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Juno Perijove 48, January 22, 2023
Gerald
post Jan 31 2023, 01:39 AM
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In the meanwhile, I've done some quantitative analysis.

The below PDF contains relative white-balancing linear radiometric factors for Jupiter from PJ43 to PJ48 for r(ed), g(reen), b(lue), together with the quotients PJ n / PJ n-1 for red (quot_r) and blue (quot_b), and quot_r/quot_b for the factor by which the white-balancing linear radiometric factors for the red and blue channel change from one PJ to the next, in the last column quot_br.
Added are plots of time series of columns r, b, and quot_br.
Attached File  wb_weights.pdf ( 34.21K ) Number of downloads: 94

I've actually used RGB images with the most frequent TDI setting within the respective PJ for the calibration. Except for PJ48, I removed images with eclipses, or when the GRS was prominent.

This animated GIF visualized the empirically retrieved reddening from PJ47 to PJ48:
Attached Image


You may be right, Björn, that the radiometric factors could change between inbound and outbound images. Juno is indeed crossing some harsh radiation belts.
However, I didn't yet try to find regression curves for the radiometric factors within a PJ.
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StargazeInWonder
post Jan 31 2023, 04:41 AM
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Responding to some of the implications of the past couple of posts: As I look at diagrams of how Juno's orbit has evolved, it looks as though the greatest radiation exposure is mainly occurring during a time in each orbit before any of the close Jupiter approaches / imagery. I.e., Juno arrives from the south, crosses Jupiter's equatorial plane and the intense radiation belt between Io and Europa while still quite far from Jupiter, and then is in (presumably?) lower radiation environments for the duration of the perijove. So, for whatever it's worth, I'd expect comparatively little radiation exposure between the northern/inbound imagery and the southern/outbound imagery.

It's also a bit ominous to see how much more time Juno will spend passing through the most intense radiation between now and the first close Io flyby, compared to how much it has spent taking radiation so far. Hopefully any operational issues don't increase in proportion to that.
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Gerald
post Jan 31 2023, 05:22 PM
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Juno's very eccentrical orbit was designed to minimize radiation dose, by quickly crossing the belts of high energetic particle flux and then diving underneath that hazard. But it was also well-known that the perijove shifting northward would increase radiation after about PJ30.
I think that it wasn't known that there is also a radiation belt low above Jupiter's equator.
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mcaplinger
post Jan 31 2023, 06:05 PM
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QUOTE (Gerald @ Jan 30 2023, 05:39 PM) *
You may be right, Björn, that the radiometric factors could change between inbound and outbound images.

I don't think he was saying that, I think he was saying that Jupiter is a different color between hemispheres. But even if he wasn't saying that, you can't prove otherwise.

Not to complain, but when people here say stuff about radiation changes, someone from the project stumbles across it, and I end up having to do more work to try to quantify it. So far I haven't found unequivocal evidence that there have been intrinsic instrument changes. You could do me a favor by being as specific as possible about what you are doing, which images and which regions of which images, attempts to control for photometric effects if any, etc. Then I can just paste that into my slides, and I'll be happy to give you all the credit. smile.gif


--------------------
Disclaimer: This post is based on public information only. Any opinions are my own.
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Bjorn Jonsson
post Feb 1 2023, 01:35 AM
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Gerald understood correctly what I was saying. However, the real color of the southern hemisphere also isn't identical to the real color of the northern hemisphere and this complicates matters. Also it is getting increasingly difficult to reliably monitor color changes because many of the images now show dimly lit areas near the terminator. This can make possible scattered light, dark current and noise a bigger proportion of the image brightness and this might mess up the color. My main (but not only) 'color reference' has been the whitish South Tropical Zone (STrZ). Getting good color measurements for the STrZ has been getting increasingly difficult due to the increasing phase angle. It is 95° in image PJ48_215, meaning that the STrZ is relatively dimly lit except near the limb. This makes me less confident in the color measurements than I was a few perijoves ago. Nevertheless I think something must have changed now. Using the color correction I used for PJ47, the color of image PJ48_215 is far too red. It is far redder than the color of comparable images at PJ47 or PJ46 when I used the color correction from the previous perijove.

The problem: I'm (almost) sure something has changed significantly at PJ48 compared to PJ47 but I doubt I can prove it (or, in particular, doubt I can prove that it is an instrument change). This "something" that apparently has changed could be e.g. optics, scattered light, filters, sensor or a combination of these.
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Gerald
post Feb 1 2023, 02:07 AM
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QUOTE (mcaplinger @ Jan 31 2023, 07:05 PM) *
Not to complain, but when people here say stuff about radiation changes, someone from the project stumbles across it, and I end up having to do more work to try to quantify it. So far I haven't found unequivocal evidence that there have been intrinsic instrument changes. You could do me a favor by being as specific as possible about what you are doing, which images and which regions of which images, attempts to control for photometric effects if any, etc. Then I can just paste that into my slides, and I'll be happy to give you all the credit. smile.gif

Give me a day or so to compile all the underlying data I've more or less readily available. I'll mail you a download link with a cc to at least two other members of the Juno science team. We've already discussed this topic in person before. I'm ready to take over whatever extra work load is required to the degree I'm authorized.
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StargazeInWonder
post Feb 1 2023, 02:49 AM
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Bjorn, can the imagery of Ganymede taken during this orbit provide insight as to any possible changes? I know that that's not quite as good as the color calibration devices on Mars landers/rovers but perhaps it offers some apples-to-apples comparisons with past imagery?
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Brian Swift
post Feb 1 2023, 07:34 AM
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FWIW, mapping my (less rigorous) color balance updates to Gerald's G=1 scaling
PJ24 {0.844983, 1., 2.32047}
PJ37 {0.773423, 1., 2.42996}
PJ43 {0.739846, 1., 2.66805}
PJ48 {0.64491, 1., 2.99845}
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Bjorn Jonsson
post Feb 5 2023, 01:41 AM
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Image PJ48_215 in approximately true color/contrast and enhanced versions. North is up.
Attached Image


QUOTE (StargazeInWonder @ Feb 1 2023, 02:49 AM) *
Bjorn, can the imagery of Ganymede taken during this orbit provide insight as to any possible changes? I know that that's not quite as good as the color calibration devices on Mars landers/rovers but perhaps it offers some apples-to-apples comparisons with past imagery?

No, Ganymede is far too small in the PJ48 image.
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Bjorn Jonsson
post Feb 5 2023, 09:31 PM
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And this is image PJ48_219:
Attached Image
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Bjorn Jonsson
post Feb 10 2023, 12:28 AM
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This is image PJ48_218, a methane filter image:
Attached Image


The version at left is the image with no special processing. The version at right is illumination-adjusted. Both of these versions were processed to reduce noise since the methane filter images are usually noisy. North is up.
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Bjorn Jonsson
post Feb 11 2023, 11:51 PM
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I should mention that interestingly, I have found that if I use any of the most recent clock kernels (JNO_SCLKSCET.00144.tsc, 143 or 142) I get very large pointing (or timing?) errors, typically ~230 (!) pixels in the vertical direction in the images. I have to use JNO_SCLKSCET.00141.tsc to get normal results. I find this interesting because JNO_SCLKSCET.00141 predates PJ48. In fact JNO_SCLKSCET.00142 and 143 also predate PJ48.

The same is true for PJ47, I get large errors unless I use JNO_SCLKSCET.00141.tsc (I suspect 140 would also work). JNO_SCLKSCET.00141.tsc predates not only PJ48, it also predates PJ47.
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Brian Swift
post Feb 17 2023, 06:58 AM
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QUOTE (Bjorn Jonsson @ Feb 11 2023, 03:51 PM) *
I should mention that interestingly, I have found that if I use any of the most recent clock kernels (JNO_SCLKSCET.00144.tsc, 143 or 142) I get very large pointing (or timing?) errors, typically ~230 (!) pixels in the vertical direction in the images. I have to use JNO_SCLKSCET.00141.tsc to get normal results. I find this interesting because JNO_SCLKSCET.00141 predates PJ48. In fact JNO_SCLKSCET.00142 and 143 also predate PJ48.

The same is true for PJ47, I get large errors unless I use JNO_SCLKSCET.00141.tsc (I suspect 140 would also work). JNO_SCLKSCET.00141.tsc predates not only PJ48, it also predates PJ47.

Thanks. Investigating this made me realize I'd processed PJ48 using the PJ47 SPK predict.
After reprocessing PJ48 using today's juno_pred_orbit.bsp and JNO_SCLKSCET.00145.tsc,
the largest offsets I'm seeing are ~9 pixels. But even using PJ47 predict and 144.tsc, I was only seeing offsets of ~15 pixels.

Below is PJ48_217, one of the large offset images, with limbs marked.
I'm curious if "mis-fit" on right will get better when PJ48 reconstructed SPK shows up.

Attached Image
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