Here is a mosaic of Xanadu that includes:

• Section of Oct 2007 Titan Map (PIA08399)
• T47 SE Xanadu - Hotei Arcus mosaic
• T13 SAR RADAR Swath (PIA08552)
• T3 SAR RADAR Swath (left part from VP's website)
• T20 SAR distant targeted look (also from VP's website)
• PIA10654 SAR image of tectonic ridges in NW Xanadu

Click to view attachment
Some of the higher latitude swaths were skewed slightly by myself to try to better fit the ISS projection. There are mismatches, particularly for the non-equatorial swaths. The resolution is approximately 6 km/pixel.

A higher resolution (ca. 1.4 km/pixel) jpeg can be downloaded here (WARNING: 7 Mb file)

This will be a handy basemap for Xanadu mosaics and the upcoming RADAR releases.

-Mike

Here is a carefully coordinated blink animation of an enhanced VIMS image of a region in E Xanadu with the corresponding T13 SAR RADAR image overlayed on the T47 ISS Mosaic.
The VIMS image originally appeared in Figure 7 (specifically Figure 7b) from Barnes et al., JGR 112 (2007) E11006. "Near-infrared spectral mapping of Titan's mountains and channels". doi: 10.1029/2007JE002932 and is reproduced here with permission of the author. I increased the hue and saturation of the VIMS sections separately for effect.

Click to view attachment
(Animated GIF-click to animate)

There is a lot of stuff going on in here (indicated in static graphic below):
Click to view attachment
1) As originally mentioned in the Barnes et al., 2007 article, the VIMS bluer unit correlates to some of the RADAR bright tectonic ridges.
(Mabon Macula is the blue peak standing alone near the end of the T13 swath.)

2) From the image above (with the T47 SE Xanadu mosaic as the basemap), one can see that the bluer tectonic ridges form a series of concentric ridges (and valleys) that appear to bend around the entire Hotei Arcus structure located just to the S (the bright section at bottom center is the NE corner of Hotei Arcus)

3) Many (but not all) of the RADAR darker terrains (in this part of Xanadu) appear to correlate to a "yellower" VIMS unit. (From the Barnes et al. 2007 article, most of these terrains are similar to Equatorial bright, but the VIMS spectra are giving information on the "flavor" of the ices - the tectonic ridges are watery-icey flavored Equatorial bright, and the "yellower" VIMS unit is "more organic-icey flavored Equatorial bright.)

4) [a] At the upper corner of the indicated T13 swath, there is a circular form that looks very much like an infilled crater. (Radar bright rim, dark center, possible RADAR-brighter central peak, and at least two breaches in the walls). Unfortunately this area is just outside the VIMS imaged area. [b] However, one of the RADAR-darker flows to the E was imaged by VIMS and correlates to the "yellower" VIMS unit.

5) At the center of the VIMS imaged area, there is a RADAR darker area that appears to embay surrounding terrain. This area correlates to to the "yellower" VIMS unit.

6) The VIMS yellowish - RADAR darkish lobate embayment is not general. There is an arc-like feature (which also extends into the T47 ISS image) that has RADAR-darker sections that are yellow, but others that are VIMS "greenish". Some of the VIMS yellowish area at this feature correlates to the RADAR bright bounding ridges of the arc structure.

7) In general, many of the southern bounding ridges of the embaying valley material appear to be VIMS bluer ridges. (The center of the VIMS image shows an alternating pattern of blue ridges and yellowish valleys)

8) General observation: if the mountain shows RADAR "layover" it correlates to the VIMS bluer unit in this graphic.

9) (The VIMS blue area at the top right of the image that is RADAR dark is part of W Fensal)

(I did try to extend to ISS imagery, but I'm not yet confident enough in my coordination of the T47 mosaic images - the T46 images might be a bit easier to deal with. At this point I weakly suspect that the VIMS yellower unit correlates to a slightly brighter terrain in the ISS)

-Mike

Very nice work -- if they are concentric with Hotei that will be interesting to compare to what we see down south,

- Jason

Mike...

Remarkable work, as always.

Xanadu fascinates me..... we call it a 'continent', yet we really do not have a proper term for this albedo feature. SAR so far has not seen a lot of positive relief, yet the dunes 'flow' around her as an obstacle. Does not appear as if the Titan "rains" wash her clean of light albedo material which some see as an accumulation of the falling haze particles.
The feature is known to be rough. If this is an active area of cryovolcanism, perhaps the "hot spot" (how you get a cryo hot spot in an ice shell disconnected from the silicate interior is another question) keeps the ice soft enough to relax quickly.
Yet this feature is not anomalous in heat output.

