Celestia Forums

Just been watching a documentary on Titan, and found Celestia default image is nothing like the latest images.

Like to find a decent hi-res image of this, but not finding any textures on it.

I know its just orange.., but its a fuzzy orange that does have detail (in shades of orange!!). Anyone know where one is, preferably 16k.

Thanks,

Seb

Seb...we will have to wait 'til January 2005 to find out what's beneath the cloud layer...hang on old boy. The default is maybe a bit too orange but you could try messing around with an image editor to get something more to your taste...It seems to be an all over cloud layer however so 16k seems a bit overkill here!

Regards...bh.

Seb wrote:Just been watching a documentary on Titan, and found Celestia default image is nothing like the latest images.

If you're talking about the BBC Horizon programme tonight, the Titan image they kept showing is a colour-and-contrast-stretched Voyager picture!

We only occasionally glimpsed a Cassini Titan picture, and that was lying on a conference table. Fridger deliberately matched the colour and absence of discernible cloud detail to "natural colour" Cassini images like this one:


Grant

bh wrote:Seb...we will have to wait 'til January 2005 to find out what's beneath the cloud layer...hang on old boy. The default is maybe a bit too orange but you could try messing around with an image editor to get something more to your taste...It seems to be an all over cloud layer however so 16k seems a bit overkill here!

Regards...bh.

Actually, the first proper Titan flyby is next week
http://www.celestiaproject.net/forum/viewtopic.php?t=6031

Yep...but Huygens doesn't go in for a week or so after Christmas.

Regards...bh.

bh wrote:Yep...but Huygens doesn't go in for a week or so after Christmas.

Huygens ain't gonna help in making a texture map of Titan's surface though. The Radar Mapper on Cassini will be doing that (since the first pass showed that near-IR is evidently too obscured by clouds to be much use).

Personally, I think it'll look like Ganymede under there. I think I saw signs of what looked like bright terrain sulci under the clouds in the last pass.

Seb wrote:Just been watching a documentary on Titan, and found Celestia default image is nothing like the latest images.

Like to find a decent hi-res image of this, but not finding any textures on it.

I know its just orange.., but its a fuzzy orange that does have detail (in shades of orange!!). Anyone know where one is, preferably 16k.

Thanks,

Seb

Seb,

as Grant mentioned, I have prepared for Celestia-1.3.2 texture + clouds files of titan, corresponding to the presently best available information about surface details and clouds. You may see the surface of Titan by toggling the key "I". Anything more detailed will come as soon as the information is available.

Bye Fridger

Evil Dr Ganymede wrote:

bh wrote:Yep...but Huygens doesn't go in for a week or so after Christmas.

Huygens ain't gonna help in making a texture map of Titan's surface though. The Radar Mapper on Cassini will be doing that (since the first pass showed that near-IR is evidently too obscured by clouds to be much use).

Personally, I think it'll look like Ganymede under there. I think I saw signs of what looked like bright terrain sulci under the clouds in the last pass.

Do you think it will look like Ganymede because of the bright terrain sulci or you think that it will look like Ganymede because it's your favourite world?

Michael Kilderry

Michael Kilderry wrote:Do you think it will look like Ganymede because of the bright terrain sulci or you think that it will look like Ganymede because it's your favourite world?

No, I think it'll look like Ganymede because (a) the dark regions in IR on the last flyby are supposed to be bright water ice, and they looked suspiciously like thick bands in places, (b) Titan is the same size as Ganymede roughly, and is being tidally heated, and (c) in the rotation animation they did on the Cassini website, you can see thin arcuate features that look very similar to the sulci that cross Marius Regio on Ganymede.

I could be wrong of course, but I'm putting my cards on the table now. We'll see

Thanks Fridger, I was being stupid, hadn’t noticed I was actually looking at the surface not the clouds.

granthutchison - yep, BBC Horizon.

bh - yep, overkill is gooood..!!

Seems to be a lot of pessimistic speculation about what’s beneath thoughs clouds. and with the Cassini changing speed to shift its radio listening frequency, this would probably shift the colours on the pictures taken, wouldnt it?

Seb wrote:Seems to be a lot of pessimistic speculation about what’s beneath thoughs clouds. and with the Cassini changing speed to shift its radio listening frequency, this would probably shift the colours on the pictures taken, wouldnt it?

No, it wouldn't (well, not by any noticeable degree - it's not going so fast as to significantly doppler-shift light).

It's using radar to see through the clouds. The images you get out of that are going to be greyscale anyway.

I still think Titan's surface looking like the biggest moon in the solar system is wishful thinking by Evil Dr Ganymede, after all, one big difference is that Titan has a big atmosphere, which could mean different surface features and that all worlds look different to each other (to a degree). If it looks like Ganymede or not, I think it's a real bummer how Titan's pictures are gong to be greyscale. I hate non colourful images! I think that the Titan radar images should be in colour, the people in charge could just do what the Magellan images of Venus had done to them, just give the Titan images speculative colours based on what they think the colours would look like. It would make the pictures look much better.

