[X] My Assistant

[mcaplinger]

First group of images, including Ganymede, now on missionjuno. More to follow.

[Bjorn Jonsson]

Here is an example of the color change I'm seeing from PJ20 to PJ35. The processing is identical for these two images. I checked the processing pipeline and can't see anything there that explains this difference so I'm pretty sure this is not a bug in my processing pipeline. In particular, the color multipliers are identical in these two cases.



In addition, at a quick glance the color I get at PJ27 is roughly intermediate between the PJ20 color and the PJ35 color.

[mcaplinger]

Here is an example of the color change I'm seeing from PJ20 to PJ35.

Probably a real change of Jupiter's. For example, https://britastro.org/node/25892 says

The EZ still has orange coloration, which has re-intensified to become darker and more vivid than it was a year ago.

[Bjorn Jonsson]

Probably a real change of Jupiter's. For example, https://britastro.org/node/25892 says

I seriously doubt this since AFAIK the color change mentioned there is confined to the Equatorial Zone but the reddening I'm seeing is global.

I have now verified with pretty good certainty that this color difference between PJ20 and PJ35 is present in the raw images. Assuming that these measurements from the raw PJ20 and PJ35 images are correct, a bug in my processing pipeline has been almost completely ruled out.

It would nevertheless be very interesting if someone (Brian maybe?) would process the PJ20_40 and PJ35_68 images and use identical color correction for PJ20_40 and PJ35_68. If the result is similar to mine (i.e. redder PJ35) it would completely rule out a bug in what I'm doing. A confirmed color change would be an interesting result regardless of what's causing it.

[Brian Swift]

...It would nevertheless be very interesting if someone (Brian maybe?) would process the PJ20_40 and PJ35_68 images and use identical color correction for PJ20_40 and PJ35_68. If the result is similar to mine (i.e. redder PJ35) it would completely rule out a bug in what I'm doing. A confirmed color change would be an interesting result regardless of what's causing it.

Here you go. Same processing run, same/fixed/constant brightness setting, linear to sRGB encoded 16-bit, 5292 × 7162 16-bit png available in Flickr download:
Jupiter PJ20_40 and PJ35_68

[Bjorn Jonsson]

Here you go. Same processing run, same/fixed/constant brightness setting, linear to sRGB encoded 16-bit, 5292 × 7162 16-bit png available in Flickr download:

Thanks! This is very similar to what I am getting and seems to confirm that there is a color change from PJ20 to PJ35. Here is a plot from a few images I processed. It shows the blue/red ratio in the South Tropical Zone (STrZ) for several perijoves. This is from decompanded images. There are some inaccuracies due to various factors (for example the illumination geometry varies a bit) but the trend is clear. The units are arbitrary in the sense that I didn't attempt to make B/R=1 for any specific perijove. As noted above, this is the STrZ but everything else in the images has also been getting redder.



The images are clearly getting redder.

Interestingly, the 1600x1600 pixel map projected color images released at the missionjuno website together with each raw image have not been getting redder. Now I am wondering how the color is corrected in these map projected images.

[Brian Swift]

...Interestingly, the 1600x1600 pixel map projected color images released at the missionjuno website together with each raw image have not been getting redder. Now I am wondering how the color is corrected in these map projected images.

I believe the the missionjuno images include a correction for illumination intensity change due to change in SOLAR_DISTANCE.
JNCE_2019149_20C00040_V01.json: "SOLAR_DISTANCE": "7.9340e+08 <km>",
JNCE_2021202_35C00068_V01.json: "SOLAR_DISTANCE": "7.5293e+08 <km>",
So, Jupiter has gotten about 5% closer to the Sun, and illumination has increased by about 11%.
But I don't see how that would lead to reddening. (Unless a SOLAR_DISTANCE correction was only being applied to one color channel)

[mcaplinger]

I believe the the missionjuno images include a correction for illumination intensity change due to change in SOLAR_DISTANCE.

Nope. The only files that use this value are the PDS-archived RDR files, which are all normalized for solar distance as described in the documentation.

The outreach map-projected RGB images on missionjuno have a lambertian shading correction applied and are then arbitrarily white-balanced, there is no explicit response function applied. The component map-projected images don't have the shading correction or the white balance, but are otherwise photometrically out of the camera (they have some blemish removal.)