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Jan 6 2006, 08:55 PM
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#101
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Senior Member Group: Members Posts: 2454 Joined: 8-July 05 From: NGC 5907 Member No.: 430 |
ADMIN NOTE: Please note that this topic was unavoidably poltical before the 'No Politics' rule. Please restrict future comments to the mission/spacecraft/news updates etc.
WHAT'S NEW Robert L. Park Friday, 6 Jan 06 Washington, DC DEEP SPACE CLIMATE OBSERVATORY KILLED. http://bobpark.physics.umd.edu/index.html -------------------- "After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance. I see that such intercourse long continued would make one thoroughly prosaic, hard, and coarse. But the longest intercourse with Nature, though in her rudest moods, does not thus harden and make coarse. A hard, sensible man whom we liken to a rock is indeed much harder than a rock. From hard, coarse, insensible men with whom I have no sympathy, I go to commune with the rocks, whose hearts are comparatively soft." - Henry David Thoreau, November 15, 1853 |
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Oct 30 2016, 03:17 PM
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#102
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Senior Member Group: Members Posts: 1669 Joined: 5-March 05 From: Boulder, CO Member No.: 184 |
Thanks fredk. The funny thing is that once I inadvertantly ran this without air and the ocean indeed looked darker. This was a goofy accidental run (image below) with Mars atmospheric pressure and Earth aerosols. The display looks somewhat reasonable, though the water looks too gray and thus would need more work. The ocean (outside of sun-glint areas) should be around a factor of 10 darker for the case of few aerosols in the sky and sediment in the water, though it could be a smaller ratio otherwise. The color would also vary depending on sediment content and the like, ranging from blue-green to sometimes more brown.
Note that sun-glint over water is different from the opposition effect that happens over the land. The sun-glint region is controlled by wave action, though I suppose this could be extended a bit depending on forward scattering by atmospheric aerosols then reflecting off of the water, diffused again by wave slopes. -------------------- Steve [ my home page and planetary maps page ]
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Oct 31 2016, 05:02 PM
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#103
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Senior Member Group: Members Posts: 4256 Joined: 17-January 05 Member No.: 152 |
The funny thing is that once I inadvertantly ran this without air and the ocean indeed looked darker. This was a goofy accidental run (image below) with Mars atmospheric pressure and Earth aerosols. Thanks a lot, Steve. This is very cool: Earth without air. Comparing your with and without air views, I can certainly see your point about the oceans being dominated by light from the sky - the Earth is the blue planet because our sky is blue. Apart from the continents, I can almost imagine these views as fish-eye views of the sky with patchy clouds from the ground. I'm still curious about one detail: switching off the air makes the oceans much darker, but how much of that darkening is due to the removal of scattered light in the air above the water, and how much is due to the removal of sky light reflected back up from the water's surface (ie, the removal of a sort of wide-angle "sky glint")? My guess would be that the former would dominate, since the water's surface is not a very good reflector (apart from large angles of incidence). |
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Nov 1 2016, 05:20 PM
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#104
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Senior Member Group: Members Posts: 2530 Joined: 20-April 05 Member No.: 321 |
The question of what Earth would look like without its atmosphere is potentially ambiguous, it could mean:
1) What would the view from space be if the light reflecting off the surface/ocean were not altered on its path up to the camera. 2) What would the surface/ocean itself look like if it had a black sky above it. 3) Both (1) and (2). A related example: In towns/cities when there is snow on the ground and cloud cover overhead, night can be astonishingly bright because streetlights reflect off the clouds, and that light reflects off the snow, in what is effectively a damped infinite feedback loop. The situation looking at normal, natural surfaces from above has some degree of this, with the sky altering how the surface looks and the surface, surely, altering how the sky looks. If you wanted to address (1), an "easy" way to do it would be to ground-truth the DSCOVR images by taking images of isotropic surfaces (e.g., the ocean, snow, certain deserts). Compare your camera's color values with DSCOVR pixels of the same surface unit and determine the function that relates the two. Then apply the inverse function to DSCOVR images of the whole planet. FWIW, I recently did something like this with images of Mercury that I took in a daytime sky. I subtracted the R, G, and B values of the background sky from the whole image, including the portions containing Mercury. The result gives a black sky and a brownish-grey Mercury approximating the colors seen by Messenger. That is the "up looking" version of what (1) would be the "down looking" version of. |
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