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Hi-res Saturn atmospheric movie, Let's eat some spots
Bjorn Jonsson
post Feb 12 2007, 11:49 PM
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The September to October 2004 Saturn imaging sequence is a gold mine for anyone interested in processing images of Saturn. This is the best sequence of high resolution images for both movies and multispectral coverage so far and as far as I know the best (and in particular the longest) one of the entire mission.

I decided to do a high resolution movie of one of the two big spots near latitude 45S. These spots are the biggest ones, at least in the southern hemisphere. I posted images of these spots in this thread early this year. Unlike these images the movie was created from CB3 images. Using this filter, the camera penetrates the atmosphere more deeply than at visible wavelengths.

I started by reprojecting the images to simple cylindrical projection at a resolution of 25 pixels/degree, removing illumination effects on the fly. Where needed, I mosaicked 2-4 images (for some of the frames, a single image covered a sufficiently large area). I then further compensated for illumination effects by manually processing some of the frames. For all of the frames, I kept the spot at a fixed location. The final step was to greatly enhance contrast in the images.

The end result is a 20 frame AVI file encoded using DivX at 4 frames/second. The individual frames still vary a bit in brightness but this does not detract attention from all of the action going on. It's especially interesting to see the big spot merge with two smaller spots at the same time. It appears to 'swallow' them although some very bright material gets ejected from the spot in the process. Some of the spots exhibit obvious counterclockwise motion and in some cases they oscillate and change shape (possibly a bit like Neptune's Great Dark Spot).

The interval between the frames varies, accounting for the apparently uneven motion between frames. In most cases it is near 10.5 or 21 hours but sometimes longer, in one case as long as 5 days. The movie starts on September 6, 2004 and ends on October 1, 2004.

Here is an 'appetizer', one of the more interesting frames that shows the big spot about to swallow the two smaller spots:
Attached Image


And here is the animation file

There are several additonal hi-res movies I'm interested in making but the next step is some software development to try to streamline the process and speed it up.

EDIT: This was done using images from the PDS.
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djellison
post Feb 12 2007, 11:53 PM
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Easy to forget that the Saturnian atmos is as complex as that on Jupiter in some respects...just a little more hidden than it's larger cousin. Stunning stuff - really shows the dynamics involved

Doug
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scalbers
post Feb 13 2007, 12:36 AM
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In some respects it could be more complex in that there are a greater number of belts and zones compared with Jupiter, once you peer beneath the haze.


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Bjorn Jonsson
post Feb 13 2007, 12:44 AM
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Additional details I forgot to mention:

The movie extends from planetographic latitude 33.52S to 62.32S. Its longitudinal extent is 38.4 degrees. I used images from the PDS that I calibrated before further processing.

And yes, Saturn's atmosphere is complex although due to the lower contrast this is not as obvious as in Jupiter's case. In many respects it is remarkably similar to Jupiter's (e.g. the spots) but there are also major differences like the very fast equatorial jet.
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Ian R
post Feb 13 2007, 12:47 PM
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This is astonishingly good Bjorn - it deserves to be showcased on the main Cassini site. ohmy.gif


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Pavel
post Feb 13 2007, 10:20 PM
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What are those bright dots - are they artifacts or real atmospheric phenomena? Strangely, they remind me martian dust devils.
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Bjorn Jonsson
post Feb 14 2007, 11:32 AM
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If you are referring to the very small white dots they are simply noise that got more visible due to the processing applied to the images. In the attached image, the arrow labeled Noise points towards a pair of such dots and towards another even smaller one that contains both dark and bright pixels (there are lots of these in the images).

The bigger, bright features are real and are labeled Real features.
Attached Image
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ugordan
post Feb 14 2007, 11:35 AM
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Is that the noise the calibration reports refer to as blooming pixels? As in pairs of bright/dark pixels? There's supposed to be an algorithm for removing them, although it comes down to fudging IIRC.


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