Galileo images and mosaics of Europa Options

[Bill Harris]

Good explanation, Ed. Photography is all smoke and mirrors, whether it be black and white, grayscale, color, silver halide or doped silicon.

--Bill

[Bjorn Jonsson]

Somehow the IR-G-V images look more "natural" to me than the ones with a synthetic blue channel. I find the orangish colors more natural than the pinkish ones using a synthetic blue channel.
That preference may have its roots in the Voyager imagery so one comes to expect an orange colored Europa -- not neccessarily its true color at all.

The C10 (global) images look more 'natural' to me than the G1 images. This may be because I altered the color balance to make the area around Pwyll whitish whereas for the G1 image I didn't change the color balance. I should probably have changed it to something more similar to the C10 image. That said, I don't think Europa is as reddish as in the C10 RGsB image but I plan to use Cassini CB1GB images where both Europa and Jupiter are visible to see what Europa looks like when I process the image to make Jupiter's color balance similar to what one sees through a telescope.

[ugordan]

That said, I don't think Europa is as reddish as in the C10 RGsB image but I plan to use Cassini CB1GB images where both Europa and Jupiter are visible to see what Europa looks like when I process the image to make Jupiter's color balance similar to what one sees through a telescope.

You might have problems there because Cassini only used CB1 when it was still far away from Jupiter. Once the imaging plan changed to a 2x2 coverage footprint, they reduced the filter set and dropped CB1, leaving only CB2 as a close alternative. OTOH, I can't remember if they even kept the GRN filter coverage.
As a result, CB1 images of Europa are very distant and color differences will probably be unresolvable on such a small disk. My experiments with CB1 always resulted in Europa being more or less white.
There are a few RED/CB1 images taken near C/A IIRC, but they're severely underexposed, see my topic on Cassini Galilean images.
Note that in no way am I saying those colors I got are even remotely accurate (in fact, they're probably very wrong), that attempt was primarily driven by me wanting to know how well Cassini could resolve the moons from such a distance.

[vexgizmo]

Does anyone know if Hapke parameters as a function of wavelength (or Galileo filter) are available somewhere ?

Unfortunately, not yet for the Galileo data. This is the only photometric study I know of from the Galileo Europa data:

Helfenstein, P., N. Currier, B. Clark, J. Veverka, M. Bell, R. Sullivan, J. Klemaszewski, R. Greeley, R. T. Pappalardo, J. W. Head III, T. Jones, K. Magee, K. Klaasen, P. Geissler, R. Greenberg, A. McEwen, C. Phillips, T. Colvin, M. Davies, T. Denk, and M. Belton, Galileo obervations of Europa's opposition effect, Icarus, 135, 41-63, 1998.

The best from Voyager data is:

Domingue, D. L. and B. Hapke, Disk-Resolved Photometric Analysis of Europan Terrains, Icarus, 99, 70- 81, 1992.

[jrdahlman]

edstrick's explanation made me think of a question of spaceprobe construction:

Why even use filter wheels at all?

Now that 1000 x 1000 pixel sensors are so cheap, we can load probes with as many cameras as we want. Look how many the MERs have. So instead of possibly-sticky mechanical wheels, or prism arrangements (imagine a gigantic 8-prism for 8 filters!), why not just have an array of 8 separate cameras all pointing the same way, each with its own dedicated filter?

Granted, for landers or other close-up features the parallax would be unacceptable, but for planetary flyby/orbits, parallax would be too tiny to see. (Wouldn't it?) Then it could take pictures with ALL the filters all at the same time--no motion shift between them! And you wouldn't even have to worry about 8x the data coming back, because you could still transmit them sequentially, or even decide which filtered pictures are worth sending.

How come they're not being built this way now?

[paxdan]

edstrick's explanation made me think of a question of spaceprobe construction:

Why even use filter wheels at all?

Now that 1000 x 1000 pixel sensors are so cheap, we can load probes with as many cameras as we want. Look how many the MERs have. So instead of possibly-sticky mechanical wheels, or prism arrangements (imagine a gigantic 8-prism for 8 filters!), why not just have an array of 8 separate cameras all pointing the same way, each with its own dedicated filter?