Just fascinating set of unknowns. Mike, keep cataloging your interpretations.

P21A-1309 AGU abstract

The Dunes of Shangri-La : New Cassini RADAR results on patterns of aeolian features and the influence of topography

"Application of monopulse radar methods to retrieve elevations from Cassini SAR images ('SARTopo') now allows us to explore the influence of topography on the local dune (and by implication, wind) patterns, and the relationship between elevation and sediment accumulation. The lack of large positive relief at Xanadu makes its influence on the dunes somewhat surprising."

Craig

Mike -- can you post a version of the VIMS/radar blink comparison with the VIMS image fully opaque? I've found that when you do a blink comparison with one image translucently overlaid over the other, the translucency makes it hard to determine which things really are a synchronicity between the images.

Anyway, awesome work. Thanks!

Sure. Here it is (I toned down the saturation to a more reasonable level for a fully opaque image):

Click to view attachment
(click to animate)

Warning: The eye tries to make a "jump" between the RADAR-dark area and the VIMS blue area. But it is the RADAR-bright areas S of the RADAR-dark areas that line up with the VIMS blue areas. (so...Titan's Blue Ridge mountains?) This is why I prefer the translucent image above. Use the mouse cursor to serve as a placemarker on the blinked images.

(In fact, when I first read these articles a while ago, my eyes were guilty of making the same jump: doing the overlay exercise really helped me understand the text.)

-Mike

When I was doing the work I used a blink to figure out what was going on. But you can't put a blinking image on paper. Yet

- Jason

You sure this is lined up right? Does it take the 0.3 pole obliquity into account -
seems like moving the VIMS plot a bit north-south makes dark line up with radar-dark
rather better....

Yup. Real sure, at least based on the reported lat-lon in the article graphics. I clipped the actual figures from the text (RADAR and VIMS) and made sure the reported lat/lon lines lined up perfectly (less <1 pixel shift N-S based on tick marks).

The T13 RADAR portion in the article was slightly lower resolution, so the GIF I made used a higher res version.

Here is a blink animation with the article's VIMS (opaque with lat-lon lines), the article's T13 RADAR image, and my T13/T47 SE Xanadu mosaic, with successive removal of the article VIMS graphic , then removal of article RADAR graphic:
Click to view attachment
(Click to animate)

(As an independant check, look at the distinctive RADAR-dark feature centered at [-8.5S,76.5W]. The VIMS yellowish unit has the exact same pattern. In the VIMS it looks like a little yellowish running man with his legs to the S, in the RADAR dark only the RADAR dark legs are easily discerned.)
Click to view attachment

It was only when I did this precise overlay that I realized the correct correspondence of the units.

-Mike

[But as I stated before, I'm not sure that the underlying T47 ISS mosaic is correctly coordinated, there may be as much as a 2 degree distortion in my ISS placement].

The pointing errors in SPICE are bad enough that I lined this whole thing up by hand even back before we knew about the pole alignment offset. Furthermore this VIMS cube was taken at a gigantially high phase angle -- something like 120 degrees. So there could be warping through the image, to the effect that it could be perfectly aligned for parts of the image and off in others. Alignment is thought to be correct, but use at your own risk

- Jason

Article on Cassini website discussing cryovolcanic activity on Titan:
http://saturn.jpl.nasa.gov/news/press-rele....cfm?newsID=890

And....they released the RADAR image just north of Hotei Arcus!
http://photojournal.jpl.nasa.gov/catalog/PIA11702

Here's my attempt to locate the recently released RADAR image of Hotei Arcus on the Xandu Mosaic.
(I'll try to to a better job with Photoshop later):
Click to view attachment

If I got this right, I think the medium gray stuff corresponds to the ISS really bright stuff. The RADAR-dark gray outer ring corresponds to the darker arc outside Hotei Arcus. The RADAR-bright white stuff at the lower portion is completely outside Hotei Arcus, and is not so impressive in ISS (typical "Xanadu stuff").

(Did I get it right?)

-Mike

The Hotei Arcus SAR segment is larger than shown in that graphic.

Has it been released anywhere?

