Juno Perijove 22, September 12, 2019 Options

[mcaplinger]

Images have started appearing on missionjuno.

[fredk]

Stunning, Bjorn. I always appreciate the attempt at true colour.

I suppose you've done some masking of the sky - the pixel values are zero in the sky, but small though nonzero in the shadow, as a gamma-tweak illustrates:

Is that just a nonzero black level in the shadow? Another idea would be real scattered illumination from the illuminated atmosphere outside the shadow, or illumination from partially sunlit moons (other than Io). Both those seem unlikely.

[Bjorn Jonsson]

Stunning, Bjorn. I always appreciate the attempt at true colour.

I suppose you've done some masking of the sky - the pixel values are zero in the sky, but small though nonzero in the shadow, as a gamma-tweak illustrates:

Yes, I did some feathered masking in Photoshop near the limb. Otherwise I'd get a sharp, unrealistic cutoff in the dark (but not totally black) area a bit outside of Jupiter's limb. This is because I reprojected the raw framelets to simple cylindrical projection and added 200 km to Jupiter's radius when reprojecting to avoid losing Jupiter's sky (which usually happens if I use the cloudtop radius value).

A related point: knowing the geometry we should be able to plot the edge of the umbra on the image, and then measure how much scattered light is visible inside the umbra - perhaps interesting from the atmospheric science point of view?

This would be difficult because the shadow contains stray light from the instrument as pointed out in an earlier post. This scattered light varies in non-trivial fashion depending on the viewing geometry, the sun direction etc. I haven't attempted to model these effects and correct for them.

However, if memory serves there are some Galileo images where a big satellite shadow is visible. These images might have less stray light and/or be easier to calibrate if measurements of the umbra brightness are desired - I suspect compression artifacts in the Galileo images might make this impossible to measure properly though.