[X] My Assistant

[Decepticon]

Another flyby coming soon. Interesting observations include radar swath of Huygens landing site.

Just before CA. http://space.jpl.nasa.gov/cgi-bin/wspace?t...porbs=1&brite=1

From above... http://space.jpl.nasa.gov/cgi-bin/wspace?t...porbs=1&brite=1

I really missed VP encounter updates So I tried my best at showing the Hemisphere to be imaged during the flyby.

[David]

Another flyby coming soon. Interesting observations include radar swath of Huygens landing site.

Just before CA. http://space.jpl.nasa.gov/cgi-bin/wspace?t...porbs=1&brite=1

From above... http://space.jpl.nasa.gov/cgi-bin/wspace?t...porbs=1&brite=1

I really missed VP encounter updates   So I tried my best at showing the Hemisphere to be imaged during the flyby.

What's the basis for the position of the Huygens landing site? Early reports always characterized it as being right on the boundary between the light-colored and dark-colored regions, but that's not how it appears on your map.

[volcanopele]

that's the entry point into the atmosphere, not the landing site.

The map is a little off. During T8, we actually look a little farther to the east before closest approach.

[Decepticon]

Only 8 days away!

Looking forward to combining Huygens data with Cassini radar.

[jmknapp]

Only 8 days away!

Looking forward to combining Huygens data with Cassini radar.

Here's a movie of the flyby, showing Huygens as a red dot on the surface:

TITAN Oct. 28 flyby (10MB mpg)

[RPascal]

One of the most exciting questions for me is, if the radar swath data will result in a definite decision how the Huygens mosaic and Cassini ISS/VIMS correlate.
Some month ago I tried to find this correlation, with the result that I felt I had to introduce a relatively large calibration mismatch to find a good visual agreement of Huygens and ISS. But now it has come to my knowledge that Huygens radar, as well as radar tracking of Huygens from earth, seems to be in good agreement with the timer height calibration, so it looks as I have to give up this idea.
http://www.beugungsbild.de/huygens/ISS_huy...correlate3.html

Does anybody know what radar resolution is expected at the Huygens landing site?
Will ISS also obtain some high resolution images?

--René

[ugordan]

Does anybody know what radar resolution is expected at the Huygens landing site?
Will ISS also obtain some high resolution images?

My uneducated guess would be that radar data won't have a very high resolution. If jmknapp's image is correct (I can't play the movie right now so I'm not sure about changing geometry during the encounter), Cassini's sub-spacecraft point is close to the Huygens' landing site at 4800 km so that's bound to move away from the site near C/A. That would make the radar illumination angle very oblique so data quality could be degraded. That said, the resolution might still beat ISS resolution and it sure wouldn't hurt to have even a low res pass over the landing site.
As far as ISS coverage is concerned, I notice that the solar phase angle is not optimal for imaging -- the landing site is fairly close to the terminator so the contrast would be degraded. They probably won't do very high resolution mosaics on this pass. At least over the Huygens site.

Just my 2c...

[alan]

One of the most exciting questions for me is, if the radar swath data will result in a definite decision how the Huygens mosaic and Cassini ISS/VIMS correlate.
Some month ago I tried to find this correlation, with the result that I felt I had to introduce a relatively large calibration mismatch to find a good visual agreement of Huygens and ISS. But now it has come to my knowledge that Huygens radar, as well as radar tracking of Huygens from earth, seems to be in good agreement with the timer height calibration, so it looks as I have to give up this idea.
http://www.beugungsbild.de/huygens/ISS_huy...correlate3.html
--René

The mosaic released by DISR was rotated counterclockwise about 20 degrees. Have you tried matching it that way? Perhaps with a spot about 30 km north of where you have it.

[jmknapp]

My uneducated guess would be that radar data won't have a very high resolution. If jmknapp's image is correct (I can't play the movie right now so I'm not sure about changing geometry during the encounter), Cassini's sub-spacecraft point is close to the Huygens' landing site at 4800 km so that's bound to move away from the site near C/A.

Here's the CA image:

[ugordan]

Here's the CA image:

Yes, that could be pretty tricky to cover with the radar. Especially since the C/A distance itself is pretty distant. IIRC, during one of the previous flybys at a similar or higher distance the RADAR team didn't expect very high quality SAR data. Nevertheless, they still managed to get nice coverage. It's fairly obvious high res ISS coverage is out of the question.
The team hasn't released the T8 guide yet, but I bet a good portion of the time around C/A will be devoted to radar due to the phase angle. CIRS nighttime coverage also comes to mind as a possibility.

