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24 um latent image removal

Requirements:

Outline of the demo:

In this demo, we remove dark latents from a 24 micron photometry observation using parallel 24 micron observations from the contemporaneous 70 and 160 micron observations. Here are before and after (gzipped postscript) images: old mosaic and new mosaic. Here is another example, in jpeg format (left is before, right is after).

Step by Step Guide

  1. Collect all 24 um BCDs from AOR, or cd into directory where you downloaded them. 

     unix% cd r5315584/ch1/bcd/

  2. Sort into "prime" and "non-prime" images using keywords PRIMEARR = 1 (prime) and PRIMEARR = 2 (not prime). You can look in each individual header separately, but this is how I do it in a more automated fashion. I use the tool "imhead" (available from the unix command line), which is part of the WCS tools package. Type "which imhead" at the unix command line to see if you have that package installed (if it says "command not found," you don't have it) and go install it if necessary. The following series of steps produces a file which lists each file and the value of PRIMEARR for that file. Based on the contents of that file, edit the file lists to reflect those files which are prime and not prime. 

    unix% imhead *bcd.fits | grep PRIMEARR  > aaa
unix% ls *bcd.fits  > bbb
unix% paste bbb aaa  > ccc
unix% cp bbb primelist.txt
unix% cp bbb notprimelist.txt
unix% nedit ccc primelist.txt notprimelist.txt

  3. Make a median image from the non-prime data using "imcombine" from IRAF (or your favorite equivalent). You can also use the prime data if any bright sources have been masked out. 

     iraf% imcombine @notprimelist.txt median.fits

  4. Normalize the median image by dividing by the mean or median value of the image. 

    iraf% imstat median.fits 
iraf% imarith median.fits / VALUE normalizedmedian.fits

  5. Divide each "prime" bcd by the normalized median image. This makes a set of corrected BCDs. 

    iraf% imarith @primelist.txt / normalizedmedian.fits @outputlist.txt

  6. Use the corrected BCDs to make a new mosaic with MOPEX or any other mosaicker.

    before and after (gzipped postscript) images: old mosaic and new mosaic

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