Rev 190 http://www.ciclops.org/view/7628/Rev190 contains a close Titan flyby (T91). At close approach Cassini radar will acquire altimetry over Ligeia Mare with millimeter resolution of surface features enough to detect small waves on the sea’s surface.

To be clear, the altimeter resolution is of the order of 10 METERS. However, the amplitude distribution of the echo samples, and the shape of the echo pulse, are strongly sensitive to surface roughness for very smooth surfaces, such that the effect of millimeter-scale ripples should be detectable.

I was just wondering about this very thing. In particular can this method clearly distinguish between waves on a liquid surface and a shiny but not perfectly flat mudflat? It seems to me that the two might smear the specular reflection in quite similar ways.

Hmm. Good point. All I can think of is that the difference in the dielectric constants between the two materials may affect the smearing...?

Agree it’s uncertain (excitingly so) if Cassini will detect waves on Titan during T91. There are concerns that the winds of the season are too calm to produce waves. http://www.jpl.nasa.gov/news/news.php?release=2013-170 The viscosity and exact composition of the liquid to be moved is uncertain. Erudite scientists using sophisticated radar techniques have been fooled before by the complex signals returned from Titan’s surface. http://www.lpl.arizona.edu/~rlorenz/glitterofdistantseas.pdf There may even be fantastic unknowns that will foil our efforts to detect waves!
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Love the cartoon !

The interpretation of the Arecibo echoes (which you so nicely worked into your cartoon) was that there were patches of low-reflectivity material some tens of km across, that had to be 'parking lot smooth'.

At the time (2003) I was not well-traveled enough to realize that such wide patches of such flat material can be generated (I was familiar with a few playa in the southwest, but these are only a few km across). The salt flats at Dallol in the Danikil depression I visited a couple of years ago - flat as far as you can see - Field_photo - would likely yield returns very analogous to those seen at Titan. Many dunefields sit on similarly flat clay or salt pans, so the presence of dunes (at Titan's equator) is not inconsistent with the Arecibo data, which deserve another look.

Now, at the time (as always) one is obliged to consider Occam's razor. Are the optically-dark areas on Titan which are giving us specular reflections that demand dead flat and low-dielectric constant materials lakes ? Or there were once lakes and seas and they have gone away leaving us mudflats as big and flat as those found in only a few places on Earth ? Extant lakes were the simplest explanation.

Turned out Titan was far from simple.....

Titan is indeed far from simple. I hope I'm still around when we get a dedicated orbiter and some sort of Rover on Titan.

--Bill

Hello! I'm new to Unmanned Spaceflight. I run "Titan Saturn's Moon" on Facebook and Twitter. I've really enjoyed reading everyone's posts here and I'd like to contribute what I can.

If you're interested, here is a false color composite I recently made of Titan's south polar cloud from T91. I also made a post on T91 on my Wordpress blog: Looking for Waves on Titan's Seas

-- Val

Hello Val ! Welcome here & nice pics you made ! Warmest regards, VM

Warm greetings, Val!

Its great to have you Val! Your image making is very impressive indeed!
TR

Not bad, not bad a'tall, sir.

--Bill

As per Val's image, I have to admit that the vortex is more indistinct from this range than I'd expected (perhaps the exposure times affected the sharpness).