No, I mean the segment released is larger than you scaled it in the image you just posted. Just a wee bit. Basically, you conclusions are correct though. The margin of Hotei in RADAR SAR corresponds to the bright arc in ISS. The dark arc in RADAR to the south of Hotei corresponds to intermediate albedo terrain on the outside of the bright arc in ISS. The dark material south of Hotei corresponds to mountains in RADAR.

Here is my latest try at a line up of the T41 chunk with the T13 and T47 ISS mosaic:
Click to view attachment

I'm having a really rough time lining up ISS with RADAR images inside Hotei Arcus.
I *think* the RADAR-dark channels insidethe arc correlate to ISS-dark channels inside the arc, but I'm not totally sure.

-Mike

Here is a graphic that compares Hotei Arcus to terrain on Earth at the same absolute km scale.
Click to view attachment

Both images are approximately 1300 km wide.
[For handy reference 1 degree longitude on Titan = 44 km, while 1 degree longitude on Earth = 111.32 km]

What is amazing is the sheer size of the Hotei Arcus structure. Note how the dark lobate flow patterns in Xanadu are immense compared to the dark basalt flows of the Great Rift flood basalts (which includes Craters of the Moon lava fields National Monument in Idaho). These are barely visible in the Google Earth image at this scale.

The subtle arc feature in the Google Earth image is the Snake River Plain volcanic province.
(The half-tone blue dot in the lower part of the GoogleEarth image is the Great Salt Lake in Utah.)

Hotei Arcus is big.

-Mike

Awhile back I was trying to find RADAR images of earth for my own sake of comparison... not really that easy. The SeaSat radar images seem to give you the same sort of scale and no clue what you're looking at without a caption.

Here's a graphic showing groundtracks that passed over Xanadu in 2008. (Almost all of them did.)
Thick line means groundtrack is in daylight, dashed line means groundtrack is in unlit terrain.

With basemap (for tomorrow's T49 flyby):
Click to view attachment

No basemap (annotations only):
Click to view attachment

-Mike

Equatorial Clouds over Xanadu just N of Hotei Arcus at ca. -19 S:
Click to view attachment
(Center frame is the Pinecone feature)

-Mike

Wow. That's somewhat unexpected, isn't it?

Maybe a sign of the changing of the seasons?

Since the white specks were gone by T46, it means that these were probably clouds, and not a long-term (>6 Earth months) surface deposit.

Another thing to look for would be to see if there are any changes in ISS in this area (especially where those big clouds were to the W). Is there a flooded playa down there?

There's been a lot of regular ISS coverage in that area (T44, T46, T47, T48). While playing around with the images, I haven't seen anything obvious, but maybe someone with better skills could spot it.

Wow, this is wonderful! I suppose these clouds are migrating ones or they might be similar to convective clouds following a monsoonal pattern here on Earth.

Thanks to VP's blink animation on the T41 thread, here is a coordinated VIMS/RADAR vs. ISS blink:

Click to view attachment
(click to animate)

(Key parts for the alignment/coordination: the brightish green yellow "C" shaped feature at upper left coordinates with a bright "C" shaped feature, and the VIMS yellowish bright splots at center coordinate with bright spots in the ISS image.)


RADAR dark lobate flow = RADAR dark (smooth) / VIMS yellowish (more organic) / ISS bright / embaying
Blue ice Tectonic ridges = RADAR bright and layover / VIMS blue (more water icey) / ISS dark / ridges and hills


In Xanadu T13 Swath, RADAR dark usually correlates with ISS bright.
In the Equatorial dune seas, RADAR dark correlates with ISS dark.

In Xanadu T13 Swath, RADAR bright usually correlates with ISS dark.
In the Equatorial dune seas, RADAR bright usually correlates with ISS bright.

In Xanadu T13 VIMS bluish (more water icey) correlates with ISS dark/RADAR bright
VIMS yellowish (more organic) correlates with ISS bright/RADAR dark.

But there are also areas that are RADAR bright that correlate to VIMS yellowish-green. These are ISS bright also.
But as a general rule for the T13 in Xanadu: The ISS brightest regions correlate to the RADAR darkest regions.

Here is a blink animation between T13 RADAR and ISS of the above region. They are anticorrelated:

Click to view attachment
(click to animate)

-Mike

In the T13 Xanadu swath The ISS brightest regions correlate to the RADAR darkest regions.

To really drive this home, here is a blink animation between an INVERTED T13 RADAR and ISS of the above region:
Click to view attachment
(click to animate)

They line up pretty good!

