Titan's upper atmosphere: blue or not blue?

[t00fri]

Hi all,

I am confused: since 1-2 days at the NASA site, there is now a so-called "natural color" image of Titan's upper atmosphere available that was obtained on the basis of regular R,G,B filters during the flyby.

Here is a small version of that image:



Carefully read the text that goes with it, here:

http://saturn.jpl.nasa.gov/multimedia/images/image-details.cfm?imageID=1512

According to the information communicated,
it seems to me now that one should really see some blue in visual light in Titan's upper atmosphere. This somehow contradicts earlier publications about this issue...

Bye Fridger

[ElChristou]

This is a very nice shot.

Have you made some change in your ssc to match this photo?

[t00fri]

This is a very nice shot.

Have you made some change in your ssc to match this photo?

NO! This is real imaging from Cassini. Before I shall try to incorporate the blue shade into Celestia, I want to be convinced that this is not due to some UV enhancement, as was claimed earlier.

Bye Fridger

[ElChristou]

This is a very nice shot.

Have you made some change in your ssc to match this photo?

NO! This is real imaging from Cassini. Before I shall try to incorporate the blue shade into Celestia, I want to be convinced that this is not due to some UV enhancement, as was claimed earlier.

Bye Fridger

Youpss, I have used the "shot" term for "photo" (in french we use sometimes "shooter" for "taking a photo")... Yet I think we can do the difference betwen Celestia rendering and reality ...

[Evil Dr Ganymede]

This is a very nice shot.

Have you made some change in your ssc to match this photo?

NO! This is real imaging from Cassini. Before I shall try to incorporate the blue shade into Celestia, I want to be convinced that this is not due to some UV enhancement, as was claimed earlier.

From the link you posted:

Images taken with the Cassini spacecraft wide-angle camera using red, green and blue spectral filters were combined to create this natural color view.

So it sounds like there was no UV enhancement.


There's a also a movie (taken in the visible violet filter) showing haze layers moving!
http://ciclops.lpl.arizona.edu/view.php?id=991

[t00fri]

This is a very nice shot.

Have you made some change in your ssc to match this photo?

NO! This is real imaging from Cassini. Before I shall try to incorporate the blue shade into Celestia, I want to be convinced that this is not due to some UV enhancement, as was claimed earlier.

From the link you posted:

Images taken with the Cassini spacecraft wide-angle camera using red, green and blue spectral filters were combined to create this natural color view.

So it sounds like there was no UV enhancement.

Yes, I am aware of that info. That's exactly the puzzling part, since earlier it seemed the blue was said to be only visible after UV enhancement.

Anyhow, it's a most beautiful sight . Let's define it to be "natural color" and I'll do it for Celestia towards the weekend (got a few days off, starting Thursday )

Incidentally, the yellow-orange shades in the image above perfectly match the previous haze & Titan surface colors. So there seems to be some "color consistency" in that atmosphere image...

[julesstoop]

Some conjecture:
Maybe it's something to do with exposure. The blue parts in the upper atmosphere are there, but would simply be most probably invisible to the human unaided eye.

[PlutonianEmpire]

http://celestiaproject.net/forum/viewtopic.php?t=7245

[t00fri]

Some conjecture:
Maybe it's something to do with exposure. The blue parts in the upper atmosphere are there, but would simply be most probably invisible to the human unaided eye.

Right that's the issue. Even if it's all "natural color" based on R,G,B filters there could have been /intensitiy/ manipulation involved. Enhance the blue relative to the rest. It's easy enough to do ...

Bye Fridger

[John Van Vliet]

well with those chem. 's in the upper atm. the blue would be there
But i think that it was color enhanced to (ie. the blue saturation and brightness) to make it more visable

[ElChristou]

...Right that's the issue...

Have you had a confirmation from the Nasa guys?

[t00fri]

...Right that's the issue...

Have you had a confirmation from the Nasa guys?

Indeed I sent off an email inquiry to a senior member of the CYCLOPS imaging team. No answer yet...

Bye Fridger

[DaveMc]

I haven't looked yet but do we know the specs of the filters used on Cassini? Is it possible the blue filer has a wide enough bandpass to allow some UV to reach the camera and be represented in the blue channel? Just a thought.

[t00fri]

I haven't looked yet but do we know the specs of the filters used on Cassini? Is it possible the blue filer has a wide enough bandpass to allow some UV to reach the camera and be represented in the blue channel? Just a thought.

Yes, clearly this is possible, but the blue-filter spectrum should be known very well such that corrections for "natural color" are easily feasible.

Bye Fridger

[t00fri]

Hi all,

just got the answer to my inquiry. The answer reads as I suspected...

Code: Select all

Dear Dr. Schrempp,

I was not involved in the processing of that image, so I can't tell you for sure, but it looks to me to have been processed in a similar manner to an image we showed in Figure 10 of our recent Nature paper (a copy of which is attached).  That image was an R-G-B combination plus an ultraviolet (UV3) image, the latter added because it's sensitive to the small particle "blue" haze.  The color is natural but the intensities have been stretched to bring out the low optical thickness haze, so with the human eye you probably wouldn't see that at all, or if you did, you'd see just the very faintest hint of a bluish haze above the North Pole, with no details.  I'm guessing that the same processing was applied to the image you ask about.  Voyager images of Titan 25 years ago (that did not have the benefit of a UV filter) do not have any visible-to-the-eye sign of the haze (though it was present at that time), although that camera system was much more primitive.

