2048,hdr),-1024,-1024),1)
  image_deconv = float(fft(fft(image,1)/fft_psf,-1))
• Result somewhat noisy, enhanced cosmic ray hits
• MEM deconvolution with image_deconvolve (T. Metcalf)
• Reduces noise and cosmic rays; slow

304 Image Deconvolved with PSF

Scaling, Aligning, etc.

Routines in "sbrowser" ssw package:

• Scale and co-align image arrays for 3D work
wcs = fitshead2wcs(index)
disp = {naxis:[480L,640L],delt_1:200.,rpix:[240.,320.], $
rval:[-90.,20.,1.],carr:0}
image = sb_gtrans(image,wcs,disp=disp)
• disp controls transformation: put location at rval [longitude,latitude,dist_from_suncenter_in_rsun] into pixel at rpix, using platescale of delt_1 pixels per solar radius. carr: 0=heliographic(earth), 1=carrington lon.
• Keywords:
• /helio : put solar N up (default: ecliptic N up)
• /sc : put plane betw. S/C horizontal. Requires swcs=wcs_of_other_observatory
• interp: 0=force nearest neighbor, 1=force bilinear, 2=force cubic

Intensity Scaling, Display

• Byte scaling of images
col = {min:0.,max:1e3,gam:0.5}
bytimage = sb_bytscl(image,col)
• Scales intensity values between min and max in original image into 0-255
• positive gam: classical gamma, e.g. 0.5=square root
• negative game: log scaling: evenly scale abs(gam) orders of magnitude into 0-255
• if min eq -max: scale symmetrically about zero
• sbrowser: EUVI image browser
• supports TRACE besides MDI and EIT
• includes simple tie-point tool suitable for 3D displays
• for general browser, use FESTIVAL (better support)

EUVI Movies

3-D movie: ssw routine to create series of frames:
ts = '2007-05-16T16:00'
te = '2007-06-16T18:00'
disp : see notes for sb_gtrans
lut = # of color table entry (in sb_colors1.tbl)

• Example 1: Anaglyph movie in 171
euvi_movieframes,ts,te,'outdir', $
naxis=disp.naxis,delt_1=disp.delt_1,rval=disp.rval, $
obs=['a','b'],wave=[171,171],lut=[7,5] ; 7=cyan,5=red
• Example 2: A/B side-by-side, 3 wavelength overlay
euvi_movieframes,ts,te,'outdir', /TWOPANEL, $
naxis=disp.naxis,delt_1=disp.delt_1,rval=disp.rval, $
wave=[171,195,284],lut=[1,2,3] ; 1-4:"standard" EIT tables
• Use tool such as QuickTime Pro to create movie file

Spectral Response Data & Software

Effective area
setenv,'EUVI_RESPONSE='+getenv('SECCHI_CAL')+'/euvi_response'
restgenx,file='$EUVI_RESPONSE/ahead_sra_001.geny',a

• a.lambda[n], a.area[n,4,4]
• for 4 channels (a.wavelnth) x 4 filters (a.filter)
Temperature response
• flux = euvi_flux(T, index)
• Reads flux data files (instrument effective area folded with Chianti spectra for range of temperatures)
• Keywords: /photons, /Feldman, /Apec (see documentation header)
• Use secchi_prep with /normal_off for any response work