T00fri's Titan @ Celestia

[t00fri]

Hi all,

although we shall get presumably much better images of Titan rather
soon, I nevertheless found it fun & instructive to
incorporate the best of our
present knowledge about this mysterious moon into
Celestia NOW.

So we can compare in detail with incoming photos as
knowledge improves!

And YES, I still remember how to do textures ...


This is what I did today:
-------------------------
1)http://www.eso.org/outreach/press-rel/pr-2004/pr-09-04.html

The ESO PR Photo 11a/04 shows the clearest view of
Titan's surface, available so far!

It was obtained through a "transparent", narrow
spectral window with the 8.2-m VLT YEPUN telescope
and the NACO adaptive optics instrument operated in the
Simultaneous Differential Imager (SDI) mode [2]. It
covers about three-quarters of the full surface and has
an image resolution (sharpness) of 0.06 arcsec,
corresponding to 360 km on the surface. One degree of
longitude on the equator corresponds to 45 km on Titan's
surface. The brightness is proportional to the surface
reflectivity (albedo). The nature of the various regions is
still unknown although it is speculated that the darkest
areas may indicate the extent of reservoirs of liquid
hydrocarbons.

2) After cutting the 1.4k image out, I used the standard
Photoshop tricks to (easily) eliminate the overlaid
grid...Before that I used the grid, however, to carefully
align the image within the full 360x180 degrees
cylindrical texture, such that the 0 meridian is located in
the center of the texture (Celestia convention!)...

3) Next, some suitable LOK background color was
chosen and the texture scaled up to 2k. To smoothe the
unpleasant digital terassing effects out, I applied a 6x6
pix Gaussian Blur.

4) The color question of Titan is tricky, indeed, since we
don't know the real colors yet.

But we know some things: namely, that the dense
haze/clouds have a transparent window in the infrared
around 1575 and 1600 nm, while at 1625 nm, the
transparency is gone again. Also, Cassini could make out
clearly the "lying H" feature at (near-infrared of) 938nm
( with a polarizing filter to block out light scattered from
the atmospheric haze).

Certainly, Titan is not dark red as often shown on photos
(and in Celestia;-)). This is just a reminder of the
infrared light used to take the image. I rather took
another "false" color image as a guide that relates at
least 3 wavelengths in a relative manner (ESO
PR Photo 11d/04) and looks much more natural.



It is probably not all that unrealistic...We shall see
soon;-)

5) Finally I made a cute semi-transparent moving 2k
cloud layer and switched on 70% of bluish haze along
with a bluish atmosphere color.

Here is the result:

The top image (July 1st) shows Titan with my
semi-transparent cloudlayer, while the lower one shows
the surface. All known features are contained in my 2k
texture that I made with much scrutiny...



I shall package the whole texture stuff for general
download tomorrow...

Enjoy,
Bye Fridger

[chris]

Very nice, Fridger! I'll be using this texture as soon as it's ready . . . It will be very useful for comparing new Cassini images of Titan (Friday!) with the best ground-based observations. Perhaps we can even use your low detail Titan texture as the foundation of a better map built using Cassini images.

--Chris

[Evil Dr Ganymede]

I wouldn't get too attached to it (though it is a very nice map ), it's liable to change very significantly soon.

[t00fri]

Hi all,

as promised yesterday, here comes my Titan texture stuff for you to
download.

[

Evil Dr.:
---------
As I clearly emphasized at the beginning of this thread, I
am ready indeed for surprises within the near future. But
nevertheless, as new information will be flowing in, it is good to see
quantitatively what the changes are, relative to the best
earthbound observations, in order to appreciate what we are learning
from Cassini...

]

The following composite gives a miniature overview over some stages of
the making of Titan's texture:



All textures in my archive below are 2k in size, but may easily be reduced to
1k or smaller without much sacrifice...

a) First image: Since the question about Titan's color is largely open, I have
decided to add the following early stage of my work: 'titan2k-start.png'.

It has still the original red color, but with the grid and other artifacts
eliminated and a 6x6 pixel Gaussian blur applied. Notably, it is
carefully aligned within a 2k texture respecting the Celestia
meridian conventions. So using it as a basis, you are easily able
to incorporate you own preferred colors!

b) The second image shows a strongly reduced view of the observed
Titan surface in my chosen colors. They were essentially cloned
with Gimp2 from the 3 IR wavelength earthbound observation at
right (which is also "false" color, but probably less so than the
red variety!).

c) The third reduced image shows the alpha channel of my cloud/haze
layer that is of course matched at the left and right sides...

