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Dust Storm
Ames
post Oct 31 2005, 10:16 AM
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new pictures...

http://nasa.exploratorium.edu/mars/opportu...cam/2005-10-31/
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dot.dk
post Oct 31 2005, 10:32 AM
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QUOTE (Ames @ Oct 31 2005, 10:16 AM)


Newst pictures are 3 days old...

But somehow Exploratorium has gone crazy updating...
Looks like all Spirit images have been reloaded on the 31'st... That's gonna kill MMB laugh.gif


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Tman
post Oct 31 2005, 03:17 PM
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This Rear Hazcam is additional one from sol 627:

http://marsrovers.jpl.nasa.gov/gallery/all...23P1315L0M1.JPG

Looks more dusty too in comparison to one sol older pics.
It's the same time like this one: http://www.unmannedspaceflight.com/index.p...indpost&p=24937

It's unbelievable how we have to scrape up the pictures in these days blink.gif


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Cugel
post Oct 31 2005, 03:28 PM
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But the shadow of the rover still looks sharp and crispy!
Most of what we're seeing is dust on the camera, isn't it?
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ljk4-1
post Oct 31 2005, 03:29 PM
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Did it ever show if the dust that accumulated on the Viking landers ever blew off?

Was a dust devil ever seen by them, even if its true nature was only realized years later? I can't believe that no dust devils ever passed by them even once during their operating lives.

dd.gif


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Bill Harris
post Oct 31 2005, 03:30 PM
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This didn't quite show what I'd hoped it would, but here it is for your FWIW file...

Here is a montage of four Forward Hazcam images from Sols 627, 626, 624 and 616 that semi-shows a build-up of dust in the atmosphere, but not conclusively.

--Bill


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Tman
post Oct 31 2005, 03:42 PM
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QUOTE (Cugel @ Oct 31 2005, 05:28 PM)
But the shadow of the rover still looks sharp and crispy!
Most of what we're seeing is dust on the camera, isn't it?

Think so, but it's really windy for a few days.


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Ames
post Oct 31 2005, 03:44 PM
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The latest hazcam pictures show the shadow as being sharp - as I would expect.
BUT the shadowed zone is lighter indicating that there is more "ambient" light.

Think of the sky here on earth and compare the shadows on a cloudless day:
1) in a smoggy city (say LA)
2) in mountains.
Both have crisp edges but the contrast in the mountains is much higher.

The latest rear hazcam images definately show a reduced shadow contrast.

Nick
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tedstryk
post Oct 31 2005, 03:46 PM
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I imaging the stretching of the "raws" wrecks havoc on our ability to determine how much the brightness of the seen is effected.


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tedstryk
post Oct 31 2005, 03:49 PM
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QUOTE (ljk4-1 @ Oct 31 2005, 03:29 PM)
Did it ever show if the dust that accumulated on the Viking landers ever blew off?

Was a dust devil ever seen by them, even if its true nature was only realized years later?  I can't believe that no dust devils ever passed by them even once during their operating lives.

dd.gif
*


Dust devils were detected by other instruments. But because the Viking cameras were slow, line scanning systems, they wouldn't have shown up in images except as perhaps a funny looking line or two. This is why Pathfinder and the MERs see them - they have framing cameras.


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Marcel
post Oct 31 2005, 03:56 PM
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QUOTE (tedstryk @ Oct 31 2005, 03:49 PM)
This is why Pathfinder and the MERs see them - they have framing cameras.
*

Did Pathfinder actually see one ? Don't remember.
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helvick
post Oct 31 2005, 04:08 PM
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QUOTE (Marcel @ Oct 31 2005, 04:56 PM)
Did Pathfinder actually see one ? Don't remember.
*

I don't think it saw one but they felt at least one with their wind and pressure sensors.
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helvick
post Oct 31 2005, 04:32 PM
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QUOTE (tedstryk @ Oct 31 2005, 04:46 PM)
I imaging the stretching of the "raws" wrecks havoc on our ability to determine how much the brightness of the seen is effected.
*


True but there are a couple of things to note that can give us something to work on.
Tau=5. There will be no clear shadows at all, at noon the diffuse illumination will be about 2 orders of magnitude more intense than direct beam illumination and it's even more extreme when the solar elevation is low.
Tau=2, There will be faint shadows, diffuse lighting at midday is about 5x the intensity of the direct beam, and once again that rises significantly further from noon.
Tau=1, Clear shadows are visible but shaded areas are well illuminated. Diffuse light is about 20% higher than direct at noon. Overall daily diffuse insolation is about 80% more than direct beam.
Tau=0.5, Crisp shadows and shaded areas are noticably dark. Direct beam is ~70% more than diffuse light at noon. Total daily beam insolation is abotu 20% more than direct beam.
Tau=0.1, Extremely well defined shadows. Beam lighting is ~10x the intensity of diffuse at noon.

Things get a bit fuzzy very early\late in the day when tau is above ~0.2 as direct beam falls off rapidly at low sun angles while diffuse light falls off pretty slowly.
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Bill Harris
post Oct 31 2005, 05:01 PM
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Here is another evaluation of the sky brightness. Using two "similar" Rear Hazcam images, I used the bottom of the solar panel as a greycard to measure the incident light from the ground onto the panel. Selecting two 75x75 pixel apertures on the right and left sides of the panel in each image and averaging the value in each aperture, I adjusted the brightness of the two images so that the value of each aperture was the same in both images. This way, I ensured that the "greycards" had the same value and this allowed me to evaluate the relative intensities of the shadowed areas in the foreground. This is meatball photometry since it disregards a lot of variables, but I think it suggests that the shadows are brighter on Sol 627.

FWIW^2.

--Bill


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RNeuhaus
post Oct 31 2005, 05:07 PM
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QUOTE (ljk4-1 @ Oct 31 2005, 10:29 AM)
Did it ever show if the dust that accumulated on the Viking landers ever blew off?

Was a dust devil ever seen by them, even if its true nature was only realized years later?  I can't believe that no dust devils ever passed by them even once during their operating lives.

dd.gif
*

The Meridiani Planum does not have dark strikes on the land as the product of dust devil. Hence, that zone does not occurs dust devils unless in the Gusev's basin has lots of dark strikes around the Columbia and Cook Hills. Thus, that zone is considered as North West (aprox 350 degree) to South East (80 degree) constant wind. You can see the formation of ripples: the west side of ripple, the surface is somewhat rough with minor canals toward the ripple and the east side, you will notice as a plain and smooth side due to the dust or sand accumulation by the wind.

Rodolfo
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