Voyager and Galileo Images of Ganymede, The Ganymede images and mosaics thread Options

[Bjorn Jonsson]

I've been processing some of the high resolution Galileo Ganymede images recently. As far as I know the two mosaics below have not appeared at the official websites (at least not in this form) so in a sense they are 'new'.

The first one was obtained during the G1 flyby in 1996. It covers a part of Memphis Facula which is centered at roughly 15°N, 132°W. The images were obtained at a distance of approximately 5000 km from Ganymede's center.


The second one was obtained during the G28 flyby in May 2000. It is centered near 14.5°S, 319.7°W. The images making up the mosaic were obtained at a distance of roughly 4500 km from Ganymede's center.


I will probably post more Ganymede mosaics later this month or next month.

[EDG]

I was going to start a new thread for this but I think for now I'll keep posting my stuff here.

I also made a global colour mosaic of the sub-jovian hemisphere of Ganymede from the Voyager 1 images, but that proved more problematic, largely because some of the blue filter images were blurry. I made global mosaics using orange, green, blue, violet and UV filters, and here's what I came up with (details are all in the captions within the images).

The OBV (Orange/Blue/Violet) is the same filter combination as my Voyager 2 mosaics posted above, but you can see the issue with the blurry blue filters in the top left part of the image.

Attached thumbnail(s)

 

[tedstryk]

Cool. That looks like the set I used in this one.

[EDG]

Cool. That looks like the set I used in this one.

Very nice! What filters did you use for that? I thought I'd used all the available images in those filters in mine, but maybe I ran out of steam and missed a few.

[ugordan]

EDG, any idea why you have color shifting in the 3-color footprints near the terminator? It looks to me the green and blue filters are darker there than their neighboring footprints, causing some reddening there. For fun I tried coaxing your O+UV color near the left limb to the OGB in the center and I can get them to match more closely than the actual OGB footprints agree.

[EDG]

EDG, any idea why you have color shifting in the 3-color footprints near the terminator? It looks to me the green and blue filters are darker there than their neighboring footprints, causing some reddening there. For fun I tried coaxing your O+UV color near the left limb to the OGB in the center and I can get them to match more closely than the actual OGB footprints agree.

Are you referring to what looks like some of the component images near the terminator being different brightness/contrast to the others? (e.g. the voyager image on the bottom right of the green mosaic looks darker than the surrounding images)? I'm not sure why that's like that - I think the images might not have been calibrated properly relative to eachother? I'll see if I can find my scripts for this one and see if there's any clue to what's going on in there.

[ugordan]

Are you referring to what looks like some of the component images near the terminator being different brightness/contrast to the others?

Yes. I assume all the frames were taken at roughly the same time so the terrain illumination as well as phase angle are pretty much constant? It looks like a calibration thing. I guess I didn't expect to see that much calibration uncertainty with ISIS, although I've never really worked with it or Voyager images in general.

See the red strip near the terminator and a yellow-green bit below it - the part of the terminator that looks ok is a synthetic red channel.

[EDG]

Yes. I assume all the frames were taken at roughly the same time so the terrain illumination as well as phase angle are pretty much constant? It looks like a calibration thing. I guess I didn't expect to see that much calibration uncertainty with ISIS, although I've never really worked with it or Voyager images in general.

See the red strip near the terminator and a yellow-green bit below it - the part of the terminator that looks ok is a synthetic red channel.

Yeah, I see that... I wonder if Ted ran into the same issue when he made his mosaic? I don't see the same problem in his image. I'm still looking for my script for this one, maybe that'll reveal an explanation.