[JRehling]

My uneducated guess would be that radar data won't have a very high resolution. If jmknapp's image is correct (I can't play the movie right now so I'm not sure about changing geometry during the encounter), Cassini's sub-spacecraft point is close to the Huygens' landing site at 4800 km so that's bound to move away from the site near C/A. That would make the radar illumination angle very oblique so data quality could be degraded.
Just my 2c...

At C/A, not only will the angle be oblique, but the Huygens site will not be at *ITS* C/A. Remember that Titan's radius is a significant fraction of the distance here, and C/A is the time when Cassini is closest to Titan -- but only at one point! The time when Cassini is closest to the Huygens site will be earlier, so viewing the Huygens site at "proper" C/A would not only give you worse coverage of the Huygens site, but also miss out on coverage of the subspacecraft point at proper C/A.

Radar pixel size drops off inverse with distance while radar illumination drops off to the inverse fourth power of distance. I suspect we'll take whatever imagining of the Cassini site we can get, and if it identifies anything at all it could still help with registering Cassini/Huygens imagery.

[ljk4-1]

At C/A, not only will the angle be oblique, but the Huygens site will not be at *ITS* C/A. Remember that Titan's radius is a significant fraction of the distance here, and C/A is the time when Cassini is closest to Titan -- but only at one point! The time when Cassini is closest to the Huygens site will be earlier, so viewing the Huygens site at "proper" C/A would not only give you worse coverage of the Huygens site, but also miss out on coverage of the subspacecraft point at proper C/A.

Radar pixel size drops off inverse with distance while radar illumination drops off to the inverse fourth power of distance. I suspect we'll take whatever imagining of the Cassini site we can get, and if it identifies anything at all it could still help with registering Cassini/Huygens imagery.

Is there any evidence of surface movement on Titan? I wonder if Huygens will "drift" during Cassini's lifetime?

[jmknapp]

The science plan has "T8 Inbound Altimetry" starting at 2005OCT28 03:43:25 UTC and ending at 2005OCT28 04:00:13 UTC. Interestingly at the end point the s/c is almost directly over Huygens at a range of 4014 km. So what is the expected resolution in that case?



After that there are two more inbound radar activities:

T8 Low Resolution Synthetic Aperture RADAR 4:00:13-4:12:25
T8 High Resolution Synthetic Aperture RADAR 4:12:25-4:18:25

The switchover from low to high resolution is just before (<1 min) c/a.

[JRehling]

Is there any evidence of surface movement on Titan?  I wonder if Huygens will "drift" during Cassini's lifetime?

Probably not so much as a meter unless Titan is extraordinarily violent. On Earth, plates move about 1 cm / yr. Except for ancient Mars, we don't yet have evidence of plates anywhere else. Titan certainly has had crustal motion in the past and may still today, but I doubt if it's much faster than on Earth, if that fast.

[RPascal]

The mosaic released by DISR was rotated counterclockwise about 20 degrees. Have you tried matching it that way? Perhaps with a spot about 30 km north of where you have it.

It was very valuable to mention it again, Alan. I read it in Emily Lakdawalla's weblog, but somehow I lost sight of that information. I was also told by a friend who visited the DPS conference and heard Larry Soderblom's talk. If I am informed correctly, the direction information now was gatherded by using the variable field strenght of the transmitter signal of Huygens, that did not have a rotational symmetric characteristic, and correlating that with the image that was taken a moment before. So for every image there is a direction information that is independent from the sun sensor.
With that new orientation, the best fit should be as in the image below. This analogy still is not sooo good, but it is better than in my previous attempt.
Placing it perhaps 40km northwest of that position may also be possible (on top of that pale triangular formation), but I think the Huygens landing site would be too far off from the position that was calculated.



One should also keep in mind that it is very difficult to make a correct large scale albedo adjustment in the mosaics. I am quite sure that north of the bright "highland" there is a somewhat darker area, resulting in this triangular shape of the highland region, but it may well be that my photometric correction leaves it slightly darker than it is in reality.

--René

[Decepticon]

Encouter Update!

http://saturn1.jpl.nasa.gov/home/index.cfm



WOW!! http://photojournal.jpl.nasa.gov/jpeg/PIA08111.jpg

[elakdawalla]

OK, what the heck is going on with the longitudes in these maps?

Maybe it's too early in the morning for me to be thinking hard but I think there are errors in the longitudes on both the imaging coverage and the RADAR maps. Can somebody please check and tell me if I'm right about that?

I think the imaging coverage map is centered at 180 degrees, but it is labeled as 0 degrees.

I think that the third RADAR globe, the one that shows the T8 swath, has a "120" where it should have a "240."

Am I crazy? They switch their convention all the time, using 180 sometimes and 0 sometimes as the center longitude, but I don't think I've noticed errors before.

--Emily

[JRehling]

OK, what the heck is going on with the longitudes in these maps?

Maybe it's too early in the morning for me to be thinking hard but I think there are errors in the longitudes on both the imaging coverage and the RADAR maps.  Can somebody please check and tell me if I'm right about that?
--Emily

You're definitely right. Look at Photojournal. The Radar releases and the T8 preview maps are almost consecutive image listings. Xanadu and Mezzoramia are clearly seen on both maps, and it looks like they either goofed the Radar map by 180 degrees, or maybe made even more serious goofs. Hope they rectify this and withdraw the mislabeled images.

http://photojournal.jpl.nasa.gov/targetFamily/Saturn

[volcanopele]

You're definitely right. Look at Photojournal. The Radar releases and the T8 preview maps are almost consecutive image listings. Xanadu and Mezzoramia are clearly seen on both maps, and it looks like they either goofed the Radar map by 180 degrees, or maybe made even more serious goofs. Hope they rectify this and withdraw the mislabeled images.

http://photojournal.jpl.nasa.gov/targetFamily/Saturn

No, we messed up. The last four flyby maps have all been centered at 0 West since that is where most of the coverage is and this is the first flyby since February to switch back to the Shangri-la side. I didn't catch the error till three hours before the image went live The map is centered on 180 West, regardless of the labels... grrr...

I'm talking about the ISS coverage map. Haven't looked at the RADAR coverage map to closely yet. Why didn't they ask us if they could use our base map?

[elakdawalla]

No, we messed up.  The last four flyby maps have all been centered at 0 West since that is where most of the coverage is and this is the first flyby since February to switch back to the Shangri-la side.  I didn't catch the error till three hours before the image went live   The map is centered on 180 West, regardless of the labels...  grrr...

I'm talking about the ISS coverage map.  Haven't looked at the RADAR coverage map to closely yet.  Why didn't they ask us if they could use our base map?

Glad to hear I'm not crazy. I've heard back from the RADAR team that that is a typo too, it should be 240.

I get so confused trying to figure out what's what in these maps (leading? trailing?) - and I forget so often that the ISS maps are truncated just above 60 degrees North -- that I've started to doctor all the maps that I use on our website so that they show a consistent point of view -- centered at 180 and (for now) truncated just above 60 N. I just did the same for the recent RADAR map -- makes it easier to compare where the coverage was. (I also corrected the ISS map longitude while I was at it.)



As for why they didn't use the ISS base map, Rosaly Lopes told me that they wanted to make it more obvious where the RADAR coverage had gotten to so far. I am looking forward to seeing more and more of that blue background getting covered up over the course of the mission.

--Emily

[volcanopele]

To make it all up to all of you, here is the RADAR coverage, adapted from PIA08111, superimposed on our base map. Enjoy!

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

[elakdawalla]

To make it all up to all of you, here is the RADAR coverage, adapted from PIA08111, superimposed on our base map.  Enjoy!

Just curious: why doesn't the base map have the detail filled in from the T4 to T7 flybys yet?

--Emily

[volcanopele]

Some thoughts:

1) If you like cat scratches, you will like this swath. I think that much of the middle third of the swath, covering the dark region now known as Belet, will be covered in cat scratches. Much of eastern Fensal was covered by them, though the spaces between the dunes were also dark, making them more difficult to see than the ones that were on top of bright bed-ice. I suspect that the equatorial region is one giant desert (at least in Titan standards) and the dark regions are sedimentary basins where sand-sized particles have come to die and form large dune seas. Polar (and maybe temperate) dark terrains appear to be dark floored playas (as well as regions near the transitions between rocky terrain and sandy terrain in the equatorial region, like where Huygens landed). Much of the equatorial regions have been shaped mostly by aeolian erosion as well as the occasional storm (sapping and cryovolcanism may also play a role).

2) RADAR will only be using Beam 3 (best SNR of the 5 beams) when it covers the landing site so look for the swath to appear similar to the thin noodle at the east end of the Ta swath (upper right most of the 3 swath taken so far). Don't expect great detail in that view in low-res mode, but it will help the RADAR team to calibrate their theories for terrains in the rest of the swath and in other swaths.

3) Adiri could be an interesting place. From images gathered thus far, it appears to be a bright feature with lots of small dark features, similar to the region north of Fensal perhaps, with small patches of cat scratches.

[volcanopele]

Just curious: why doesn't the base map have the detail filled in from the T4 to T7 flybys yet?

--Emily

We are currently experimenting with techniques to process Titan images. We are close to a solution to the problems we have encountered, so hopefully we will have a new base map out soon.

Remember, Titan is not like the other icy satellites. You can't just pick clear filter images, run a simple photometric function on it, then be happy. Titan is very different from other solid bodies in the solar system, and a lot of the assumptions used by our processing software, can't be applied to Titan.

[JRehling]

To make it all up to all of you, here is the RADAR coverage, adapted from PIA08111, superimposed on our base map.  Enjoy!

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

Fantastic stuff, and clarifications. I've delayed my project of making my own Titan globe since the new data just keeps coming in... which is a good kind of delay.

As for superimposition, and Emily's comment, one convenient solution would be to tint the ISS map (blueish captures the proper sequence of the wavelengths) and to put white-ish RADAR data on top. But it seems to me the best thing would be to tint ISS aqua, tint RADAR orange, and use RADAR as a layer added to the ISS map, because RADAR and 938nm are after all, mapping quite different things -- RADAR happens to be higher resolution, but doesn't replace ISS where both things are available.

My ideal Cassini map of Titan might use ISS (938 nm) as the blue channel, VIMS data from 2 and/or 5 microns as the green, and RADAR as the red (although that's, of course, still not quite right!, because radar reflectance isn't just albedo in a long wavelength). This is all contingent on getting a proper normalization of VIMS channels, so that it is surface albedo being isolated, and not merely the nature of the atmosphere and the spectral holes. Ultimately, all three instruments should be able to provide excellent resolution for the purposes of, say, a 12-inch globe, and all we need to do is see the coverage fill in as the extended missions go by.

Finally, overlay that color map on a proper BW shading indicating topography, and we have the dream map/globe. I've got a corner of my desk all saved for it.

[jmknapp]

Question on Cassini pointing: does the pointing of the RADAR at Titan mean that the ISS cameras are pointed in some other direction?

Or, put another way, do the ISS cameras look at the same point that the RADAR is aimed at?

Wondering if there will be any closeup ISS images...

[ugordan]

Question on Cassini pointing: does the pointing of the RADAR at Titan mean that the ISS cameras are pointed in some other direction?

Or, put another way, do the ISS cameras look at the same point that the RADAR is aimed at?

Wondering if there will be any closeup ISS images...

The HGA points along the spacecraft axis, while the optical remote sensing instruments point perpendicular to that, they're mounted on the spacecraft body and point away from it. There's no way RADAR and optical observations could be made simultaneously. Besides, the solar phase angle will be unfavorable around C/A anyway so there's no big loss.

[jmknapp]

There's no way RADAR and optical observations could be made simultaneously.

Thanks.

Does anyone have the exact location (lat,lon) of the Huygens probe?

[volcanopele]

Near 11.3 South, 190 West.

[jmknapp]

Thanks--here's a cool animation. I've been working with the SPICE c-kernels, which give instrument pointing. The animation shows the huygens landing site as a red dot on the Titan globe, and the radar beam aim point (the five separate beams) as yellow dots. It starts from 20000 km out, & it can be seen how first the radar scans back and forth repeatedly, then swoops by the Huygens site at about 4000 km range, and then on the outbound side repeatedly scans up and down in latitude. Pretty neat to see how the observations map out.

Titan/RADAR animation (9 MB mpg)

[Decepticon]

Are there any NT on this Rev?

[jmknapp]

Are there any NT on this Rev?

Non-targeted flybys?

There's something on Oct. 30:

MP_017CA_FLYBYNT001_NA

2005 OCT 30 02:50:12 UTC
Nontargeted outbound 107741 km flyby, v = 9.4 km/s, phase = 66 deg

I think the CA in the code means that the target is Calypso?

[ugordan]

Nontargeted outbound 107741 km flyby, v = 9.4 km/s, phase = 66 deg

I think the CA in the code means that the target is Calypso?

108000 km from Calypso hardly deserves the term "nontargeted flyby". At that distance the observation resolution would be crappy, besides, I don't see a pointing request listed so could that mean no turning to Calypso will actually happen?

[jmknapp]

108000 km from Calypso hardly deserves the term "nontargeted flyby". At that distance the observation resolution would be crappy, besides, I don't see a pointing request listed so could that mean no turning to Calypso will actually happen?

You may be right, because there was a similar entry in August and no image showed up on the raw image website at least.

Is the Voyager image of Calypso http://nssdc.gsfc.nasa.gov/imgcat/html/obj...g2_4399741.html the best one to date?

If so, a Cassini image at the Oct 30 range would improve on the resolution (about 2.5 times more pixels across)--still pretty small, but something perhaps.

[volcanopele]

Best image I am aware of:

http://saturn.jpl.nasa.gov/multimedia/imag...4/N00040024.jpg

[RPascal]

Mosaic North-direction

During my last attempts to find possible positions for the Huygens mosaic within the Cassini images for the upcoming flyby, I realized that the information regarding the correct north-direction was perhaps hidden in one of my early panoramas all the time, but I did not realize it...
The slightly brighter horizon around the images 476, 400, 526, 446, 380, 455 of the panorama "Huygens distant view" (blue arrow) marks the direction opposite to the sun! Backscatter in the atmosphere results in a brightening of the haze around that point. I do not think that it is an artifact, since it can also be well seen as an inclined horizon brightness when looking at the SLI raw images, the
numbers 476, 455 and 400 for instance.
With the information where Huygens approximately was when shooting the corresponding images (green ellipse) the sun direction can be determined with an uncertainty of perhaps +-3 degrees (the two red lines in the upper left). The resulting rotational orientation (north direction) very well fits the new orientation reported recently, by Larry Soderblom for instance.
And I did not see it...




http://www.beugungsbild.de/huygens/huygens_distant_view.html

[scalbers]

Interesting that the azimuth answer may have been right under our noses.

I have a general question about these wonderful mosaics for Rene. Have you considered applying some type of low-pass filter selectively to those images with pronounced small-scale artifacts? I have tried this on individual images and for me the real details stand out better without the distractions.
It would be interesting to see a version of your mosaics with that type of processing applied.

I have posed a similar question with regard to the radar data.

[RPascal]

I have a general question about these wonderful mosaics for Rene. Have you considered applying some type of low-pass filter selectively to those images with pronounced small-scale artifacts? I have tried this on individual images and for me the real details stand out better without the distractions.
It would be interesting to see a version of your mosaics with that type of processing applied.

I have posed a similar question with regard to the radar data.

You are right, in many images the visibility of some details can be improved by a low pass filter. But it is often difficult to estimate what is detail and what is noise, so I decided to use the images without filtering them. I know that applying a filter now on the mosaic is more difficult than filtering each image alone, because the images at the rim are increased in size with respect to the inner ones. But if I had filtered the images before it would be irreversible. Now you can define several areas in the mosaic and filter each with an appropriate low pass adjustment. It is on my list, (and has been there for some time) like so many things...

--René

[Decepticon]

I wonder if everything is OK?

[Toma B]

I wonder if everything is OK?

I'm sure that everything is OK...
They do know how much some of us like to see new images or (RADAR images) so they are teasing us a little... I think it's not werry nice of them...

[elakdawalla]

I'm sure that everything is OK...
They do know how much some of us like to see new images or (RADAR images) so they are teasing us a little... I think it's not werry nice of them...        

Patience, patience! I think maybe they just didn't want to work over the weekend. The science team assuredly was checking stuff out over the weekend, but it takes a large staff in the public information office to put together the public releases, review the text, okay it, post it, issue the image advisory to the media, etc. etc. I'm sure we'll see something later today. Actually, I'd rather they take a little time to refine the RADAR images before posting them. With a little work refining the spacecraft trajectory and such they can get rid of a lot of the artifacts you'd see in more hurried image products.

