Galileo images and mosaics of Europa Options

[tedstryk]

I have worked on sprucing up some global views of Europa from Galileo. There are a few more global views I hope to get to eventually. But the best two at nearly full phase benefited a lot.



[Moderator note: There are several more threads containing Galileo Europa images but they all contain several inactive image links. The main threads are:
http://www.unmannedspaceflight.com/index.php?showtopic=2016
http://www.unmannedspaceflight.com/index.php?showtopic=2174
http://www.unmannedspaceflight.com/index.php?showtopic=2222
http://www.unmannedspaceflight.com/index.php?showtopic=2082
http://www.unmannedspaceflight.com/index.php?showtopic=2142 ]

[Bjorn Jonsson]

Conamara Chaos revisited

Conamara Chaos was particularly well observed by Galileo. Others (especially machi) have posted great versions of the E12 hi-res images so here I'm concentrating on the E6 images plus the E12 color images. Here is a 2x3 mosaic from a range of 19000 km. It shows all of Conamara Chaos below the big "X" feature:


About 40 minutes later Galileo obtained four hi-res images of southern Conamara Chaos from a range of 6600 km. Here they have been blended into the big mosaic. This version shows all of Conamara Chaos:


During orbit E12 Galileo obtained the well known ultra hi-res images that have appeared earlier in this thread. But it also imaged Conamara Chaos in violet, green, 756 nm and 968 nm from a range of 18000 km. This is an RGB version from the 756 nm, green and violet images:


I had to create a synthetic 756 nm image from green and violet for the center of the "X" feature and everything above it but this worked very well when I used a non-linear formula instead of the more common w*GR+(1-w)*VI. I then created synthetic red and blue images.

It's interesting to combine the color data with higher resolution data. This was posted way back in 2006 (!) by vexgizmo:

Here's a challenge that I hope one of you might accept. During the E12 Galileo orbit, there was a sequence of Galileo color images obtained of Conamara Chaos. Below is work by the Galileo SSI team to assemble these into color mosaics. This color imaging is enough to paint much of the famous E6 Conamara Chaos mosaic in true color (or near-true color extrapolated from 2 colors)--unfortunately we still only see this region painted by false bluish color based only on the E4 Europa albedo images. Can someone accept the challenge of painting Conamara with its true E12 color?

Others have done a very good job with the true color earlier in this thread so I'm not repeating that (even the very hi-res E12 images have been nicely colorized). But I noticed that there seemed to be some very subtle color variations and it is also well known that the dark terrain is redder than the light terrain. I wanted to clearly show these color variations and after some experimentation I came up with the following image where the IR756/green ratio is displayed as red, green simply as green and the violet/green ratio as blue. I then used this to colorize the E6 data (both the hi-res data and the lower resolution data):


The features that appear red or purple are 'redder' than the greenish/cyan terrain. This reveals lots of interesting things. One particularly interesting observation is that the matrix in Conamara Chaos is usually redder than the large blocks with ridged terrain. A look at page 267 in Europa published by University of Arizona Press (a must-have for anyone seriously interested in Europa) confirms this. Another interesting thing is the Pwyll ejecta. The two grayscale images near the top of the post show a north-south ray of bright ejecta material from Pwyll that overlaps western Conamara Chaos (this ejecta is particularly obvious in the G2 global image). In the false color image the westernmost part of Conamara Chaos has a strong green color caused by the ejecta. What I find interesting is that in this area both the matrix and the rafts are green. Is this evidence that Pwyll is younger than Conamara Chaos? At least I think I have managed to find a particularly good example of just how useful color/multispectral data can be.

All of the images above are in orthographic projection with the subspacecraft point at lat=11.5, lon=273. North is up. The images here are slightly bigger than the originals to avoid loss of details from the many resampling and reprojection steps.

[tedstryk]

Lovely work! I'll also add that the shapes of Galileo mosaics are sort of a signature.