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Venus Express
Guest_DonPMitchell_*
post Jul 12 2006, 08:55 PM
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Venus Express is the first time a decent camera has been placed in orbit around Venus, which is very exciting. Exploiting the narrow near-infrared windows, VIRTIS should show new details about the atmospheric circulation, cloud formation, and perhaps surface vulcanism.

I believe it was the Australian astronomer, David Allen, who first realized that these infrared windows existed into the deep Venusian atmosphere (Nature, 1984). Images were taken by the Galileo spacecraft during a flyby, and Mark Bullock has done some intersting work using Earth-based astronomy to peer through these windows: Hawaii Telescope

I am also disapointed by the PFS failure. This provides added incentive now for JAXA to send Planet-C and hopefully answer some of the questions about the chemical makeup of the Venusian clouds.
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elakdawalla
post Jul 12 2006, 11:41 PM
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OK, so now I have a question about the images and movies.

Looking at the very first movie captured in ultraviolet from VMC, the caption states: "The spacecraft was flying over the northern hemisphere approaching the planet, over distances ranging between about 39 100 and 22 600 kilometres from the surface. The images were taken at 365 nanometres, starting respectively 03:30 and 01:45 hours before reaching the pericentre." But if you watch the movie it looks like we are actually moving from one hemisphere toward the equator on approach. The shape of Venus Express' orbit is such that you approach over the southern hemisphere, fly close over the equator and northern hemisphere, and then retreat back out over the southern hemisphere. And if you look at the orbit diagram (here's one I pulled from Håkan Svedhem's VEXAG presentation), the times and distances do imply that we're looking primarily at the southern hemisphere, moving toward the equator, I think. Am I seeing this right?

--Emily

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Bob Shaw
post Jul 12 2006, 11:44 PM
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QUOTE (DonPMitchell @ Jul 12 2006, 09:55 PM) *
I believe it was the Australian astronomer, David Allen, who first realized that these infrared windows existed into the deep Venusian atmosphere (Nature, 1984). Images were taken by the Galileo spacecraft during a flyby, and Mark Bullock has done some intersting work using Earth-based astronomy to peer through these windows: Hawaii Telescope


Don:

My understanding of Mark Bullock's image is that it actually provides a negative view of the dark side of Venus - so here's an inverted version:

Bob Shaw
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Guest_DonPMitchell_*
post Jul 13 2006, 12:39 AM
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Emily, I believe you are correct. The "flying over the northern hemisphere" phrase in their press release is confusing. I believe the movie we are seeing is "upside down" and we are coming up from the south. BY the way, the orginal gray version of the movie is much clearer than the blue-colored one.

Bob is right too. In the original Bullock image, the bright regions are thin spots in the clouds, where heat from the surface is shining through. That goes for the VIRTIS images too, I believe.
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Guest_DonPMitchell_*
post Jul 13 2006, 12:51 AM
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I think ESA is following the standard NASA algorithm for how to ruin a beautiful space image:

step 1. Expand the contrast until light and dark areas pop.
step 2. Apply a Laplacian sharpening filter until noise artifacts are prominant.
step 3. Enlarge the image with a nearest-neighbor filter, so pixels are big and square.
step 4. Pick an ugly primary color, like orange or purple, and colorize the image.

Just to illustrate, here is the original Hubble image of Venus, and the one released to the press:


[attachment=6650:attachment] [attachment=6649:attachment]
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bdunford
post Jul 13 2006, 03:45 AM
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A meaty new Venus Express release is now online at the ESA site. It includes several animations and a wealth of science findings.


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Malmer
post Jul 13 2006, 04:10 PM
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QUOTE (DonPMitchell @ Jul 13 2006, 02:51 AM) *
I think ESA is following the standard NASA algorithm for how to ruin a beautiful space image:

step 1. Expand the contrast until light and dark areas pop.
step 2. Apply a Laplacian sharpening filter until noise artifacts are prominant.
step 3. Enlarge the image with a nearest-neighbor filter, so pixels are big and square.
step 4. Pick an ugly primary color, like orange or purple, and colorize the image.

Just to illustrate, here is the original Hubble image of Venus, and the one released to the press:
[attachment=6650:attachment] [attachment=6649:attachment]


Its like they think that reality is too boring for the public. I think its ok to distort colors of objects that are commonplace and that people have a firm grip on. but anything that are uncommon exotic or in any way hard to reach for the common man should be depicted as close to reality as possible. otherwhise its deception.

I hate oversaturated contrast stretched space images. It only takes away the original beauty and subtleties of the real scene.

The first pictures from mars express are discustingly badly processed. the person that did it should be fired. The hubble picture is also quite garish.

why not just publish calibrated raw images?

/M
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Guest_DonPMitchell_*
post Jul 13 2006, 08:16 PM
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In one of the early Venera-13 papers, the Russian authors discussed the need to apply the inverse method (solving an integral equation) to correctly create RGB color from sensor inputs. They knew their math and radiometry, but didn't have easy access to computers to do it. In the West, you have the opposite -- big computers and relatively ad hoc image processing. I don't believe the colors in any of NASA's images, even when they are not "false".

