Enceladus PDS image products |
Enceladus PDS image products |
Jul 22 2010, 03:22 PM
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#1
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IMG to PNG GOD Group: Moderator Posts: 2254 Joined: 19-February 04 From: Near fire and ice Member No.: 38 |
Following discussions in the Image Processing Techniques subforum (see in particular this thread but also this one) I have now managed to create DEMs of acceptable quality of Enceladus using shape from shading and extensive post processing (mainly destriping). I now have a DEM mosaicked together from 5 images obtained during Cassini's first flyby of Enceladus in 2005. This will eventually become a global 23040x11520 pixel DEM but finishing it is going to be a lot of work (I will probably be using 50-100 images or more). Not all of Enceladus has been imaged at this resolution but there are many high resolution patches and I want a DEM big enough for these.
This 5 image DEM was big enough for me to really want to see what an Enceladus DEM animation would look like. So here we go: enceladus_sfs_umsf.avi ( 7.74MB ) Number of downloads: 1318 The field of view is 50 degrees. Most of the animation is at an altitude of 25-30 km. This is similar to Cassini's altitide during the closest flybys and the speed is not far from Cassini's speed either. However, the animation starts and ends at higher altitudes and we also swoop down to an altitude of ~10 km where the resolution of the DEM is highest. This is the Cassini image I used for the highest resolution part of the DEM: And a single frame from the animation showing a part of this terrain: The DEM should be fairly accurate - in particular the animation should give a very good general idea of what Enceladus looks like even though some details are inaccurate. Also a higher resolution DEM is really needed for these low altitudes - the surface should look less smooth than it does here. Most of the striping is real though as there are lots of parallel ridges and grooves on Enceladus. There may be some spurious stripes but these are very subtle - the obvious ones are real. I'll do a new animation once I have a significantly bigger DEM. It will probably have better optimized illumination. Shadows are really needed in the first half of this one because I optimized the illumination for the highest resolution part of the DEM. We fly over that part of the DEM at roughly 00:30. EDIT: To play the animation you need to have an H.264 codec installed (if you are using Windows you can find one here for example). |
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Oct 6 2011, 02:09 AM
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Member Group: Members Posts: 399 Joined: 28-August 07 From: San Francisco Member No.: 3511 |
Wondrous !
-------------------- 'She drove until the wheels fell off...'
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Oct 10 2011, 08:33 PM
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Senior Member Group: Members Posts: 3648 Joined: 1-October 05 From: Croatia Member No.: 523 |
Subject: Enceladus plume temporal variance. 3 NAC clear frames taken roughly at 50 second intervals, unsharped and contrast enhanced:
Can you pick up material from a couple of vents going up in "puffs"? I don't think this can be explained by parallax/rotation, the observed rotation of Enceladus is too small for that. I strongly believe this is a genuine variation in output flux on a timescale of a minute. -------------------- |
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Oct 10 2011, 08:43 PM
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#4
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Senior Member Group: Members Posts: 3648 Joined: 1-October 05 From: Croatia Member No.: 523 |
Here's a ratio flicker gif. First frame is frame #2 divided by #1, second frame is frame #3 divided by #2. Shows subtle change in plume appearance from one frame to another better.
Notice alternating dark/bright clouds in the plume to the left and to the right. At least two distinct puffs seem to be present in each plume. There's a hint of variation in a third plume at around 12 o'clock but it's much less convincing than these two. I tried to do a (very) rough measurement of the displacement in the right hand plume during the 50-ish seconds between snapshots and I got a radial velocity of ~250 m/s. I haven't double-checked this. In reality the flow is not in the viewing plane so any number would probably underestimate the real speed. I've been looking to see if anything like this could be noticed in past plume images and I don't recall seeing anything convincing before. -------------------- |
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