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Posted by: volcanopele Nov 1 2005, 06:34 PM

The RADAR team today released portions of the SAR swath acquired during the T8 encounter Friday morning. For reference, a map of their coverage is available at :

http://pirlwww.lpl.arizona.edu/~perry/T8_RADAR_coverage.jpg

I will be updating this map to include boxes showing the locations of the sections released.

Tectonic Features
http://photojournal.jpl.nasa.gov/catalog/PIA03566
This image shows feature in the central part of Adiri. For comparison, check out the http://photojournal.jpl.nasa.gov/catalog/PIA07239 released in January. The areas covered in cat scratches in this RADAR view are the dark features seen in the middle of Adiri near center left in the VIMS mosaic. The somewhat lighter band running from top to bottom in the RADAR view just left of center is the bright north-stripe in the middle of the dark patch in the VIMS view. Other cat scratchless areas in the RADAR view correspond to bright albedo features in VIMS and ISS.

Note here chains of ridges and hills within Adiri, suggesting tectonic activity. The ring of material at far left may be a degraded crater but that hasn't been confirmed.

Dunes Galore
http://photojournal.jpl.nasa.gov/catalog/PIA03567
This image shows cat scratches, thought to be longitudinal dunes, in southeastern Senkyo. Again, in the equatorial regions of Titan, we see these dunes covering much of the landscape. You can see stream line forms assocated with aeolian erosion (not caused by liquid methane flow, these dunes are WAY too big for that).

Diverse Geology
http://photojournal.jpl.nasa.gov/catalog/PIA03568
This image covers several large islands in the divide between Senyko and Belet. Note the dark, stubby channel terminator in good sized smooth region without cat scratches. So there is at least some evidence for fluid flow in the equatorial regions.

Pinpointing Huygens Landing Site
http://photojournal.jpl.nasa.gov/catalog/PIA03569
This composite shows the Huygens landing site region. Note that the position may shift slightly over time, probably slightly to the north east, as I think the island to the north of the current position is the large island seen in Huygens images. The two cat scratches seen in the RADAR swath north of the landing site maybe the two dark lines seen in Rene's mosaic. Definitely will need confirmation of this. Note once again the prevalence of dunes north of the landing site, forming stream-lined forms (once again let me stress that the fluid is the atmosphere).

Posted by: djellison Nov 1 2005, 06:42 PM

Wow.

This place just keeps asking more questions that we're able to answer

Doug

Posted by: imran Nov 1 2005, 07:01 PM

Awesome! Thanks!

The "cat-scratches" seem more common here, although I should caution myself that we have seen just a tiny percentage of the equatorial region.

Posted by: volcanopele Nov 1 2005, 07:05 PM

This swath, while thin, covers a significant chunk of the trailing hemisphere of Titan, longitude wise, giving us a greak cross-section of terrains. Considering that we saw these cat scratch dunes filling much ofthe northeastern Fensal in T3, so I don't think it is unreasonable to think that much of the dark terrain at low latitudes consist of these dunes.

Posted by: RPascal Nov 1 2005, 08:30 PM

Thank you, Jason!!!

Looks as if it would not be so easy to position the Huygens mosaic within the radar map...
Is it possible to get the radar map of the Huygens landing site without the mosaic inset?

--René

Posted by: volcanopele Nov 1 2005, 09:21 PM

Unfortunately no :-(

Posted by: wohba Nov 2 2005, 05:32 AM

Enhanced the radar images a bit to bring out height of features based on grayscale.

http://wohba.com/2005/11/another-titan-pass.html

Posted by: David Nov 2 2005, 05:55 AM

Evidently the radar doesn't have the resolution to pick out even the largest of the runoff channels visible in the Huygens imagery. That's too bad, but it's good to know.

Posted by: alan Nov 2 2005, 01:05 PM

I don't care for the way they stitched together the various strips in the view of the landing site. The middle strip, you can see how jutting out on the far right, has the most contrast. Instead of letting all of it show they covered 2/3 of it with the lower contrast strips above and below it so we loose most of the contrast in the landing area.

Posted by: Bill Harris Nov 2 2005, 01:48 PM

In the image attached to your post: There is a lineation horizontally across the center of the image. Is this an artifact of the stitching or is it an actual ground feature? It looks a lot like strike-slip fault...

--Bill

Posted by: The Messenger Nov 2 2005, 02:56 PM

The magnitude, the orientation, and the continuity of the dunes just floors me. It is hard to find an analogy.

Posted by: exoplanet Nov 2 2005, 03:41 PM

Just curious - is it possible that these dunes were not created by wind but by liquid? I remember seeing what are called "linear tidal dunes" (hope this term is right) on tidal flats. They appeared to be nearly perfectly straight and shaped similarly to what is seen in the radar swaths on Titan.

From what Huygens determined upon landing, there is a crusty upper layer with a mud like texture underneath. When I see all those cleanly washed rounded pebbles - I can't help to think that the landing site was a tidal flat and not nessesarily a playa. Very near the landing site - these dunes start to appear and are usually in the "lowland" areas.

Posted by: volcanopele Nov 2 2005, 05:22 PM

wohba: remember, brightness in SAR images is based on many different factors, not so much altitude. These factors include the roughness of terrain, the dielectic constant (and thus composition), volume scattering, and slope. So making it a DEM isn't telling us much.

exoplanet: these dunes are WAY too big, as I noted earlier, as well as being too widespread. Many of the smaller "islands" in the cat scratch terrain/equatorial dark terrain look stream lined, so they were definitely shaped by a fluid. On Titan we do have a fluid that is thick enough and forceful enough to produce these scales of features, and it's the atmosphere. Could we find a place where all the liquid went to die, so to speak, akin to the northern plains on Mars, sure, but until then, I think the simplest explaination is that these dunes were caused by winds.

