Mission description:
http://saturn.jpl.nasa.gov/files/20090521_...description.pdf

"RADAR: The SAR swath sweeps down across the Shangri-La dunefields and into high Southern latitudes. This begins a sequence of near-parallel SAR swaths HiSAR north of Xanadu and over southern polar regions"

Sweeeet!

When do we get to observe Ontario Lacus with SAR - in a mode that can produce a "visual" image??

On my birthday, July 8th
http://saturn.jpl.nasa.gov/mission/saturntourdates/

T58.

But what is a "visual" image? (or more specifically, what is a nonvisual image?)
.

'Looking ahead' for T55:
http://ciclops.org/view/5641/Rev111

I believe the last observation of this feature was altimetery? I mean data that's able to produce a radar "image"

T49 was altimetry over Ontario.

But you can make an 'image' with altimetry - y-axis is range, x-axis is along-track distance -
to form a 'radargram' (the MARSIS soundings of the Martian polar cap are plotted this way).

Radar data is just the voltage vs time on the antenna - you
can process it into an image, or a plot, or whatever you want. We have even made maps of Titan with
just radiometry - those are 'visual images' too. For that matter, the Zebker paper on Titan's shape
is an 'image' of surface height - from altimetry data.

Sorry, I'm being pedantic. The answer to the short version of your question (when do we get SAR imaging)
is T58. But 'visual image' is meaningless...

To get really, really pedantic: "visually" = what we would see with our own eyeballs from that location.

From orbit, Ontario Lacus would look like the rest of the lit portion of Titan, a big fuzzy orange ball.

But you can create 'visual representations' of data that can penetrate the haze: infrared, multispectral infrared (VIMS), RADAR, radiometry, altimetry, and derived dielectric constant. Each of the 'visual representations' is in effect a projected data map that has been contrast-stretched to put the data into a useful rescaled range.

The resulting 'visual representation' needs to be interpreted with respect to the acquired data. Ontario Lacus is dark by RADAR not necessarily because it is visually black, but because RADAR dark means smooth.

I recall reading that you would be able to see the surface features with your own eyeballs by the simple expedient of viewing through red glass. For some reason I find that fact comforting. It conjures up scenes of tourists in an observation lounge being issued with special specs. "Titan coming up on the left - you'll need your red glasses to make out the dark shape of Ontario Lacus and the channels draining into it."

....and since the detached haze layer stands out better in blue light, you could use your red-blue 3-D glasses to get the detached haze layer in one eyeball and the surface features in the other eyeball.

I think you *might* be able to see the surface through red-filtered glasses, but the contrast would be very low still. I did a couple of enhancements of RGB images that show the red filter does show hints of the surface, but it's far from obvious unless you stare really hard:

http://www.flickr.com/photos/ugordan/819214959/
http://www.flickr.com/photos/ugordan/820441390/

Technically it can be just detected with an orange filter, as was demonstrated with Voyager images.

http://www.astro.cornell.edu/~richardson/vgertitan.html

New images are up!

http://saturn.jpl.nasa.gov/photos/raw/rawi...?imageID=191773

What the hey???

The images were up, but a few seconds later they are not....now just an empty square with the title identifier. But older raw images pictures are still available on the site.

(Man, I really hate the new site...)
(And yes, I sent a detailed 'helpful suggestion' e-mail several months ago)

[/frustration mode]

Is that a cloud streak? Whereabouts are we here?

http://saturn.jpl.nasa.gov/multimedia/imag...0/N00136311.jpg

Here's the image, quick before it disappears!

N00136304.jpg
Click to view attachment

[EDIT: This is a picture of "Little Adiri" in the S Senkyo sand sea. The Playboy Peninsula is on the right hand side in the image. In the N00136304 image S is at the top. The image is centered at approximately [-10S, 340 W]]

Mike, it's my recent impression that the site goes screwy mainly when new images are being posted then settles down to normal function.

Yeah, these images are popping in and out on the Cassini mission website right now. It's almost (but not quite) amusing. I feel like I'm playing whack-a-mole with the raws.

Maybe the server is being overloaded as everyone wakes up to download the fresh images?

Here is a quick mosaic of the T55 Flyby raw images:
Click to view attachment

The image that Nigel mentioned is at the lower left. (Images reoriented so that N is roughly at top)

T55 mosaic with potential cloud streaks indicated (more tentative streaks in dotted arrow). These are located at approximately -50 S.

Click to view attachment

The streaks are in images N00136311.jpg, N00136312.jpg, N00136313.jpg (longer streak at lower left)
and N00136301.jpg and N00136302.jpg (smaller streak at center).

-Mike

It can't handle both of us at once, obviously.

Thanks for posting that useful mosaic.

Sweet is putting it mildly!!!!
The caption says this was acquired on the 25th? but I thought the RADAR sweep was to be on the 21st?? of May. This photo appeared today on a NASA Cassini update link.http://www.nasa.gov/mission_pages/cassini/main/index.html

Click to view attachment
Complex and unique canyon systems appear to have been intricately carved into older terrain by the ample flow of liquid methane rivers on Saturn's moon Titan, as seen in this radar image taken by NASA's Cassini spacecraft on May 25, 2009.