So here comes the URL (my 'Grandpa' TextureFoundry, of course
[cite Psykotik]) for downloading the whole stuff:

http://www.shatters.net/~t00fri/images/titan.zip

There is also a ssc sniplet, titan.ssc, that contains all my settings
along with atmosphere colors, haze settings (important!) etc.

I assume that people meanwhile know what to to with all this. I am not
available for "basic lectures on texture implementation", given the fact that
we have a perfect manual explaining every trivial detail of that...

Enjoy,
Bye Fridger

[danielj]

Very good work,Fridger.Finally we have the main moons of Saturn in 2k.I am very pleased.

Hi all,

as promised yesterday, here comes my Titan texture stuff for you to
download.

[

Evil Dr.:
---------
As I clearly emphasized at the beginning of this thread, I
am ready indeed for surprises within the near future. But
nevertheless, as new information will be flowing in, it is good to see
quantitatively what the changes are, relative to the best
earthbound observations, in order to appreciate what we are learning
from Cassini...

]

The following composite gives a miniature overview over some stages of
the making of Titan's texture:



All textures in my archive below are 2k in size, but may easily be reduced to
1k or smaller without much sacrifice...

a) First image: Since the question about Titan's color is largely open, I have
decided to add the following early stage of my work: 'titan2k-start.png'.

It has still the original red color, but with the grid and other artifacts
eliminated and a 6x6 pixel Gaussian blur applied. Notably, it is
carefully aligned within a 2k texture respecting the Celestia
meridian conventions. So using it as a basis, you are easily able
to incorporate you own preferred colors!

b) The second image shows a strongly reduced view of the observed
Titan surface in my chosen colors. They were essentially cloned
with Gimp2 from the 3 IR wavelength earthbound observation at
right (which is also "false" color, but probably less so than the
red variety!).

c) The third reduced image shows the alpha channel of my cloud/haze
layer that is of course matched at the left and right sides...

So here comes the URL (my 'Grandpa' TextureFoundry, of course
[cite Psykotik]) for downloading the whole stuff:

http://www.shatters.net/~t00fri/images/titan.zip

There is also a ssc sniplet, titan.ssc, that contains all my settings
along with atmosphere colors, haze settings (important!) etc.

I assume that people meanwhile know what to to with all this. I am not
available for "basic lectures on texture implementation", given the fact that
we have a perfect manual explaining every trivial detail of that...

Enjoy,
Bye Fridger

[Bob Hegwood]

Dr. Schrempp,

Is this the same Titan that's currently shown in Celestia as a fuzzy orange
ball?

How is it that the original image came to be so far off from reality? Just curious...

Thanks, Bob

PS - Much as I *hate* to agree with DanielJ, these are some great textures.

Take care, Bob

[Evil Dr Ganymede]

Dr. Schrempp,

Is this the same Titan that's currently shown in Celestia as a fuzzy orange
ball?

How is it that the original image came to be so far off from reality? Just curious...

Fuzzy Orange Ball = Titan seen in visible light. High, orange atmospheric haze blocks the view of the surface.

Cassini View = Titan seen in near infrared, IIRC. That wavelength can see through the haze, so we see features on the surface.

[t00fri]

Evil Dr., Bob,

thanks for getting me focused again on the issue of
Titan's haze color in visible light. Here I have
definitely got to do some further tuning...

The Voyager images in visible light from 1980 studied
Titan's haze color extensively. Indeed, as Evil Dr.
pointed out, this makes Titan's haze look pale orange
(and quite structureless) in visible light.

Here is a reminder



So I shall work on getting this right now...


Anyway, since the images revealing surface details are a
pure albedo map in the IR domain , we have no
evidence for the colors of the surface markings.


Bye Fridger

[Brendan]

Once we have nice textures for Titan, maybe the orange haze texture could be used as a cloudmap like the Venus cloud one is. Maybe there should be alternate cloudmaps so we could switch between the orange haze and the clouds for the near infrared view.

Brendan

[t00fri]

Hi all,

here comes the next iteration of my Titan textures. While
the (cloudless) surface view is only a little enhanced, the
haze has turned orange now as indicated by the Voyager
images (cf above).