The Messenger: I agree, but considering the possible amount of available particles and the lack of major topographic barriers for much of Belet and Shangri-la, it is not completely surprising to find such dunes running for so long. what is curious to me, if you look at PIA03568 ("Diverse Geology"), you will note that the winds on Titan are not always E-W, but seem to curve either northward, or southward in this case in response to major topographic boundaries. You can see this also in an http://photojournal.jpl.nasa.gov/catalog/PIA06991 (formerly "Great Britain"). Here the small, stream-lined "islands" SW of Shikoku, divert to the northeast and southeast, apparently because the winds in this region divert because of the Xanadu topographic obstacle.

Bill Harris: As alan noted, that is a seam between the beams in the RADAR swath. Remember, the SAR data in composed of 5 beams top to bottom, with the center beam, Beam 3, having the highest SNR. And alan, you are not missing much by the swath being composed this way.

Posted by: RPascal Nov 2 2005, 05:23 PM

I figured out this position of the ISS image to the radar swath data. It would mean that, if the Huygens landing site is indeed the eastermost tip of Adiri, it is perhaps not or not completely included in the radar swath, or am I wrong?

Posted by: volcanopele Nov 2 2005, 05:27 PM

actually, it was trimmed, the swath continues for probably another full length of the portion that was released. So that isn't the very end of the swath.

You got the positioning correct though. In terms of positioning, I somewhat agree with the RADAR teams position, though I think it could be a little farther to the north, closer to the island just north of where they marked the landing site. The biggest problem with positioning, is that, unlike the T3 swath, where RADAR bright ~ ISS/VIMS bright, that correlation breaks down in eastern Adiri, as you can seen in your ISS/RADAR merge. So if there isn't a correlation, it may make it a bit more difficult.

Posted by: Phil Stooke Nov 2 2005, 06:50 PM

Volcanopele, I agree with you that the 'island' north of the indicated site looks like a much better match.

Phil

Posted by: wohba Nov 2 2005, 08:19 PM

Good point. I understand.

I do think there is value in looking at the raw data in alternate forms. After doing the enhancements, the "dunes' begin to look more run-off related which seems to make more sense. And it is easier to see the landmasses between the dunes as "landmasses". The enhancements help me see alternate interpretations from the data that I had problems visualizing otherwise.

Posted by: volcanopele Nov 2 2005, 08:41 PM

okay, if it helps you visualize the data, that's fine. But quanitatively, it isn't as useful because there is definitely not a one-for-one correlation between SAR brightness and altitude. I just wanted to make the point that one has to be careful when looking at that image you produced,

Posted by: wohba Nov 2 2005, 11:51 PM

Actually this is an interesting discussion. Gonna push back a little - not to be antagonistic - but to present a point-of-view and gain some insight.

I think I could argue that we should be just as careful looking at the "raw" SAR image. The problem is that the process actually creates false "shadow" artifacts that cause us to see the image in 3D relief - with an assumed light-source from the "up" direction. Our brains perceive the "dunes" as sticking up because they have a radar shadow on their "down" side.

I think that by presenting an alternate ("enhanced" is the wrong word I suppose) version of the image we may gain something. My point in the previous post was that by processing the image the "dunes" begin to look more like "rifts". By presenting the alternative look, everyone has a chance to realize that they might have percieved the "raw" SAR image incorrectly - something they may not have realized otherwise.

I think your point would be that perhaps by presenting those images as "enhanced" people might have assumed they were more accurate than the "raw" images. I would concur (even as I hold to the possibility that they indeed might be more accurate.)

Thanks for your comments and the chance to chat about it. Honestly not trying to stir anything up. I am open to the fact that I might not have an accurate understanding of the SAR image data.

Posted by: alan Nov 3 2005, 01:30 AM

After comparing the images from Huygens, Radar and ISS I think this position would give a better match between the three images.

The Huygens image (from Rene's website) should be rotated ~30 degrees counter-clockwise to be oriented correctly.

Posted by: Phil Stooke Nov 3 2005, 02:00 PM

I think this new location marked in Alan's post is correct (see my previous post and Volcanopele's). But look north of the bright 'island' in both the Huygens mosaic and the radar image... two parallel dark stripes in pretty much the same place in each image. The Huygens images are very messy at a distance because of extreme compression, but still those dark stripes cross 2 or even 3 images... are they real? If so, they appear to be cat scratches!

Phil

Posted by: Phil Stooke Nov 3 2005, 02:05 PM

A reply to wohba regarding data visualization.

I think any image manipulation process which helps interpretation is OK, and there are lots of examples elsewhere on here, like the rover panoramas with extreme vertical stretching to enhance subtle topography. False color, pseudo-stereo from one image (see Hayabusa thread) and so on. But... a person who views the result without knowing what was done to achieve it can be SERIOUSLY misled. So it's very important to (1) understand the possibility for misinterpretation, and (2) accompany any image with a statement about what was done to it.

Phil

Posted by: Olvegg Nov 3 2005, 07:25 PM

I think that's right. Position chosen in official release looks oddly enough. There's no any contrast "shore" neither in RADAR swath nor in ISS picture.

I outline the best matched position both in RADAR and ISS images. The coast looks degraded in RADAR image, though some other "shorelines" look distinct (for example, "island" in the right bottom corner). I think the reason is that surface near the coast where Huygens landed is covered with centimeters-sized, radar-bright pebbles, delivering by rivers. It's getting smoother gradually to the east, forming sand dunes.

Posted by: ngunn Nov 4 2005, 12:30 PM

I was wondering: 1/ Would not the known strong relief pattern of at least the southern edge of the Huygens bright area ensure that it would be bright in radar too? 2/ Is there any direct evidence for vertical relief in the cat scratch areas? If so which are higher, the dark or he light stripes? And 3/ How accurate is the positioning of the possible cat scratches in Rene's mosaic? Is there an 'official' mosaic of this area?

Posted by: BruceMoomaw Nov 5 2005, 10:04 AM

I first saw these radar views at the COMPLEX meeting Tuesday, during Elizabeth Turtle's presentation. She mentioned Jason Perry (by name) as noting the possible correlation between the radar-detected cat scratches and those two dark lines in Rene Pascal's Huygens mosaic -- so she certainly thinks this may be correct. She didn't really have anything to say scientifically about the new radar mosaics, however, other than what's since been announced in the captions.