Emily

[volcanopele]

Everything is fine.

[volcanopele]

Mosaic North-direction

During my last attempts to find possible positions for the Huygens mosaic within the Cassini images for the upcoming flyby, I realized that the information regarding the correct north-direction was perhaps hidden in one of my early panoramas all the time, but I did not realize it...
The slightly brighter horizon around the images 476, 400, 526, 446, 380, 455 of the panorama "Huygens distant view" (blue arrow) marks the direction opposite to the sun! Backscatter in the atmosphere results in a brightening of the haze around that point. I do not think that it is an artifact, since it can also be well seen as an inclined horizon brightness when looking at the SLI raw images, the
numbers 476, 455 and 400 for instance.

North is in the direction of those dark parallel lines and those lines are in the east-west direction.

[The Messenger]

Patience, patience!

Agreed, we are very spoiled by how quickly the Cassini Raw images have been made available. It is reasonable that Jason & Co should get first shot at aligning Huygens' landing site with the Cassini images, just as I am sure Carolyn would have loved to have been able to be the first to announce that the 'spokes' were returning.

I will be pleasantly surprise if anything is posted today, and not disappointed if it takes considerably longer, but I doubt anyone was sitting on their hands this weekend

[Guest_Sunspot_*]

http://ciclops.org/view_event.php?id=41

Some RAW images at the CICLOPS site

[tfisher]

http://ciclops.org/view_event.php?id=41

Some RAW images at the CICLOPS site

The one of these that I find interesting is Preview #9. They don't label which filters this is through, but it clearly is something that shows a difference in the atmosphere between the northern and southern hemispheres. Here is a false color and a contrast-stretched version of that image, so you can see what I mean.

[volcanopele]

That is MT3

[RPascal]

North is in the direction of those dark parallel lines and those lines are in the east-west direction.

So, if I understand it right, my orientation is correct (north up) in that image?
The blue arrow only marks the brightening of the horizon I was talking about, it does not mean the north direction. North is simply up. I should have mentioned that, was perhaps a little bit misleading, on my Homepage I also included a marker for north (bottom of that page):
http://www.beugungsbild.de/huygens/ISS_huy...correlate3.html

[tfisher]

On his pagehttp://www.beugungsbild.de/huygens/ISS_huy...correlate3.html,
Rene writes:

The reason for the disagreement between the two surface maps, Cassini and Huygens, now is supposed to arise from the different imaging wavelength of the instruments: Huygens DISR was working at a broadband range from red to near infrared, 660nm - 1000nm, while the Cassini ISS had to obtain the images around a center wavelength of  938nm (CB3 filter) to penetrate the thick smog of Titan's atmosphere.

I wonder if a better comparison image could be produced from the VIMS data. They have a fairly high resolution image of the landing area in the whole range of wavelengths. Perhaps the wavelengths that are opaque in the atmosphere also mean there is no illumination of the surface in those wavelengths, so a weighted sum of the VIMS data (with wavelengths weighted by transparency of the atmosphere) might come out about like what Huygens saw...

I think that VIMS data is out on the PDS release earlier this month, no? So far I've been too lazy to figure out how to process VIMS qubes, but maybe someone would try...

[JRehling]

The one of these that I find interesting is Preview #9.  They don't label which filters this is through, but it clearly is something that shows a difference in the atmosphere between the northern and southern hemispheres.  Here is a false color and a contrast-stretched version of that image, so you can see what I mean. 

This effect has been known since Voyager (when the brightness was reversed, as were the seasons), but the reason is unknown.

I suspect that it pertains to the fact that cloud activity seems to take place in the summer hemisphere -- although we can't see precisely what is happening in the winter polar area. I might go on to guess that lightning produces a small amount of darker aerosols that end up well distributed within one hemisphere, but don't ever make it to the other hemisphere. But that is speculative.

Voyager spotted a dark polar ring around the summer pole, which is perhaps analogous to the bright cloud ring sometimes seen by Cassini around the summer pole -- but I haven't seen yet that Cassini has shown a *dark* ring.

[volcanopele]

Yes, but their resolution in that frame (7 km/pixel) is worse than our effective resolution (~3 km/pixel) in the Antillia/eastern Adiri region.