My favourite moon isn't Titan anyway, my favourite has to be Saturn's other moon Tethys. I like it because it doesn't get much attention, similar to why Evil Dr Ganymede likes Ganymede. Evil Dr Ganymede thinks it is unfair how Europa gets more attention than Ganymede, as he thinks Ganymede's underground oceans would be deeper than Europa's anyway. I think it is unfair how Mimas gets so much attention compared to Tethys, just because it has a big crater which is something Tethys also has. Tethys' crater is also more interesting than Mimas' because it seems to have flattened since it was formed early in the moon's lifetime.

Michael Kilderry

Michael Kilderry wrote:I still think Titan's surface looking like the biggest moon in the solar system is wishful thinking by Evil Dr Ganymede, after all, one big difference is that Titan has a big atmosphere, which could mean different surface features and that all worlds look different to each other (to a degree).

It's not entirely wishful thinking - we've already seen (very fuzzily) through the atmosphere. Have a look at these for example:

http://saturn.jpl.nasa.gov/cgi-bin/gs2. ... type=image
http://saturn.jpl.nasa.gov/cgi-bin/gs2. ... type=image
http://ciclops.lpl.arizona.edu/view.php?id=215

Then, bearing in mind that dark regions in IR are bright cleaner icy in visible light, have a look at these:

http://www2.jpl.nasa.gov/galileo/images ... lobal.html

So we have bands of dark material in the IR on Titan, and look! We have bands of bright material in visible on Ganymede. You can even see some faint lineaments in the Titan animation in the ciclops link above too, that look rather reminiscent of the smaller sulci on Ganymede.

If it looks like Ganymede or not, I think it's a real bummer how Titan's pictures are gong to be greyscale. I hate non colourful images!

I dunno if they'd use more than one wavelength of Near IR to look through the clouds, but they could at least make a false colour image from that.

I think that the Titan radar images should be in colour, the people in charge could just do what the Magellan images of Venus had done to them, just give the Titan images speculative colours based on what they think the colours would look like. It would make the pictures look much better.

Yes, but the colours they used for venus bear no resemblance whatsoever to what's on the surface. For starters, bright material in radar just indicates that the surface either has a highly radar emissivity or is very coarse in texture. In reality rocks on venus would look uniformly black or dark brown tinted a yellowish colour by the atmosphere - this website has the closest to real colour (and highest resolution) images of Venus' surface that we've got. Though I really wish someone would "unwrap" the Venera images so the horizon was straight.

I think it is unfair how Mimas gets so much attention compared to Tethys, just because it has a big crater which is something Tethys also has. Tethys' crater is also more interesting than Mimas' because it seems to have flattened since it was formed early in the moon's lifetime.

Well, the cool think I like about Tethys is that you could fit all of Mimas into its big crater.

I guess you have a point when you say that Titan's surface looks a bit like Ganymede's, but you wait. When more detailed images arrive, there will be big Tethys-like craters that can fit ten Mimas' in each at least!

I always thought that the Venusian radar images were pretty much correct to what the surface would really look like, but obviously not.

Michael Kilderry

Michael Kilderry wrote:I guess you have a point when you say that Titan's surface looks a bit like Ganymede's, but you wait. When more detailed images arrive, there will be big Tethys-like craters that can fit ten Mimas' in each at least!

Even Ganymede's biggest impact basin (Gilgamesh) is about as big in total as Odysseus on Tethys. Titan could conceivably have a big impact basin like that too, I guess. I think that there'll certainly be a lot more large craters on Titan than small ones, because the smaller impactors would burn up in the atmosphere.

So I'm thinking Titan's gonna look like the illegitimate child of Ganymede and Venus (and yes, I know that's so mythologically wrong it'd make your head explode )

I always thought that the Venusian radar images were pretty much correct to what the surface would really look like, but obviously not.

The radar images of Titan are going to be quite interesting because it's going to be the first time that we'll use radar to look at an icy surface on another world - but as I indicated, it's harder to interpret what you're seeing. I remember the fun they had with overlapping pancake domes on Venus, until they realised that they were actually seeing a rader echo effect . That said, I do love radar imaging. You can tell so many things from it - roughness of the surface, emissivity, altimetry from the radar returns, 3D views from radar stereo observations (sometimes on a single pass)... you can even use it to look through the uppermost surface layers if its the right wavelength. Every mission should have SAR! In fact, Magellan's been my favourite mission so far (well, behind Voyager of course), but I think Cassini will beat it.

Cassini's Titan Encounter A surface photos and radar are amazing! The scientists aren't commiting yet, but permit some wild speculation...

Tantalyzing streaks in optical - islands in a hydrocarbon sea?

Sinuous, smooth features in radar - drainage features?

Radar altimeter indicates very flat surface - surface highly eroded by methane/ethane rain?

And missing light nitrogen in atmosphere - metabolyzed by Titan critters?

Well, the last one is a long shot, but boy am I looking forward to Huygens. Maybe the last shot before landing will show hydrocarbon grazers scurrying away from that bizarre contraption! What a time to be alive!

