The two PDS releases for the first six months of 2011 contain lots of images of Saturn, including observations of the great storm. The images obtained in February and March are particularly interesting. Here is a false color image processed to bring out various details and 'color' differences:

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This is a composite of MT3, CB2 and MT2 wide angle images displayed as red, green and blue. The images were obtained on March 21, 2011 from a distance of 883500 km from Saturn's center. The images are part of a multifilter sequence covering this area of Saturn's northern hemisphere - mosaicking is not possible though since the sequence did not include coverage further east (otherwise I would have created a mosaic).

Here is a quick RGB composite of Saturn from WAC images obtained on June 11, 2016 when Cassini was 2.1 million km from Saturn's center. This is from the data released at the PDS a few days ago. This is a true color image where the source images have been calibrated and the resulting color then adjusted slightly based on Saturn's spectrum. The north polar vortex has a remarkably strong bluish color, probably indicating a deep, clear atmosphere and Rayleigh scattering (this is also evident from images obtained in the near-infrared).
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Beautiful work! These colors are richer than we often see with Saturn renditions and I like the result.

The blue presumably owes some of its origin to methane absorption as well as Rayleigh scattering between the local cloud tops (if any) and the camera. A methane-band image of the polar vortex would clarify that.

11 years ago…

https://www.jpl.nasa.gov/news/news.php?release=2006-137

Here are older observations of the polar vortex but unlike the June 2016 observations, narrow angle images are also available. The wide angle image was obtained on September 9, 2014 at a distance of 2.8 million km and the narrow angle image a day later at a distance of 2.7 million km. These images are true color images made from PDS data that has been calibrated.

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Yes, methane absorption is definitely a factor as well. Below are continuum band and methane band images obtained around the time of the RGB observations above. The images are calibrated but no additional processing was performed (except for reducing noise and rotating them). First CB1 and MT1:
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CB2 and MT2:
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CB3 and MT3:
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Interestingly, the central brighter cloud inside of the bluish ring completely disappears in the MT3 image. In the MT2 image it is also dark but at least it is faintly visible. In the MT1 image it is clearly visible.

On March 28, 2017 Cassini obtained many wide angle camera images of Saturn's north polar region at close range using various filters. Here is an orthographic mosaic of 8 RGB color composites. It shows the north polar region from directly above. This is processed from calibrated images with minor modifications to the color balance. The effects of the variable solar illumination across the image have been removed.

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However, even though the color is approximately correct it is too saturated compared to Saturn's visual appearance. This is all highly subjective though but should nevertheless be pretty obvious to anyone who has ever looked at Saturn through a reasonably big telescope. Here is a version of the above image processed to more closely approximate Saturn's visual appearance by modifying the gamma:

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And finally an image where color differences have been greatly exaggerated. This reveals some faint seams between the images. There are also color variations that are probably due to the sun's different elevation at different longitudes; areas with the sun low in Saturn's sky appear redder.

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These images are preliminary in the sense that I'm still working on the exact color balance. Any changes there will be minor (if any) though so I'm posting these images now.

Cassini spacecraft view of the Large Magellanic Cloud from Saturn
https://pds-imaging.jpl.nasa.gov/data/cassi...56147_1.IMG.png

Beautiful! Curious, what is your process for removing the solar illumination in these? That's one process I haven't yet been able to do.


-- Kevin

I'm using software written by myself for the combined illumination removal and reprojection steps. I know this is possible in ISIS3 too but I don't remember exactly how (possibly by using photomet?).