[X] My Assistant

[Guest_AlexBlackwell_*]

The mission description document is now online (1.06 Mb PDF).

[remcook]

looks like we should get some better north polar coverage

[ugordan]

How come? I see the flyby is pretty much equatorial with the C/A latitude 23 deg N. The 3 snapshots included also illustrate that.

[angel1801]

Please remember that right now that ISS imaging of Titan can only go up to about 70N latitude at present and because at high northern latitudes is in low sunlight, it is hard to get good ISS images of such areas.

We had a similar view of Rhea centered on 25N, 300W on August 17, 2006 and we did not see the north pole of Rhea at all!

It is only possible with radar to see the north pole area rof Titan right now. And the October T19 flyby will do this. Some of the path will overlap the T16 coverage with the additional bonus of going further north than the T16 swath.

[remcook]

I am mostly talking from a CIRS perspective

[Thorsten]

Will there be SAR during this flyby? According to the “Planetary Society” Website, T17 should include some SAR imaging, ride-along with INMS and at less than optimal attitude.

[remcook]

How come? I see the flyby is pretty much equatorial with the C/A latitude 23 deg N. The 3 snapshots included also illustrate that.

23 degrees is still better than 0 degrees. From the snapshots you can see the north pole 'from above' instead of 'from the side'.

about the SAR, the last page of the linked document shows a radar observation called T17RASAR001_INMS. I assume that will be a SAR measurement riding along with INMS.

[Thorsten]

about the SAR, the last page of the linked document shows a radar observation called T17RASAR001_INMS. I assume that will be a SAR measurement riding along with INMS.

You’re right. I was only wondering how briefly SAR is mentioned in the mission description document, given the attention that is normally paid to a RADAR swath during a flyby. Is this maybe because it’s going to be only a "half swath" or because they're unsure about the quality of SAR measurement riding along with INMS?

(Thorsten, a helpless SAR junkie)

[Littlebit]

The mission description document is now online (1.06 Mb PDF).

Nearly 47 days after Titan-16, Cassini returns to Titan for its eighteenth targeted encounter.

The closest approach to Titan occurs on Saturday, September 7, at 20:16 spacecraft time
(September 7 at 2:16 p.m. Pacific Time) at an altitude of 1000 kilometers (625 miles) above
the surface and at a speed of 6.0 kilometers per second (13,422 mph). The latitude at closest
approach is 23° N (near equator), and the encounter occurs on orbit number 28.

I'm not in the Pacific Time Zone, which appears to be somewhere a very long ways away from the zulu.

Would that be Thursday 7 Sep or Saturn day, Sep 9 for those of us stationed on earth?

[volcanopele]

The flyby took place approximately 23 hours and 15 minutes before this post. Images from this encounter should be showing up in 6-7 hours.

[alan]

T17 images are up now, right on schedule

[remcook]

looks like the mid-latitude clouds are still there

http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=81780

http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=82260

[ugordan]

Quite, they're visible in both wide angle and narrow angle frames :

[Guest_AlexBlackwell_*]

Released today: PIA09172: Titan (T17) Viewed by Cassini's Radar - Sept. 7, 2006

[volcanopele]

Here is the T17 swath overlain on the latest ISS Titan map + SAR swaths. The swath at center is T17, the swath just above it is portions of the T3 swath, and the swath at bottom left is from T13.

[elakdawalla]

Thanks, Jason! Any chance you could put together a blink gif comparing how the crater looks between SAR and ISS?

--Emily

[volcanopele]

here you go!

[nprev]

Extremely interesting...thanks, VP!

Just an impression here, but this comparison reminds me of Mars in some ways. We found that the classical albedo features had only a weak relationship to the physical attributes of the landscape, and it seems as if we're seeing something similar between the SAR & ISS views of Titan. Maybe this just means that the frequency of observed EM radiation makes things look differently, but perhaps there are some other principles to be derived from this analogy...odd.

[David]

I don't think it's quite like Mars; there we have dark materials sporadically overlaying the physical features of the landscape (I'm not familiar with the principles governing their distribution, but I assume somebody knows something about it). Here there really is a correlation between the visually bright areas and the radar-rough areas; most of the visually bright areas are radar-rough, though the reverse is not necessarily the case. Which suggests that the dark materials can overlay rougher terrain, but that, perhaps, where they are densest, the terrain is smooth. Which I suppose can mean that the dark materials are fine-grained sands or silts that collect in the lowlands, while the lighter materials are exposed highland rock/ice.

