Titan's topography, strange.... Options

[machi]

Fantastic work, thanks Ralph!

I have one question. First altimetric measurements for Martian surface were made by the spectrometers and photometers which measured intensity of the CO2 bands.
It's something similar possible for Titan (with VIMS)?
I suppose that it's difficult or impossible due to much higher amount of atmosphere over Titan's surface, but still if we can found some suitable chemical substance which is both detectable and present only in troposphere, it will be interesting complement to radar altimetry.

EDIT

I found one LPSC abstract in which authors tried to derive topography information from the VIMS cube.

[rlorenz]

Is there a place to download the entire T83 swath? Was there any topographic info to add to 'hot-cross bun' to make its possible volcanic geomorphic status more compelling?
EDIT: ditto for the T84 SAR swath !

I believe both T83 and T84 are on the PDS http://pds-imaging.jpl.nasa.gov/volumes/radar.html

[rlorenz]

I have one question. First altimetric measurements for Martian surface were made by the spectrometers and photometers which measured intensity of the CO2 bands.
It's something similar possible for Titan (with VIMS)?
I suppose that it's difficult or impossible due to much higher amount of atmosphere over Titan's surface, but still if we can found some suitable chemical substance which is both detectable and present only in troposphere, it will be interesting complement to radar altimetry.
EDIT
I found one LPSC abstract in which authors tried to derive topography information from the VIMS cube.

In principle methane absorption should work, just outside the center of the windows where the absorption is weak but nonzero. Like water vapor on Earth, the methane is concentrated in the lowest few km of atmosphere, so an extra km of column should be detectable in a careful analysis. With the topo map published (and it identifies where there is real data and where there is interpolation) it should be possible to calibrate an empirical VIMS approach and perhaps use it to fill in the gaps.

This of course is just one of many correlative studies that could be done. Maybe the elevation signal shows up in the CIRS surface temperature retrievals too (although of course there could be surface emissivity effects that correlate with elevation, as is the case on Venus and Earth..)

[rlorenz]

Someone-- jog my ailing memory, I don't work with tidally-locked bodies that often-- on longitudes, what is the sub-Saturnian point, and what is the leading hemisphere? I'm thinking that 0* is sub-saturnian, 90* is leading, and so on...

your first bit is correct - zero is sub-saturnian (actually since the orbit is elliptical, Saturn has an apparent libration back and forth by 3 degrees of longitude IIRC) so I think the IAU defines the zero as the subsaturn point at the first periapsis after the epoch.

The second bit reminds me of the mantra that 'there is no such thing as longitude' There is only East Longitude, and West Longitude, and the L-word should not be uttered without saying which, otherwise it is meaningless. Xanadu is around 90W on the leading hemisphere.

There is a separate issue, which is that I like to show Titan maps, as I always have done - since the HST map published in 1996 by us (Smith et al., Icarus) with 180 at the center, and hence Xanadu at right. This in part was to de-emphasize a coverage gap in the original HST coverage. A few other workers prefer 0 at the center.

[Bill Harris]

I tend to think in that ancient cartographic convention where one starts at zero and counts westward (left-ward) to 360 degrees. Sometimes I'll slip even more and put South upwards. I need to work myself up a set of crib-sheets outlining "the usual" carto-conventions so I can jog my own memory...

One thing I notice from the topo map (Figure 3) is that the series of isolated topographic highs from 0W to 180W (and 30S to 45S) are neatly lined up (implying something episodic and moving) and from 0E to 180E there are corresponding topographic lows. Hmmm. Major highs along the equator, as expected, are at the sub-saturnian and anti-sub-saturnian points.

As they say, the importance of geology to geography is that without geology, geography (topography) would have nothing to rest upon...

--Bill

[ngunn]

the series of isolated topographic highs from 0W to 180W (and 30S to 45S) are neatly lined up (implying something episodic and moving) and from 0E to 180E there are corresponding topographic lows.

I wouldn't read too much into the alignments since the distribution of the elevation data is itself very stripey. http://www.lpl.arizona.edu/~rlorenz/titant...distancemap.tif
There are large unsampled areas either side of those apparent alignments where more of these features could be lurking. Regarding the isolated topographic lows I find these more puzzling than the the highs. I'm struggling to come up with any plausible way to form them.

[Bill Harris]

Maybe. Maybe not. I don't see a correlation between the stripes and these highs and other highs. I've noted them and we'll know more when we get more data...

--Bill

[ngunn]

In the case of Titan 'something episodic and moving' is quite a big suggestion. I don't by any means dismiss it and I agree that the alignment of highs in the current data set (and their roughly equal spacing) is eyecatching.

[Bill Harris]

What I'm thinking is a process akin to the Hawaiian island chain: the Pacific seafloor is moving over a long-lived mantle hotspot (superplume) which forms volcanic island after island after island. Similarly, the mobile icy crust of Titan may be sliding over a plume of warm, buoyant ice to cause these presumptive diapirs (topographic highs). And since the icy "mantle" of Titan is not as active or voluminous as the Earth's rocky mantle, the material displaced to the "diapirs" has to come from somewhere, hence the corresponding depressions. This may well be farfetched, but we're engaged in armwaving now. I'm sure that the truth will prove to be even stranger...

--Bill

[stevesliva]

I wouldn't read too much into the alignments since the distribution of the elevation data is itself very stripey.

If you look at the map of Earth with similar sampling, the Andes and Greenland both turn into basically round blobs. Also, the Tibetan Plateau disappears. Pretty neat display of data coverage in that regard. The Andes and Greenland are not mantle plume stratovolcanoes.

That said, I think the paper addresses whether those highs are isolated.

[titanicrivers]

T83 has a possible volcanic construct at 38.5N and 203W as shown in the map below from http://www.lpl.arizona.edu/~rlorenz/titantopo/
The structure (green arrow) has the up-close appearance (right SAR image from http://photojournal.jpl.nasa.gov/catalog/PIA16165 ) likened to a hot-cross bun.
I have downloaded T83 SAR from the PDS (thanks for the link Ralph) but have not been able to open the large file (perhaps VP can update his Radar Swath Maps again and get bothT83 and T84 entered.)