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On the Bias Jumps » History » Version 2

Eli Rykoff, 10/31/2013 04:58 PM

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h1. On the Bias Jumps
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-Eli Rykoff
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Something strange is going on with the bias jumps at 2048...
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I'm taking as an example 180985, CCD 41, somewhat arbitrarily.
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I use swarp to subtract the sky and rebin to a 2" scale to highlight the sky levels.  This is the finalcut image which shows the problem:
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|!{width=750px}180985_41_finalcut.jpg!|
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But if we go back to the raw_obj image (same scaling) which has had DECam_crosstalk run on it then it looks fine!  (Well, it could use a good flat-fielding).
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|!{width=750px}180985_41_raw_obj.jpg!|
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Similarly, the raw-raw image looks fine (though it's hard to get the scaling right because of the dynamic range).
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So this is being inserted into the image somewhere along the line...Alex suspects the flat field...
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Looking at the flat field applied to this image:
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https://desar2.cosmology.illinois.edu:7443/DESFiles/desardata/OPS/red/20130725170742_20130217t0227/flatcor/flatcor_i_41.fits 
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And rebinning we see:
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|!{width=750px}flatcor_41_problem.jpg!|
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A-ha!  A bias jump made its way into the flat field and has now corrupted the downstream images.