Cassini's VIMS (Visual and Infrared Mapping Spectrometer) instrument has started issuing public release images on our website at approximately weekly intervals. Just thought this might be of interest. Full disclosure: I work for VIMS, so yes, this is a shameless advertisement. But we do color good -- it's pretty, and it's real data. If you have specific requests for images or something that you'd like us to work up a website image-release for drop me an email or reply to this post.

Cool! I should note that the last image on that page, a mosaic of VIMS cubes from T16, shows approximately the same view as an ISS daily release from a few weeks ago: http://ciclops.org/view.php?id=2144 . In the ISS view, you can see many of the same cloud features that VIMS sees, near the 38th South parallel. However, you can only see the eastern clouds, not the westernmost ones pointed out in the VIMS release.

BTW, nice to see ya here, Jason. Like dvandorn, you may have to sign your posts, "- the other Jason"

Did Cassini take any image cubes of Venus during flyby?

I can't speak for ISS, but VIMS has only a few, and they're not very good. Since we were so close to the Sun, the Infrared half of VIMS still had it's cover on to prevent it from overheating, and the IR half is what would really be able to penetrate Venus' atmosphere to get surface images. The VIS half stuff that we have isn't very inspired.

So far as I know, Doug Ellison (source of all forum rules and policy) has not legislated against the advertisement here (shameless or otherwise) by planetary scientists of their work, particularly when they release their data to the public. :->

It's always a treat when working scientists take the time to share and discuss their discoveries with the enthusiasts who gather here. Thanks for the pointer to your site.

TTT

Thanks for the heads up Jason - always nice to see a science team stepping up to the plate and spreading the wealth

Full disclosure is always appreciated - we have quite a few members who for one reason or another wish to remain comparatively anon. - and that's fine - but it's alwyas nice to know exactly where someone is coming from.

Doug

Absolutely gorgeous, especially the mid-latitude cloud bands! I had the impression that clouds were generally quite scarce lately – now that southern summer is over. I remember that there were south polar clouds on the VIMS mosaic from Dec. 26, 2005 (PIA02145, Mapping Titan’s Chance) and on the clear-filter view form Aug. 31, 2005 (PIA07597, Faint Southern Clouds), but I can’t recall many more. Great stuff!

Well, since VIMS can acquire detailed spectra of targets of interest, can you reproduce more accurate (if lower spatial resolution) "natural" color views of, say, Saturn and maybe some of the major moons (Titan, Tethys, Rhea, Iapetus, Hyperion are those that at least have some color to them)? Yes, I'm aware "natural" is somewhat subjective, but I figure detailed spectra should allow better accuracy than discrete, broadband filtered images ISS acquires.

Something I have been wondering for a while, and which I haven't seen discussed at any conference, is whether VIMS sees any of Titan's 'morning fog'/'morning haze', i.e. an east-west asymmetry. These asymmetries are clear from ground-based observations which cover the same wavelength regions as VIMS, so VIMS should be able to see them clearly if they are really there.
Any comment on this would be very nice . cheers

This is something I would be very interested in as well - I have been making a very high resolution map of Saturn based on ISS images and getting more accurate color information would be interesting. The same is true of the overall color of the rings, both the lit and unlit side - I have been working on color profiles of them as well for use in 3D rendering.

And of course false color images of the rings showing compositional variations would also be interesting.

I'm also quite interested in the 3D rendering problem. Computer graphics is my day job, so I'd like to get the colors right of course, and do proper bump mapping of solid planets. Most synthetic planet images I've seen, such as from Celestia, look very fake to me. I think they are also using bad bidirectional reflectance formulas, and in the case of atmospheres and gas giants, sub-surface scattering is probably essential to get a realistic look.

There's an update to the public release images, including a rather neat movie showing evolution of Titan's mid-latitude clouds.

That movie is pretty cool. At the end though, because of the low resolution of the original data, it becomes a bit difficult to interpret the cloud activity near the end of the movie.

The Saturn cloud-layer release is also very interesting: much sharper than equivalent studies done by NIMS on Galileo (of Jupiter, of course). That's a very impressive "X-ray specs" penetration down to the lower cloud layer.

Saturn and Jupiter become specific cases of a general gas giant model, with lots of extrasolar planets in the same category. I haven't registered a lot of Saturn-atmosphere science breakthroughs, but the individual observations look like they supply the raw material for a good model.

'Chinese Lantern' Technique Helps Track Clouds at Saturn
October 5, 2006
(Source: Jet Propulsion Laboratory)

http://saturn.jpl.nasa.gov/news/press-rele....cfm?newsID=694

By processing images shot with different sun angles its relatively easy to create normalmaps that look great for solid planets. (i usually do it by using a simplyfied shape from shading algorithm that only recover the normal for each point and skip the heightfield integration step.)

Usually 3d rendered pictures have very simple shading models. And even more often they have strange gamma errors. a common error people do is to use nonlinearized textures (gamma 2.2). That makes the shading look dark and dirty. One has to linearize all textures that goes into the 3d renderer and then convert the linear rendering into sRGB afterwards. Most 3d software have very limited support for these things.

Its probably really hard to render gas planets really realisticly. All realworld pictures of the gas planets have the scattering already "built in" to them. One has to recover the actual volumetric data to be able to render the subsurface scattering correctly. i have no idea how. But i think that using any SSS is better than none.

/M

A question for Jason (Barnes, not Perry ):
Why TIFF format releases? PNG is better suited for the task as it achieves much smaller file sizes with lossless compression. A 30 megabyte VIMS mosaic just seems like an overkill.

The PPJ has always done tiff's - never figured out why.

Doug

I try to aviod PPJ when it comes to Cassini releases. For CICLOPS stuff, I grab it off their home page in PNG form, though the server used to die a lot in the past during heavy demand. I get annoyed to see other PPJ releases such as VIMS mosaics blown up 4x and finding the JPEG version is badly artifacted, while the TIFF is several megs in size. For a 250x250 image. Furthermore, I've seen cases of images that were submitted to PPJ as obviously badly compressed JPEG, only to be presented there as a losslessly encoded TIFF as well.

There is generally little understanding by people on the net which format suits which use the best. Things like posting windows dialog screenshots as 150 kb lossy, smudged JPEGs when the same thing comes down to under 10 kb in PNG, lossless!
Ah, rant over...