It's become painfully clear that, to understand Titan, one thing we need BADLY that Cassini can't provide is high-resolution topography profiles -- its resolution is only 20 km.

Posted by: Decepticon Nov 5 2005, 10:50 AM

I say dedicate future flybys to Radar mapping.

Posted by: RPascal Nov 5 2005, 05:35 PM

The two dark lines in the Huygens mosaic are real, I am rather shure about that, they can be seen in several SLI raw images: (better have a look at the panorama at the bottom; and may be the images 470 and 440 should have a somewhat larger overlap):
http://www.beugungsbild.de/huygens/huygens_distant_view.html

But I don’t think that the two cat scratches from the radar image are the two dark lines Huygens saw. If that would be the same two dark lines visible in the Huygens mosaic and panorama, we would have to think about a size calibration error again. With my old positioning that assumed a calibration misfit of a factor of 2.5, the two cat scratches should have been close to that position where they are now. But there are cat scratches (dunes) in many places, all running in west-east direction. I think the two lines visible in the Huygens images are invisible in the radar data, perhaps because they would be located close to the seam where details are less clear.

--René

Posted by: tfisher Nov 5 2005, 08:29 PM

How confident are you in the geometry of your projections of the more distant features? Just glancing at it, it looks like the DISR team's mosaic (http://www.planetary.org/news/2005/0505_New_Mosaics_of_Huygens_Titan_Images.html -- sorry I can't find the official link) has the a greater size scale out there. For instance, there is a dark "wishbone"-shaped feature at the far left of your huge mosaic. Its size is smaller than the length between the Huygens landing spot and the tip of the bright "arrow" feature. The "wishbone" appears in the lower left of the official mosaic, and is about double then length between the Huygens landing site and the tip of the "arrow".

If your projection has a systematic bias, maybe the dark lines are twice as large and twice as far away, which would help bring them to the scale and distance of the radar "cat scratches".

Posted by: Phil Stooke Nov 5 2005, 09:06 PM

The difference in geometry we are talking about here is basically a matter of which map projection each image is using. Are the different views point perspective, azimuthal equal area, gnomonic etc.? I don't know right now, but eventually we will get standard products in known projections, and then meaningful measurements can be made of didtant features. The choice of projection doesn't matter at the nadir (centre of the map) (because they all look the same), but it becomes increasingly important at a distance.

Anyway, it's interesting to speculate. I must admit I hoped to see more in the radar, but that may come later. The raw images may show more than these press versions...

Phil

Posted by: RPascal Nov 6 2005, 05:52 PM

I am not an expert concerning the projection methods, but to follow the classification used by these two ESA image products:
In stereographic Projection:
http://saturn.jpl.nasa.gov/multimedia/images/image-details.cfm?imageID=1527
and in gnomonic projection:
http://saturn.jpl.nasa.gov/multimedia/images/image-details.cfm?imageID=1528

my mosaics are all displayed in gnomonic projection.
Only the fisheye view:
http://www.beugungsbild.de/huygens/povray/Titan_fisheye.jpg
is rendered in stereographic projection.

Up to now I only knew these different projection methods for projecting curved surfaces to a plane. But that is not the problem with Huygens images, since the imaged area is so small that it can be assumed as being flat, the errors in stitching the images will be much larger.
This stereographic method (or fisheye view as I call it) is a nice method combining HRI, MRI and SLI images. Using the gnomonic projection method for the mosaic, as I did, has the disadvantage, that the images with the worst resolution and contrast at the rim are displayed with largest magnification. But you can directly compare them with the Cassini images after scaling them. You can read them like a topographical map (without topography included of course)
The position of the two black lines in my mosaic should be not too far away from the truth - such a large difference that it could be the two lines in the radar swath with one of the mosaic positions suggested up to now is not possible I think. You can check that by yourselve, one line (and a little bit of the second) is even visible in one of the MRI images (Nr.280):
http://www.beugungsbild.de/huygens/huygens_mosaic.html
and from geometrical considerations (Position of Huygens during that imaging sequence) it is not possible that these two lines are so much farther away that they could correspond with the two cat scratches from radar. Only if the position (or size) of the mosaic would change this could could be considered again.

--René

Posted by: Phil Stooke Nov 6 2005, 06:37 PM

Rene, thanks for this. I am very impressed with your work, by the way.

I'm a cartographer, so I always think in terms of map projections. I think we are talking about projections of two different things.

A region of a planet's surface can be plotted using standard map projections which will be based on the geometry of the body, with coordinates centred at the planet's centre of mass. But whenever we view the world we see it as if it's centred on us - like the astronomer's celestial sphere. So these Huygens images can be thought of as being projected onto the 'visual sphere' surrounding the camera at any particular height and moment in time. I think the stereographic projection you and others have used for the descent mosaics is a projection of the camera's 'visual sphere' (at certain standard heights). It's not the same result as you would get by projecting that image onto the surface of Titan and then making a standard map projection of that.

None of this matters - the mosaics are still really good. But it does mean they cannot be just laid over the orbital data to create a perfect match. The nadir will always look OK, but the distant areas will not match properly. Pov-ray could be used to switch from one to the other... if I have this right.

I'm not completely certain I do have this right... so I am very happy to be corrected.

Phil

Posted by: tfisher Nov 6 2005, 08:00 PM

Okay, when I overlay Rene's huge mosaic with the large DISR team's gnomic overview, and try to match distant features, this is what I get:

Rene's version is in green; the "official" version is in purple. The yellow ellipses mark the locations where I've made the two versions match. A couple of things stand out. One is that the smaller details near the landing site are significantly larger in Rene's version than the official version. Another is that the scale bars are out of whack by maybe a factor of two. I suspect this is because Rene's scale bar is valid for terrain near the landing site, but not more distant terrain.

Going by the DISR team's scale bar, the dark parrallel lines in Rene's mosiac are nearly 15 km north of the bright terrain and are separated by nearly 5 km. I would guess that since the dark lines are farther away from the landing site than the places where I matched the projections, in fact the scale is a bit more exaggerated out there.

