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Cape York - Northern Havens, Sol 2780 - 2947
Deimos
post Jan 30 2012, 10:31 PM
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The points are not MGS, ODY, or MRO: these couldn't have been that direction, then. I think you can rule out Mariner 9, Mars 2,3,5, Viking 1 and Phobos 2: the inclination is wrong, but there may be a special alignment to get them to move that way. Most of those are too slow (except VO-1 near perigee). VO-2, if near perigee, could do that speed. It would be hard to show it really could have been there, then. Mars Express also might have been able to do something like that, but only near perigee (peri-ares, whatever). That'd be easier to check. So, if you wanted to follow this up, those two are the ones I'd suggest focusing on (especially MEX, since there exists someone who knows the answer to that).

That said: the second dot is a point source. The first is elongated in a direction other than aimed at the second (i.e., wrong for a motion streak). Both look just like many cosmic rays, and not like real objects.

The previous day, a similar sequence was run (pan rather than movie, but same exposure and downsampling). I see 1 obvious CR. Based on that and experience, 2 CRs in 4 images would not be unusual (these are short images, so I'm not comparing them to Pancam L7s). Given an image with a CR, figure there is a 10-40% chance the next image has a CR and you end up chasing spacecraft. On the other hand, there's a much lower chance one of the spacecraft has perigee in the right direction, times a small chance it is near perigee, times a small chance that it is going the right way.

So, no, it does not show an orbiter.
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rickyjames
post Jan 30 2012, 10:55 PM
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QUOTE (Deimos @ Jan 30 2012, 04:31 PM) *
So, no, it does not show an orbiter.


Thanks for checking.
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PDP8E
post Jan 31 2012, 04:49 AM
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Here is a zoom GIF of Phobos in the NAVcam 2847 cloud sequence (in all its jpeggy glory)
Attached Image


--------------------
CLA CLL
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walfy
post Jan 31 2012, 06:06 AM
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Interesting pillar of a rock downslope. It looks paper-thin, only its shadow visible!

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JayB
post Feb 1 2012, 07:13 PM
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Was playing around with Content Aware Fill in PS CS5 for something for work this morning. Thought I'd give Ant's Shadow Pan a treatment. Not bad right off, just needed a few tweaks... (and yes I know it has "reconfigured" Oppy's solar panels but I figured she could use a few more for the winter wink.gif
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stevesliva
post Feb 1 2012, 08:10 PM
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QUOTE (JayB @ Feb 1 2012, 02:13 PM) *
Was playing around with Content Aware Fill in PS CS5 for something for work this morning.


Anyone know of how to do something similar in GIMP? I tried for awhile to remove a thumb from blue sky at the corner of one photo, and the suggested plugin just didn't cut it, even after a fair amount of experimentation. I handed a camera to a thumb-imparied guy, and had a series of photos I was hoping to tweak. I was discouraged from thinking the GIMP version could handle them.
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Pertinax
post Feb 2 2012, 04:15 PM
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My apologies if I have missed existing discussion regarding my impending question. I've looked and found nothing.

I've been watching tau at http://www.lpl.arizona.edu/~lemmon/mars-tau-b.html as I'm sure many here are, and have been surprised by the higher than typical tau for a given Ls since roughly sol 2630. I wouldn't think that the tau would vary locally enough at Endeavour to have this long and sustained of a delta. That leaves me at least with assuming that the variance from the past several years is at least regional. If so this thinking is sound, any thoughts as to what might be influencing the higher than typical taus this year?

-- Pertinax
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fredk
post Feb 2 2012, 05:27 PM
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I've noticed that too. One thing to keep in mind is that it can be hard to distinguish dust in the sky from dust on the pancam window and on the solar panels. That needs to be calibrated based on modelling (I think), and that calibration can be off. Check out this post for an example of that. So maybe unaccounted-for dust on pancam is making tau look higher than it really is. Or, of course, it may really just be a hazy winter.

This makes me wonder - since (I believe) there's no way to directly measure the amount of dust on the pancam window, and so the tau measurements are dependent on how well you model that dust, does the team provide uncertainties from those models? In other words, if tau is reported as around 0.7 now, but the modelling uncertainties give 0.7 +/- 0.3, then that tau value would actually be consistent with the previous Martian years. On the other hand, those previous years look entirely consistent with each other, so maybe the modelling uncertainties are small.

Another thing that's unclear to me is is the dust modelling accounted for each sol, or are corrections only made periodically?
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Deimos
post Feb 3 2012, 04:06 PM
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I'll try a "brief" clarification about the opacity page for now. As fredk notes, there's dust in the camera and in the sky. A single measurement sees both. A series of measurements that holds the observation geometry through the camera constant, but varies that through the sky significantly, and holds all else equal, cleanly separates the window and the sky. "All else" is hard to control, so in practice a statistical sample of at least 25 calibrations is needed (a calibration, in this case, might be a measurement at noon and a same-sol one with the Sun near 30 degrees elevation, and maybe an even lower one--the slant-path optical depth of the atmosphere can change by a factor of 2-4). We used to get these several times a week, almost every day way back when. Now, to avoid over use of the PMA azimuth actuator, we get them about once per week.

1) The window-dust model is updated with a timescale of months. Data that are many more months old are affected. The correction being used now is overdue.

2) The random uncertainties in the tau measurement are not so hard to deal with. The systematic ones are hard. The PDS deliveries have uncertainties from all sources, including the window dust model. So, they get worse when the calibrations are more sparse. Data are not delivered until the model has been recently updated. Uncertainties with the window-dust model on auto-pilot could hit 0.3 (the correction has exceeded 1); uncertainties with it fixed will be much less. (However, there are a few archival points with a stated error bar near 1.)

3) An update should come this month. It will likely make it onto that page (which is tactically updated), but it will make it to the PDS. The post fredk links to mentions why we might rather live with small errors some times.

4) Earlier in the winter, it was clear from inspection of the calibrations (aka, chi-by-eye) that any correction would be small. It seemed that the interannual difference was real (due to late MY 30 regional storms, maybe). Recently, it looks like the calibrations will drag the number down toward past years.

5) If the data manage to stay off trend through Ls 0 to 90 or 120, I'll start to believe the calibration is not capturing something. Both rovers have shown tremendous repeatability that used to surprise me. Take a look at Spirit from Ls 40-135. Many bumps and wiggles are repeated. The one problem is that MY29 is high -- there were almost no calibrations that winter, and the systematic uncertainty is high. So I do not believe that difference, even though it is <0.1, but I cannot prove it is wrong either.
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fredk
post Feb 3 2012, 06:25 PM
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Absolutely fascinating stuff - thanks for all the details, Deimos.

So ideally, imaging the Sun at two different elevations can separate out the pancam window and sky contributions. I suppose then that cloud covering the Sun in one of those observations would throw you off. But doing enough observations at different times would beat down those errors. And I'd guess there are many more things that could throw you off.

This has gotten me curious - I don't recall ever hearing quantitatively how bad the dust obscuration of pancam is, for example a "dust factor" for the windows, though it must come out of the models. Since pancam usually points horizontally or downwards, the window dust factor should be less than that of the solar panels?
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mhoward
post Feb 3 2012, 08:08 PM
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Nice later-in-the-day Navcam mosaic on sol 2852

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walfy
post Feb 4 2012, 06:46 AM
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Latest micro, from sol 2852:

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Deimos
post Feb 6 2012, 04:54 PM
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QUOTE (fredk @ Feb 3 2012, 07:25 PM) *
This has gotten me curious - I don't recall ever hearing quantitatively how bad the dust obscuration of pancam is, for example a "dust factor" for the windows, though it must come out of the models. Since pancam usually points horizontally or downwards, the window dust factor should be less than that of the solar panels?


For the arrays, the dust factor is a net transmission--even light that scatters off the array-dust counts if it keeps going down. For Pancam, we actually track it as an optical depth, since the amount of extinction of the direct solar beam can be measured.

You'd think the dust would be less; sometimes it is. The windows can also be more sheltered from cleaning events--although cleaning events for the arrays may be the worst for the cameras. For the first 1+ Mars year, Spirit had negligible build up ion Pancam; Opportunity had low build up. Most of the dust that ever got onto the Pancams did so during the global dust event in the sol 1250 vicinity. It could have happened over sols, or in a sol, or in a single gust. Impossible to say for sure. I doubt the single gust end member, since that seems so dependent on chance (which way was it looking ...). Both rovers got hit, somewhat similarly, although Opportunity was worse (delta tau ~1 vs. ~0.6). There's a paper in the works with the details.
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Pertinax
post Feb 6 2012, 05:34 PM
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Thank you Deimos for your much valued insights!

-- Pertinax
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walfy
post Feb 8 2012, 04:47 AM
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Another new micro, from Sol 2858. Interesting feature in upper-left region.

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