new THEMIS color releases, Images showing color variations. Options

[DDAVIS]

First of a new series:

http://themis.asu.edu/zoom-20060622a

[djellison]

Bloody hell Don, I don't know how you get such smooth data out of those released files!

[Stu]

Amazing work Don, thanks... THEMIS doesn't get NEARLY as much credit or exposure as it deserves, methinks...

[climber]

If I read it correctly, these are true colours. Details and the whole picture are just magnificent. True artistic work.

[DDAVIS]

If I read it correctly, these are true colours. Details and the whole picture are just magnificent. True artistic work.

Thanks! I have actually done less 'editorial' colour adjustment in this series than with the Meles Chasma image, the goal being to try to show what the camera was seeing while removing the distracting light leak stripes. When the judgement has to be made on supressing bright or dark discontinuities in an image, the direction this would bring the color balance toward or away from the known range of Martian colors recieves consideration. There are some images where the 'purple' cast common to RGV images shows in dark parts of the image, and others where the scene may have a haze overlay giving a blueish to violet 'wash' over much of the scene, but not all. Anything that looks like it's not an obvious camera related artifact is left in. Seeing subtle color variations within a frame are among the strengths of the THEMIS camera, and images showing such are paramount among the ones I look for.

A slightly dated page on color filters and color images can be seen here:
http://www.donaldedavis.com/2003NEW/CLRWORK/CLRTEST.html

The examples suggest something of the color fidelity of various spacecraft cameras, including the R(green faked from clear)B New Horizons imaging system.

Don

[edstrick]

The sad fact is that the Mars Odyssey cameras have fairly serious design defects that were not caught by enough testing and review, possibly another victim of smaller-faster-better-cheaper. We've had a consistant problem over the years designing cameras that can do more than just good monochrome imagery of low-color-contrast planetary targets.

Voyager, Galilleo and Cassini have done a pretty good job (earlier missions were on the slope of the learning curve), but missions like NEAR (dinky little, noisy, non-square-pixel-CCD), Global Surveyor (wide angle camera's red/blue color data is hard/impossible to align perfectly and the blue channel's noisy), Odyssey (multispectral data's got terrible uncalibratable (more or less) internal reflection defects), Stardust (outgassing on optics, stuck filter wheel), Deep Impact (grossly out-of-focus hirez camera)... just don't perform up there where they should have.

<sigh... rant.. rave..>

[djellison]

HRSC's all right

Doug

[Nix]

Amazing work Don!

Nico

[Guest_AlexBlackwell_*]

The sad fact is that the Mars Odyssey cameras have fairly serious design defects that were not caught by enough testing and review, possibly another victim of smaller-faster-better-cheaper. We've had a consistant problem over the years designing cameras that can do more than just good monochrome imagery of low-color-contrast planetary targets.

Voyager, Galilleo and Cassini have done a pretty good job (earlier missions were on the slope of the learning curve), but missions like...Odyssey (multispectral data's got terrible uncalibratable (more or less) internal reflection defects...

I'm not sure if it's been mentioned previously but McConnochie et al. have a paper entitled "Calibration and in-flight performance of the Mars Odyssey Thermal Emission Imaging System visible imaging subsystem (THEMIS VIS)" (3.15 Mb PDF preprint) that, as I understand it, will be published online tomorrow in JGR-Planets.

[djellison]

A similar design was used for MARCI as well, sort of half-push-broom-half-discreet-ccd, and looking through that paper, it looks like at utter barsteward to process - why would one choose that over a normal pushbroom?

Doug

[mcaplinger]

A similar design was used for MARCI as well, sort of half-push-broom-half-discreet-ccd, and looking through that paper, it looks like at utter barsteward to process - why would one choose that over a normal pushbroom?

We call this a "pushframe" system. An N-color pushbroom system needs N separate linear CCDs and N different signal chains. An N-color pushframe needs one area CCD and one signal chain. MARCI weighs 350 grams; it would be simply impossible to build a linear pushbroom system for anything like that mass.

As for the difficulty of processing: who cares? Computers are fast and cheap.

See http://www.msss.com/mro/marci/images/2006/...tail/index.html

[djellison]

You see - this is why we need you around here

I must admit - the MARCI Orbit 7/8 imagery did make me go "ooo - that's all a bit complicated...but if it works..what the hell"

Doug

[Guest_AlexBlackwell_*]

I'm not sure if it's been mentioned previously but McConnochie et al. have a paper entitled "Calibration and in-flight performance of the Mars Odyssey Thermal Emission Imaging System visible imaging subsystem (THEMIS VIS)" (3.15 Mb PDF preprint) that, as I understand it, will be published online tomorrow in JGR-Planets.

As promised.

[edstrick]

A FUNDAMENTAL problem pushing Mars camera designers toward pushframe systems is the relatively low light levels and low to very low contrast levels of surface imaging at moderate to low sun angles through that hazy atmosphere. The dwell-time of a single-pixel-wide, gadzillion-pixels-long detector's pixels on the surface is "NanoSized" as the resolution of the camera gets "SuperSized".

A pushframe system, perfectly (to a subpixel scale) perpendicular to the moving field-of-view, multiplies that dwell time by the number of pixels the detector is wide. Signal-to-noise ratio goes from c__p to good or realliy fine. That's particularly important for color work on a low-color-contrast (in many areas) planet.

Whatever lead to the multiple internal reflection problems and whatever else is wrong or marginal in the Themis camera, seems to be fixed or avoided in ouir spiffy new "Ancient-Martian-Astronauts-Espionage-Orbiter" ... oops... I mean Mars Reconnaisance Orbiter's supercam. The test images taken under unfavorable conditions show vanishingly small brightness or color artifacts in the released data (made using preflight or first-draft inflight calibration files and software). You can see some stitching-errors in the overlaps between adjacent CCD's in the multi-detector system, but that's not bad at all for first-try tests.

[mcaplinger]

A pushframe system, perfectly (to a subpixel scale) perpendicular to the moving field-of-view, multiplies that dwell time by the number of pixels the detector is wide.

I think you're confused. What you're describing is called Time Delay Integration or TDI, and has nothing to do with pushframe, which is a multispectral technique. It's true that these can be combined, but I don't know of that being done in any previous flight instrument (though our JunoCam instrument will do it to a limited degree.)