[X] My Assistant

[ngunn]

Today's big news?
http://ciclops.org/view/5471/CASSINI_FINDS...ILL_TITAN_LAKES

Changes in the south polar region were announced late last year. Is there more to this story now??

[HughFromAlice]

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!).

[rlorenz]

To me this looks like a brilliant conclusion to the work of a highly multiskilled team! Congratulations.

It was Lauren who did all the work. One of those discoveries that starts with 'that's odd....'
(namely that the amplitude histogram of the echoes was nonGaussian. Essentially the surface is
so flat that the echo power is dominated by returns from a small area (almost a point target)
and the echoes are sufficiently in phase that the saddle-shaped histogram of the transmitted
chirp is retained.) Thus we can get information showing that few-hundred-meter-wide areas
on Ontario are flat at a fraction of a radar wavelength.)

The effort was complicated by the saturation of the signal, which was then lossy-compressed,
although Lauren managed to reverse-engineer the processing chain to recover some quantitative
backscatter numbers nonetheless.

This experience let us fine-tune the re-observation on T60 with stronger attenuator settings.
Unfortunately that data were lost due to the DSN outage.

So, the elevation profile (reported in my LPSC abstract) shows Ontario is flat to ~10m over
tens of km, and the echo histogram data show it is flat to ~3mm over ~100m scales.

Flat as a millpond, as they say

[djellison]

Flat as a millpond, as they say

Minus the ducks. Their wake would have ruined the 3mm factor