Hubble Space Telescope
CTE Tools

QUICK-START ADVICE TO RUN REVERSE CORRECTION

 STEP 1) DOWNLOAD THE SOFTWARE PROGRAM FROM HERE
        For full-frames:
         wfc3uv_ctereverse.F

        For subarrays:
         wfc3uv_ctereverse_wSUB.F
        
        Parallel processing version:
         wfc3uv_ctereverse_parallel.F


 STEP 2) COMPILE THE PROGRAM IN SOME DIRECTORY 
         (NOT NECESSARILY THE EXECUTION DIRECTORY)

        For full-frames:
         g77 wfc3uv_ctereverse.F -o wfc3uv_ctereverse.e  
                     or
        For subarrays:
         g77 wfc3uv_ctereverse_wSUB.F -o wfc3uv_ctereverse_wSUB.e


        For parallel compilation:
         gfortran wfc3uv_ctereverse_parallel.F -o wfc3uv_ctereverse_parallel.e
         -fopenmp

             * you can also use gfortran instead of g77
             * the capital F is important; it invokes the 
               pre-compiler (which it needs)

         Then you can run the program.  This particular routine 
         insists that all the exposures be in the same directory.  
         The executable can be in a different directory, but the
         images you're reading in and operating on *must* be in 
         your current directory.  The reason is that the routine
         takes the first 8+q characters as the image root, then 
         assumes that the 3-character image type designation 
         follows an underscore (ie, _raw, _flt, etc).

         If you do not have access to gfortran or g77, then let
         us know.  It may be possible to construct a few executable
         versions of the routine.


 STEP 3) TEST THE COMPILATION AND LOOK AT OPTIONAL PARAMETERS

         If you run the program without any arguments, you 
         get a list of its arguments:

        For full-frames:
         ./wfc3uv_ctereverse.e
                or
        For subarrays:
         ./wfc3uv_ctereverse_wSUB.e

        For the parallel version:
         ./wfc3uv_ctereverse_parallel.e

         The full README at the top of the program has a detailed
         discussion of the individual arguments.  This quick-start 
         README will only touch on the "standard" operation.


 STEP 4) EXAMPLE OF BASIC OPERATION

         The most basic way of running the routine would be 
         to correct an "_flt" image and generate an "_flc" image. 
         This is akin to what the ACS pipeline produces, but
         the UVIS routine is unable to operate on the _flt alone,
         since the _flt may have had some post-flash electrons
         removed, and these electrons are important to help the
         routine estimate how charge may have been redistributed
         during readout.

         ./wfc3uv_ctereverse.e ibxd90xeq_raw.fits FLC+ 


         Running it without the FLC+ option will generate the
         correction, but the routine will stop after generating
         the "rac" file (the corrected "raw").  Without the FLC+
         flag set, the program will not presume that there is 
         an "flt" file to correct and thus will not generate 
         an "flc" file.  

              *** NOTES for subarray data ***

         a) The subarray routine does not output an "rac" file.

         b) The current routine requires access to pre-scan bias pixels. 

             Subarrays that are currently supported:

             UVIS1-2K4-SUB

             UVIS1-2K2A-SUB

             UVIS1-2K2B-SUB

             UVIS1-2K2C-SUB

             UVIS1-2K2D-SUB

             UVIS2-C1K1C-SUB

             UVIS2-C512C-SUB

         c) There are some subarrays that do not have pre-scan pixels; 
             these are not supported at this time.  However, please see STAN Issue 18  
             for a work-around solution for CTE-correcting unsupported subarrays.

         d) The different timing of the readout-cadence of the various
            subarrays will have some impact on the CTE trailing, but at this point,
            the model appears to work reasonably well.

 STEP 5) EXAMINE THE IMAGES

         Blink between the "flt" and the "flc" images; if you
         output various intermediate images (with the "I+" option), 
         look at what has changed at each stage.


 STEP 6) CONTINUE PROCESSING AS USUAL

         If you made the "flc" images, then just analyze them
         or astro-drizzle them as you would "flt" files.


 ADDITIONAL INFORMATION

         The forward model is also available here:

             wfc3uv_cteforward.F  

         A brief document describing the correction is
         available here:

             wfc3cte_alpha.docx

         The document describes the data used to constrain the 
         model and shows what the model can and can't do.  In 
         particular the model has to be conservative to avoid 
         amplifying readnoise.  As such, it under-corrects faint 
         sources on low backgrounds.  At the same time---and 
         somewhat counter-intuitively---the underlying model 
         over-predicts losses of faint sources on low backgrounds, 
         so users of the forward model should beware of this.  We 
         think we understand the cause of this and improvements 
         are in the works; but the fix will require a tweaking 
         of the algorithm itself, and not just parameter adjustment.


REGISTRATION AND FEEDBACK

         Since this is an alpha version, we reserve the right to 
         make significant changes.  Some improvements are planned, 
         but many will likely come as a result of user input 
         regarding tweaks needed to make it run on different 
         platforms.  As such, we will be updating the code and 
         providing notes below on changes/improvements.

         If you would like to be notified when updates are made,
         send an e-mail to majordomo@stsci.edu with
         "subscribe update_wfc3uv_cte" in the body.
       

Code Updates: