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Voyager mosaics and images of Jupiter, A fresh look at some ancient stuff
Ian R
post Aug 20 2016, 01:21 PM
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Another little offering of mine: a OBV Voyager 1 composite from February 1979:

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Bjorn Jonsson
post Aug 26 2016, 11:10 PM
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Here are two very high resolution Voyager 1 images of Jupiter - the resolution is ~5 km/pixel (this corresponds to a JunoCam altitude of ~9000 km). The processing is probably best described as quick and dirty and the intention was to show two very different areas at very high resolution.

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One of the images shows a lot of interesting features, including obvious cloud shadows and vertical relief (and maybe I should mention in passing that I have only been able to detect cloud shadows around bright clouds - probably a normal result since they would be more difficult to detect around darker clouds). The other image is rather uniform and shows no obvious small scale features. Both of these images are contrast enhanced, especially the one that lacks obvious small scale features.

Juno's closest approach occurs tomorrow and I'm looking forward to see the JunoCam images. As these images show the highest resolution JunoCam images might show lots of features or they could look relatively featureless - or we might see both 'kinds' of images (perhaps most likely). And of course we'll see color images (Voyager 1 was imaging with its clear filter only when the above images were obtained).

Note: I have edited one of my recent Voyager mosaic posts - the one showing the Great Red Spot. I added a schematic context view that I forgot to include when I posted the mosaic last week.
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Brian Burns
post Aug 27 2016, 12:35 AM
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QUOTE (Bjorn Jonsson @ Aug 26 2016, 06:10 PM) *
Note: I have edited one of my recent Voyager mosaic posts - the one showing the Great Red Spot. I added a schematic context view that I forgot to include when I posted the mosaic last week.


I've never seen a view like that showing the scale of the closeup images - I didn't actually realize how zoomed in some of the images are.

Well, before Juno starts sending back its close ups, here are some of my favorite Voyager 1 images - can't wait to see what JunoCam captures!

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JRehling
post Aug 27 2016, 04:06 AM
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Bjorn, the image on the left shows detail – shadows of higher clouds onto lower clouds – that I have never seen in any Jupiter image, ever! Certainly a testament to your work, as well as a happy coincidence of the lighting and shot selection; perhaps the single-filter is a good choice as well. I suspect that the shadows are visible around the bright clouds because they are at a distinctly higher level than the clouds below them, like the tops of thunderheads on Earth, but that is just an educated guess.

I will look this image over in great detail – interesting as well as beautiful!
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jccwrt
post Aug 29 2016, 12:20 AM
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I had some time to work on Voyager images this weekend and it seems like there's a never-ending well of neat stuff to work on.

Here's a 4 frame mosaic made from orange/violet pairs taken on March 1. I've applied a white balance and a color correction to subjectively match what Jupiter looks like through a telescope.



Full-size here

And a 5 frame narrow angle mosaic taken through the green filter and colorized with an orange/violet pair of wide-angle shots. This one hasn't been color-balanced.



Full-size here
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Bjorn Jonsson
post Sep 12 2016, 08:12 PM
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Here is one final Voyager mosaic of Jupiter that (probably) finishes the sequence of seven mosaics I posted 4 weeks ago (the last mosaic back then is mosaic 7). It is composed from narrow angle and wide angle Voyager 1 images.

Mosaic 8: Highest resolution pre-Juno Jupiter color data. The full size version is too big too post here, this is an enhanced image at 40% the original size:

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And here are links to the full size versions (7400 x 5550 pixels):

Click here for enhanced full size version
Click here for approximately true color/contrast full size version

Range: ~650,000 km from Jupiter's center. Resolution of original data: ~6 km/pixel.
Juno, corresponding height above Jupiter's cloudtops: ~10,500 km (applies to the Voyager narrow angle data)

Less than 8 hours before closest approach Voyager 1 obtained a green and violet filter mosaic with its narrow angle camera (NAC) covering most of the Great Red Spot (GRS) - a total of 28 images. Here the effects of the varying illumination across the mosaic have been removed. At ~6 km/pixel this is the highest resolution pre-Juno color data for Jupiter (all of the higher resolution Voyager images are clear filter images). Lower resolution orange, green and violet images from Voyager 1's wide angle camera (WAC) are also used to show the GRS periphery and surrounding areas. The color in this mosaic was rather difficult to process. The WAC filters are significantly different from the corresponding NAC filters and the left/right edges are not covered by all three WAC filters. There are also some areas in the NAC mosaic where only green or violet was available (especially near the corners of the NAC area). The color is somewhat less accurate there.

The white box in the image below shows the area covered by the NAC images.

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The NAC data has two times higher resolution than the GRS cross mosaic I posted earlier. Interestingly, large parts of this higher resolution mosaic do not show significantly more details than the GRS cross mosaic. It's rather as if that mosaic has simply been enlarged by a factor of two. Many of the cloud features become more fuzzy and the boundaries between dark and bright features do not appear as sharp as they appear at lower resolution. There are some exceptions from this, for example in the GRS's northeast periphery where relatively bright, elongated clouds are visible. These clouds change very rapidly and cast noticeable shadows when the illumination geometry is favorable and the resolution high enough. It would be interesting to see Juno images of the GRS northeast periphery and also of the bright convective feature that frequently appears northwest of the GRS.

Two other versions of the NAC data and some of the WAC data have been seen earlier (here and here). Despite this I decided to make my own version of this mosaic because this is the highest resolution pre-Juno Jupiter color data.
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Brian Burns
post Sep 12 2016, 09:07 PM
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QUOTE (Bjorn Jonsson @ Sep 12 2016, 03:12 PM) *
here are links to the full size versions (7400 x 5550 pixels)

The color in this mosaic was rather difficult to process. The WAC filters are significantly different from the corresponding NAC filters


Wow, 41MP! I wish I had a bigger monitor - my laptop is just 1MP or so. I'm constantly amazed at the images Voyager was able to get with its one-shot flybys, and look forward to seeing what Juno is able to get when it comes across the great red spot.

I've also come to appreciate how difficult putting together mosaics like this can be, and I didn't even realize the WAC and NAC filters were different.

Do you use ISIS to help align and process these, or is it something you've developed? Or are these images flat enough that you can work on them in 2D? If it's a trade secret that's alright, just curious what your process is like. smile.gif
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Bjorn Jonsson
post Oct 6 2016, 12:42 AM
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QUOTE (Brian Burns @ Sep 12 2016, 09:07 PM) *
Do you use ISIS to help align and process these, or is it something you've developed? Or are these images flat enough that you can work on them in 2D? If it's a trade secret that's alright, just curious what your process is like. smile.gif


No trade secrets here. I don't use ISIS much for processing images of gaseous targets, largely because the clouds change very rapidly in hi-res images. Instead I usually use a Windows command line utility I wrote using the SPICE toolkit. It takes as input a list of SPICE kernels, UTC, spacecraft and target name and outputs the viewing geometry. It can also be used to correct the pointing in a somewhat similar way to what the ISIS deltack program does. I usually determine the correction by using 3D software to render the target using the uncorrected viewing geometry from the SPICE kernels and then determine the correction in pixels using either limb fits or the location of features in the image/render (using the location of features works if I have already processed one or more images that overlap the image I'm processing - and of course this is necessary if the limb isn't visible). I also use homegrown software for reprojecting the images to e.g. simple cylindrical projection once the viewing geometry has been determined.

When I'm processing images of solid bodies (e.g. the Galileans or Saturn's major satellites) things are often different. In that case I use ISIS fairly frequently to refine the pointing in a bunch of images using deltack, qnet and jigsaw. The result is a C kernel.

One thing that has probably made me use ISIS less than I really should do is that I'm dual booting between Windows and Linux. However, I have noticed that apparently it is becoming common to use virtual machines instead of dual booting (the plus here is I wouldn't need to stop using Windows while I'm using ISIS). Somewhere in a different thread I noticed that you are using a virtual machine to run Linux/ISIS. Does this work well? I suspect graphical programs like qnet might be more affected than something like jigsaw but it is very important for qnet to work smoothly since it's used for creating/editing/measuring the control point networks.
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jccwrt
post Jan 3 2017, 03:07 AM
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A few cloud mosaics from Voyager 2 about 3 days before closest approach:






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