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[Enceladus] What am I looking at?, Weird distortion here!
EDG
post Nov 28 2010, 05:45 AM
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http://saturn.jpl.nasa.gov/photos/raw/rawi...?imageID=216998



What's going on here? The limb of Enceladus looks like it's all melted like wax! smile.gif

I'm going to hazard a guess at some kind of really strange image saturation from an over-bright Saturn maybe? If so, I've not seen that look so 'curvy' before.

The next image in the sequence is also strange: http://saturn.jpl.nasa.gov/photos/raw/rawi...?imageID=216997
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tasp
post Nov 28 2010, 05:56 AM
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I wonder if spacecraft motion combined with image sensor saturation might be a fuller explanation.

We get through the holiday weekend, I'm sure we'll get the real explanation when the appropriate folks check back in here.

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volcanopele
post Nov 28 2010, 07:34 AM
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Two possible explanations: Either "That's no moon..." or it is as you said, over exposure from Saturn.


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ZLD
post Nov 28 2010, 07:36 AM
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This looks like image bleed to me. The description tells us that both color wheels are set to clear so this is a straight black and white, with all recordable colors contributing. The affected regions in both photos appears to be roughly the same region along the edge of Saturn and is likely the most intense region in both photos, causing bleeding into the edges of Enceladus. Dropping the gamma and trying a few other tricks turns up little around the edges. Seems to be a case of overexposure.

After looking at some of the other photos taken on that date, it seems like the camera was possibly in need of a calibration as well.
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ugordan
post Nov 28 2010, 12:21 PM
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It wasn't in need of calibration. The exposure was deliberately set for Enceladus high phase imaging.


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dilo
post Nov 28 2010, 02:32 PM
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Very simple explaination, indeed: CCD images suffer of smear in the direction of charge transfer when pixels are close to saturation. In this case, charge shift is vertical and saturation occurs on the brightest part of the Saturn limb...



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EDG
post Nov 28 2010, 06:51 PM
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OK, I suspected as much. I just thought it looked very odd!

What about this one?
http://saturn.jpl.nasa.gov/photos/raw/rawi...?imageID=228082 (If you do a search for Enceladus on the Raw Images page, this is on page 3)

You can barely see Enceladus in the middle of the image, but the rest has all these splotches on it - I'm just wondering if those are just normal dust blotches, or if Cassini had flown through a plume or something shortly before the image was taken?
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volcanopele
post Nov 28 2010, 07:10 PM
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Yep, those are the WAC equivalent of dust donuts. We can remove those via flatfielding when we calibrate this data.


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dilo
post Nov 28 2010, 07:11 PM
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You're right, EDG... you see diffraction images from dust grains on the optics, revealed from diffuse light of sun entering in the optical system... you can barely see also Enceladus jets and contribution from diffuse E-ring light (the night side of Enceladus appear slightly darker than background). Hard to say if dust amount increased from first images, however I see another feature (lens reflection near the center) which I never noticed before! ph34r.gif


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ugordan
post Nov 28 2010, 09:19 PM
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QUOTE (volcanopele @ Nov 28 2010, 08:10 PM) *
Yep, those are the WAC equivalent of dust donuts. We can remove those via flatfielding when we calibrate this data.

Flatfield or subtract out? These are apparently due to scattered light in the optics so they represent additional unwanted light hitting the detector. Doesn't look like something you can just divide out like your normal dustring flatfield variations.


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EDG
post Nov 28 2010, 09:45 PM
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I'm just surprised at how much dust is on the lens (and how good the pictures are that are taken through it despite that!)!
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nprev
post Nov 28 2010, 10:16 PM
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That poses an interesting question, actually. VP, have you guys noticed any changes in the lens contaminants over time (locations, sizes, quantities, etc.?) Doubt that anyone's tracking that, of course, and such changes undoubtedly have occurred for a variety of reasons...but it's a fascinating thought that there just might be a particle or two of Enceladian material on there. wink.gif


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