At least I am much more content now. Let me know what
you think before I package the whole lot.




Bye Fridger

[t00fri]

And here is finally the sky-view from Titan's surface:
thick orange-purple-red structured cloud patterns...

Bye Fridger

[danielj]

I really like the results.The haze was missing.Next days,we will see if Cassini can do a better job

[Bob Hegwood]

Hey, these look great Dr. Schrempp...

Pardon my ignorance of what I was looking at. In my haste and excitement over
new Titan images, I hadn't realized that we weren't looking at the visible.

The revised textures listed here though, look - to my untrained eye - to be much
better substitutes for the current Titan options.

Many thanks, Bob

[maxim]

Apart from it looking really nice, two points:

- The haze cloud layer seems to be REALLY hight above surface. Are your sure about that? Or is it for demonstration purposes only?
- I can see a color seam on the picture with titan in front of saturn.

maxim

[t00fri]

Apart from it looking really nice, two points:

- The haze cloud layer seems to be REALLY hight above surface. Are your sure about that? Or is it for demonstration purposes only?
- I can see a color seam on the picture with titan in front of saturn.

maxim

Thanks Maxim,

your are right. I had also noticed this myself and currently work on further improving the atmospheric appearance after reading a lot more about what is known.

Bye Fridger

[Evil Dr Ganymede]

Well, IIRC, Titan's atmosphere is actually supposed to be about 400km high...

[t00fri]

Well, IIRC, Titan's atmosphere is actually supposed to be about 400km high...

Evil Dr.,

right now, I am precisely struggling with the complex issue of Titan's atmosphere thickness. It is very large indeed. There has recently be a "once in a lifetime" direct determination of Titan's atmosphere thickness from an observation of an extremely rare Titan transit of the Crab Nebula on 5 January 2003 with the {\it Chandra} X-ray Observatory. The resulting X-ray atmosphere thickness comes out as 880+-60 km!

http://arxiv.org/abs/astro-ph/0403283

The (wavelength dependent) definition of the atmosphere thickness is clearly not what Celestia calls atmosphere height...

Typically my best estimate is that above 250 km the atmosphere should be blue, while the hydrocarbon cloud layer extends up to 60-70 km.

Another compromise is the haze transparency (again being strongly wavelength dependent). I have chosen a relatively high transparency in order that the main surface features can be still made out. Then there arises the clash, however, that Saturn can still be spotted from Titan's surface! In reality, the visibility on the ground is presumably at best like on a very foggy day in Britain;-)

Bye Fridger

[granthutchison]

The cloud layer is what would prevent you seeing Saturn from the surface, or seeing the surface from orbit - shouldn't it just be rendered as opaque, since the spectral "windows" that are being used to show surface features are all in the infrared, and therefore invisible to our eyes?

Grant

[t00fri]

The cloud layer is what would prevent you seeing Saturn from the surface - shouldn't it just be rendered as opaque?

Grant

Yes clearly, if we are "narrow minded (oops: "banded")" and refer all vision to naked eye observation. I am in since long for wavelength switching in Celestia, but active followers are lacking, it seems...

Nothing is easier than to make the haze untransparent!

But then we are back at the dull orange ball. Pushing the 'I' key gets rid of the haze but clearly then produces the most unnatural view of the surface (cf Venus!) where we see radar surface data with our naked eyes!

Whatever we do (as long as we cannot apply filters in Celestia!) will lead to a clash with reality at some point. My 'semi transparent' compromise has the sole big advantage that it looks nicer;-)

Bye Fridger

[Evil Dr Ganymede]

The cloud layer is what would prevent you seeing Saturn from the surface, or seeing the surface from orbit - shouldn't it just be rendered as opaque, since the spectral "windows" that are being used to show surface features are all in the infrared, and therefore invisible to our eyes?

I was thinking about this earlier - maybe I'm being utterly dense here, I dunno....

What I don't get is that if you need a near-IR filter (at about 900 nm) to see through Titan's haze, and the view is obscured at visible wavelengths, then does that mean that no visible light can get through to the surface?! Surely not.

Or is it that visible light can get through from outside, but the stuff that's reflected back to the camera won't be able to get out from under the haze unless it's at near IR wavelengths? In which case, what wavelengths can get through the atmosphere from outside?