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Image name: Straylight_Grills_II.png (click image to enlarge)
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Date submitted: 14-Nov-1995
L. Acton
14-Nov-95
SXT THIN ALUMINUM STRAYLIGHT GRILL PATTERNS - II
This figure examines the grill properties of 3 Al.1 terminator images.
0 2-OCT-95 08:49:06 QT/H Open /Al.1 Half Norm C 23 2668.0 512x512
1 3-OCT-95 22:05:56 QT/H Open /Al.1 Half Norm C 23 2668.0 512x512
2 10-OCT-95 11:16:23 QT/H Open /Al.1 Half Norm C 23 2668.0 512x512
The upper LH panel is a single image that has been dark-subtracted and
despiked but not otherwise smoothed. The grill patterns and a slight
vestige of the "network" pattern is evident.
The upper RH figure is prepared preparing all 3 images as the one in the
upper left and 3 corresponding SFC (highly smoothed) images. The 3
difference images from these 3 pairs of images were summed, rotated 32
degrees CW and display in the upper right. The area analyzed is indicated
by the black box.
X and Y sums were prepared from the boxed area. These were then fourier
analyzed using SLOFO.PRO to learn the dominant periodicities and then
summed modulo that period to form the average profiles of the grill
structures. The grill structure with lines running horizontal in the UR
panel is strong and well defined. Two periods of that structure are
displayed in the lower left. Both X and Y grills had the same primary
period, 10.46*2=20.92 FR pixels. This is in good agreement with the
results presented in Straylight_Grills_I. The angle is also in agreement.
Although the Y (lines vertical) grill is very faint to the eye the summed
signal shown in the LR figure leaves no doubt that it is there. However,
the inner sub structure appears to be somewhat different.
The NE-SW (-13 degrees) grill structure is also clearly present in the UR
figure. I had concluded in /calibration/Al1_straylight_grills that this
pattern was not stable on the CCD. I now believe that conclusion is
incorrect. However, it does seem that the brightness of this pattern may
be sensitive to pointing.
Conclusions:
1. All these grill patterns are produced by visible straylight.
2. The grill patterns are stable on the CCD.
3. The "network" pattern is still present after 16-Aug-95.
4. The "network" pattern still moves around in a, so far, unpredictable
manner.
5. Corrections for the grill patterns should be included in the Al.1 SFCs.
