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Global True Color View Of Venus?
machi
post Oct 15 2010, 09:26 PM
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It looks like old UV image from Pioneer Venus.
I think this one:
http://www.nasaimages.org/luna/servlet/det...ioneering-Venus


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CJSF
post Oct 16 2010, 12:26 AM
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QUOTE (scalbers @ Oct 15 2010, 05:12 PM) *
Is this web page with a Venus image showing some real data or an artistic work?

http://rocksfromspace.open.ac.uk/Venus.htm

If I can find a "full" Venus image I can try to see what it looks like with Science On A Sphere.

Thanks,

Steve


I agree- that is a UV image of Venus. True color images look pretty much like a billiard ball. See this thread for more information.

CJSF


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4th rock from th...
post Oct 16 2010, 03:33 PM
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Here's my Pioneer Venus image galery: http://www.astrosurf.com/nunes/explor/explor_pvenus.htm
Most of the images I had acess to were very degraded and from old magazines and books, but at least they are organized by date.
I think most of the images were taken with the Near UV (365nm?) filter, but the camera was capable of operating on other wavelengths.


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Phil Stooke
post Oct 16 2010, 04:18 PM
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Nice set of pictures! The last image on your page, the one with the question mark, looks like it is probably from Mariner 10.

Phil


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scalbers
post Oct 16 2010, 05:53 PM
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QUOTE (CJSF @ Oct 16 2010, 12:26 AM) *
I agree- that is a UV image of Venus. True color images look pretty much like a billiard ball. See this thread for more information.

CJSF

Right, though perhaps it might be interesting to try colorizing the Pioneer UV images by using information from missions like Venus Express and MESSENGER? Perhaps some subtle color might be visible and would give us a reasonable approximation of a "global true color" image.


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ugordan
post Oct 16 2010, 06:01 PM
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It's not merely about color, it's about contrast. And quite frankly, in visible wavelengths there just isn't any appreciable contrast.


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scalbers
post Oct 16 2010, 06:06 PM
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Yes indeed the actual contrast is much more subtle than in the Pioneer UV images. For example Ricardo Nune's images show Venus Express processed into approximate RGB, showing rather subtle hues. This procedure might be applied to the Pioneer UV images perhaps, even though these are monochromatic. It's kind of interesting to me to consider whether the human eye can perceive at least some faint contrast/color with Venus. Perhaps it relates to violet light sensitivity that can vary between individuals.

I haven't found too many spectra of Venus or its cloud features. Here is a VIMS spectrum of Venus for reference, though I'm unsure of the field of view.

http://vims.artov.rm.cnr.it/data/res-ven.html

More discussion is here:

http://www.unmannedspaceflight.com/index.p...amp;#entry20237

Here is a book excerpt showing illustrations of visual observations of Venus' clouds, so the contrast is detectable to some, seen right here from planet Earth:

http://books.google.com/books?id=LqwUuMYIE...ope&f=false


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EDG
post Oct 17 2010, 12:52 AM
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Has anyone actually tried to make a true-colour map of Venus' surface directly from the Magellan radar data? I know there's separate topo data available but IIRC that was pretty low resolution - is it possible to extract data directly from the SAR images (e.g. pulse travel time) to get higher-res altimetry? And then make a global topography map from that, coloured as if we were looking at basalts?
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nprev
post Oct 17 2010, 01:37 AM
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I don't know how you could ever make a 'true color' map of the surface of Venus. We've only seen a very few small spots from the Venera probes--not enough to generalize about the entire planet--and there's no way to extract color from radar data. If that wasn't enough, lighting conditions, surface compositions, etc. undoubtedly do vary for a variety of reasons, so even if we could somehow obtain visible-light surface images of the entire surface that wouldn't necessarily correspond with what the human eye would actually see.

Even doing this for Mars is a formidable challenge; there's inevitably some degree of interpolation/assumption involved, as our resident imagemages will surely attest.