-Mike

Using ISS to model/predict the VIMS ratio'd image in Xanadu:

Click to view attachment
(click to animate)
(VIMS actual vs. VIMS model)

Close.....

-Mike

Here are the pseudocolorized T13 and T41 SAR RADAR Swaths over my T46 + T47 partial ISS mosaic of the Hotei Arcus region:

Click to view attachment

I used the "Xanadu Color scheme" but with my homemade mosaic as basemap.

-Mike

A 25% RADAR Swath version (64 pixels per degree, ca. 1 km / pixel resolution) is available here: http://www.flickr.com/photos/31678681@N07/...0/?reuploaded=1

Recent articles provide evidence that Hotei Arcus is ACTIVE!

"[Hotei Arcus] may be the largest active surface region in the Solar System" (Nelson, Icarus, 2009)

Nelson, R.M. et al. Icarus 199 (2009) 429-441. "Saturn's Titan: Surface change, ammonia, and implications for atmospheric and tectonic activity." doi: 10.1016/j.icarus.2008.08.013.

Nelson, R.M et al. Geophysical Research Letters 36 (2009) L04202. "Photometric changes on Saturn's Titan: Evidence for active cryovolcanism". doi: 10.1029/2008GL036206.

Wall, S.D., et al. Geophysical Research Letters 36 (2009) L04203. "Cassini RADAR images at Hotei Arcus and western Xanadu, Titan: Evidence for geologically recent activity". doi: 10.1029/2008GL036415.

Stofan E.R., et al., LPSC 40 (2009) Abstract 1043. "Morphology of Four Flow Fields on Titan: Implications for Modes of Origin."
(freely available here: http://www.lpi.usra.edu/meetings/lpsc2009/pdf/1043.pdf)

Kirk, R.L. et al, LPSC 40 (2009) Abstract 1413. "Three-dimensional views of Titan's diverse features from Cassini RADAR Stereogrammetry."
(freely available here: http://www.lpi.usra.edu/meetings/lpsc2009/pdf/1413.pdf )

Nelson, R.M. et al., LPSC 40 (2009) Abstract 2262. "Cassini Evidence for active cryovolcanism on Saturn's moon Titan."
(freely available here: http://www.lpi.usra.edu/meetings/lpsc2009/pdf/2262.pdf)

Evidence includes:
* Varying brightness (increasing, then dropping, then increasing, then dropping again) [Nelson et al., Icarus, 2009, figure 2 in text]
* Brightening also correlated to areal extent of change (big brightness, bigger area affected) [Nelson et al., Icarus, 2009]
* VIMS spectral signature during brightening events consistent with NH3 deposit on water ice grains. [Nelson et al., Icarus 2009, figure 3 in text]
* RADAR medium-bright digitate lobate features overlaying darker terrain AND overlaying bright channels [Wall et al. Geophys Res. Lett., 2009 and Stofan et al., LPSC 40 (2009).
* RADAR medium-bright digitate lobate features are topographically lower.
* VIMS changes observed between November 19 (T47) and December 5 (T48) of 2008 (3 months ago!!!!)

Some quotes lifted from the articles:
"We interpret these [light gray features] as multiple, coalescing cryovolcanic lava flows where the SAR-brighter unit has flowed over the darker substrate." (Wall et al., 2009)

"The flows at Hotei [Arcus] appear to have multiple sources and have flowed in a relatively flat area, resulting in coalescence fo multiple flows." (Wall et al., 2009)

"We conclude that the best interpretation of these [changing VIMS results] involves ammonia being deposited episodically on Titan's surface and is covered [or chemically decomposed] over on a short time scale." (Nelson, Icarus, 2009)

"We note that the areas that has changed [photometrically] is twice the size of the big isalnd of Hawaii and comparable to Io's Loki. If the entire reflective region is part of the activity, it size is of Krakatoan proportions." (Nelson, Icarus, 2009)

"The high resolution [VIMS] images also suggest that changes in brightness and morphology occured between the T47 and T48 flybys." (Nelson et al., LPSC, 2009)

-Mike

Animated GIF of T44-T46-T47-T48 flyby's of the Hotei Arcus "Pinecone" feature.
(Indicated as Hotei Arcus lobate flow feature "F2" in figure 2 of Nelson et al., LPSC 200 (2009) Abstract 2262.)
Click to view attachment
(click to animate)

(These were made from Cassini raw images by using variable contrast gradients to try to cancel out haze and lighting effects. There is no obvious change in the Pinecone feature that could not be an artifact from my processing).

