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Venus Express
Bob Shaw
post Jul 8 2005, 01:59 PM
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QUOTE (edstrick @ Jun 26 2005, 11:31 AM)
On Cassin, the VIMS is the best instrument we could design with early 90's mid-infrared imaging technology.

We now have real mid-infrared imaging detectors.  Not 10 megapixel, but still real camera chips, that can take quality images with really good resolution in the mid-IR  (1 to 5 micrometers, more or less).  We just @#$@# didn't back then.
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Well, obviously we need a Shuttle mission to replace the instrument...


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JRehling
post Jul 8 2005, 02:23 PM
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QUOTE (edstrick @ Jun 26 2005, 03:31 AM)
On Cassin, the VIMS is the best instrument we could design with early 90's mid-infrared imaging technology.

We now have real mid-infrared imaging detectors.  Not 10 megapixel, but still real camera chips, that can take quality images with really good resolution in the mid-IR  (1 to 5 micrometers, more or less).  We just @#$@# didn't back then.
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It seems apparent that the 938nm wavelength, which is the best one ISS has to use on Titan, is not the best penetrator of Titan's haze, and that VIMS can thereby make up for (some of) ISS's edge in intrinsic resolution by utilizing better IR wavelengths. Not only by choosing the best possible single wavelength (the best ones are longer than 938nm, at other spectral "holes"), and taking one-wavelength images in that. Surely VIRTIS will beat ISS in that respect. On the other hand, CO2 will block different holes than CH4, and I'm not sure if it leaves us a better hole than CO2 or not.


I think the best IR products of Venus's surface will come from compiling repeated coverage of the same areas and "stacking" or somehow integrating the data to average out over varying cloud thicknesses.

Finally, note that IR is complicated terribly at Venus, but not at Titan, by thermal effects. If all we see is a thermal record of the surface, then we may not get much more than crude altimetry we already knew about. Sorting out the albedo may be impossible.
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Gsnorgathon
post Jul 9 2005, 04:10 AM
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I suppose it's possible, if not easy, to subtract images taken at night from daytime images. "Not easy" might be too much of an understatement.
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JRehling
post Jul 9 2005, 05:09 AM
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QUOTE (Gsnorgathon @ Jul 8 2005, 09:10 PM)
I suppose it's possible, if not easy, to subtract images taken at night from daytime images. "Not easy" might be too much of an understatement.
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One problem is, can you project an image onto a map accurately? It depends upon whether you are looking at a cloud-level sphere or a surface sphere. And there is undoubtedly refraction. My guess is that you would assume that a cloud level sphere is what you're looking at, assume that when you look at a point in the clouds you are trying to collect albedo data from a diffuse area centered below that point, and use multiple images to integrate observations.

Subtracting night from day -- what does this buy? There will be a lot of thermal interference at both times, but you can't assume that it is precisely the same. You'll get some combination of thermal inertia and albedo -- messy!

When it comes right down to it, trying to observe Venus from above the clouds and learn a lot is pretty tricky. Unless some mineral of interest has a heck of a wicked IR spectrum and that happens to fall inside one of the CO2 windows, I'm just plain skeptical that we'll get good geological data from this mission. Hope I'm wrong.

Surface spectra are, IMO, going to have to come from below the clouds. That still doesn't solve the problem of atmospheric interference, but the fact that the horizons are so clear in Venera imagery provides a lot of cause for optimism. A camera-to-horizon "chord" of 5km will cut through more than or the same as atmospheric interference than a vertical line from surface to clouds (surface air is the densest, and a horizontal chord is entirely through dense air, whereas a vertical slice only goes through the densest air at the bottom). So, with clear images at the surface, I think we can get good images from several km up. A balloon could do the trick.
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TheChemist
post Aug 10 2005, 04:33 PM
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Venus Express arrives in Baikonur

She's got it ..... (Am I allowed to quote Bananarama in a space forum ? smile.gif )

This post has been edited by TheChemist: Aug 10 2005, 04:35 PM
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Bob Shaw
post Aug 10 2005, 07:42 PM
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QUOTE (TheChemist @ Aug 10 2005, 05:33 PM)
Venus Express arrives in Baikonur

She's got it ..... (Am I allowed to quote Bananarama in a space forum ?  smile.gif )
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It ain't what you do, it's the way that you do it!


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Guest_BruceMoomaw_*
post Aug 29 2005, 02:10 AM
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Here's my long-promised entry on whatever I've got regarding VIRTIS' possible ability to map Venusian surface composition.

Unfortunately, the two most important documents on this aren't available for free on the Web: the Nov. 2000 Icarus article by Langevin et al ("Detection of Sub-Micron Radiation from the Surface of Venus by Cassini/VIMS"), and the March 2002 article by V.I. Moroz in "Planetary and Space Science" ("Estimates of Visibility of the Surface of Venus from Descent Probes and Balloons"). I have a photocopy of the former, but can't find the copy I thought I had of the latter. Anyway, the former is optimistic about the possibility: "The 5 spectral windows between 0.85 and 1.18 microns now proven to be sensitive to surface spectral sensitivity provide a potentially effective means for remotely mapping the mineralogical composition of the surface of Venus" [something co-author Kevin Baines was saying for previously]... [They] can be effectively used to distinguish ferric (hematite) and ferrous minerals (e.g., the pyroxenes augite and hypersthene, and olivine). The hydrous mineral tremolite -- thought to be stable on geologic timescales on Venus -- also displays a detectable absorption feature...Both wollastonite -- a CO2 buffer mineral thought to be relating the CO2 surface pressure -- and pyrite are spectrally flat, but have distinctly different ablbedos." There's an accompanying graph of these various minerals' near-IR reflectivities, with the Venusian surface spectral windows overlaying it.