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4th rock from th...
post Oct 17 2010, 01:26 PM
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QUOTE (scalbers @ Oct 16 2010, 07:06 PM) *
...It's kind of interesting to me to consider whether the human eye can perceive at least some faint contrast/color with Venus. Perhaps it relates to violet light sensitivity that can vary between individuals...


My personal experience is positive. I can see "something" on Venus through a telescope. My best description would be of a white crescent with some brighter parts. Those bright spots look slightly fluorescent. But it's not obvious, the contrast is very subtle and there's no color at all. Like looking at snow deposited over snow.

I think it has to do with the Rod cells on our eyes. Those are most sensitive to wavelengths of light around 498 nm and are responsable for the Purkinje effect http://en.wikipedia.org/wiki/Purkinje_effect. Perhaps something like that works for Venus.


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EDG
post Oct 17 2010, 07:02 PM
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QUOTE (nprev @ Oct 16 2010, 06:37 PM) *
I don't know how you could ever make a 'true color' map of the surface of Venus. We've only seen a very few small spots from the Venera probes--not enough to generalize about the entire planet--and there's no way to extract color from radar data.


Well, it'd definitely be "simulated true colour". I was thinking more "this is what the surface could look like, assuming basaltic composition". I know that bright (reflective) radar patches aren't necessarily bright in visible light, for example - they're just rough surface (unless they're on mountaintops IIRC, in which case they might actually be pyrite deposits?).

Someone could take a small feature on Venus (e.g. a dome or crater) and translate the radar bright/dark into visible (using appropriate rules like "radar bright = rough surface, radar dark = smooth surface") that would be nice. I guess it's more a space art/visualisation thing than anything "scientific", but it'd be nice to be able to look at a view of Venus and say "that's what we might see if we looked at this feature in visible light".
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tedstryk
post Oct 17 2010, 07:45 PM
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How on earth would that be any less simulated than one based on the Venera pictures?


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scalbers
post Oct 17 2010, 08:59 PM
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QUOTE (4th rock from the sun @ Oct 17 2010, 01:26 PM) *
My personal experience is positive. I can see "something" on Venus through a telescope. My best description would be of a white crescent with some brighter parts. Those bright spots look slightly fluorescent. But it's not obvious, the contrast is very subtle and there's no color at all. Like looking at snow deposited over snow.

I think it has to do with the Rod cells on our eyes. Those are most sensitive to wavelengths of light around 498 nm and are responsable for the Purkinje effect <a href="http://en.wikipedia.org/wiki/Purkinje_effect" target="_blank">http://en.wikipedia.org/wiki/Purkinje_effect</a>. Perhaps something like that works for Venus.

Pretty neat that you've been able to see such features. It seems to me Venus is bright enough so it would work more with cones rather than rods.

While color may not show up with a small crescent, I can speculate that if one can see features from Earth, then orbiting in a spacecraft it would look large enough to have a chance at seeing a slight hue.


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EDG
post Oct 17 2010, 09:20 PM
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QUOTE (tedstryk @ Oct 17 2010, 11:45 AM) *
How on earth would that be any less simulated than one based on the Venera pictures?


I dunno, I didn't say it would be wink.gif
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JohnVV
post Oct 18 2010, 02:53 AM
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QUOTE
Has anyone actually tried to make a true-colour map of Venus' surface directly from the Magellan radar data?

true color - not possible
now a "better" than that old red/orange and yellow/white
http://photojournal.jpl.nasa.gov/jpegMod/PIA00481_modest.jpg
http://photojournal.jpl.nasa.gov/jpegMod/PIA00104_modest.jpg

the color i settled on
http://www.unmannedspaceflight.com/index.p...st&p=164503

now as to clouds
They change SO fast that there is no "real" up to date data
-- artist concept --

that i use a 100% artistic map for it
a link to a artistic thread
http://www.shatters.net/forum/viewtopic.php?f=5&t=16019
( the last post is the above image)

the color is adjusted so that some of the clouds can be seen and it looks like "bright smog"
basically it is darker than if "you" were in orbit looking down at it
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