When downloading Lunar Reconnaissance Orbiter LRO NAC images from the website https://pilot.wr.usgs.gov/ a significant portion of them have no useful data -- they have a sort of plaid pattern. Does anyone know what's going on here? Are these some kind of dark image for sensor calibration? Some examples of the affected images:

M159144761RC, M161499633RC, M156784061RC, M156784061LC, M165038842RC, M169754968RC, M167400488LC, M167400488RC, M176828812LC, M176828812RC, M182720706RC, M180361835RC, M1135749148RC, M185079577RC

some LRO images

Example of some "plaid patterns":

some dark LRO images which illustrate "plaid patterns"

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    $\begingroup$ I would guess that these are darks for CCD calibration. But usually data from the PDS is already calibrated. $\endgroup$ – Phiteros Feb 7 '18 at 0:20
  • $\begingroup$ @Phiteros, LRO NAC images start out as Experimental Data Records (EDR), then you spiceinit, calibrate, and echo-remove them to make Calibrated Data Records (CDR). These are the EDR. As far as I know, blank data is kept in SPICE kernels but I don't know the details of how that works. $\endgroup$ – foobarbecue Feb 7 '18 at 2:25
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    $\begingroup$ @uhoh, wow, you went to town on that edit! I'll make all those image numbers into links to .tif files shortly here. $\endgroup$ – foobarbecue Feb 7 '18 at 2:27
  • $\begingroup$ Some of those definitely look like some form of bias calibration. You can see the telltale brighter values in the top right. $\endgroup$ – Phiteros Feb 7 '18 at 2:57
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    $\begingroup$ No worries, it's a 1-minute job in a decent text editor. $\endgroup$ – foobarbecue Feb 7 '18 at 3:44

These images are taken during local night. i.e. LRO is flying over an area of the moon which is not illuminated by the sun at that time. An easy way to confirm this is to click on the "info" icon next to the image in USGS Pilot, and look at the "local solar time" field. If the time is between about 06:00 (6am) and 18:00 (6pm), you will see a dark image or a plaid pattern. The plaid pattern presumably ocurrs because the brightness is nearly uniform at the CCD, and processing has adjusted the range of the displayed images so that small variations in brightness (and small errors in calibration) are amplifed.

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