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Titan's changing lakes
ngunn
post Feb 7 2009, 07:20 PM
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Brilliant discovery - brilliant paper title!

I'm not so sure that we can deduce anything much about the depth. The shoreline gradient is very small, yet even for the (one would think) shallows near the shore no bottom reflection is detected, presumably because the direct reflection from the surface is just so much brighter. I note that "T60 will provide another . . opportunity where the observation can be tuned better" - maybe to look specifically for a bottom echo?? And before that there is the T58 SAR. How much will it resemble the northern lakes?

Exciting stuff.

Oh - I almost forgot there's a few other abstracts to look at as well smile.gif !!!
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ngunn
post Feb 8 2009, 08:37 AM
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Taking this together with earlier VIMS results, may we tentatively conclude that the ISS- and SAR- areas hitherto coloured blue on published images actually comprise significant areas of gently sloping 'mudflat' as well as areas of standing liquid? If so we have to question how much of the large northern lake district is actually liquid-covered. Are the SAR details seen inside the inferred shorelines mudlats, lake bed features, or a mixture of the two? Will it require altimetry to find out? What are the implications for the proposed lake boat?
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rlorenz
post Feb 9 2009, 06:22 PM
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QUOTE (ngunn @ Feb 7 2009, 02:20 PM) *
Brilliant discovery - brilliant paper title!


But apparently not perceived as such by the program committee - I got postered.
Apparently the tired old story of salts on Europa and some other reruns were
considered more worthy of oral presentation... :-{
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nprev
post Feb 9 2009, 07:57 PM
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Hmm. Sorry to hear that, Ralph; it was indeed a great paper!

I wonder sometimes if the community as a whole is kind of intimidated by Titan in some ways. It's SO different that interpreting even basic surface features is a significant challenge.


--------------------
A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
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ngunn
post Feb 9 2009, 09:15 PM
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Or perhaps other 'disadvantaged' topics were felt to be in need of positive discrimination?

Anyhow, for us distant abstract-consumers one format is much like another and each new revelation is a treasure.

Perhaps Ralph will take a question from the floor here. It's about surface gravity waves on the lake. I would like to ask whether this observation, or others like it, can be used to place limits on either the height or gradient of surface waves. For example can we say from this that the surface (in the brightest part) is smooth and flat right down to centimetre scales?

Or is there still the possibility of an oily swell? (sorry)
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Jason W Barnes
post Feb 10 2009, 01:52 AM
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QUOTE (rlorenz @ Feb 9 2009, 12:22 PM) *
But apparently not perceived as such by the program committee - I got postered.
Apparently the tired old story of salts on Europa and some other reruns were
considered more worthy of oral presentation... :-{


WTF? Program committee on crack is what that is.

- Jason
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rlorenz
post Feb 15 2009, 04:21 AM
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QUOTE (ngunn @ Feb 9 2009, 04:15 PM) *
Perhaps Ralph will take a question from the floor here. It's about surface gravity waves on the lake. I would like to ask whether this observation, or others like it, can be used to place limits on either the height or gradient of surface waves. For example can we say from this that the surface (in the brightest part) is smooth and flat right down to centimetre scales?
Or is there still the possibility of an oily swell? (sorry)


Yes, the echo shape and amplitude (and the radiometry) pose severe constraints on how flat the lake
surface must be - a detailed modeling effort is ongoing.
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ngunn
post Feb 15 2009, 07:51 PM
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Great - another potentially variable lake property accessible for occasional monitoring by Cassini. I look forward to the first results.
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Jason W Barnes
post Apr 10 2009, 11:32 PM
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VIMS Ontario Lacus paper is now out in print from either Icarus ( http://www.sciencedirect.com/science?_ob=A...b490613a43ebb98 )
or from my website ( http://www.barnesos.net/publications/paper...s.Shoreline.pdf ). We only have one look, so no direct evidence of changes, but the bathtub rings certainly imply lake level changes over time, anyway cool.gif .