Lets try to get a version of the radar image with a scale bar. If I match the scale-bar-equipped DISR team mosaic above with the inset in the image, this is the resulting scale:



(there has been a noticable revision in the stitching between the older DISR mosaic and the one they use for this graphic, but not I'm pretty sure this is within a percent or so of the correct scale according to the size of the inset)

The scale looks right for the cat scratches to be Rene's lines, if the actual descent location is the radar-bright terrain directly north of the yellow-outlined location, rather than east as has been suggested above.

Hmmm...

Posted by: Decepticon Nov 10 2005, 01:03 AM

Has the T8 full radar swath been released?

Also was the last Radar swath fully released?

Posted by: tfisher Nov 11 2005, 02:40 PM

I want to make a case for the more northerly option as Huygen's landing place.
I've combined the radar and ISS images, with ISS orange-brown and radar gray. Here's an animation going from mostly radar to mostly ISS and back:

(I tried to readjust the contrast in the upper-left part of the ISS image, where the original mosaic has a big jump...)

And here I've cartooned in the outlines of the light colored areas and the "cat scratches", with Rene's beatiful "distant view" inset for comparison.




The 15km scale bar comes from the ISS mosaic scale.

Posted by: The Messenger Nov 11 2005, 03:08 PM

Does anyone know how wide the error bars are on the Huygens' Landing site? Were they able to triangulate a position from the VLA signals? How great is the possibility the probe is literally off-the-radar?

Posted by: tfisher Nov 11 2005, 04:49 PM

I'm not sure I've heard an error figure, but its pretty safe to say they hit within, say, the ring labeled "50km" http://photojournal.jpl.nasa.gov/jpeg/PIA06172.jpg. (Note, that isn't the diameter of the ring, but rather the estimate of field view of Huygens from 50km elevation.)

The radar coverage of that ring is not quite complete on the eastern edge: only the center band of the 5 reaches all the way to the east.

Posted by: ljk4-1 Nov 11 2005, 04:54 PM

Did they try to pick a specific area to land on Titan, or was it a case of let's just try to land on the moon, period?

Posted by: tfisher Nov 11 2005, 05:29 PM

To quote an old page on the Planetary Society's news (from google cache--it doesn't seem to have survived their web revamping):



I suspect the original selection was based on what was convenient for Cassini's orbit to to arrange the geometry so that doppler effects wouldn't ruin Cassini's radio reception of Huygen's signal (remember, they discovered mid-flight the radio design had a flaw that it couldn't handle much doppler shift, so they had to replan the early orbits to get a more favorable geometry for the Huygens descent...).

Posted by: ngunn Nov 11 2005, 07:04 PM

Your case looks pretty good to me. I am particularly fascinated by the prominent circular feature near the west end of the more southerly cat scratch. Since the radar came out I've been trying to correlate this dark circular patch on the radar image with something on Rene's 'huge' mosaic but just couldn't make it fit. Now your interfading image provides the answer: The circle fades from dark-against-light to light-against-dark as you go betwen radar and ISS - a very striking change, I think.
Now there is a more or less circular bright feature in Rene's mosaic that is in just the right place, in agreement with the ISS. It would have been very difficult to find this correlation without all three images to compare. Could you get together with Rene and do three-way interfades perhaps?

Posted by: volcanopele Nov 16 2005, 03:40 PM

Low resolution versions of the complete T8 swath are now available:

http://photojournal.jpl.nasa.gov/catalog/PIA03571
http://photojournal.jpl.nasa.gov/catalog/PIA03570

Posted by: tasp Nov 16 2005, 03:56 PM

Watching the image shift back and forth I find myself amazed at how perfect the registration is.

Also, the top half of the image has numerous circular features. Craters?

What is the smallest crater size expected on Titan from atmospheric effects weeding out the smaller rocks?

Posted by: Matt Nov 16 2005, 04:55 PM

There shouldn't be any impact craters smaller than about 20 km across.

Anything that would produce a crater smaller than that would likely be screened out by the atmosphere.

The only unambiguous features I have seen have been on the 100 km-plus scale.

There are some smaller candidates which appear to have been mostly buried.......but they could just as likely be something else.......

Posted by: elakdawalla Nov 16 2005, 05:09 PM

The story is now posted on the new site at http://www.planetary.org/news/2004/1028_Cassinis_First_Close_Flyby_of_Titan.html
--Emily

Posted by: chris Nov 16 2005, 05:52 PM

Nice write up Emily

Chris

Posted by: tasp Nov 16 2005, 06:25 PM

Even an analog to polygonal arctic terrain seems to exist in the upper left. I assume the scale is wrong for that interpretation.

Geysers? Tar pits? Mud pots? Fumaroles?

Posted by: Matt Nov 16 2005, 08:51 PM

They could be fractures

Posted by: Phil Stooke Nov 16 2005, 09:08 PM

The features referred to as polygonal terrain are too close to the scale of the speckled pattern (which is just noise) to be interpreted with any confidence. Actually, more useful results would be had by merging the two images (after removing artifacts like frame boundaries, and being certain of correct registration), as that would reduce noise to some extent.

Phil

Posted by: BruceMoomaw Nov 17 2005, 02:25 AM

The pre-Cassini estimate was that there should be about 90 craters more than 20 km wide on the part of Titan seen by the craft so far if the surface is a billion years old. So far there are still only 2 confirmed ones, and about 6 other possible ones -- so the surface is, at absolute most, only a few hundred million years old, and maybe a lot younger.

Posted by: Decepticon Nov 17 2005, 02:37 AM

Are there any future radar passes over Elba Facula?

Posted by: jmknapp Nov 18 2005, 03:22 AM

I don't think they're planning any for the main mission. Here's a map showing the radar tracks for the flybys up to T44, May 2008, (click for larger image):

http://cassinicam.com/titanflybys/titantracks.html

Looks like they miss Elba Facula (at far right).