-Mike

Based on the Wall, S.D., et al. Geophys. Res. Lett. (2009) article, here is an annotated view of the T41 RADAR section over Hotei Arcus placed over my ISS mosaic (contrast enhanced).
Click to view attachment

The medium-gray digitate lobate flow is proposed to be a series of geologically young cryobasalt flows.
They are at lower altitude.
The darker material is the older substrate.
The outermost arc of RADAR-bright mountains and ridges is presumably the outer edge of the cryovolcanic province
The channels drain down into the "caldera" floor. At the base of the floor, the cryolava oozed and and creeped along the lowest parts of the dark-filled basin.
(Presumably, the Pinecone feature is also a cryobasalt flow)

-Mike

Using Kirk et al., LPSC 40 (2009) Abstract 1413 stereogrammatry plot of the T41-T43 overlap region, I made a cross section of the T41 Hotei Arcus across a prominent flow and up the southern rim of the entire feature:
Click to view attachment

The track direction is from NW to SE.
The medium-gray lobate digitate flow is LOWER than the RADAR darker gray-black material. In fact, it appears that a darker gray-black material "ridge" is bounding the toe-front of the flow. The medium-gray digitate flow superposes the channels (according to Wall, S.D. et al., 2009).

As one moves away from the flow front, one climbs in elevation to cross more RADAR dark material (which also looks kinda lobate). This RADAR-darker material is crossed by bright channels.

This is similar to the RADAR-dark lobate flows seen in the eastern end of the T13 SAR RADAR swath (whose RADAR bright channels were VIMS dark blue unit) and also near the Flower Petal crater near Adiri in T8. (Is this related to other RADAR-bright channels seen on RADAR dark terrain in Adiri?)

Could this be older-eroded cryo-flood basalt? Channels superpose this terrain.

And finally, at the SE end of the indicated track one climbs up to the rim of the entire structure onto more "typical" mountainous terrain with a predominant E-W orientation (seen at the E edge of the T41 Swath).

A higher-resolution version with annotations is here: http://www.flickr.com/photos/31678681@N07/...157614820589732
-Mike

February 22, 2008 SAR released in NASA Photojournal.

http://photojournal.jpl.nasa.gov/catalog/PIA11822

Craig

Fantastic! The right hand bottom corner - where do those streams come from? The 'sunless sea' under Xanadu?

No shortage of sinuous rill[e]s, either...

Hotei Arcus: Hi-resolution and in 3-D!!!
http://photojournal.jpl.nasa.gov/catalog/PIA11831

VIMS of Hotei Arcus released! PIA11839 available here: http://photojournal.jpl.nasa.gov/catalog/PIA11839

Here is a graphic with a combination of [ISS combo (mine), T13 SAR RADAR Swath, VIMS graphic from Barnes et al., T41 SAR Swath] compared with the recently released VIMS image of Hotei Arcus:
Click to view attachment

The Pinecone feature (indicated by red arrow) is tinted slightly reddish, indicating something slightly different from surrounding Hotei Arcus terrain. [Nelson et al. indicated this was an area also that changed brightness between flybys].

Towards the SE, indicated by red fiduciary marks and yellow arrow, there is a region that is "chemically distinct from its surroundings, which may correspond to the most recent location of activity." [quote from planetary photojournal page).

-Mike

I took my work-in-progress T46,T47, and T48 Hotei Arcus ISS mosaic and combined with a blurred VIMS image from PIA11839.
Contrast-enhancement and color saturation were done profusely.

Here is the ISS-VIMS combination image:
Click to view attachment


A higher resolution image can be found here (orginal size is 10 Mb): http://www.flickr.com/photos/31678681@N07/3423408742/

-Mike

Interim ISS mosaic of Hotei Arcus region Xanadu from T46 and T47 Cassini raw images near Hotei Arcus available here:
http://www.flickr.com/photos/31678681@N07/3426532140/


Six frames around Hotei Arcus from the T46 flyby are overlaid on a T46 wider angle (but still NAC) image of the western section of Hotei Arcus, which is in turn overlaid on the T47 raw image mosaic.

It is still a work-in-progress...

-Mike

Latest version of Hotei Arcus region ISS mosaic assembled from Cassini T46 flyby raw images:
http://www.flickr.com/photos/31678681@N07/3441583062/

(Still working on this....)

-Mike