IPB

Welcome Guest ( Log In | Register )

4 Pages V  < 1 2 3 4 >  
Reply to this topicStart new topic
Ceres Geology
mcgyver
post Mar 15 2015, 10:13 PM
Post #31


Member
***

Group: Members
Posts: 107
Joined: 1-August 14
Member No.: 7227



QUOTE (Phil Stooke @ Mar 15 2015, 04:08 AM) *
"Final confirmation of volcanism should occur by May or June, when central pits show up in those bright spots."

...could occur, if central pits show up...

Phil

It looks like there's actually "something high" under the bright spot!

hipass of the baked dem ( 0 to 360 mapping)


http://www.unmannedspaceflight.com/index.p...st&p=218867
Go to the top of the page
 
+Quote Post
marsbug
post Mar 16 2015, 02:01 PM
Post #32


Member
***

Group: Members
Posts: 324
Joined: 5-January 07
From: Manchester England
Member No.: 1563



QUOTE (mcgyver @ Mar 13 2015, 09:42 AM) *
Recent paper:
"THE POTENTIAL FOR VOLCANISM ON CERES DUE TO CRUSTAL THICKENING AND PRESSURIZATION OF A SUBSURFACE OCEAN."
http://www.hou.usra.edu/meetings/lpsc2015/pdf/2831.pdf


Having read that paper I'll float (he, he, he.. geddit.. no?)an idea that may be rediculously naive: wouldn't a major impact be good way for a pre existing a crack partway through the crust (due to the mechanism proposed in the paper) to be opened up and form a vent? The paper mentions impacts as a source of fracturing sans tensile cracking, why not combine them?


--------------------
Go to the top of the page
 
+Quote Post
mcgyver
post Mar 18 2015, 11:42 AM
Post #33


Member
***

Group: Members
Posts: 107
Joined: 1-August 14
Member No.: 7227



Some ceres maps I found around can help studying the bright spots:




Near infrared mapping of Ceres surface
http://www.spaceref.com/news/viewpr.html?pid=21032


The composite albedo deviation maps of Ceres through F555W (upper panel), F330W (middle panel), and F220W (lower panel) filters
http://eclipsephase.com/ceres-surface-geography



Go to the top of the page
 
+Quote Post
mcgyver
post Mar 18 2015, 12:47 PM
Post #34


Member
***

Group: Members
Posts: 107
Joined: 1-August 14
Member No.: 7227



And my 3d reconstruction of bright-spots crater (4 MB animated gif png):

http://i.imgur.com/c7WRvT7.png

STL file:
http://lc84.altervista.org/vba4.stl
Go to the top of the page
 
+Quote Post
fredk
post Mar 18 2015, 01:41 PM
Post #35


Senior Member
****

Group: Members
Posts: 3792
Joined: 17-January 05
Member No.: 152



The DEM has got to be considered very preliminary near "feature 5" (ie the brightest bright spot). For one thing we may be seeing more PSF than real structure, which would affect the calculation of elevations. For another, if, as recent reports claim, the brightness of feature 5 varies with time, that could also affect the DEM, since you'd normally assume that to be constant when calculating the elevations.
Go to the top of the page
 
+Quote Post
mcgyver
post Mar 18 2015, 03:07 PM
Post #36


Member
***

Group: Members
Posts: 107
Joined: 1-August 14
Member No.: 7227



QUOTE (fredk @ Mar 18 2015, 02:41 PM) *
The DEM has got to be considered very preliminary


How is it calculated? And what does PSF stand for?
Go to the top of the page
 
+Quote Post
Paolo
post Mar 18 2015, 03:20 PM
Post #37


Senior Member
****

Group: Members
Posts: 1603
Joined: 3-August 06
From: 43 35' 53" N 1 26' 35" E
Member No.: 1004



the first result when you google it
en.m.wikipedia.org/wiki/Point_spread_function
Go to the top of the page
 
+Quote Post
fredk
post Mar 18 2015, 03:56 PM
Post #38


Senior Member
****

Group: Members
Posts: 3792
Joined: 17-January 05
Member No.: 152



QUOTE (mcgyver @ Mar 18 2015, 04:07 PM) *
How is it calculated?

