[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