Posted by: elakdawalla Nov 18 2005, 04:01 AM

JMKnapp, you are incredible. I have been begging and pleading with various RADAR people for a long time to get a map like this. Who knew the necessary data was out there in the public domain! Thank you for putting this together and sharing it with us.

--Emily

Posted by: JRehling Nov 18 2005, 06:33 AM

Blockbuster post, JMK!

Back on the main page of that site, the flyby info shows something I've long wondered -- even more than the RADAR track info: How long until the last major midlatitude region (around Belet -- formerly known as the Dragon) is imaged in ISS/VIMS? And the answer is: Summer 2007, with only one flyby in the entire primary mission showing that region in daylight. That is by far the most unique value Titan flyby of the primary mission, since the other regions will be flown over multiple, even many, times. If you're waiting for the IR map (south of the now-dark north polar region) to be reasonably complete, that's your deadline, about 20 months away.

The Fensal region won't get any good IR looks until Oct 2006, 11 months away.

Of course, the north pole will have to wait until an extended mission for it to even be illuminated, although about 9 RADAR tracks pass somewhere north of 60N, which makes that almost the region of greatest scrutiny by RADAR.

Roughly speaking, it'll take about 75 RADAR tracks to map Titan fairly completely. (That won't actually complete things, leaving no blanks, but it'll cover the great majority of the area, show us representative terrains, probably, of the whole globe, and let us interpolate with guesswork the rest.) That would comprise about 5 years' worth of flybys beyond the primary mission if every single orbit was a Titan RADAR orbit -- and if orbital mechanics kept passes from duplicating each others' efforts too much. Realistically, it would take about 7 years (when you factor in non-Titan priorities and inevitably lack of total serendipity in getting new coverage with every pass). So, assuming the extended missions resemble the primary mission, but with RADAR taking over almost totally the Titan passes, we have about a ten-year process from 2005-2015 during which Titan will gradually fill in for our benefit. A marathon, not a sprint.

Posted by: ljk4-1 Nov 18 2005, 01:55 PM

Are there any plans in the works for a Titan orbiter, which could reduce the radar mapping time of the moon?

Could a lander come along with it too, even if it was just a souped up version of Huygens?

Posted by: ugordan Nov 18 2005, 02:28 PM

As someone already put it nicely, Europa and Titan both struggle for a flagship mission (which an orbiter for either of the two will probably need to be). As I understand, a Europa orbiter mission is of a higher priority and it, by itself, cannot launch before sometime in the next decade. That would put a potential Titan orbiter quite a long way in the future. Probably second half ot the next decade at the earliest...

As for a lander, I don't know how much cheaper or more feasible it would be to drop an RTG powered aerobot into Titan's atmosphere and have a small, light relay orbiter in Saturn orbit. The aerobot would need to be dropped off before Saturn orbit insertion, to cut down on fuel mass. It could probably be done, but would wind up pretty expensive by itself.

I'd rather like to see a high spectral and spatial resolution imager (sort of like VIMS on steroids) in Titan orbit than a radar instrument.

Posted by: tasp Nov 18 2005, 02:39 PM

Has entry into Saturn orbit via Titan atmospheric grazing been studied?

It seems on a scale of 28 years or so, Titan's atmosphere should be very predictable (but I could be wrong if random Titan volcanic activity heats the atmosphere)

This technique might even help a craft wind up at a relatively low speed near another moon of Saturn for orbit insertion.

Posted by: ugordan Nov 18 2005, 03:04 PM

Aerobraking was most probably already studied, it's in fact hard to resist such an obvious and relatively cost-effective way to get rid of excess velocity. The problem is, aerobraking hasn't been tested yet at reasonably high drag (apart from Mars-bound spacecraft which brake very carefully and slowly, they don't perform orbit insertion that way, only orbital trimming). New materials ("ballutes") will need to be developed and the concept proof tested before it'll get deployed on a mission of such a magnitude as a Titan orbiter would be.


That brings me to another issue I'm wondering about: Of all the Saturnian inner moons, around which ones could you get into orbit? I've been playing around with Orbiter (I know, probably not the most precise app for testing stuff like that), trying to get into orbit around Enceladus, but I always drift away.
My gut feeling would be that only around Rhea and maybe Dione you could get a fairly stable orbit. I take it that's because of the small mass of most of the inner moons, compared with vicinity to Saturn itself make that moon's sphere-of-influence fall below its surface.
Apart from Titan, I'd guess an Iapetus orbit could be pretty stable as well?

Posted by: jmknapp Nov 18 2005, 03:59 PM

Glad to be of help. I had the suspicion that this info probably WAS out there somewhere in digested form & I was just putting it together from scratch (http://naif.jpl.nasa.gov/naif/ kernels) for my own jollies. But it's not--so much the better for the effort.

It really is a great resource to have these government missions where so much info is quickly released into the public domain. The NAIF files have predicted spacecraft position and state info to the nth degree for several years into the future. So much meticulous planning is evident. At this point the spacecraft just runs itself?

Posted by: jmknapp Nov 18 2005, 04:20 PM

Interesting point. Maybe because it's in darkness the northern region gets more scrutiny from the RADAR? There will be a nice direct radar pass over the south pole though in Dec. 2007 (T38).

Posted by: volcanopele Nov 18 2005, 05:42 PM

Nice! But I want to add a few comments:

1) I notice that a lot of your tracks have "tails", for example the western end of T8. These tails are often altimetry data, not SAR. Is there a distinction in the kernels files between altimetry and SAR that can be displayed on this map?

2) One of the reasons why no map like this is out publically is that these are always in flux. The RADAR team may switch to a different look angle, they may gain or lose encounters based on trades with other instruments, the C/A altitudes may change (as will be the case for all those 950-km flybys, that will need to be raised by 100-300 km). These factors may change the appearance of this map. jmknapp brought up T38, which is currently still being decided between RADAR and ORS. T39 covers much the same territory (not Ontario Lacus though), which may be okay. Finally, some flybys have RADAR riding along with INMS. T18 is one example. In your chart, T18 is shown as it would look if RADAR had their full pass. But INMS is controlling pointing, so RADAR may only get the central 700 km of that swath.