Basically you would combine images from different viewpoints (different frames from the rotation sequences). That contains depth information just like an anaglyph does. But if the details of the bright spot aren't reliable then the elevations you get also aren't reliable.
Go to the top of the page
 
+Quote Post
mcgyver
post Mar 19 2015, 08:46 AM
Post #39


Member
***

Group: Members
Posts: 107
Joined: 1-August 14
Member No.: 7227



Well, then the DEM data in that area are totally useless. :-(

Better focusing, then, on tweets about #LPSC2015 in these days: there's a lot of talking on Ceres, and one tweet on the fact that the bright spot is visible above the rim (in unreleased images) and hence is probably a "geyser" ( http://twitter.com/Laurent_Montesi/status/...0697387008?s=02 )
Go to the top of the page
 
+Quote Post
mcgyver
post Mar 19 2015, 09:06 AM
Post #40


Member
***

Group: Members
Posts: 107
Joined: 1-August 14
Member No.: 7227



Nature article on Ceres about icy plume over bright spot:
http://www.nature.com/news/bright-spots-on...=TWT_NatureNews
Go to the top of the page
 
+Quote Post
elakdawalla
post Mar 19 2015, 03:04 PM
Post #41


Administrator
****

Group: Admin
Posts: 5046
Joined: 4-August 05
From: Pasadena, CA, USA, Earth
Member No.: 454



Great find on the DEM -- I'm really surprised to see it released!

If a DEM is calculated from image pairs, I think positional accuracies are no better than some small number of pixels, right? Which is to say it's not really worthwhile to use this one to analyze the detailed rim and floor structure of the crater that the bright feature is in.


--------------------
My blog - @elakdawalla on Twitter - Please support unmannedspaceflight.com by donating here.
Go to the top of the page
 
+Quote Post
algorimancer
post Mar 19 2015, 04:23 PM
Post #42


Member
***

Group: Members
Posts: 655
Joined: 20-April 05
From: League City, Texas
Member No.: 285



QUOTE (elakdawalla @ Mar 19 2015, 10:04 AM) *
If a DEM is calculated from image pairs...

I'm not sure how these DEMs were produced, but in principal all the images from the rotation sequence could contribute simultaneously to the DEM, potentially yielding sub-pixel resolution of the topography. Also, the shadowing along the terminator might contribute further. Or it could be all shape-from-shading, in which case take with a grain of salt. Tracking common features in multiple images is tricky and error prone. Anyway, I agree that the bright spots are indeed so poorly resolved that I'd hesitate to make much of their DEMs.
Go to the top of the page
 
+Quote Post
Phil Stooke
post Mar 19 2015, 04:26 PM
Post #43


Martian Cartographer
****

Group: Members
Posts: 7310
Joined: 5-April 05
From: Canada
Member No.: 227



The basic rule is always going to be... don't expect reliable results when you are looking at things close to the resolution of the data. For images, we can't interpret reliably if we have fewer than 4 or 5 pixels across the object of interest - and even more would be better. Stereo DEMs are even more removed from the raw data (the images), so their effective resolution is lower still. Their resolution will be determined by the spacing between common points, the identifiable points matched in the two images so parallax can be measured. If you look at the images you can get a sense of how far apart those points would be.

So please don't read too much into tiny details in images or DEMs.

Phil


--------------------
... because the Solar System ain't gonna map itself.
Go to the top of the page
 
+Quote Post
JohnVV
post Mar 24 2015, 08:37 PM
Post #44


Member
***

Group: Members
Posts: 827
Joined: 18-November 08
Member No.: 4489



QUOTE
"If a DEM is calculated from image pairs..."
-- and this
I'm not sure how these DEMs were produced,


the dem was extracted from the vertex plate model
baked the displacement using blender
and compensated for the difference in radi of the mesh and sphere

ftp://naif.jpl.nasa.gov/pub/naif/DAWN/misc/ceres
the README
ftp://naif.jpl.nasa.gov/pub/naif/DAWN/mis...s/aaareadme.txt
a 32 bit isis3 cub is here
https://drive.google.com/file/d/0B6ZYAd08tZ...iew?usp=sharing
Go to the top of the page
 
+Quote Post
algorimancer
post Mar 25 2015, 05:17 PM
Post #45


Member
***

Group: Members
Posts: 655
Joined: 20-April 05
From: League City, Texas
Member No.: 285



QUOTE (JohnVV @ Mar 24 2015, 03:37 PM) *
the dem was extracted from the vertex plate model
...

To clarify... I was referring to the photogrammetry leading to the creation of the shape (or vertex plate) model. Given that model, the DEM is simply the difference between the shape model and the corresponding ellipsoid fit. Eventually that will be a geoid fit, but these are early days.
Go to the top of the page
 
+Quote Post

4 Pages V  < 1 2 3 4 >
Reply to this topicStart new topic

 



RSS Lo-Fi Version Time is now: 23rd November 2017 - 01:13 PM
RULES AND GUIDELINES
Please read the Forum Rules and Guidelines before posting.

IMAGE COPYRIGHT
Images posted on UnmannedSpaceflight.com may be copyrighted. Do not reproduce without permission. Read here for further information on space images and copyright.

OPINIONS AND MODERATION
Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators.
SUPPORT THE FORUM
Unmannedspaceflight.com is a project of the Planetary Society and is funded by donations from visitors and members. Help keep this forum up and running by contributing here.