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Eis_prep
Eis_prep

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At line 12 added 16 lines
The standard way of calling eis_prep is:
IDL> eis_prep, filename, /default, /save
which will create the level-1 FITS file and associated error FITS file in the working directory. Additional keywords that you may want to use are:
/quiet - eis_prep runs without popping up information widgets
/retain - see Step 2 discussion below
/noabs - calibration is not performed (Step 6 below), so the final units are DN
/photons - instead of erg/cm2/s/sr/Angstrom, the final units will be photons/cm2/s/sr/Angstrom
The full list of keywords is given in the header of the eis_prep routine.
At line 49 added 6 lines
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.
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).
This page (revision-7) was last changed on 07-Dec-2016 14:14 by PeterYoungTop