I'm not sure these guys even know about the sRGB standard. If you know the spectrum of a color, there is a clear algorithm for creating a 24-bit color value. That's fine for some of the latest cameras that record huge spectral image cubes. But if you have signal levels from several sensors, with various spectral responses, then the problem of deriving the maximum-likelihood color value is nontrivial.

Malmer, I was impressed by how you processed the Mariner-10 images, calibrating the sensor weights with Mariner's Earth images.
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Malmer
post Jul 14 2006, 06:48 PM
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i actually ended up relatively close to the responsecurve that where in that paper you sent me...
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Guest_AlexBlackwell_*
post Jul 19 2006, 05:02 PM
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QUOTE (elakdawalla @ Jul 12 2006, 01:41 PM) *
OK, so now I have a question about the images and movies.

There's an interesting tidbit about the Venus Monitoring Camera (VMC) in the News section of the July 20, 2006, issue of Nature:

'You can't have a mission without a camera'
Jenny Hogan
Nature 442, 234 (2006).
doi:10.1038/442234a; Published online 19 July 2006
Full Text

A sister of the Mars Express probe has made it to Venus. And scientists have travelled to Beijing to discuss its first results. Horst Uwe Keller, who is presenting images from the craft's camera, spoke to Nature from the meeting.

I work on the Venus Monitoring Camera (VMC). One of our main objectives is to study the highest clouds, around 70 kilometres above the planet's surface.

The VMC is the only instrument newly developed for this mission, the rest were reused from Mars Express and the comet mission Rosetta. They didn't have a camera, so I stepped in and said: "You can't have a mission without a camera." We built something very small, 1–2 kg, to replace the tiny camera on Mars Express that had watched the Beagle 2 lander as it separated.

The VMC is four cameras, one for ultraviolet light, one for visible and two for infrared. The results so far are qualitative — we haven't finished calibrating the instrument yet. But in the sequences of ultraviolet images I presented on Monday you can see the clouds moving, showing the wind direction.

As a young postdoc in the 1970s, I remember being at a meeting where a well-known astronomer claimed that Venus's clouds were made of droplets of sulphuric acid. At the time I thought he was crazy, but now we know this is true.

What we don't know yet is the nature of the 'ultraviolet absorber' that creates dark features in our cloud images. We hope one of the spectrometers will work out what it is.

We are also working on the infrared images, which we'll check for hot spots that might be active volcanism. The surface of Venus is very young, so we know there must be some volcanism, but no one has definitively seen it. If we're lucky we could also find out something about Venus's lightning using the visible-light filter.

Some of the most remarkable results at the meeting have come from VIRTIS — a spectrometer that probes the atmosphere from top to bottom. The pictures of the south pole are really spectacular: they show a double vortex created by the movement of the atmosphere between the equator and the pole.

For our team, however, the challenge is simply getting high-quality images. While the spacecraft was cruising into orbit, our camera ended up pointing at the Sun for about 50 hours. The Sun burnt its image into the photodetector. But it's not a complete disaster: we have been able to compensate for the damage by re-measuring the sensitivity of each pixel.
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ugordan
post Jul 20 2006, 08:51 AM
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QUOTE (AlexBlackwell @ Jul 19 2006, 06:02 PM) *
While the spacecraft was cruising into orbit, our camera ended up pointing at the Sun for about 50 hours. The Sun burnt its image into the photodetector. But it's not a complete disaster: we have been able to compensate for the damage by re-measuring the sensitivity of each pixel.

Ouch. sad.gif
I noticed the VMC images aren't fully flatfielded, but I didn't realize this was the reason.
How'd the thing get pointed at the sun for 50 hours? Safe mode? Isn't it supposed to be... well... SAFE?


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peter59
post Jul 20 2006, 07:33 PM
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QUOTE (ugordan @ Jul 20 2006, 08:51 AM) *
Ouch. sad.gif
I noticed the VMC images aren't fully flatfielded, but I didn't realize this was the reason.
How'd the thing get pointed at the sun for 50 hours? Safe mode? Isn't it supposed to be... well... SAFE?


Don't worry, images will be perfect. Images taken by ... Messenger.
Please forgive me my sarcasm, but waiting for ESA's images is like
"Waiting for Godot". wink.gif


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Guest_DonPMitchell_*
post Jul 21 2006, 03:05 AM
Post #238





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VMC is kind of a primitive camera (VMC), but that doesn't mean it won't spot something interesting. I think VIRTIS is a more sophisticated experiment, but probably won't take as large a volume of images as VMC. As for learning what the UV absorber is, I'm afraid that rested with the PFS. Its failure cost them the chance to learn a major new thing at Venus.

I think there is one other major new things that VEX could discover -- IR images of active volcanism on the surface. That would be incredibly exciting.
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edstrick
post Jul 21 2006, 11:07 AM
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Assuming <I hope otherwise> that the PFS stays disabled, there could be a real opportunity to fly a backup/flight-spare/engineering-model of the instrument on the Japanese Venus atmosphere orbiter mission. It's moderately well along the design development cycle, but I suspect that it's not too late to refly the PFS on that mission.
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ugordan
post Jul 21 2006, 11:44 AM
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What guarantee do we have that the backup wouldn't fail the same way this one failed? Wouldn't it be wise to reevaluate the weak points in the design and improve it if necessary. Meaning additional costs?


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