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Posted by: MarcF May 16 2006, 09:27 PM

Hi everybody,
I just registered to this wonderful site, the best in my mind to get fresh and clear informations about our favourite subject since Jason's Titan Today (Guabonito times, I think now).
I'm a little bit frustrated by the poor resolution of the ISS pictures and the poor coverage by SAR (at least for the moment).
Does someone know about the variability of the haze density around Titan ? Is it the same at all latitudes or would it be possible to find some windows where ISS could increase its resolution (as for exemple near high latitudes) ?

I also know that VIMS is able to get better resolution than ISS (like the one of Tortola macula in which the now famous sand dunes might be seen).
I'm just amazed to find so few VIMS high resolution pictures. Does this mean that they do not exist or just that they are not published yet ? A lot of interesting features schould be targeted for high resolution VIMS pictures (Ganesa, Omacatl, Hotei, Ontario lacus, ...).

Posted by: volcanopele May 16 2006, 09:43 PM

1. Haven't seen evidence for clearer areas yet in the haze.
2. VIMS can get higher resolution views than ISS, but only at very close range. Even at best, VIMS can only get 1 or 2 images at better resolution than ISS per flyby, and these cover a very small portion of the surface. The only press release image from VIMS at better resolution than ISS is of Tortola Facula (formerly the snail), though there were some decent ones from T4 and T5 in the PDS.

Posted by: djellison May 16 2006, 10:06 PM

VIMS is the Mini-TES of Cassini...you know it's there, and you know it must be doing a lot of very interesting stuff....and you even see it getting dumped into the PDS (but can't figure out how to use it)...but for some reason there just isn't a lot of press material from the VIMS team.

I think there's one barrier in the way of a LOT of interesting work by people here with VIMS data..and that's because it's not easy to get in to. ISIS - The big linux software suite seems to be the only means to read VIMS data unfortunately.

There is 'browse' data
http://pds-imaging.jpl.nasa.gov/data/cassini/cassini_orbiter/covims_0001/extras/browse/

But it's not a patch on using the proper data.

Doug

Posted by: edstrick May 17 2006, 08:31 AM

"...Does someone know about the variability of the haze density around Titan ? Is it the same at all latitudes or would it be possible to find some windows where ISS could increase its resolution..."

The haze is a non-condensable (cause it's already condensed) fog or more precisely dust-fog, since the particles are largely or entirely solid. As such, it can't evaporate and clear-out to form distinct windows to let us see through to the surface. The rare methane rains may partially wash it out, I don't know the theoretical effeciencey, and it can settle out onto the surface. Clearly, it doesn't uniformly cover the surface with a dust-coat everywhere or everything would be the same color.

We do see increased hazes at least at high altitude in the winter polar region though whether it adds much to the total opacity looking straight down isn't clear. There does seem to be seasonal variations in the latitude distribution of hazes but it's not enough to obviously help.

The REAL solution to the problem is a true middle-infrared camera. The ISS CCD detectors run out of ability to detect near IR photons at about 1 micrometer wavelength, twice the wavelengt of yellow light, more or less. In methane windows near 2 micrometers <microns> or longer, VIMS has excellent views of the surface, perhaps with enough contrast to see shadows cast by the topography. But the 1990 or so technology built into the VIMS didn't have high-resolution CCD or CCD-like camera chips available at all, and VIMS is an imaging spectrometer, trading resolution for spectral coverage.

The next Titan orbiter <and any balloon or dirigible or ... mission> will be able to carry a circa 2010 technology mid-infrared camera that will probably let us take multi-spectral stereoscopic mapping coverage of the entire moon with (depending on camera optics size and datarate back to Earth) a resolution of perhaps 100 to 25 meters/pixel or even better. Imaging a mid-IR version of HiRise at Titan. It could do something like 5 meters/pixel at 2 microns from 1000 km. (hard to orbit lower... you end up de-orbiting. Anybody know the minimum altitude for long-term circular Titan orbit?)

Posted by: remcook May 17 2006, 12:07 PM

you can see a little bit of variation e.g. here:
http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=75060

but probably doesn't affect the surface pictures much, since this is much higher.
All in all, aerosols seem to be pretty uniformly distributed in most of the atmosphere

Posted by: ugordan May 17 2006, 12:24 PM

Are you sure such high a resolution is possible at Titan? Given the staggering height the atmosphere towers upwards, how strong is the Rayleigh scattering at 2 microns? Would it be a contributing factor at all in blurring the surface view or does the effect merely reduce surface contrast?

Posted by: BruceMoomaw May 19 2006, 12:06 PM

Quoting Ralph Lorenz from 7 years ago ( http://www.lpi.usra.edu/meetings/LPSC99/pdf/1088.pdf ):

"The extended nature of Titan's atmosphere makes it impossible to sustain an orbiter for substantial (>1 month) durations against drag unless the orbital altitude is significantly larger than 1200 km. This is an appreciable fraction of the planetary radius of 2575 km -- this altitude makes subsurface radar sounding essentially impossible. Further, scattering by the thick atmospheric haze which extends to about 200 km altitude makes optical remote sensing difficult. High-resolution surface and subsurface sensing therefore requires a platform beneath the haze -- at a few tens of km altitude at most. Most of what can be achieved from orbit will be done by Cassini."

No wonder he expressed such fondness to me recently about the possibility of a nonlanding balloon as the next Titan mission.

"Subsurface radar sounding at metre wavelengths [from an aerial platform] is an attractive technique, and is much easier to perform from a few kilometres altitude than from orbit. This would allow the detection of subsurface structures and inventory subsurface reservoirs of organics, as well as probing the depths of lakes and seas. This instrument could also supply an altitude measurement."