Juno Perijove 49, March 1, 2023 |
Juno Perijove 49, March 1, 2023 |
Feb 14 2023, 09:35 PM
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Senior Member Group: Moderator Posts: 3241 Joined: 11-February 04 From: Tucson, AZ Member No.: 23 |
I'm going to choose to be optimistic about PJ49, so with that in mind, I have added previews of JunoCAM's observations of Io for PJ49. Obviously, JunoCAM's real observation plan will likely differ but I added previews for the first and last opportunities to image Io on the pass, a preview of an image nearest closest approach, and one for when Io is near the center of the JIRAM FOV. The observation at closest approach also has the Marduk plume which has a good chance of being observed on this encounter, presuming it is active. The Volund plume might also be visible near the terminator.
The previews use the Voyager/Galileo basemap. The left images were originally projected at the same resolution as JunoCAM but were then enlarged by 5x while the image on the right is the basemap reprojected to 5x the JunoCAM pixel scale. https://pirlwww.lpl.arizona.edu/~perry/Juno/pj49.htm -------------------- &@^^!% Jim! I'm a geologist, not a physicist!
The Gish Bar Times - A Blog all about Jupiter's Moon Io |
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Mar 7 2023, 02:39 AM
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IMG to PNG GOD Group: Moderator Posts: 2254 Joined: 19-February 04 From: Near fire and ice Member No.: 38 |
A montage of the five PJ49 Io images. The viewing geometry is also shown using computer generated images that include a latitude/longitude grid. They are based on a Voyager/Galileo map of Io.
The images are enlarged by a factor of 5 relative to the original data. The color balance is preliminary. Io's color is a remarkably complex subject - hopefully this is not very far from Io's real color. More on this later. |
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Mar 7 2023, 10:30 AM
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Senior Member Group: Members Posts: 3648 Joined: 1-October 05 From: Croatia Member No.: 523 |
Io's color is a remarkably complex subject Isn't that just a roundabout way of saying it's the most colorful and contrastful world apart from Earth. -------------------- |
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Mar 16 2023, 01:07 AM
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IMG to PNG GOD Group: Moderator Posts: 2254 Joined: 19-February 04 From: Near fire and ice Member No.: 38 |
Io's color is a remarkably complex subject Isn't that just a roundabout way of saying it's the most colorful and contrastful world apart from Earth. I guess so. The problem seems to be that the color of processed Io images apparently is very sensitive to the exact camera filter properties - far more so than when processing images of Europa, Ganymede or Callisto. For example the red terrain (e.g. the red 'ring' around Pele) isn't obvious in Voyager images processed in a 'normal' way where an orange filter is used as red (it is visible with extreme processing though, see e.g. this thread). The problem is that these reddish areas start to get brighter relative to other terrain when you use a red filter instead of orange and they are even brighter in the near-infrared. This brightening relative to other areas has barely started at the wavelength of orange light. The JunoCam filters are different from the Galileo filters. There is a blue filter (Galileo had violet) and the JunoCam red filter bandpass is 600-800 nm (i.e. into the near-infrared) with an abrupt cutoff at both ends. The CCD is sensitive to light in this wavelength range. This is different from the Galileo red filter. It is apparently impossible to make Io's color in the JunoCam images very similar to Io's color in the Galileo images by simply combining the R/G/B channels into a color image. Colchis Regio turned out greenish if I made the average global color roughly identical to the global color of the computer rendered images I posted earlier (in these computer generated images I attempted to correct the color by using synthetic blue instead of violet). If I make Colchis Regio roughly gray I 'lose' most of the yellow color in areas that are yellow in the Galileo images. If desired, it might be possible to 'fix' this using channel mixing, possibly by making a synthetic red image as some a weighted average of the red and green channels. It will be interesting to see JUICE's images of Io. Its camera has red, green and blue filters (it has a total of 14 filters). But it's also going to be interesting to see data from the MAJIS instrument. It is an imaging spectrometer that covers wavelengths from 0.4 to 5.7 µm by simultaneously collecting 480 spectra. If I understand correctly the highest resolution for Io should be something like 50-100 km/pixel (take this with a grain of salt). Not exactly high resolution but enough to be very useful for getting a better idea of exactly what Io's color looks like to the human eye. |
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