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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.