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Altimetry Profiles Titan
Byran
post Apr 29 2006, 07:17 PM
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I search Altimetry Profiles Titan. Where their possible find?


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Guest_BruceMoomaw_*
post Apr 29 2006, 10:39 PM
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They do exist -- although the one from the last radar pass (T7) was lost along with the second half of the SAR strip, due to the software error that led to Cassini's second recorder failing to turn on. When I get the time tonight, I'll try to dig up the altimetry profiles from the earlier radar passes for you.
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volcanopele
post Apr 29 2006, 11:15 PM
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Don't bother. the only one that I think has been publically released has been inbound Ta (though I think I posted a bootleg version of outbound Ta on my blog at some point). I haven't even seen any of the others. Not quite sure when more altimetry profiles will be released.


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Guest_BruceMoomaw_*
post Apr 30 2006, 02:37 AM
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You're right -- but I'm pleased to say that you posted bootleg versions not just of Outbound Ta, but of both Inbound and Outbound T3. You naughty boy. They're awfully fuzzy, but at least we've got them:
http://volcanopele.blogspot.com/2005/03/ca...-altimetry.html

In fact, R.L. Kirk and Charles Elachi both say that the only altimetry profile returned from Ta was the Outbound one. That's the only one which has been officially released yet (and it does match your bootlegged copy of that one):
http://www.lpi.usra.edu/meetings/lpsc2005/pdf/2227.pdf
http://sci.esa.int/science-e/www/object/do...fobjectid=37161

As for the two altimetry profiles returned from the T8 pass, Elachi says: "Rudimentary threshold processing of the T8 altimetry indicates modest regional slopes and no major topographic features in the ~300 km-long swaths. More sophisticated processing to account for off-nadir pointing and the use of reconstructed ephemeredes is needed for more robust conclusions." ( http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1252.pdf )

Finally, there are several interesting LPSC abstracts on the use of clinometric techniques to try to calculate topography (although Jason himself has expressed doubts about the use of this, at least on optical and near-IR wavelengths, given both the haze-fuzziness and our uncertaintities about local albedo variations on the surface). These include Kirk's abstract, and also:
http://www.lpi.usra.edu/meetings/lpsc2005/pdf/1869.pdf
http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1007.pdf

And we have the analysis of the startlingly rugged topography at the Huygens landing site from stereo DISR images: http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2089.pdf . (Note that the extremely nice color-coded 3-D topographic map is described as having "no vertical exaggeration", with the italics being theirs. Steep local slopes produced by liquid runoff erosion seem to be one of the biggest threats confronting future Titan landers.)
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Guest_BruceMoomaw_*
post Apr 30 2006, 02:58 AM
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It turns out that there should also be an Inbound altimetry profile returned from T7 -- unless it was overwritten because of the recorder error, which I strongly doubt.

Correction: I see that you did say that the recorder problem also led to the loss of that Inbound T7 altimetry profile. (Of course, your advance word on the data loss on that pass is, alas, what annoyed JPL enough to get your blog cancelled -- which I think we all still regard as a major loss.)
http://volcanopele.blogspot.com/2005/09/ca...for-090805.html
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The Messenger
post May 1 2006, 02:26 PM
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QUOTE (BruceMoomaw @ Apr 29 2006, 08:37 PM) *
And we have the analysis of the startlingly rugged topography at the Huygens landing site from stereo DISR images: http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2089.pdf . (Note that the extremely nice color-coded 3-D topographic map is described as having "no vertical exaggeration", with the italics being theirs. Steep local slopes produced by liquid runoff erosion seem to be one of the biggest threats confronting future Titan landers.)

It seems to me like the rugged topography, and wide arroya-like alluvial flows should have created heartbeat-like blips in Huygens' radar altemeter as it approached the surface. This is certainly not the case in the radar profile in the 'Nature' articles, although there is no information about smoothing and processing of the radar.
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Guest_BruceMoomaw_*
post May 1 2006, 09:58 PM
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That may depend on how wide the Huygens radar altimeter beam was (which I don't know at the moment) -- those arroyos are alarmingly steep, but they're also narrow.
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The Messenger
post May 11 2006, 05:06 AM
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QUOTE (BruceMoomaw @ May 1 2006, 03:58 PM) *
That may depend on how wide the Huygens radar altimeter beam was (which I don't know at the moment) -- those arroyos are alarmingly steep, but they're also narrow.

I can't find a spec, but I remember reading that both radars did frequency sweeps with wide beams. Also, the radar was considered more-or-less useless for the last 200 meters; so the radar may not have picked up much terrain variation. We extracted the blip widths from the audio, plotting the blip widths as altitude, and the spacing between blips (which also gets smaller as the probe falls) as time. It is an interesting, but almost meaningless plot without scaling information. The first derivative 'looks' somewhat periodic. Near the end - the last 30 seconds - the acceleration picks up, which would normally mean the probe was passing over rising terrain.
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RNeuhaus
post May 11 2006, 06:56 PM
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Up to still there is still no altimeter map of the Titan. At least, my view is that Titan's surface is relatively rougly with small variations of slope (5-10 degree) and the hills does not surpais the 500 meters and the average is 300 meters.

That is very smooth comparing to our moon Selene.

Rodolfo
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