The channels seen here indicate that fluids flowed from high plateaus on the right to lowland areas on the left. In the center of the image, the wide distribution of the channels' tributaries suggests that rainfall is effectively eroding the surface. The bright terrain toward the bottom of the image is interpreted as high cliffs and broken bedrock.

These canyon systems remind us that Titan is (or has recently been) a dynamic world with a complicated geological history. Multiple channels have flowed into a wide, dark arc in the center of this mountainous region. Here, the canyons appear to have been filled by fine-grained materials that appear dark (smooth) to Cassini's synthetic aperture radar. These canyon-filling materials were later carved by a large river channel that winds from the bottom left of the image toward the left center.

The image center is at 71 degrees south latitude, 240 degrees west longitude, and its dimensions are 335 by 289 kilometers (208 by 179 miles). The radar illuminated this area from the top of the image at 18 degrees incidence angle. The areas seen here are typical of other regions observed near Titan's south pole in other flybys (see PIA10018).

Another recent (?May 25th,2009) SAR image. (a thousand pardons if someone has already posted this!)

Click to view attachment

An intricate, fingerprint-like pattern of dunes is seen in this dramatic radar image of Saturn's moon Titan captured by NASA's Cassini spacecraft on May 25, 2009 from an altitude of 965 kilometers (about 600 miles). The dunes likely consist of sand-sized particles made of organic material.

On Earth, dunes preferentially form in low-lying regions as hills or mountains present an obstacle to the movement of sand-sized particles. The general absence of dunes on the bright patches seen here supports the notion that they are likely topographically high regions or mountains that block the dunes. The forked tongue of dunes crossing the bright patch at right may have formed in a relatively low-lying valley in the bright terrain.

The significant variations in spacing and density of the dunes indicate a variation in the sand supply and/or local differences in winds at the surface. The dunes are roughly symmetrical around the irregular bright region in the left half of the image, suggesting that the bright region is somehow responsible for creating the pattern.

The area imaged is 225 by 636 kilometers (140 by 395 miles), centered just north of the equator at 0.5 deg N latitude, 154.2 degrees W longitude. Radar illumination is from the top at an incidence angle of 24 degrees. North is to the right in this image. The obvious horizontal stripes across the center and top of this preliminary version are artifacts of the way the image is produced.

Very cool for the rapid release of the image!

The funky splotty looking thing is the splot in Shangri-La to the immediate NNW of Kerguelen Facula.

For context for you guys for the second segment titanicrivers posted:

Fantastic images! Looking at the dunes one carefully I'm starting to think that the dune spacing correlates with the brightness of the substrate - brighter substrate, wider dune spacing. I wonder if there's any mileage in that idea? I haven't even begun to guess what that might imply if true - except that it could be something to do with winds.

Well, wider spacing would reveal more substrate hence making it look brighter anyway, regardless of the actual brightness of the substrate itself.

OK I've just been in to read the image captions - should have done that before posting I guess. Note this paragraph.

QUOTE:
The significant variations in spacing and density of the dunes indicate a variation in the sand supply and/or local differences in winds at the surface. The dunes are roughly symmetrical around the irregular bright region in the left half of the image, suggesting that the bright region is somehow responsible for creating the pattern.
UNQUOTE

It seems that topographical control of the dune distribution is being played down pretty rapidly now in favour of a 'somehow' involving winds and albedo.

Edit: remcook - I think we can see enough interdune over large portions of this image to map its brightness independently of the proportion of dune cover.

Albedo seems to correlate to elevatoin roughly on a local scale. (But not regional - Shangri La is elevated relative to SW Xanadu)

So the RADAR bright spot mentioned in the caption (probably VIMS Equatorial Bright terrain) that the dunes are going around is likely elevated and deflecting the winds.

Check out some of the "islands" in central Belet in the T8 Swath for really cool examples of this effect.

The RADAR medium gray spot (further N) with lower density of dunes is likely VIMS dark blue unit (ice sands?) and is sitting in the sand sea at the same elevation as the dunes. (These are usually downwind of some sort of Equatorial Bright terrain).

Granted, local topography is likely one piece in the puzzle that comes into play in certain cases, but is it a necessary or sufficient condition for the formation and maintenance of a 'bright island'? Time will tell.

"The image center is at 71 degrees south latitude, 240 degrees west longitude, and its dimensions are 335 by 289 kilometers (208 by 179 miles). The radar illuminated this area from the top of the image at 18 degrees incidence angle. The areas seen here are typical of other regions observed near Titan's south pole in other flybys (see PIA10018)".
[/quote]

Here's a rough context for PIA12036 image (see below at arrow) with the river dissected high southern polar region in post #23 above. I'm not sure of the exact orientation of the image but have tried to place it at scale, at the -71 latitude and 240 W longitude center indicated in the caption. Such gorgeous geography gives one hope many of the albedo alterations not yet imaged in high resolution will turn out to be exciting erosional edifices. (sorry 'bout the alliteration attempt).

Click to view attachment

That beautiful 2007 (T27) VIMS image (PIA12005) provides intriguing speculation that some of those cool river valleys of PIA12036 may have some misty methane mornings or even puddles on their floors!

Click to view attachment

T55 RADAR swath.
Click to view attachment