Sincerely,
Tony Del Genio

At 09:03 PM 5/4/2005 +0200, you wrote:
> Hi,
>
> besides being a theoretical particle physicist, I happen to be also a developer and co-author of the real-time 3d space simulation "Celestia".
> http://www.shatters.net/celestia/
>
> In both functions, I am very curious to learn whether the conspicuous /blue/ color in the higher Titan atmosphere,  apparent in the recent "natural color" image PIA06236, would be visible with the naked eye. This beautiful image is said to be based on R,G,B filter composition and hence to represent "natural color". Yet nothing was communicated about whether the blue shade was artificially enhanced in /intensity/ or not.
> The latter would be easy enough to do...
>
> Thanks & best regards from Hamburg,
>
> Fridger Schrempp
>



Anthony D. Del Genio
NASA Goddard Institute for Space Studies
2880 Broadway
New York, NY  10025
Phone:  (212)678-5588
Fax:      (212)678-5552



Bye Fridger

[PlutonianEmpire]

Hi all,

just got the answer to my query. The answer reads as I suspected...

Code: Select all

Dear Dr. Schrempp,

I was not involved in the processing of that image, so I can't tell you for sure, but it looks to me to have been processed in a similar manner to an image we showed in Figure 10 of our recent Nature paper (a copy of which is attached).  That image was an R-G-B combination plus an ultraviolet (UV3) image, the latter added because it's sensitive to the small particle "blue" haze.  The color is natural but the intensities have been stretched to bring out the low optical thickness haze, so with the human eye you probably wouldn't see that at all, or if you did, you'd see just the very faintest hint of a bluish haze above the North Pole, with no details.  I'm guessing that the same processing was applied to the image you ask about.  Voyager images of Titan 25 years ago (that did not have the benefit of a UV filter) do not have any visible-to-the-eye sign of the haze (though it was present at that time), although that camera system was much more primitive.

Sincerely,
Tony Del Genio

At 09:03 PM 5/4/2005 +0200, you wrote:
> Hi,
>
> besides being a theoretical particle physicist, I happen to be also a developer and co-author of the real-time 3d space simulation "Celestia".
> http://www.shatters.net/celestia/
>
> In both functions, I am very curious to learn whether the conspicuous /blue/ color in the higher Titan atmosphere,  apparent in the recent "natural color" image PIA06236, would be visible with the naked eye. This beautiful image is said to be based on R,G,B filter composition and hence to represent "natural color". Yet nothing was communicated about whether the blue shade was artificially enhanced in /intensity/ or not.
> The latter would be easy enough to do...
>
> Thanks & best regards from Hamburg,
>
> Fridger Schrempp
>



Anthony D. Del Genio
NASA Goddard Institute for Space Studies
2880 Broadway
New York, NY  10025
Phone:  (212)678-5588
Fax:      (212)678-5552



Bye Fridger

Hmm.... well, we could add the blue, but make it very faint, like the guy in t00fri quoted says it is, meaning it could be like this in the atmosphere part of the ssc file:

Code: Select all

Upper [ 0.000 0.000 0.100 ]

I did that for the upper atmosphere while editing the terraformed pluto thing, and it looks pretty good and as faint as 'Anthony' said titan was.

[t00fri]

If you think this was the whole story....

NO... read on

It seems either my "email-boilerplate" (that I erased here ) or Celestia's fame was sufficiently important, to promptly trigger two further responses from the CYCLOPS imaging team. Notably, the following reply, apparently came from 2 members actually involved in preparing the above "natural color" atmosphere image of Titan:

Read it for yourself:

Code: Select all


Almost all of the color images we (the Cassini ISS team) release to the press or to the web are true color, as best we can do.  Some are not but we always make this clear in the figure caption.  Therefore we believe our color images are an accurate representation of what the eye would see  from the position of Cassini.

Regards,
Bob West

Mail address: MS 169-237
                         Jet Propulsion Lab
                         4800 Oak Grove Dr.
                         Pasadena, CA 91109
Telephone: 818 354 0479
FAX:           818 393 4619
Alternate e-mail: raw@west.jpl.nasa.gov

DISCLAIMER: JPL now requires notice in all electronic
communication that all personal and professional opinions presented herein are my
own and do not, in any way, represent the opinion or policy of JPL.


And then once more from Tony Del Genio, who wrote the first reply to my query:

Code: Select all

Dear Dr. Schrempp,

I stand corrected.  My ISS colleagues Bob West and Preston Dyches claim that this is their best attempt at what the eye actually would see.

Sincerely,
Tony Del Genio

At 03:33 PM 5/5/2005 +0200, you wrote:
> Many thanks for your explanations! Sounds precisely like I suspected...
>
> Best regards
>
> Fridger Schrempp


In summary:

I find it very helpful indeed that we got direct and prompt feedback from the CYCLOPS imaging experts about this important question.

I also find their answer most interesting and shall start right away to incorporate the blue layer into Titan's upper atmosphere...

Bye Fridger

[t00fri]

With his response to my inquiry, Tony Del Genio sent me a PDF copy of their recent article about Titan in NATURE! It's really a great summary of their state-of-the-art.

I would make it available for download, here (1.5 MB), but I am not sure about Copyright constraints in case of public posting.

If you are interested, drop me a line and I send you the URL on a private basis...It's really worth it!


Enjoy,

Bye Fridger

[ElChristou]

...If you are interested, drop me a line and I send you the URL on a private basis...It's really worth it!...

Cool!! I'm quite interested in reading this...
Try to keep those great contacts for further works...