I keep wondering how true to colour the textures in Celestia really are, they are all taken from different sources, heavily processed differently and then converted.

These missions should have special calibrated cameras that can take various spectrums in a single shot, RGB, IR and maybe radar, so that we can overlay the results without having much trouble. I think this is important, because the whole point really is too see what is at these places.

Also, I think Celestia should also work with actual luminance data, and to level the brightness of the whole screen at the last stage, (as to make images displayable). This I think would give a more realistic view how things would look if we were really out there, floating in orbit around some planet. (Whist watching your blood bursting out through our veins into space..!!)

Apparently displaying color as a human would see it is non-trivial. I just read an article that says all the images from Spirit and Opportunity are way too red. Mars is the ochre planet, not the red planet. And they even have RBG filters available. But to accomplish the most with the least bandwidth, they use near-infrared and near ultraviolet instead of true red and blue, getting more analytical data with an approximation of the true color.

Not to mention that there is no color data on lots of images, or color is difficult to interpret, like the radar images from Cassini. And then, how do you account for the Sun being a different distance away (the surface of Titan would be about the same as a night on a full moon), and the effect of a different color atmosphere? Also, your eyes get somewhat used to different colors, so something you might think looked white under Titan's haze when you first get there might look like a different color after a while.

Guess the only way to find out is to go there. Me first!

BTW, Seb, did you live in Spain in 1991? If so, I may know you!

Drake wrote:Apparently displaying color as a human would see it is non-trivial. I just read an article that says all the images from Spirit and Opportunity are way too red. Mars is the ochre planet, not the red planet. And they even have RBG filters available. But to accomplish the most with the least bandwidth, they use near-infrared and near ultraviolet instead of true red and blue, getting more analytical data with an approximation of the true color.

Sorry to respond so late, but there's been a certain amount of misinformation going around about this subject. Displaying colors as a human would see them is indeed nontrivial, and early Viking pictures of Mars were often poorly color corrected and far too red. But the Spirit/Opportunity photos are pretty well-calibrated, as far as I can tell. They've got a color calibration target and they use it.

The photos you see that are identified by JPL as "natural-color" are actually taken through the RGB filters. More often, they release what they call "approximate natural color" photos taken through infrared, green and blue filters (usually not ultraviolet). But these get color-corrected so that the ground and sky colors are approximately the same as in the natural-color pictures, so the colors are not so far off. In the natural-color pictures, Martian soil and sky usually do appear more ochre than red. In the approximate-natural-color pictures, to my eye the ground typically looks a tiny bit redder and the sky more gray, but the difference is not large.

One thing that changes markedly in the IR/green/blue pictures is the appearance of the rover itself, and particularly its sundial calibration target (the thing that looks like an old Atari joystick): the red/yellow/green/blue color chips on it turn different shades of orange and red. The color chips were purposely chosen to look different in those photos as a sanity check. But the odd appearance led to lots of idle speculation by conspiracy buffs (see below).

You may occasionally hear that the colors are actually completely wrong, and the sky on Mars is really always blue. This is an assertion originally popularized by Gilbert Levin, a researcher who believed that Viking photos were showing green vegetation on the ground and that the red overcorrection made to those pictures was obscuring it (and incidentally de-blueing the sky). The claim has been kept alive by conspiracy buffs who believe that NASA is covering up life on Mars for some nefarious reason. Occasionally they misinterpret completely uncorrected composites with blue skies (and blue rocks!) as a sign that NASA is gradually acclimating us to the truth, or fantasize some sort of internal struggle with brave moles in the organization letting the true colors slip. But as far as I can tell, the much more carefully color-corrected Mars Pathfinder and Spirit/Opportunity photos have invalidated the claim.

Now, that said, the difficulties involved are real and the color information in Celestia textures does vary in quality. It's gotten better over time as the many contributors to Celestia refine their work and incorporate new information.

Voyager photos released in the 1970s and 1980s often had inaccurately reproduced colors; Voyager had a slightly peculiar collection of color filters on its vidicon tube, and the publicly released photos often had wildly oversaturated, garish colors.

Galileo did better and Cassini does much better, but some of their images are in pseudo-color incorporating UV and IR filters, and different color channels are often taken with different exposure times. Usually JPL will identify what filters were used to make a released color image, and they're pretty good these days about saying whether or not they were trying to be naturalistic if you read the image captions carefully. But this information can get lost in nth-hand reproductions in the news media.

It's particularly interesting comparing the colors of Voyager images of Titan, which look like a Day-Glo supermarket orange (sometimes bearing an electric purple fringe), with Cassini's pictures showing it to be a much less saturated orange-tan color with subtle hints of blue around the margins. The most recent Titan cloud texture released with Celestia incorporates the color from Cassini photos, though I suspect it should be a slightly more uniform color than it is.

One thing I have been wondering is whether the released Cassini pictures of Saturn's atmosphere near the limb and terminator are exaggerating the blue of atmospheric scattering there. But some Hubble Space Telescope pictures of Saturn look similar, and I think that the publicly released Voyager Saturn photos tended to be far too yellow.