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elakdawalla
I'm creating a website with views of the worlds of the solar system, to scale with each other (it'll march up and down the few orders of magnitude necessary), and I am having a terrible time finding a global view of Venus to include in it that fits the criteria I'm trying to apply. To the extent possible, I am searching for:

- Full-disk, global view
- Minimum phase angle available
- Approximate true color, as would be perceived by a human observing the globe from space

For Venus, the only global views I am finding are either based on Magellan data (radar views, nothing like what a human would see) or are colorized ultraviolet views (which greatly overemphasize the visibility of cloud patterns in the Venusian atmosphere). I've seen the lovely partial global view of Venus on Don Mitchell's website -- that's the sort of thing I'm looking for, but I need a full disk. Does anybody have any suggestions? Anybody done any work with Mariner 10 or Galileo data that produces a nice, realistic view?
BruceMoomaw
You might look into the images from Pioneer 12's spin-scan photopolarimeter -- it took visual as well as UV images of Venus (I've seen one, although it was only a half-Venus). Surely there are a few full-disk visual images of Venus in its 14-year backlog of data.
JRehling
QUOTE (elakdawalla @ Aug 8 2005, 11:53 AM)
I'm creating a website with views of the worlds of the solar system, to scale with each other (it'll march up and down the few orders of magnitude necessary), and I am having a terrible time finding a global view of Venus to include in it that fits the criteria I'm trying to apply.  To the extent possible, I am searching for:

- Full-disk, global view
- Minimum phase angle available
- Approximate true color, as would be perceived by a human observing the globe from space
*


When I wanted the same thing, I once took a global image of Titan and played with the color until it was white instead of orange. Another time, I used Uranus. A blank sphere is a blank sphere...

Alternately, I might take a cylindrical map of Venus and project it onto a sphere.

If you want the genuine article, I don't think any exist, with Earth-based telescopy coming closest.
tedstryk
Yes, but I don't think it took multiband images in the visible. Just visible and UV.
4th rock from the sun
My best attempts, using Mariner 10 "clear" and "blue" filter images:

Click to view attachmentClick to view attachment

These are two versions of the same image. One is processed to show a neutral white Venus, the other was based on the yellow atmosphere seen from the surface.

I've searched the internet for some Venus visible specta and found some interesting data. I'll post some images based on this data but for now my conclusion it that the planet's general color is pale-yellow, with some bright white-blue clouds (better visible in UV).
4th rock from the sun
Click to view attachment

Ok, here's a Venus atmospheric profile. It shows brightness and color variations from 70km up to the surface. On the right part of the image brighness variations were removed and only color changes remain.

When I have time I'll post some more Venus stuff I have around ;-)
elakdawalla
QUOTE (4th rock from the sun @ Aug 8 2005, 04:48 PM)
My best attempts, using Mariner 10 "clear" and "blue" filter images:

*


These are exactly the kind of thing I was looking for, thank you! I'm glad that someone got around to giving this a try.

The atmospheric profile is also very cool information. I assume it could be used to make some simulated views of Venus as you descend through the clouds, just as Rene Pascal did for Titan?

Emily
4th rock from the sun
Check my page http://www.astrosurf.com/nunes/explor/explor_m10.htm for some more images.

But take into account that the human vision is very different from a camera. Venus clouds are VERY bright, so I don't know what a person would see on that conditions.

They can be used on your page if you like, just put a link to my page somewhere and give credit for the image processing ;-)

Yes, you could simulate going down Venus atmosphere, that's a very interesting idea.
One more thing to do when I have time....
4th rock from the sun
Click to view attachment

OK, here's all the data I have. This atmospheric profile updates the previous one and is a better match to the sky color visible from the surface.

