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Processed Cassini Jupiter Images, Fun with the PDS files
Bjorn Jonsson
post Jul 10 2012, 02:20 PM
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This is a 2x2 mosaic of Cassini images obtained on November 30, 2000 from a distance of 30 million km:

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The majority of global images of Jupiter includes the Great Red Spot (GRS) and in most of these the GRS is near the center of the disc or a bit towards the terminator. This one is an exception and shows the GRS near the limb.

CB2 (near infrared) and BL1 (blue) images were used. At this time Cassini wasn't taking green filtered images so I created a synthetic green image as GRN = 1.126959 x (0.481 x CB2 + 0.519 x BL1). I also created a synthetic red (CB1) image as CB1 = 1.106251 x (0.774 x CB2 + 0.226 x BL1) using CB1, GRN and BL1 images obtained at a greater range a few weeks earlier as a guide. I then altered the color balance slightly to make the bright zones more whitish and less yellowish (actually the real color of the zones might be slightly yellowish so in retrospect maybe I should have omitted this processing step).

The images were reprojected to simple cylindrical projection, mosaiced and then rendered using the viewing geometry Cassini had when it took one of the BL1 images. The final step was to sharpen the resulting image slightly.
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Bjorn Jonsson
post Jun 11 2019, 07:41 PM
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The recent Great Red Spot (GRS) 'disruption' has been very interesting. Anticyclonic spots have been moving towards the GRS from the east, entering the red spot hollow and then moving around the GRS. This has sometimes managed to distort the apparent shape of the GRS. This is especially noticeable in methane band images (these images are indicative of cloud altitudes with bright areas in these images being high altitude clouds or hazes). Red blades/flakes also appear to separate from the GRS when this happens.

I took a look at the Cassini Jupiter images because I vaguely remembered seeing a distorted GRS shape in the Cassini MT3 images (the MT3 filter is centered at 889 nm, a very strong methane absorption band). I found an interesting image obtained on December 15, 2000. Here it is map-projected; notice the western end of the GRS:

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Comparing this to enhanced color images reveals that the bright 'lane' of material emanating from the western end of the GRS in the MT3 image has an orange color. Below is a blink comparison (an animated GIF) where an enhanced color image and the MT3 image are blinked. The color image is created from CB2, synthetic green and BL1 filtered images and has been contrast enhanced and processed to increase color differences.

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A look at what happened leading up to this is interesting. Here is an animated GIF from seven MT3 images obtained between December 9 and 15, 2000. The images are not evenly spaced in time.

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It's interesting that the shape of the area of high altitude clouds/haze associated with the GRS does not stay constant.

Here is an animated GIF from a sequence of seven enhanced color images obtained at roughly the same times as the MT3 images. An anticyclonic spot can be seen entering the red spot hollow from the east:

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Converting the enhanced color images to an animated GIF results in some loss of image quality since the GIF format only supports 256 colors per image or less. Here are the original map-projected frames I used to create the animated GIFs. They are of slightly higher quality:


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These interactions between the GRS and the incoming spot are considerably more subtle in true color images than in the enhanced images above. Below are approximately true color images processed from the original image data:

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I think the events visible in these images are a 'miniature' version of what has been happening to the GRS recently. Red/orange material seems to be torn out of the GRS and the GRS shape gets distorted. The effects of this are not nearly as pronounced as what has been happening recently though.
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JRehling
post Jun 12 2019, 07:02 AM
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Fantastic and fascinating stuff, Bjorn. I've been watching Jupiter through my own telescope the past five years now, and surely the GRS has gone through some unusual activity this year, as you note (which may be concluding?), and as the Juno images make quite striking.

That's a nice catch to note the similarity to the Cassini-era weather patterns. I would add that other things going on near the GRS are quite different now than then. Currently, there is a very obvious pair of dark, thin bands east of the GRS and the South Temperate Belt is particularly bright (or, at least, wide) southwest of the GRS.

Juno's ultra-zoom mode means that the regional context isn't always captured, so here's one of my pictures of Jupiter from June 9 to add the context.

It is fascinating to watch this planet change over time. The duration of one Earthly year is, of course, in no way causally related to anything on Jupiter in a meaningful way, but it does seem, by coincidence, to be a useful unit for measuring visible changes on a planet-wide basis. It seems to look about the same for months at a time, but always be different when it swings around for another opposition.
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