[volcanopele]

Voyager spotted a dark polar ring around the summer pole, which is perhaps analogous to the bright cloud ring sometimes seen by Cassini around the summer pole -- but I haven't seen yet that Cassini has shown a *dark* ring.

There has been discussion that the dark ring maybe due to the raining out of haze particles at high latitudes in the summer, and that these particles provide nuclei for clouds.

[tfisher]

Here's a false color view of Titan's surface using CB2, CB3, and IR5 images from the last pass. Personally, I'm excited to see more of these alternate color bands being used. You have to stretch colors more than the usual CB3 to see surface detail, but it is still there, and you see things like the variation in coloration of Xanadu in different wavelengths.

[tfisher]

I worked a bit harder to balance the curves for the three channels. Here's an improved false-color image. I love the way Tui Regio shows up in the multiband imagery!

[tfisher]

I love the way Tui Regio shows up in the multiband imagery!

Well... maybe take this picture with a grain of salt. I used independent non-linear curve adjustments to the three different channels, to try to balance out atmospheric effects. That sort of processing could have the effect of making the brightest region one color, the next brightest region another color, and so on. The processing needs to be more careful to be sure the things that show up aren't an artifact of the nonlinear adjustments. (Still, its a pretty picture, isn't it?)

[Decepticon]

I'll take it a grain of salt and 2 shots of whisky!

Just kidding. That is one of coolest pics of titan I've seen so far!

[tedstryk]

This is some great stuff! It will be interesting to see the learning curve processing of Titan ISS images takes over the next few years.

[ljk4-1]

This effect has been known since Voyager (when the brightness was reversed, as were the seasons), but the reason is unknown.

I suspect that it pertains to the fact that cloud activity seems to take place in the summer hemisphere -- although we can't see precisely what is happening in the winter polar area. I might go on to guess that lightning produces a small amount of darker aerosols that end up well distributed within one hemisphere, but don't ever make it to the other hemisphere. But that is speculative.

Voyager spotted a dark polar ring around the summer pole, which is perhaps analogous to the bright cloud ring sometimes seen by Cassini around the summer pole -- but I haven't seen yet that Cassini has shown a *dark* ring.

Scientists found that the few images of Titan taken by Pioneer 11 had also revealed the differences in the moon's hemispheres, but sadly this was not realized until well after the Voyagers - those publicity hogs.

[tfisher]

Okay, one final attempt for me. This time I stacked three CB3 images to improve the signal-to-noise ratio in the green channel and I was much more gentle with the adjustment curves so Tui Regio isn't so exaggerated. There is a bit of a rainbow effect, which I think is different atmospheric illumination for the different wavelengths, but I think the coloration that differentiates Tui from the rest of Xanadu is definately real.

[jmknapp]

Okay, one final attempt for me.  This time I stacked three CB3 images to improve the signal-to-noise ratio in the green channel and I was much more gentle with the adjustment curves so Tui Regio isn't so exaggerated.  There is a bit of a rainbow effect, which I think is different atmospheric illumination for the different wavelengths, but I think the coloration that differentiates Tui from the rest of Xanadu is definately real.

Out of curiosity, what kinds of geometrical tweaks do you do on the different images? Seems like since they are taken in sequence there will be slight scaling, translation and perspective differences?

[Decepticon]

"Naming New Lands"

New CICLOPS Update.

http://ciclops.org/view.php?id=1637

[tfisher]

Out of curiosity, what kinds of geometrical tweaks do you do on the different images? Seems like since they are taken in sequence there will be slight scaling, translation and perspective differences?

These required a tiny bit of rescaling and a few pixels of translation. Cassini doesn't usually rotate (someone described it as "like a tripod in space") so at least that reduces by one the degrees of freedom needed for alignment. I think actually I only rescaled the two CB3 images that were taken a little while away from the rest of the sequence. I'm doing it all by eye, of course, which on Titan means trying to line up the coastline and islands as well as possible.

To decide how much to rescale, I crop the two images so there is no extra space around the edges, view them together in an overlay mode (either red+green or difference of gray scale images), then count the pixels required to slide the smaller image so features on the left edge line up to where features on the right edge line up. I enlarge the smaller image by that many pixels, and realign again. If it doesn't look quite lined up I repeat.