Still, all the data points to a green/cyan Venusian color when seen from space!
planet_guy
If you are interested in the surface stuff done by VIRTIS on VEX you can take a look at
http://solarsystem.dlr.de/TP/VIRTIS_en.shtml
and
http://irsps.sci.unich.it/~luciam/VEX/
The beauty of VIRTIS is that we will for the first time get global multispectral imaging from the surface of Venus over a long time period.
algorimancer
QUOTE (planet_guy @ Aug 25 2005, 08:17 AM)
If you are interested in the surface stuff done by VIRTIS on VEX you can take a look at
http://solarsystem.dlr.de/TP/VIRTIS_en.shtml
and
http://irsps.sci.unich.it/~luciam/VEX/
The beauty of VIRTIS is that we will for the first time get global multispectral imaging from the surface of Venus over a long time period.
*


Of course, if Mars Express is any guide, we won't get to see much of the results :/
tedstryk
QUOTE (planet_guy @ Aug 25 2005, 01:17 PM)
If you are interested in the surface stuff done by VIRTIS on VEX you can take a look at
http://solarsystem.dlr.de/TP/VIRTIS_en.shtml
and
http://irsps.sci.unich.it/~luciam/VEX/
The beauty of VIRTIS is that we will for the first time get global multispectral imaging from the surface of Venus over a long time period.
*



Great links! I wonder about something...it is thought that, despite up to 16 km/pixel resolution, atmospheric bluring will reduce resolution to 50-100 km. With this being a hyperspectral imager, are they sure that there are no holes where better might be obtained....I know the predictions, but, as they say, he who lives by the crystal ball eats glass. I also wonder if something like a spacecraft role could be used in selected areas for coverage inside of 10,000 km. I am really confused about coverage though. Some of the documents indicate that there will only be coverage of the southern hemisphere, but others indicate the best coverage will be of the northern hemisphere!
planet_guy
well the 16km/pix are using the 'holes' smile.gif the holes are in the co2 absorption, but you still have the clouds which are responsible for the blurring. of course since it has not been tried before these are only very cautious predictions. it might turn out to be somewhere between 16 and 50km/pixels
regarding the coverage - it will be mainly for the southern hemisphere. everything in the north can be done only by stacking several orbits or (maybe) by trying some slew of the spacecraft. However, surface imaging is not the main task of VEX so this will surely not be done in the beginning of the mission
tedstryk
QUOTE (planet_guy @ Aug 26 2005, 03:18 PM)
well the 16km/pix are using the 'holes' smile.gif the holes are in the co2 absorption, but you still have the clouds which are responsible for the blurring. of course since it has not been tried before these are only very cautious predictions. it might turn out to be somewhere between 16 and 50km/pixels
regarding the coverage - it will be mainly for the southern hemisphere. everything in the north can be done only by stacking several orbits or (maybe) by trying some slew of the spacecraft. However, surface imaging is not the main task of VEX so this will surely not be done in the beginning of the mission
*


Sounds like an extended mission task. 16 km was the resolution/pixel, 50-100 was the estimated realistic resolution, thanks to the atmosphere. I am just hoping that the predictions don't hold up cool.gif
planet_guy
trust me.. I'm also hoping the predictions are wrong wink.gif
JRehling
QUOTE (tedstryk @ Aug 26 2005, 08:25 AM)
Sounds like an extended mission task.  16 km was the resolution/pixel, 50-100 was the estimated realistic resolution, thanks to the atmosphere.  I am just hoping that the predictions don't hold up  cool.gif
*


I'm worried more about the spectral resolution -- All the Galileo image really shows is that areas of higher altitude are cooler, and if all we get out of this is thermal information at >10 km resolution, it'll be of very little interest.

Even with excellent data, spectral resolution has a tough time converting into mineralogy (note TES @ Mars, and the very vague assessments of the non icy compositions of the Galileans). In the case of Venus, we'll have so much spectral interference from numerous species (some unknown!) not to mention thermal noise, really the best I hope for is that we get a good cumulative, length-of-mission differentiation between planitia, tessera, fresh lava flows, and the radar-bright areas at high altitudes. Anything evidentiary about mineralogy between those four unit types would be great, and the recognition of any units that show up in IR but not in radar would be a godsend.

As far as eye candy goes, the best we could dream of would be to get low res data that could be used to "color" the radar maps illustratively or realistically.