EDIT: one further note. In addition, RADAR has decided to extend many of their swaths by 5 minutes on either end. This is especially evident on T3, which extends to the east past Bazaruto Facula and to just north of Quivira.

3). T13 looks a little too far north. The central beam should cross Guabonito, not Kerguelen, unless you are not modelling the central beam. Which beam is being displayed here?

Posted by: volcanopele Nov 18 2005, 05:43 PM

well,that's largely because the spacecraft uses high north polar passes to get up to the high inclinations needed in the latter part of the mission

Posted by: jmknapp Nov 18 2005, 07:40 PM

No distinction that I can find, but maybe that info is available somehow. I saw a reference in the events kernel to a "predicted events file" which might have such info (and other good data like camera shutter times). In lieu of that, one source says that the SAR is effective out to about 4,000 km, so I just plotted the points where the range is less than 5,000 km. That includes sometimes the turning from altimetry mode or whatever.



So that means they are going well beyond 5,000 km in range?



The central beam. It could be a bug with my software, I don't know, or maybe a problem with the kernel files used. Will check it...

Posted by: jmknapp Nov 18 2005, 09:15 PM

Well, volcanopele, I looked at T13 more closely and can't see where the dicrepancy comes from.

Here's the track of all five beams (click for larger version):

http://cassinicam.com/t13radar.jpg

...which all miss Guabonito by a bit.

There are a number of CK kernel revisions for that time (April 30, 2006) but they don't vary much, except for the first version which had the ORS pointing to Titan rather than the radar.

On a tangential note, I see that Guabonito is the "Taino Indian
(Antilles) sea goddess who taught the use of amulets."

Before then people had no idea what to do with them.

Posted by: volcanopele Nov 18 2005, 09:21 PM

Well, my info on T13 is a few months old, so the pointing (or groundtrack) may have changed since then. Check the trajectory files. Compare the track using 041001AP_SCPSE_04275_08222.bsp and 050720AP_SCPSE_05119_08222.bsp (or SK, instead of SCPSE). If we miss Guabonito, I will be VERY disappointed.

Posted by: volcanopele Nov 18 2005, 09:23 PM

On a completely unrelated topic, here is a look from Google Maps, at longitudinal dunes in SE Libya, that are similar in scale to those seen on Titan:

http://maps.google.com/maps?ll=22.643165,20.577393&spn=0.321485,0.538158&t=h&hl=en

EDIT:

Here are a few more:

Simpson Desert, Australia:
http://maps.google.com/maps?ll=-27.020137,137.516727&spn=0.081501,0.134540&t=h&hl=en

Saudi Arabia:
http://maps.google.com/maps?ll=18.503052,48.239594&spn=0.347030,0.538158&t=h&hl=en

Posted by: BruceMoomaw Nov 18 2005, 09:46 PM

I'm beginning to wonder if those dark lakebeds aren't so much filled with mud as with Titanian quicksand. Bar-Nun's team has concluded from the Huygens data that their advance prediction was true that the solid smog particles harden very quickly in the air and are totally non-sticky long before they settle to the ground, and the fact that we're clearly now seeing DUNES of dark organic material in huge amounts seems to confirm this. Nor do we have any chemical reason I've seen so far to think that the compounds being talked about would dissolve, even slightly, in liquid methane or ethane.

On the other hand, we have plenty of evidence now that Titan has a very active subsurface "hydrological" cycle, with lots of liquid methane and ethane first trickling underground, then being drawn much more deeply into the crust by Titan's very active cryovolcanic cycles -- and then flowing back up to the surface elsewhere because of that same volcanism. This is exactly the kind of upward flow that produces quicksand beds on Earth, and they may be far commoner on Titan -- but with the "sand" being made of equally insoluble water-ice grains and fine insoluble organic-smog grains, and the "water" being liquid methane and ethane. (Add to this the fact that water ice is almost positively buoyant in liquid methane, and IS firmly buoyant in liquid ethane -- whereas silica is far higher-density than liquid water on Earth, and thus requires a far stronger upward fluid flow to keep it in semi-suspension.)

Posted by: mike Nov 18 2005, 10:09 PM

Come on now, you're just being silly. Clearly Guabonito INVENTED the amulet, then melted away..

Posted by: jmknapp Nov 19 2005, 01:36 PM

Interesting... looks like the track did move a bit north between those two revisions. The tracks below show the middle beam, yellow for 050720AP_SCPSE_05119_08222.bsp and red for 041001AP_SCPSE_04275_08222.bsp (click for larger image):

http://cassinicam.com/t13change.JPG

Posted by: The Messenger Nov 19 2005, 03:35 PM

These are excellent, and clearly indicate the Huygens' penetrometer was on the right track when it indicated the surface has the grainy consistancy of sand.

Waves like this - don't they form perpendicular to prevailing winds? Don't the cat scratches run roughly north and south on Titan, indicating the prevailing winds would have a polar alignment?

Posted by: Matt Nov 19 2005, 05:26 PM

Interesting..........and yes I don't see any way that surface winds blowing west to east could have formed the cat-scratches.

There is also a similairity between the cat-scratches and radar images of Antarctic Megadunes.

The Megadunes are formed in a different way to sand dunes, however.

They are apparently formed by katabatic winds that begin to 'bounce' as they gather speed downslope, probably with the help of small hills in the ice.

They can have lateral extents of 100 km or more.

Posted by: elakdawalla Nov 19 2005, 05:32 PM

Ttitan's prevailing winds do run east-west, and the cat scratches run generally east-west as well. Most familiar sand dunes on Earth have crests that are perpendicular to the prevailing wind direction or are crescent-shaped with the horns of the crescent parallel to the wind and the center of the crescent perpendicular to the wind, but a few types are "longitudinal," running parallel to the winds. That appears to be the favored theory for the cat scratches on Titan, that they are longitudinal dunes -- though most people are quick to say that that explanation is just a guess, the best one that can be made based on the available data.

