[X] My Assistant

[Juramike]

T47 Mission description available here!

VIMS noodling near Huygens Landing Site
CIRS looking at nitrile and hydrocarbon concentrations near the Equatorial limb
UVIS looking at aerosol concentrations in upper atmosphere (particulate data) from 2 (two) stellar occultations

And ISS will get some nice images of Hotei Arcus, E Xanadu, and W Fensal region (looks like Sotra Facula will be in the dark).

-Mike

[Juramike]

Here's a very rough lineup of the T47 narrow angle images over SE Xanadu superimposed on a wide angle view:


The red box image (N00124292) ID pretty solid, the other two are less clear.
The distinctive dark "caudal" shape in N00124292 looks similar to a feature central Adiri, - is it the same type of formation? (bright tectonic ridge cutting across a dark undulatory graben?)

I think N00124920 is a shot of Hotei Arcus.

[Man, figuring these out was pretty tough...]

-Mike

[ngunn]

I think N00124920 is a shot of Hotei Arcus.

I agree. It looks a lot like this one from the last encounter (posted 5 November):

"Is this Hotei Arcus? It will be interesting to look for any topographic shading at the terminator. Can't wait to see the processed mosaics.
http://saturn.jpl.nasa.gov/multimedia/imag...ID=173100"

Mind you, nobody supplied the confirmation I was fishing for in that post. . .

--

Mike and everybody - do you think the recent Titan raws have got blander than usual (as happened once before when they changed some contrast setting) or is it just the terrain we're looking at here?

[Hungry4info]

Quick question, my Titan map is a bit outdated (2006). Where can I find the most up-to-date Titan map?

[Decepticon]

http://photojournal.jpl.nasa.gov/catalog/PIA08399

I think Jason did this. Not sure if it's been updated recently.

[Juramike]

Do you think the recent Titan raws have got blander than usual (as happened once before when they changed some contrast setting) or is it just the terrain we're looking at here?

I've been wondering if they changed the way that they stretch the image when creating the raw image .jpeg files.

Another key factor may be the phase angle. The higher the phase angle, it *seems* the lower the contrast image. (I could be way wrong here, that's just been my supposition).

I was getting kinda nervous until the full-on shots from the Nov. 13 distant look showed a reassuring nice contrast.

[Juramike]

Playing around with compensating for the frustrating gradient exposure of surface images of Titan anywhere close to the terminator, I think I've got a method that might work OK. It worked on a test image, that with a distinctive "arrowhead and chevron shape" that is just to the W of Hotei Arcus.


Here's the recipe:
Converted the raw jpegs to 16-bit images then
Stack and averaging the images
Add a grayscale gradient that approximates the shading, adding an offset and gradient such that the bright white terrain is uniform across the image and the dark terrain is uniform across the image. (Add 0 to the brightest part of the image)
Then stretch the contrast.

-Mike

[jekbradbury]

For comparison, here's a version of the same image, processed with just a high-pass filter:



The issue with such processing is that it gets rid of precisely the features that we're looking for: large albedo features like the "chevron".

[Juramike]

Here's a work-in-progress mosaic of the T47 ISS images around Hotei Arcus:


They are aligned, but not a contrast balanced ensemble. (I switched to 8-bit processing, I couldn't get a negative offset to work with the 16-bit images.)



And like it seems after every home project, there are spare parts leftover. I have no idea where this goes. (There is a similar piece in the T46 mosaic):


Any suggestions?

-Mike

[rlorenz]

..... that with a distinctive "arrowhead and chevron shape" that is just to the W of Hotei Arcus.

Mike

I hope you or someone can figure out what the arrowheads are. I remember we saw one (radar-bright)
in TA, and it always bugged me as something interesting whose origin is not obvious...

[ngunn]

Intriguing, but I'm not sure what arrowheads we are talking about here. If there is a common class of them worth considering as a group then it would be nice to start a catalogue of annotated images. What scale range are we talking about? Huygens landed near a couple of beautiful arrowheads but the're a lot smaller than the shapes visible on ISS images. Can you point out the RADAR one(s) you have in mind? If there is a real case to crack here I'd like to be on the volunteer team. Perhaps we need to do a sort of 'arrowhead zoo'.

[rlorenz]

Can you point out the RADAR one(s) you have in mind? If there is a real case to crack here I'd like to be on the volunteer team. Perhaps we need to do a sort of 'arrowhead zoo'.

go for it!.

This is from TA, shown at 128 pix/degree (i.e. 375m/pixel or so, close to the intrinsic
resolution in this part of the swath). North is roughly up. This is (eyeballing) about 700km
East of Ganesa macula

Evidently acquired too long ago - isnt radar-bright after all; radar dark (compared to immediate
surrounds..)

[ngunn]

Aah right. It does jump out at you, I agree. However I can't see much difference between the ground inside the V and outside to the right of it. Perhaps the right stroke of the V is the 'feature' - a straightforward linear one. Cover that up and the rest of the area reverts to quasi-random (fractal) light/dark boundaries. It will be interesting to look for more, though.

Also maybe Mike or one of the others who did so well analysing those Meridiani dunefields might be able to answer the question: How many 'arrowheads' would we expect to find in the Titan images through chance alone, without a special cause? I would guess a few, given that linear streaks and linear boundaries seem to be fairly common.

Leaving the maths to the experts, I will when I get home empty a box of matches on the carpet and count the V's. I'll also take note if any happen to coincide with patterns on the carpet in a 'suggestive' way.

Results here later.

[Juramike]

Back to the T47 flyby...

I modified my method to deal with the gradient of Titan images near the terminator. Here is my latest processing of the T47 Hotei Arcus images side-by-side with my older 8-bit image:


Recipe:
Converted the raw jpegs to 16-bit images then
cosmic ray hit removal - Add median filter layer for each image, median filter 2 pixel, set layer opacity around 90%
Stack and average the images
Add a grayscale gradient that approximates the shading, (dark towards terminator, subtract 220 at brightest part of image)
Subtract the image and add a 50-100 unit offset.
Add curve layer for Anti-vignetting, add mask for AV layer (center dark, periphery bright)
Then stretch the contrast.

-Mike

[ngunn]

Making V's -the match experiment result as promised.

100 matches scattered on flowery carpet: just one well-formed V (defined as match ends meeting neatly at an acute angle). No correlation with carpet albedo features.

Nice work with Hotei Arcus images Mike.