One good subcloud aerobot with a camera would take a much better whack at this, with an easy time of making visible light spectra on the surface unit level, if not decameter level. Hopefully soon...
BruceMoomaw
I promised fully 2 months back to dig up whatever stuff I had on the possible ability of VIRTIS to map surface composition, and I'm putting up that entry now back on the "Venus Express" thread.
t_oner
It is unbelievable that Venus is the nearest planet and we still don't have a single global true color image of it. Galileo could have done it but did not, I don't know if Cassini could do it because of technical issues. It may or not have a scientific value but it should be done. I hope Venus Express has a suitable camera and filters for this job. (Pluto not yet explored, Venus not yet explored in true color).
JRehling
QUOTE (Tayfun Íner @ Dec 4 2005, 10:41 AM)
It is unbelievable that Venus is the nearest planet and we still don't have a single global true color image of it. Galileo could have done it but did not, I don't know if Cassini could do it because of technical issues. It may or not have a scientific value but it should be done. I hope Venus Express has a suitable camera and filters for this job. (Pluto not yet explored, Venus not yet explored in true color).
*


We don't have many great pictures of the far side of the Moon in true color, and not very many near-full phase pictures of the Earth in true color!

As I mentioned earlier, there are some pretty good pictures of Venus taken from Earth, in which case, it is never a full Venus, but at least we can start to imagine the real deal!

FWIW, Mercury is the third-nearest planet, and the impoverishment of good imagery there in anything approximating true color is astonishing. Even FROM Earth!
DonPMitchell
There is a spectral albedo for Venus. That can be turned into XYZ, via the CIE tables. Then convert that into Standard RGB ("sRGB"), which is a set of phosphor chromas that the computer industry and the HDTV people all more or less agree on. It has a gamma of 2.2.

Here's a set of planet colors, with brightnesses proportional to the total albedo:Planetary Palette
JRehling
QUOTE (elakdawalla @ Aug 8 2005, 11:53 AM) *
I'm creating a website with views of the worlds of the solar system, to scale with each other (it'll march up and down the few orders of magnitude necessary), and I am having a terrible time finding a global view of Venus to include in it that fits the criteria I'm trying to apply. To the extent possible, I am searching for:

- Full-disk, global view
- Minimum phase angle available
- Approximate true color, as would be perceived by a human observing the globe from space


[resurrecting a long-dead thread]
The lack of this has always bothered me. Messenger took an image of an almost full Venus, but cropped two edges, and only the plain filter image was made public.

Thanks to the blandness of Venus, it's not too hard to patch that image up. I used its own north end to fill in the cropped-out south and used a Titan image (appropriately tweaked from orange to BW) to sub in the cropped-out west. Then I took an amateur's earth-based image to find the right color balance. And... voila. A little bit of fiction is involved, but I think it fits the above criteria, that said.
scalbers
Well, I guess this wouldn't be true color, yet the past two issues of Sky and Telescope magazine have had some nice Venus shots from Earth. These show some cloud features utilizing ultraviolet filters.
Gladstoner
.
4th rock from the sun
Hi all,

I've updated my webpage with some Venus Express images processed in approximate real color.

The images seem to show the Venusian atmosphere extending from the limb with a bluish color. The general tone of the planet is yellowish, in accordance to similar processing I've done with Mariner 10 images, available on this site. The brightest clouds are bluish, given that they reflect strongly on the UV parts of the spectrum.

RGB channels were computed from NIR1, VIS and UV images using the following averages:

Red = 0.3 x NIR1 + 0.7 x VIS = 0.3 x 965 + 0.7 x 513 = 649
Green = VIS = 513
Blue = 0.5 x VIS + 0.5 x UV = 0.5 x 513 + 0.5 x 365 = 439

Here's one image, you can see more at http://www.astrosurf.com/nunes/explor/explor_vex.htm

ugordan
I've been messing around with the MESSENGER calibrated data and even though it's not a complete global view, I thought I'd share it here. From the filter choice standpoint, it's the closest we get to a RGB image for the time being. I already posted a few of those in the MESSENGER PDS threads, but those were quick-n-dirty versions.

Below is the familiar inbound view by the wide-angle camera, but this time I approached it somewhat differently. Instead of the typical E/D/C "red/green/blue" filter combo, I used E/D/F. Even though the "F" filter is labeled as violet, at 430 nm central wavelength it's actually much closer to the peak sensitivity of the blue light-sensitive cones in the human eye (437 nm). The "C" filter is shifted way too much toward green at 480 nm and also much more narrowband. Venus composites using the "blue" filter as a result fail to capture the bright clouds that reflect strongly in the UV, while the "F" filter does exactly that while still being inside human vision boundaries, i.e. not being UV.

