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PostPosted: Sat, 19-12-09, 23:05 GMT 
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Hi all,

Andrew (aka ajtribick) posted that amazing NASA link
http://www.nasa.gov/mission_pages/cassi ... 91217.html
at the shatters.net forum the other day...

Image

One can clearly see that specular reflection of sunlight (at IR wavelength) that has been determined to come from the first glints of sunlight reflected off a huge Titan lake ( 400 000 km^2 !!) near the North pole, called Kraken Mare. This spectacular event happened after the northern Titan hemisphere was shrouded in darkness for nearly 15 years! The observation of such a specular reflection confirmed the presence of liquid also in the moon's northern hemisphere!

For some of us, an obvious question is of course: What about this effect in Celestia(.Sci)?? Well Kraken Mare is on my latest, hires Titan texture (2009) that I made for Celestia.Sci (<= Feb 26 2009, CICLOPS team http://ciclops.org/view.php?id=5492).

Image

Here is a nice image from NASA's photojournal that includes also radar data.

Image

There is even a great video about the exploration of Kraken_Mare

http://photojournal.jpl.nasa.gov/archive/PIA08365.mpg

While due to infra-red wavelength filtering, the specular reflection in the original photo was able to penetrate the dense atmosphere of Titan, this is impossible in Celestia, due to its limitation to the visible light domain! One day, Celestia.Sci will hopefully offer multi-wavelength visualization...

But in Celestia we can just switch off the atmosphere by hitting a key ;-) . So let's see what Titan looks like without its atmosphere in Celestia, at the discovery day, July 8th 2009, from the proper distance of ~200000 km.

Using GIMP, it is an easy task to generate a specular texture with the shape of Kraken Mare as depicted in my 2009 Titan texture image above.

Image

Not bad at all, I would say.

Clearly, it would be interesting to further complete Titan's specular reflection texture in terms of the further lakes that have been discovered also in the southern hemisphere. Perhaps novel, "specular predictions" could be made this way?

I am confident that I will present further progress along these lines in the near future...
So stay tuned.

Fridger


Last edited by t00fri on Mon, 21-12-09, 9:39 GMT, edited 4 times in total.

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PostPosted: Sun, 20-12-09, 15:21 GMT 
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Hi all,

here are the South pole and North pole Celestia views with my 2009 Titan texture, along with an annotation of the biggest proven (liquid) lakes.

South pole:

Image

Besides the outstanding Ontario lake, virtually most visible smaller dark lake-like shapes around the pole have been meanwhile identified as true lakes (with the help of radar).

So there is plenty of clearcut input for a more complete specular map of Titan!

North pole

Image

One clearly sees besides the gigantic Kraken Mare two further smaller ones that are already part of my specular map.

Fridger


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PostPosted: Sun, 20-12-09, 17:23 GMT 
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Hi again...

you know presumably that the level of liquid (hydrocarbon) in the lakes around Titan's South pole is known to vary substantially. http://ciclops.org/view.php?id=5458
Here are two such scenarios:

Specular reflection scenario1: normal level of liquid (hydrocarbon)
======================================================

Image

The lake Ontario is annotated for better orientation!

Isn't it nice??

Specular reflection scenario2: lots of of liquid
=======================================

Image

Wow!

Another game I played concerns a look into the future: 2013 with Titan's North pole area now fully illuminated! Here is how the specular reflection of the sun in Kraken Mare then looks like...

Image

This should really be hard to overlook...

Enjoy,
Fridger


Last edited by t00fri on Wed, 23-12-09, 8:23 GMT, edited 3 times in total.

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PostPosted: Mon, 21-12-09, 9:30 GMT 
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Let me add for completeness these nice Jan 2009 polar maps by the CICLOPS team

http://ciclops.org/view.php?id=5457

that list all known lakes both around the South and North poles of Titan.

(Click for Big)
Image

[/img]Image

Fridger


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PostPosted: Mon, 21-12-09, 23:11 GMT 
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t00fri wrote:
Another game I played concerns a look into the future: 2013 with Titan's North pole area now fully illuminated! Here is how the specular reflection of the sun in Kraken Mare now looks...

You should let Carolyn Porco or someone else at Ciclops know about all this. But perhaps they already know. Perhaps they even use Celestia...

Merry Christmas, everybody!

G


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PostPosted: Tue, 22-12-09, 0:06 GMT 
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Wow... never really had any idea of how big Kraken Mare was in relation to Titan as a whole... quite a substantial feature isn't it?


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PostPosted: Wed, 23-12-09, 18:25 GMT 
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I was thinking this would be a nice thing for Celestia to do and am glad to see that Fridger is trying this out. Looks like Kraken Mare even gets higher potential solar elevations than my ~40 degree quick guess as time progresses. We can perhaps figure out what the value would be for the Cassini mission end.

I've linked to this discussion in the UMSF forum, so maybe some Cassini VIMS members (who would be planning future imaging opportunities) will see this, or at least word will get to them. I do know that some CICLOPS folks use Celestia as well.

It seems like the intensity of the reflection is somewhat higher in the actual image compared with Fridger's rendering. Perhaps related to this is that to me the phase angle looks a bit higher than 130 degrees in the actual image. There is a also a potential "clipping" issue that is mentioned here:

http://www.shatters.net/forum/viewtopic.php?f=4&t=7659

Any chance of posting some specular reflection maps online? I note the "size" of the reflection can be adjusted somewhat according to assumed wave action, using the specular power parameter. Does the specular reflection algorithm show non-spherically symmetric effects? I'm thinking about the appearance of a "pillar" type of reflection near sunset on a wavy lake.


Last edited by scalbers on Wed, 23-12-09, 19:36 GMT, edited 5 times in total.

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PostPosted: Wed, 23-12-09, 19:04 GMT 
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Hi Steve,

welcome over here! Good to have more texture experts around...

My above specular map is matched to my latest 2009 Titan texture (<= Feb 26 2009, Ciclops imaging)

http://forum.celestialmatters.org/viewtopic.php?t=305

and cannot be used with my official Celestia 1.6.x texture that is a year older. Because of some disagreements with ChrisL, I have discontinued to provide textures for the official Celestia distribution. Instead, my new Titan map as well as any other textures will be part of my forthcoming Celestia.Sci package.

Fridger


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