--Emily

Posted by: Matt Nov 19 2005, 05:58 PM

It is a guess at this stage, but it is probably the right interpretation. You can see how they appear to flow around the hills and ridges.

So do you think the radar is detecting slopes only?

Would it be possible for the radar to view them from a different angle of illumination?

Posted by: elakdawalla Nov 19 2005, 06:21 PM

Eventually, yes. Cassini RADAR scientist Rosaly Lopes talks about this subject in http://www.planetary.org/news/2005/1102_New_RADAR_Images_of_Titan_The_Features.html...

--Emily

Posted by: The Messenger Nov 20 2005, 05:36 AM

I don't think it fits. Look at Volcanopele's dunes on the Earth, and you see similar flows around ridges, and these are normal, transverse wave patterns. The most straightforward interpretation is that the surface winds on Titan, at least in the regions we have observed close enough to tell, are in the general North/South direction.

This is not necessarily inconsistent with prevailing winds in the upper atmosphere flowing East-West, and the corollas effect bending these winds towards the poles at lower altitudes. It is difficult to predict, given the much lower total energy and phase kinetics.

It is only one data point, but I which we had VLA confirmation of the atmospheric descent of Huygens.

Posted by: JRehling Nov 20 2005, 07:29 AM

Titan is about 40% the radius of the Earth and rotates 16 times more slowly, meaning that the Coriolis Effect is about 2% as strong on Titan as on Earth. It seems doubtful that that would change the windflow 90 degrees and still leave it strong enough to cover the planet with dunes.

Posted by: BruceMoomaw Nov 20 2005, 11:07 AM

At the COMPLEX meeting, Liz Turtle was quite firm that the Cat Scratches are shown by the T8 radar images to be dunes. As for wind direction, it certainly did some dramatic swerving during the last 2 km or so of Huygens' descent in response to local geography, but for the entire distance above that it was easterly -- so presumably the Scratches are indeed caused by winds in that direction, in areas where the geography does not cause a change in wind direction at low altitude. (We really badly need good altimetry on Titan, but unfortunately Cassini's radar altimetry has a horizontal resolution of no better than 20 km.)

One thought: since the Titanian dunes are likely made of VERY fine organic dust particles, may this material react in a radically different way to winds than the coarser sands of Earth do, producing longitudinal rather than transverse dunes?

Posted by: jmknapp Nov 20 2005, 08:17 PM

Here's a comparison of the Titan cat scratches with an SAR image of the Antarctic megadunes, at the same scale:



Titan original: http://photojournal.jpl.nasa.gov/catalog/PIA07009
Antarctic original: http://nsidc.org/antarctica/megadunes/research.html

Posted by: Decepticon Nov 21 2005, 06:46 PM

I just noticed T9, T10, T11 are not shown on the RADAR tracks seen http://cassinicam.com/titanflybys/

Are no radar observations planned for these flybys?

Posted by: volcanopele Nov 21 2005, 06:55 PM

The next RADAR pass is in late April with T13

Posted by: The Messenger Nov 21 2005, 07:38 PM

Tidal and wind blown waves, snow drifts, sand drifts, rubber tyres on unpaved roads, magnetic flux, acoustic transducers - every linear energy function I am aware of produces primarily transverse waves in a flowing, resistive medium, so this should be expected on Titan as well. On the other hand, continuety of the waves suggests the wave patterns change very little, consistent with the prevailing winds...

Maybe the lack of a strong Coriolas effect is a factor: Near the suface, North-South winds are generated by seasonal solar heating - these winds would not be strong, but they could be strongly periodic and directional, and over a very long period of time, set-up the patterns we are observing.

Titan is too obstinate!

Posted by: jmknapp Nov 21 2005, 11:12 PM

The pointing data for T12 (March 2006) indicates that the HGA will be pointed towards Titan. So RADAR is not on tap? What will be the primary activity?

Posted by: dvandorn Nov 22 2005, 12:20 AM

Remember that the air is very thick on Titan, too. Even mild winds have a much stronger erosional impact on the surface than they would if the air were thinner.

-the other Doug

Posted by: BruceMoomaw Nov 22 2005, 08:36 AM

I just today got a huge pile of material -- all the slides from the COMPLEX meeting, including a bar chart from Liz Turtle's presentation showing the planned science observations for all the Titan flybys. Admittedly they take a lot of squinting, but they definitely list radar for the T12 flyby in mid-March -- plus T13, 15, 16, 19, 20, 21, 23, 25, 28, 29, 30, 36, 39, 41, 43, and maybe 44 (two alternative plans for that one).

Posted by: ngunn Nov 22 2005, 05:42 PM

I have some comments in response to BruceMoomaw's point quoted from the Huygens news thread above - hope this is the right place to post them!

I am interested in the possibility that the cat scratches could be very thin surface features. The way they deviate around what are probably quite low (tens of metres elevation?) islands does suggest a formation process confined to a near-surface atmospheric layer which for some reason (density contrast / turbidity / electrostatics / mechanics of saltating grains) does not lift over obstacles. Their appearance reminds me of the longitudinal streaks formed by wind blowing over a flat sandy beach at low tide. In that case the patterns are linked to an underlying distribution of drier and damper patches, with sand drifting from the former and tending to stick to the latter. I wonder if a similar mechanism involving differential stickiness could be at work on Titan. The fact that the cat scratches show albedo contrast and the closeness of the surface temperature to the triple points of important organic compounds suggests that there could be a feedback mechanism maintaining the patterns. Something along these lines perhaps: darker surface – more solar IR absorbed – slightly higher temperature – drier (or stickier) – more (or less) drifting – darker surface . . . and so on.

How does this sound to the experts ? Has it already been suggested ?
Oh, and one more question. If there is no detectable relief how can we be sure whether it is the darker or the brighter material that is doing the drifting ?

Posted by: Bob Shaw Nov 22 2005, 06:37 PM

Bruce:

The Antarctic Megadunes are made, it would appear, from large crystals of ice (and in a process mediated by what amounts to a sub-zero freeze-thaw cycle using water vapour rather than liquid water). Oh, and they aren't homogenous, but have different average crystal sizes in different locations, with the lee and windward sides of the dunes behaving differently. So we're already looking at some local Earthly effects due to dissimilar materials properties...