I used the ground calibration tables when calibrating the data as the inflight-derived results look inconsistent across filters to me. Next, I took the central filter wavelengths and compared them to the sRGB colospace central wavelengths. I calculated approximate channel mixes to bring the "average" wavelength in all 3 RGB channels to sRGB, this is what I used:

red = 0.72*E + 0.28*D
grn = 0.93*D + 0.07*F
blu = 0.73*F + 0.27*D

Finally, I boosted saturation by +15 to compensate for a slight loss of saturation by above mixing.

Here is the resulting composite:
Click to view attachment

It looks as it's in the same ballpark as some other versions here. This one is not gamma-corrected because absolutely all contrast would be washed out and you'd end up with a shiny white billiard ball.

Here's a high-pass enhancement to bring the clouds out a bit:
Click to view attachment
Stu
Absolutely beautiful images, thanks for posting them here. Hope you won't mind me using them in my talks? That second one is just sublime.
ugordan
Sure, no problem at all, Stu. Glad you like them.
4th rock from the sun
QUOTE (ugordan @ Jun 1 2009, 06:48 PM) *
... I calculated approximate channel mixes to bring the "average" wavelength in all 3 RGB channels to sRGB...
...This one is not gamma-corrected because absolutely all contrast would be washed out and you'd end up with a shiny white billiard ball.
....


Nice results. I think that the channel mixing to average center wavelenght works very very well and can be used with almost any filter set. I'm not shure it saturation suffers that much, because that would have more to do with each filter bandwidth. Nevertheless, results are consistent. I think that you could include a gamma corrected version, because that would show exactly why the details are dificult to see at the telescope. It would also be closer to what we might see if in orbit of the planet.
ugordan
QUOTE (4th rock from the sun @ Jun 2 2009, 11:55 AM) *
I think that you could include a gamma corrected version, because that would show exactly why the details are dificult to see at the telescope. It would also be closer to what we might see if in orbit of the planet.

Well, you asked for it:
Click to view attachment

This was done on the 8 bit PNG above, not the 16 bit one I worked with as I'm at work now, but this only induces a slightly higher noise near the terminator. I continue to be amazed at just how sharply defined the planet's limb is. It really looks like someone put a solid ball in space - no limb brightening or other Rayleigh scattering effects.
Stu
Wow, there really would be b****r all to see if you went there, wouldn't there? Makes Uranus look positively psychedelic! laugh.gif
ugordan
Yep, and every time I see a montage of all solar system planets with Venus depicted by the brown-red Magellan surface globe, I die a little inside...

*cough*Photojournal*cough*
tedstryk
QUOTE (ugordan @ Jun 2 2009, 10:43 AM) *
Yep, and every time I see a montage of all solar system planets with Venus depicted by the brown-red Magellan surface globe, I die a little inside...

*cough*Photojournal*cough*


The coloration is based on Venera images from the surface, not the cloudtops. Granted, the coloration is due to the filtering of light in the atmosphere, but if we are going to be anal about coloring it like we would see it from space, then the clould should be covering it as well. I will add that the color is still a bit red, mostly owing to the fact that the Venera images have been better calibrated since the Magellan mission ended.
ngunn
QUOTE (tedstryk @ Jun 4 2009, 10:42 PM) *
coloring it like we would see it from space


Late night trivia I know, but I'm anatomical about this too. If the viewpoint is out in space then indeed the image should show what would be visible from there - if the aim of the image is to inform the public directly. Other kinds of image useful for scientific purposes that strip away atmospheres, represent invisible frequencies using visble colours, stretch contrast, or vertical scale, should be accompanied by health warnings if posted on public websites. The latest VIMS paper is exemplary. The images come with an explanation of what the colours stand for in each of the two ways the data are represented. It's clear that they do not mean "this is what it would look like". Making an artificially coloured radar map serve as the 'appearance' of Venus is a travesty. (Don't look too closely, it may also be vertically exaggerated.)
Stu
QUOTE (ugordan @ Jun 2 2009, 11:43 AM) *
Yep, and every time I see a montage of all solar system planets with Venus depicted by the brown-red Magellan surface globe, I die a little inside...


