The Martian Sky |
The Martian Sky |
Oct 11 2009, 06:41 PM
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IMG to PNG GOD Group: Moderator Posts: 2254 Joined: 19-February 04 From: Near fire and ice Member No.: 38 |
I have been attempting to make computer generated images of the Martian atmosphere, both as seen from the surface and from space. To check the results I have been looking for spacecraft images to use as ground truth. I have found lots of images - by far the best ones I have found are from UMSF in this thread: http://www.unmannedspaceflight.com/index.php?showtopic=3324
However, I'm always looking for more ;-). So if anyone knows of more and/or better images I'm interested in them. What would be best are mosaics showing the sky from the horizon (with the horizon/surface visible) and towards the zenith. The sky varies a lot because of variable amount of dust but the general impression I get is that the sky is bright near the horizon (usually brighter than the surface) but gets much darker higher in the sky. There is probably a fairly large, bright area in the sky near the sun, possibly less reddish (lower R/B ratio) than parts of the sky farther from the sun. I'm already getting fairly interesting results, this one has a field of view of 90 degrees: (needless to say this one is 'overexposed' near the horizon; dynamic range is sometimes a problem) The problem is that even though this may not be bad the limb currently appears far too bright as seen from space : This shows that my atmospheric model is erroneous in some way - I suspect that as seen from the surface the Martian sky is darker high above the horizon than I have been assuming. |
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Jan 26 2014, 11:06 PM
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Senior Member Group: Members Posts: 1669 Joined: 5-March 05 From: Boulder, CO Member No.: 184 |
Nice animation above by Bjorn from 2009. Here's what I get so far for an animated whole sky simulation with the sun dropping lower in the sky.
Full Resolution Animation The animation shows just the scattered light so I'll want to add the actual sun in as well. Some increased blueness shows up at low phase angles. I'm basing this (wavelength dependent extinction, single scattering albedo and asymmetry parameter) on a Pollack et al paper and using a Henyey-Greenstein (HG) function. A second HG function is used to add some back-scattering. Dynamic range of brightness is compressed a bit for display. This post is a continuation of a discussion I started in Earth Observations, with Mars related results now being posted in this thread. The latest version shown here has somewhat improved handling of multiple scattering and has the sun's disk added in. To help with rendering, phase functions for different wavelengths (red/blue) can be checked in a 2014 paper mentioned in the post linked below. It's interesting that the phase function near 90 degrees scattering angle is about the same for red and blue implying the sky should be gray at right angles to the sun, and only turning reddish at roughly 130 degrees. The blueness in the glow around the sun is predicted to be showing up at scattering angles less than about 28 degrees. http://www.unmannedspaceflight.com/index.p...mp;#entry212746 Perhaps though a fuller consideration of reflection from the ground would shift things more to the red at somewhat smaller phase angles. -------------------- Steve [ my home page and planetary maps page ]
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