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Processed SFC Straylight-Correction Images

Image name: All_Filter_Straylight_Figure.png (click image to enlarge)
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Date submitted: 19-Dec-1994


     This figure illustrates the straylight pattern for each of the SXT
analysis filters.  These HR images have all been rebinned to 256x256 for
display here.  They were all taken between 17 and 21 seconds before FEM
sunset and all are DPE=25 (5 sec) exposures.  Location and size of the
sun is indicated by the circles.  The smoothing produced by the lataest
version of SFC_PREP is quite good for HR images through all filters.  It
has not been tested on QR or ND filter images as yet. 

     Two examples are given for Al.1 to demonstrate the effects of
pointingfor this filter.  These two images (A and C) are displayed with
SFD_COMP scaling.  All of the others are scaled linearly.  Image B is a
difference image of SFC A and the corresponding dark_subtracted SFT
image, clipped to +/- 4 DN to show some of the fine scale structure of
the straylight image.  Image E is a corresponding difference image for
Mg3 -- image D.  It was a bit of a surprise that Mg3 shows so much
interesting structure. 

     Panel J illustrates the strength of the straylight signal for each
of the filters.  The righmost Al.1 datum (#6) corresponds to east
offpointed image C.  It is clear why we use AlMg for our dark exposures
and a bit surprising that the straylight for Be is so bad.

     I am now confident with the quality of the smoothed SFT images. 
Since these are prepared from DARK_SUB corrected images they will be
improved further in accuracy when the orbit-corrected dark subtraction
is available.  The streak in the upper right of image A is an example of
spurious over-correction by bad dark frames in the present SDC data

     Once we fully understand the criteria for time to sunset selection
we should be able to fully automate the preparation of SFC correction
images.  The problem of better correction for the Al.1 "network" fine
structure must still be addressed.

					L. Acton  12/19/94

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