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Juno Perijove 22, September 12, 2019
fredk
post Sep 17 2019, 04:05 PM
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Averaging over the pixels in a large-enough shadow might help. But it sounds like stray light will be the limiting factor.

About the Io-Europa-Ganymede resonance, that should be for the sidereal periods, not solar (synodic). So there's no reason you couldn't have some of those three moons fat crescent or gibbous when Io casts it's shadow on Jupiter. Here's the view during PJ22 from the solar system simulator:
Attached Image

Ganymede was a fat crescent at that time.

It shouldn't be too hard to estimate the level of scattered Ganymede light at that time.
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Kevin Gill
post Sep 17 2019, 04:41 PM
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Fisheye Composite for the Io Shadow

JNCE_2019255_22C00023_V01
JNCE_2019255_22C00024_V01
JNCE_2019255_22C00025_V01
JNCE_2019255_22C00026_V01
JNCE_2019255_22C00027_V01
JNCE_2019255_22C00028_V01

Rendered from the perspective of '28.


Perijove 22 - Io Shadow Composite
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Sean
post Sep 17 2019, 06:38 PM
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Awesome results Kevin!


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JRehling
post Sep 18 2019, 03:14 AM
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Thanks, fredk!

If the HST took a picture of Jupiter while the former was in the Earth's shadow, that would seem to limit stray light profoundly, but trying to limit noise to zero is difficult.
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Brian Swift
post Sep 19 2019, 04:29 AM
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Animation of Io shadow eclipse progressing across Jupiter - https://youtu.be/N5A7fXWMt6k
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Bjorn Jonsson
post Sep 29 2019, 11:40 PM
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An approximately true color/contrast version of PJ22_28 processed to give an idea of what a fairly typical consumer type camera (or even a phone) might have seen if no zoom was used:

Attached Image


North is to the upper left. Here Juno was very close to Jupiter's cloud tops (altitude ~7900 km) and about 12000 km from the center of Io's shadow. Because of this close range it is impossible to capture all of Jupiter's globe in a single image. For that a fisheye type lens would be needed (for a fisheye view see Kevin's image in his post earlier in the thread).
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Kevin Gill
post Oct 14 2019, 11:10 PM
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A wide pole-to-pole map view using PJ22 imagery. Blending and alignment was done largely by hand.


Jupiter - Perijove 22 - Map Composite


And a flyover video on YouTube: https://youtu.be/s8smStabXqg

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Sean
post Oct 15 2019, 10:46 AM
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This is beautiful Kevin! Amazing job!!


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Bjorn Jonsson
post Oct 16 2019, 12:01 AM
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Perijove 22 was not a 'Great Red Spot (GRS) flyby'. Despite this, map-projected images show some details in the GRS' western half (the GRS was on the limb in a few PJ22 images). And the convective area west of the GRS was fairly well imaged during this flyby. This is a map-projected mosaic of PJ22 images 39 to 43 in approximately true color/contrast and enhanced versions:

Attached Image

Attached Image


From this it is clear that the convective area west (or WNW) of the GRS is still active. The appearance of other parts of the South Equatorial Belt (SEB) has recently at least sometimes been as if the SEB was about to fade (turn whitish) but if history is any guide, this shouldn't happen unless the convective activity west of the GRS shuts down.

It's going to be interesting to see what happens here.
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Bjorn Jonsson
post Nov 3 2019, 10:28 PM
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This is an orthographic mosaic of images PJ22_20 and PJ22_21 in approximately true color/contrast and enhanced versions:

Attached Image
Attached Image


The small and very bright cloud below center is located near planetographic latitude 51.6 degrees north and is about 250 km across. The effects of the varying solar illumination across the image have been removed (otherwise the northern half of the image would be darker relative to the southern half than it is here).

Lots of interesting details are visible, including cloud shadows and evidence of vertical relief in the clouds. Many interesting and beautiful small ovals are also visible. Some of these appear to be connected by 'lanes'. An obvious example is the pair of brownish ovals at upper right. North is up in the images.
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mcaplinger
post May 6 2020, 05:21 PM
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QUOTE (Bjorn Jonsson @ Oct 15 2019, 04:01 PM) *
This is a map-projected mosaic of PJ22 images 39 to 43 in approximately true color/contrast and enhanced versions...

Bjorn, could you describe your workflow for getting the brightness matching to work so well from image to image for these products? I've been using a simple lambertian removal and it doesn't work very well at all, at least for the full range of geometries over the orbit.


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Disclaimer: This post is based on public information only. Any opinions are my own.
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Bjorn Jonsson
post May 11 2020, 01:18 AM
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QUOTE (mcaplinger @ May 6 2020, 05:21 PM) *
Bjorn, could you describe your workflow for getting the brightness matching to work so well from image to image for these products? I've been using a simple lambertian removal and it doesn't work very well at all, at least for the full range of geometries over the orbit.

These image products are several months old and involved a significant amount of work in Photoshop to reduce color and brightness seams - too much work for my taste. As a result I have made changes that greatly reduce the manual cosmetic enhancements and post-processing needed in Photoshop. What I currently do is this:

(1) Added flat fielding in December 2019. This change is probably what resulted in the biggest improvement in brightness/color matching in the overlap areas between adjacent images (not framelets). Without flat fielding the images are a bit brighter near the left/right edges relative to the center than they should be. Flat fielding also greatly reduced the seams between adjacent framelets. The flat field I'm currently using can be found here.

(2) Use a slightly modified Lambert function, i.e. cos(i)^0.95 instead of the usual cos(i). Earlier I was using a modified Lommel-Seeliger function but the modified Lambert function works better in conjunction with (3). Areas near the terminator require special handling though since there is faint illumination on the nightside near the terminator.

(3) Multiply the result of (2) with a new/experimental limb darkening function that is a function of the emission angle. This worked almost perfectly for PJ24 and PJ25 but results are slightly worse for PJ26. It also worked rather well for making a quick-and-dirty global map of Jupiter from the G1 marble movie images. I'm now in the process of modifying the function to include the phase angle (its 'weight' must change with phase). An additional complication is that the photometric properties of the polar regions are different from areas closer to the equator. I plan on making some of the photometric parameters vary as a function of latitude. Also I'm currently using identical parameters for R/G/B in the limb darkening function but this will change.

(4) Following the previous processing steps I have several cylindrical maps that I mosaic in Photoshop and decide which one(s) has priority in overlap areas by cutting away parts of some of the mosaics in the overlap areas. This is fairly trivial and could probably be automated.

(5) Following (4) there are usually some residual color/brightness seams in overlap areas that are close to the terminator and/or limb but these are usually not big and can be easily corrected in Photoshop by modifying the brightness and color balance of one or both images near the overlap area. This processing step used to take a lot more time before the changes described in steps 1 to 3.

It should be noted that I haven't tested this for the full range of geometries but I suspect it would work well once the phase angle is taken into account in (3).
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scalbers
post May 11 2020, 09:01 PM
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Just drawing an analogy to how I sometimes handle Earth clouds, a linear combination of the Lambert illumination with a single scattering phase function can be a good approximation. I'm continuing to work on some additional empirical BRDFs.


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