Every time - EVERY time - I start work on a new kids book about space I have a fight with an editor who is adamant that they should use garish false colour images of the planets instead of more accurate ones. That bloody psychedelic Voyager pic of Saturn is one I have to argue against, as is the UV pic of detail in venus' clouds. Oh. and they just lurve the migraine-inducing false colour Voyager shots of Uranus too... mad.gif
tedstryk
QUOTE (Stu @ Jun 5 2009, 12:21 AM) *
Every time - EVERY time - I start work on a new kids book about space I have a fight with an editor who is adamant that they should use garish false colour images of the planets instead of more accurate ones. That bloody psychedelic Voyager pic of Saturn is one I have to argue against, as is the UV pic of detail in venus' clouds. Oh. and they just lurve the migraine-inducing false colour Voyager shots of Uranus too... mad.gif


I agree with the false color Voyager shots. However, if you are going to show Venus the way it looks from space, you shouldn't show it from the surface at all. Using the rough apparent color of the surface to a viewer under the clouds who can actually see the surface should not be put in the same league with this.
Juramike
Personally, I don't like the wavelength limitations of visible light. Hyperspectal imaging, false color imaging, topgraphical coloration, mineral maps based on diagnostic bands - all these things make comparisons and contrasting of features easier (and pretty!).

But I totally agree with the points above: if you are going to show false color or enhanced images, it is important to put a warning lable that they are false color views. And if you are going to show a set of comparison images of planets, they should be all treated similar. If you strip the atmosphere and clouds off one of the terrestrial planets (like Venus), you need to do it for the other similar planets.

If you are only going to show the upper atmospheric structure of Venus, Earth's also needs to be shown for a comparison (but obviously not using the the same technique). [How are they similar? How are they different? Why?]

I always thought the perfect kids book would show a topographic representation of the terrestrial planets for comparison:
["Gee, without water, Earth still has ocean basins and continents....how come the other worlds don't have this? And what's going on with that ridge going down the Atlantic basin? How come Mars has those deep holes? Why are parts of the Moon so smooth?"]
tedstryk
I would say that there is a difference between false color imaging that shows, say, infrared wavelengths, so that the colors contain real information that can't be conveyed in a "true" color image and images that are simply colorized to look "cool." Juramike, I fully agree on the visible light issue. Our eyes evolved for our purposes here on earth, but there is so much to be gained from adding non-visible wavelengths. That is why I really prefer to call , for example, a color-shifted Voyager image G-V-UV color instead of "false" color. It isn't entirely false, in the sense that the colors really do mean something.
Stu
The problem I encounter is that editors want to use a garish false colour pic without explaining that it IS false colour, which would obviously lead to young readers being led to believe that Saturn really is decorated with poster paint blue, red and green clouds. I once had to fight - not literally! - with an editor to have a false colour view of Victoria Crater (you know, one of the "everything looks blue" images) removed and replaced with a natural colour one, because they wouldn't give me room to explain the nature of the pic. That would have meant a big header saying "Mars - the Red Planet" with a picture of a kingfisher-blue cliff face beneath it... rolleyes.gif
tedstryk
I agree, but I still think that showing the Venusian surface as it would appear in the light that filters through the atmosphere much less "deceptive" than the examples you use, especially when the image is a radar image, so it isn't going to be visually realistic no matter how you portray it.
Stu
It's this image I have had to fight to stop editors using...

http://www.pietro.org/images/VenusByPioneer.jpg

sad.gif
tedstryk
Not only is the color bad, but that is a Mariner 10 image.
Stu
Okay, but you get the idea, right? Editors can be hard to convince; they're - understandably - looking for visual impact, something to grab the attention of young readers, and once they've found a "wow" pic to use (don't know how they managed before Google!) you almost have to wrestle it out of their clutching hands...
brellis
When's Google Venus gonna be up and running? smile.gif
tedstryk
Yes, I get the idea. However, to me, the fact that a lot of Magellan imagery is shown with 20x vertical exaggeration is in that category, but using Venera-based colorization isn't.
scalbers
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
machi
It looks like old UV image from Pioneer Venus.
I think this one:
http://www.nasaimages.org/luna/servlet/det...ioneering-Venus
CJSF
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
4th rock from the sun
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.
Phil Stooke
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
scalbers
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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