Granted, for landers or other close-up features the parallax would be unacceptable, but for planetary flyby/orbits, parallax would be too tiny to see. (Wouldn't it?) Then it could take pictures with ALL the filters all at the same time--no motion shift between them! And  you wouldn't even have to worry about  8x the data coming back, because you could still transmit them sequentially, or even decide which filtered pictures are worth sending.

How come they're not being built this way now?

Because the cost of the sensor isn't the limiting factor, it is the size and weight of the camera(s). Mass and volume constraints are very tight on space craft. A filter wheel is a far more elegent solution to capturing a variety of wavelengths than duplicating the entire camera. A filter wheel weighs very little and occupies very little space, far far less than duplicating the sensor, optics and camera body multiple times.

The problem of motion shift is an interesting one for orbiters/flyby craft. There has been recent discussion regarding the use of 'sport mode' on the MER PANCAM. This cuts the interval between frames to 3 seconds from 10-20. While the interval between frames for Cassini is longer, one wonders wheather the use of subframe images or better routines will be able to squeeze a higher frame rate from the camera.

It is important to remember that spacecraft are primarily scientific instruments. Thus when spacecraft are designed, and choices made between returning scientifically calibrated data or pretty pictures the former must take priority and thus we should be thankfull that the latter is so often acheived as well.

[JRehling]

I have been trying to make (true ?) color images of Europa using mainly Galileo data. I am using red (IR756 in some cases), green and violet images.

Great stuff.

The area in the left image is an example of terrain where bright ice was seen to vary in IR brightness even though it was fairly uniform in visible. That might mean that it's impossible to interpolate/extrapolate between 756nm (near IR, actually just on the fringe of the visible spectrum) and 650nm (more of a central "red"). The differences between the "whites" can be seen vaguely in your image, and might not in "true" color. But beautiful stuff, and probably otherwise very on target, IMO.

[Decepticon]

Exploitcorporations Did you find any global images that have not been seen yet?

[Exploitcorporati...]

Exploitcorporations Did you find any global images that have not been seen yet?

No, that mine has been exhausted, and was unfortunately not very deep. Partial 1-4km scale mosaics were obtained on G1, E4, E6, G7, E12, E14, I25 and one nice full-frame view on E17. More distant, full-globe images were obtained on G2, C9, C10, G28, and I33. Eclipse and very distant plume search view were taken on C10 and C20. The exquisite color work seen here by Ted Stryk, Bjorn Jonsson, Mattias Malmer, and others covering these views, particularly the E14 mosaic, are as good as it gets.

[DDAVIS]

Has anyone here cleaned up this picture? It one of my favorite images of Europa http://photojournal.jpl.nasa.gov/jpeg/PIA02528.jpg

Yup. Here is my initial attempt at this, which has been crudely colorized as well.

Don

Attached thumbnail(s)

 

[Decepticon]

Nice!

[tedstryk]

Yeah, global color views and what the Cassini folks would call "Kodak Moments" were some of the big losers to Galileo's woes.

C10 images were more intended to study the rings, but Europa happened to be there, and kind of stole the show. It is a pretty set, but is black and white.



The two C20 images are so underexposed and extremely noisy, making them almost unrecognizable. Here is the best I have been able to pull from them.

[mgrodzki]

Yup. Here is my initial attempt at this, which has been crudely colorized as well.

Don

that is one awesome image of europa. for one of the most important bodies in the solar system… its shocking how few there are of this. #59 that is.

[remcook]

pretty map
http://news.bbc.co.uk/1/hi/sci/tech/6454039.stm

[PhilHorzempa]

The remarkable mosaics on the "Ganymede Revisited" thread got me thinking
about what might have been done for Galileo's Europa images on UMSF.
Lo and behold, there are earlier threads that included Europa mosaics. I say that
in the past tense because if you check out threads such as "Europa's Northern
Plains" and "Thera, Thrace, and Agneor Linea," then you will see that most, if not
all, of those mosaics are gone. It appears that the host for those data may no longer
exist, as such.

Can the members of UMSF re-create some of those Europa mosaics, which, from
the comments in those threads, were impressive?


Another Phil