[ngunn]

Quite often the radar bright patches are bigger than the IR bright 'islands' they overlie, as if the radar is seeing through the shallowest deposits of smust around the 'shorelines'.

[elakdawalla]

I'm preparing the T17 swath to post on my Cassini RADAR images of Titan page but am a bit confused on its scale. So far the team seems to be releasing everything projected to 128 pixels per degree (0.351 km/pixel), which would make the T17 swath, at 9,000 pixels wide, cover about 70 degrees of longitude, which seems to make sense. But in the caption describing the crater, they say it's 30 kilometers in diameter, which should come out to about 85 pixels, give or take. But I measure it at roughly 210 pixels from scarp edge to scarp edge, which would be closer to 75 kilometers in diameter. What am I missing?

--Emily

[Bart]

I couldn't speak to pixel size, but the T17 swath was quite a bit shorter than other recent swaths. I would estimate closer to 40 degrees long.

Compare the relative swath sizes here (T17 is the smallish one right of center on the 90-degree-centered-hemisphere):
http://photojournal.jpl.nasa.gov/jpeg/PIA09035.jpg

I also always like to refer to Joe Knapp's excellent RADAR map:
http://cassinicam.com/titanflybys/titantracks.html

Bart

[Guest_AlexBlackwell_*]

I couldn't speak to pixel size, but the T17 swath was quite a bit shorter than other recent swaths. I would estimate closer to 40 degrees long.

As I recall, the T17 pass wasn't optimized for RADAR; indeed, it was a ride-along with INMS.

[elakdawalla]

Yeah, I knew it was a ridealong, and I knew it was shorter; but I hadn't realized how much shorter. Your estimate of 40 degrees seems pretty close to the mark, bart...but that unfortunately leaves me a bit adrift as to the scale of the pixels in the release. If the whole thing were 35 degrees, that would mean the release was at 256 pixels per degree (.176 km/pixel), so our 210-pixel crater would be 37 kilometers in diameter. I guess that's pretty close to the 30 quoted in the caption, but not close enough for me to be confident...

--Emily

[Bart]

I'm not sure how much it helps, but a few months back they released an image of just the crater:
http://photojournal.jpl.nasa.gov/catalog/PIA08737

I compared this with the new release and it looks like they are close to (if not the same) resolution. The caption of the older release specifies the dimensions, and it comes out pretty close to your 0.176 km/pixel number.

Bart

[nprev]

Quite often the radar bright patches are bigger than the IR bright 'islands' they overlie, as if the radar is seeing through the shallowest deposits of smust around the 'shorelines'.

Yeah, that's kind of what I meant: the IR "albedo" features don't really seem to correspond 1:1 with topographic features, except for a few things like fresh craters which have nice angular surfaces for strong radar reflection. Seems like one big wild card is that we don't really know the radar permittivity of the surface, whatever it is (and whether we're looking at the same cryomineral(s) every time). Lots of interesting variables here...

[Decepticon]

Emily is the T12 Jan 07 release correct?

[elakdawalla]

None has been released; it's unclear if there was supposed to be one. See this discussion.

--Emily

[tedstryk]

Isn't this it?

http://pdsimg.jpl.nasa.gov/data/cassini/ca...er/CORADR_0078/

[JTN]

Isn't this it?
http://pdsimg.jpl.nasa.gov/data/cassini/ca...er/CORADR_0078/

Looks like just scatterometry and radiometry. Perhaps this quote from ERRATA.TXT explains the confusion? (Disclaimer: this is the first time I've dived into the PDS.)

2. Although this is a Titan Flyby, there are no SAR images or altimetry. An experimental procedure was applied to produce a SAR image from scatterometer mode data, but the procedure failed due to pointing and SNR issues. The experiment resulted in the development of a technique that has produced useful imagery in other subsequent flybys.

[volcanopele]

AAHA! So that explains it. They tried to get distant SAR images on T12, but it failed. For future reference, it did work on later flybys. Thanks, JTN!