- VIMS Jason
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ngunn
post Apr 11 2009, 07:26 AM
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A huge thank you (again) for making another fascinating paper available to all. I haven't had time to digest it fully, but noticing this concluding sentence

Knowledge of the amplitude of the changes will require reliable topographic
information over Ontario Lacus with both high precision
and fine spatial resolution the T49 RADAR altimetry pass, should
it occur, will shed light on these processes.


reminded me that we already have a link to that altimetry profile in post 15 of this thread.
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titanicrivers
post Apr 11 2009, 12:28 PM
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As above. A very readable and yet compelling paper with great figures and a nice discussion. Appreciate the work and especially the free link posted here, Jason.
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ngunn
post Apr 11 2009, 10:04 PM
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Is anybody going to have a go at matching the altimetry to the VIMS map of the lake's southeastern margin? Did the altimeter track pass over those red islands in the VIMS interpretation diagram?

A nice feature of the VIMS is the clear boundary between unit 1, interpreted as standing liquid, and unit 2, interpreted as possible mudflat. The distinction seems to be less marked in radar SAR images of the northern lakes, presumably because the liquid is just too transparent to microwaves and it's surface virtually invisible (unless you're looking straight down in altimetry mode at the specular reflection of the transmitter).
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Jason W Barnes
post Apr 12 2009, 06:25 PM
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QUOTE (ngunn @ Apr 11 2009, 03:04 PM) *
Is anybody going to have a go at matching the altimetry to the VIMS map of the lake's southeastern margin? Did the altimeter track pass over those red islands in the VIMS interpretation diagram?

A nice feature of the VIMS is the clear boundary between unit 1, interpreted as standing liquid, and unit 2, interpreted as possible mudflat. The distinction seems to be less marked in radar SAR images of the northern lakes, presumably because the liquid is just too transparent to microwaves and it's surface virtually invisible (unless you're looking straight down in altimetry mode at the specular reflection of the transmitter).


I saw a profile across it somewhere -- which probably means that Ralph showed it to me. So hopefully he'll put an explicit comparison in an upcoming Ontario Lacus altimetry paper.

- Jason
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HughFromAlice
post Aug 23 2009, 06:08 AM
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The variation in the height of the surface of Ontario Lacus has been constrained to within a range of a few millimetres.

There is an abstract (you will have to pay for the full research paper) pubished in Geophysical Research Letters on Aug19 on the - Smoothness of Titan's Ontario Lacus: Constraints from Cassini RADAR specular reflection data. Available at http://www.agu.org/pubs/crossref/2009/2009GL039588.shtml It has recieved good publicity in the popular scientific press, such as http://www.newscientist.com/article/dn1766...ping-rocks.html

As an amateur who is fascinated by Titan - and in particular its lakes and 'methano-ethanological' cycle - I thought that this 19Aug abstract was v interesting. While not proof that Ontario Lacus is filled with liquid, I think that there would be few people who would bet a week's wages on it having any sort of solid surface after reading about how incredibly smooth it is.

It is interesting to see how this research has been built on data from the T49 Dec08 pass. I read a paper a while ago by Ralph (Lorenz - who posts regularly right here) on this pass. Very interesting regarding the specular reflection. http://www.lpi.usra.edu/meetings/lpsc2009/pdf/1990.pdf ....Now team member Lauren Wye (whose speciality is signal detection) has built on this, by working out a way to more accurately analyze the strength of the specular return by partly overcoming distortion factors caused by the flash. This has allowed an upper boundary in height variation of the surface to be set at 3mm.

To me this looks like a brilliant conclusion to the work of a highly multiskilled team! Congratulations. (No pun intended - it is more than a flash in the pan!).
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Gsnorgathon
post Aug 23 2009, 05:29 PM
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Hey! I got lucky and got the whole article. (Does that make me a criminal?) ph34r.gif
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