This page (revision-7) was last changed on 07-Dec-2016 14:14 by PeterYoung

This page was created on 07-May-2008 18:05 by PeterYoung

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Eis_prep
Eis_prep

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[{ALLOW edit EISMainUsers}]
[{ALLOW view Anonymous}]
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For full CCD spectra, a different approach is used. Sections of the CCD have been identified where there are no (or very weak) emission lines and so it can be assumed that the background here represents a measure of the CCD background. The regions are then averaged to yield the background level which is subtracted from the spectra.
It is to be noted that both of these methods will yield some pixels with negative DN values. For window data it will only be 1 % of pixels because of the method used, but for full CCD spectra it can be up to 50 % of pixels if the raster contains very weak emission (e.g., coronal holes or off-limb spectra). ''The default mode for eis_prep sets pixels with zero or negative DN values to be missing data.'' This is because it is not possible to assign a photon noise error to the data points. (Note that negative DN values are expected since, if there are zero solar counts, then the uncertainty in the CCD counts will be 0 +/- read noise.)
By setting the /RETAIN keyword in eis_prep, pixels with zero or negative DN values will not be flagged as missing. The errors for the pixels will be set to the dark current error estimate (see Step 6).
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Spectrometer (CDS) data-sets ([Thompson et al., 1998|http://solar.bnsc.rl.ac.uk/swnotes/cds_swnote_46.pdf]; [Pike
& Harrison, 2000|http://adsabs.harvard.edu/abs/2000A%26A...362L..21P]). For CDS data processing it was typical
Spectrometer (CDS) data-sets (Thompson et al., 1998; Pike
& Harrison, 2000). For CDS data processing it was typical
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with an error estimate for the dark current. This varies from 2.24 to 2.37 DN for the four CCD quadrants.
with an error estimate of the dark current of 2.5 DN.
This page (revision-7) was last changed on 07-Dec-2016 14:14 by PeterYoungTop