The Moroz article is much more pessimistic: "Constraints on the mineral surface composition would be difficult to derive from orbital observations due to multiple reflections between the surface and the atmosphere." The VIRTIS group itself, the Japanese VCO group and the Vernadsky-Brown Venus group are all intermediate in optimism: they think that it will almost certainly be possible to map FeO, thus distinguishing between felsic and mafic minerals and thus between granites and basalts, and also looking for magnetite on the highly radar-reflective mountaintops -- but aren't sure they can go any farther. (The two longest-wavelength windows seem to be the most useful.) Moreover, it seems much more possible to do this in the north polar regions than elsewhere (which, by an agreeable coincidence, is where Ishtar Terra -- Venus' most likely continent -- is located).

As for spatial resolution (including for temperature and near-surface volcanic gases), estimates are all over the place. Moroz sets it at 50-100 km, the VCO group at 100 km, and David Crisp at no better than 250 km (based on Galileo's flyby results). The VIRTIS group itself initially set it as high as 30 km, but now seems to have it pegged at 90-150 km ( http://irsps.sci.unich.it/~luciam/VEX/DOC/...ence_VIRTIS.pdf and the May 2005 report at the VIRTIS site: http://irsps.sci.unich.it/~luciam/VEX/ ).

As for quake detection through sensing pressure waves in Venus' dense CO2 air, they are still very interested in that -- although it will require special observational techniques (see the Dec. 2003 and May 2005 reports at the VIRTIS site).
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Guest_BruceMoomaw_*
post Aug 29 2005, 02:15 AM
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Two more notes:

(1) The VIRTIS team is fully ready to filter out altitude effects from their maps, using Magellan's altimetry maps (see their May 2005 report).

(2) There's another good paper on the possible detection of Venusquakes through atmospheric pressure waves at http://www.lpi.usra.edu/meetings/lpsc2005/pdf/2274.pdf .
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tedstryk
post Sep 11 2005, 01:35 PM
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http://messenger.jhuapl.edu/the_mission/im...ine_full_sm.jpg

You gotta love the ESA press people.

"Venus Express will be making the first global examination of the atmosphere of Venus."

Pioneer Venus Orbiter? And to some degree the Venera orbiters?



"The scientific teams of the seven very precise instruments and multi-wavelength cameras on board expect to collect infinitely more science data than all previous missions combined - with the exception of Magellan more than 500 megabits of data received every day."

Yes, it is a lot more than missions besides Magellan, but infinite? I think there is a bit of grandstanding here. rolleyes.gif


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mike
post Sep 12 2005, 07:08 PM
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America will just have to make a new probe that returns infinitely more data than the infinite amount ESA is getting.
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4th rock from th...
post Sep 12 2005, 08:46 PM
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QUOTE (tedstryk @ Sep 11 2005, 02:35 PM)
...

Pioneer Venus Orbiter?  And to some degree the Venera orbiters?

...

Yes, it is a lot more than missions besides Magellan, but infinite?  I think there is a bit of grandstanding here.  rolleyes.gif
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If the PVO data where avaliable on the net this type of statement wouldn't be possible. Someone would gather that data and make some time lapse movies, global maps, etc, etc.

The best I could find is this: http://www.cg.its.tudelft.nl/~freek/venus/...ults/04-07.htmlhttp://www.cg.its.tudelft.nl/~freek/venus/report/last_results/04-07.html
Not much really.

So no wonder that ESA is selling their "product" as best as they can!


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Bob Shaw
post Sep 12 2005, 09:04 PM
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QUOTE (mike @ Sep 12 2005, 08:08 PM)
America will just have to make a new probe that returns infinitely more data than the infinite amount ESA is getting.
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Mike:

It wouldn't take all that much more!

Oh, and the thing that the ESA Press Office left out is that they'll also be releasing the Venus Express data infinitely s-l-o-w-l-y...

Bob Shaw


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tedstryk
post Sep 12 2005, 09:59 PM
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Well, I doubt there would be time-lapse images. The cloud photopolarimeter built scans slowly like Pioneers 10 and 11, so there wouldn't be many sequences close enough together, and changes in position throughout the scan would be a problem.


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TheChemist
post Sep 13 2005, 11:52 AM
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QUOTE
Oh, and the thing that the ESA Press Office left out is that they'll also be releasing the Venus Express data infinitely s-l-o-w-l-y...

laugh.gif laugh.gif
Although "infinitely more" is a very common expression and should not be taken literally. the ESA press office really deserved this biggrin.gif
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tedstryk
post Sep 13 2005, 03:01 PM
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QUOTE (TheChemist @ Sep 13 2005, 11:52 AM)
laugh.gif  laugh.gif
Although "infinitely more" is a very common expression and should not be taken literally. the ESA press office really deserved this  biggrin.gif
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Yes, but especially when compared with PVO, even in common usage it doesn't fit (well, maybe in shear bits, but not in the scope of investigations)


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