Clouds? |
Clouds? |
Jul 8 2008, 01:38 AM
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#1
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Senior Member Group: Members Posts: 1465 Joined: 9-February 04 From: Columbus OH USA Member No.: 13 |
Was looking at some MGS imagery:
Kind of a low-contrast scene with some darker splotches here and there. Running that through an equalizing filter gives this image: Some surprising detail brought out there--it looks to me like there are small clouds casting shadows on the surface. Can that be right? They could be little hills I suppose. -------------------- |
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Jul 8 2008, 01:49 AM
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#2
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Member Group: Members Posts: 128 Joined: 10-December 06 From: Atlanta Member No.: 1472 |
QUOTE Some surprising detail brought out there--it looks to me like there are small clouds casting shadows on the surface. Can that be right? They could be little hills I suppose. Likely JPEG lossy-compression artifacts. |
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Jul 8 2008, 01:55 AM
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#3
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Senior Member Group: Members Posts: 1465 Joined: 9-February 04 From: Columbus OH USA Member No.: 13 |
Likely JPEG lossy-compression artifacts. The original images are from IMG files (256 pixels per degree MGS images http://www.msss.com/mgcwg/mgm/), only converted to JPG in the final step. I believe IMG files are lossless. -------------------- |
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Jul 8 2008, 01:56 AM
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#4
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Member Group: Members Posts: 213 Joined: 21-January 07 From: Wigan, England Member No.: 1638 |
Some surprising detail brought out there--it looks to me like there are small clouds casting shadows on the surface. Can that be right? They could be little hills I suppose. They look like puffy water-ice clouds; here's a similar image from Icaria Planum. -------------------- "I got a call from NASA Headquarters wanting a color picture of Venus. I said, “What color would you like it?” - Laurance R. Doyle, former JPL image processing guy
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Jul 8 2008, 02:08 AM
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#5
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Senior Member Group: Members Posts: 1465 Joined: 9-February 04 From: Columbus OH USA Member No.: 13 |
They look like puffy water-ice clouds; here's a similar image from Icaria Planum. Interesting comparison. Equalizing that photo shows some similar shadows under those clouds in the expected direction too: -------------------- |
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Jul 8 2008, 04:16 AM
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#6
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Senior Member Group: Members Posts: 3419 Joined: 9-February 04 From: Minneapolis, MN, USA Member No.: 15 |
I dunno -- look at the semi-regular spacing. Personally, I think you've discovered the dust clouds kicked up by the annual thoat drives into the great abattoires of Helium...
-the other Doug -------------------- “The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain
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Jul 8 2008, 11:33 AM
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#7
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Senior Member Group: Members Posts: 1465 Joined: 9-February 04 From: Columbus OH USA Member No.: 13 |
I dunno -- look at the semi-regular spacing. Personally, I think you've discovered the dust clouds kicked up by the annual thoat drives into the great abattoires of Helium... Looks somewhat less than semi-regular to me, if that isn't an oxymoron! Anyway, what do you think might cause semi-regular artifacts (other than said helium)? BTW, here's the location of the image (arrow) on a map of water-ice cloud opacity predicted for early northern summer: *from Malin et al, "Climate, weather, and north polar observations from the Mars Reconnaissance Orbiter Mars Color Imager," Icarus 194 (2008) So it seems to be in the area of likely suspects at least, on the north slope of the plateau of the Tharsis volcanoes. The striations near the top of the image are part of Ceraunius Fossae. A paper, THE SEASONAL BEHAVIOR OF WATER ICE CLOUDS IN THE THARSIS AND VALLES MARINERIS REGIONS OF MARS: MARS ORBITER CAMERA OBSERVATIONS noted clouds in this area: QUOTE Clouds were also seen around 12° S latitude, 100° W longitude, in the region of Syria Planum, near 27° N latitude, 107° W longitude, near Ceraunius Fossae at 26° N latitude, 93° W longitude...
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Jul 8 2008, 11:42 AM
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#8
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Member Group: Members Posts: 128 Joined: 10-December 06 From: Atlanta Member No.: 1472 |
The original images are from IMG files (256 pixels per degree MGS images http://www.msss.com/mgcwg/mgm/), only converted to JPG in the final step. I believe IMG files are lossless. I'm not sure. I agree, IMG per se is lossless, but MOC had the ability to compress images on board using Walsh-Hadamard or Discrete Cosine techniques, which are lossy. I wonder whether you can see the same low-contrast, semi-regular patterning in other MOC wide-angle images. |
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Jul 8 2008, 11:59 AM
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#9
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Senior Member Group: Members Posts: 3648 Joined: 1-October 05 From: Croatia Member No.: 523 |
I don't see these as compression artifacts, the features very much look like real fuzzy bright objects with corresponding darker shadows in the right places. DCT doesn't do that, it just produces blocky artifacts more or less.
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Jul 8 2008, 01:55 PM
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#10
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Senior Member Group: Admin Posts: 4763 Joined: 15-March 05 From: Glendale, AZ Member No.: 197 |
I don't think there is any question that we are looking at clouds in both images.
-------------------- If Occam had heard my theory, things would be very different now.
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Jul 8 2008, 02:02 PM
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#11
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Senior Member Group: Members Posts: 1465 Joined: 9-February 04 From: Columbus OH USA Member No.: 13 |
I wonder whether you can see the same low-contrast, semi-regular patterning in other MOC wide-angle images. Here's one of interest, from a simulated view from MRO as it was approaching the Phoenix site the day after the landing: So there's a bit of the "cloud" effect on the left but not so much elsewhere. Could that be an area where ground ice is subliming and condensing again at height? Unfortunately there's a bit of a dataset problem around the Phoenix site, approximately at the center of this MGS mosaic: Looks like some inconsistent lighting on the stitched-together sections. Also, maybe clouds were there for one pass and absent the next? Here is what MRO was looking at just a minute or so later: Some pretty large clouds? Anyway, there are plenty of different kinds of artifacts (stitching, posterization, dropouts, etc.) but not compression per se, IMO. Note that the HIRISE field of view is much less than this image (like 1/50th the height). -------------------- |
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Jul 8 2008, 04:09 PM
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#12
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Senior Member Group: Members Posts: 3419 Joined: 9-February 04 From: Minneapolis, MN, USA Member No.: 15 |
I wouldn't be at all surprised to see clouds around the Phoenix site. In fact, I'm pretty certain Phoenix herself captured some images of clouds from the ground. Here's a highly downsampled image from Sol 5:
This is just one of several sky images from that sol. They all show patterning in the sky that seems to suggest clouds, to me. Besides, we're in the Land of the Polar Hood Clouds. This latitude on Mars has been observed from Earth as developing cloud decks which regularly obscure the scene from telescopic observers. -the other Doug -------------------- “The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain
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Jul 9 2008, 09:15 AM
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#13
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Senior Member Group: Members Posts: 1870 Joined: 20-February 05 Member No.: 174 |
.....the annual thoat drives into the great abattoires of Helium.......
I can imagine Tars Tarkas having to file an environmental impact statement on that, and verifying to PETA that no thoats were abused during the drive. |
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Jul 9 2008, 05:54 PM
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#14
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Senior Member Group: Members Posts: 1465 Joined: 9-February 04 From: Columbus OH USA Member No.: 13 |
This is just one of several sky images from that sol. They all show patterning in the sky that seems to suggest clouds, to me. Interesting... makes sense, as the subliming H2O has to go somewhere! -------------------- |
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