...and on Titan? Is the organic material just glop, or can it form structures? Is there a freeze-thaw cycle (I bet there is!). Does the 'rain' evaporate/runoff/erode preferentially dependent on the materials it falls onto?

All interesting points - perhaps, as you say, the simple 'standard issue' sand dune analogue isn't appropriate on Titan!

Bob Shaw

Posted by: Phil Stooke Nov 22 2005, 06:43 PM

The radar operates in more than one mode. Is this the solution to the T12 puzzle?

Phil

Posted by: volcanopele Nov 22 2005, 06:50 PM

T12: This is a bistatic pass, not a RADAR SAR pass.

Cat scratch topography: remember, the incidence angle of the RADAR swaths may not have been conducive to showing glints in topography. At least the small sections publically released...

Posted by: Decepticon Nov 22 2005, 08:01 PM

New word for the day. Bistatic


http://apollo.lsc.vsc.edu/classes/remote/lecture_notes/bistatic/bistatic_intro.html

Posted by: jmknapp Nov 22 2005, 09:29 PM

Which might explain the weird nature of the predicted track (click for larger image)?

http://cassinicam.com/t12radar.JPG

It seems like the s/c must be rotating at the end, and there's a break in the track, unlike most radar passes.

Posted by: AlexBlackwell Nov 23 2005, 01:46 AM

Yes, I agree that jmknapp's plot is nice work; however, like you I think there are some (at least minor) differences with the latest projections from the RADAR team (e.g., the map presented at the TOST workshop last Friday).

Posted by: JRehling Nov 23 2005, 04:24 AM

...tracks may be only half-received by DSN because of software glitches...

Well, it's nice to see a strawman map of the approximate number of RADAR swaths in any case -- I wouldn't have been able to picture 19 tracks on a cylindrical projection map in my mind's eye. Even if the targets change a bit, it's nice to have an idea of how dense of coverage we'll get in the primary mission, how many loci will be double-covered at different angles (which could tell us a lot about dunes, liquids), etc.

When I first saw the primary mission profile, I winced because there were so few targeted flybys of the non-Titan moons. Now I can't wait for every other orbit to be a Titan RADAR orbit so we can see this world unfurl slowly, six or so noodles per year.

Posted by: BruceMoomaw Nov 23 2005, 06:25 AM

Another thing in Liz Turtle's presentation was a map of the parts of Titan that are supposed to be SAR-mapped by the end of the mission (although the swaths aren't numbered, alas). I imagine it's pretty much up to date, and I may try to scan it and post it here a bit later. She also included maps of the areas which Cassini will try to observe close up with ISS, and the points where ISS will look for specular reflections.

Posted by: jmknapp Nov 24 2005, 03:54 PM

But up to 5 noodles at a time though. I updated the map to show all five beams for each pass:

http://cassinicam.com/titanflybys/titantracks.html

Posted by: tasp Nov 24 2005, 04:29 PM

Is it anticipated that where the 'noodles' cross, if the width of the track (and therefore the resolution) are similar, we could get a 3D view of that spot?

I am thinking this would be of great benefit in understanding this alien scape.

Looks like there are several areas around Titan were this might work.

Posted by: exoplanet Jan 1 2006, 06:52 AM

Any idea when the full radar swath from the T-8 flyby will be released publically (as of now - I think all that has been released is near the Huygens landing site - which was the very end of the swath).

Posted by: Decepticon Jan 1 2006, 07:08 AM

Yeah I almost forgot about that pass.

If I remember right a PDF file posted on this board had some bits and peaces from that swath.

Should be easy to find.

Posted by: exoplanet Jan 29 2006, 12:32 AM

I do have these bits and pieces on file but the only radar images that were publically released were of the Huygens landing site (or nearby). These were taken at the very end of the radar pass and were supposed to be of lower quality than the first part of the radar image. The majority (75%) of the radar swath has yet to be released. It has historically taken 2-3 weeks after a flyby to release the full radar image. I wonder why this one has been delayed.

Jason, if you are there - can you give us a timeframe when the entire T-8 swath will be released. Thanks so much.

Posted by: JRehling Jan 29 2006, 02:29 AM

Isn't this it? I'm pretty sure this is the full RADAR swath, because the ISS coverage of these areas certainly doesn't have this resolution. You could ask for a better presentation of the data, but I think this is it:

http://photojournal.jpl.nasa.gov/catalog/PIA03570

Posted by: exoplanet Jan 29 2006, 02:39 PM

Thanks JRehling,

I do have this image but this is not what I am looking for. I am looking for the close-up detailed full swath (this is normally a large file to download). The image takes forever to load but once it does you can scroll left to right or top to bottom to see the complete radar image.

Posted by: Decepticon Jan 29 2006, 03:44 PM

It has not been released, yet. I'm having a hard time lining up the sections that where released with the Low resolution Coverage map.

I can't wait to see it myself!

Posted by: Matt Jan 29 2006, 07:34 PM

I know the first two radar swaths were available on the Planetary Society website, in all their full high-resolution splendour. I haven't seen the others yet though. I really hope they get around to releasing the full T8 swath also.

Did they release the full swath that included that very evident Shoreline terrain?

Posted by: volcanopele Jan 30 2006, 07:16 PM

The other swaths weren't officially released until the time they were in the PDS: October 1 for Ta and January 1 for T3. T8 should be in the PDS on October 1 of this year and T7 (the one with Mezzoramia/"shoreline") should be in the PDS on July 1 of this year.

The Ta and T3 swaths were released unofficially on a Stanford RADAR site but have been removed. The other swaths will not be released in full until their PDS release or if and when the RADAR team decides to release it early.

Posted by: volcanopele Jan 30 2006, 07:17 PM

Actually, they've released close to 70% of the T7 swath already. Due to issues during T7, only 40% of the planned swath was returned.