That is true, but at the same time it's bound to only be a few pixels across, and if you take a look at the high-resolution color images, there are a fair number of small pixel effects that creep in. Still, there is the hope, but first we have to find pathfinder, and then we can worry about Sojourner.

My reasoning on those color fringing effects is that they arise due to small stereo effects from the 3 color CCDs being offset vertically. That means that while the central detector (let's say) looks at a given point directly nadir, the other two will have a slightly different viewing angle when the groundtrack brings that point into their view. It should be fairly easy to match up the 3 channels locally if the terrain is approximately flat as the stereo effect differences will be negligible. It's bound to produce drastical fringes on sharp topography, such as that famous Victoria image - you could register correctly for the flat terrain outside OR you could register for the crater floor, but you can't have both. Unless you come up with a 3D terrain model and properly reproject all channels a-la Mars Express imagery.

Remember that the color channels are typically binned 2x2 or even 4x4 pixels, and Sojourner is only a half meter long or so.

I'm betting we'll be able to identify it unless it's moved far from where we last saw it.

Coolest would be to see tracks from a "rock" fading back toward the lander, indicating recent movement.

But it's not likely. Both the lander and rover have been subjected to 5 winters at 20N latitude, colder than Spirit's suffered at Gusev (and with working batteries to keep warm nights).

-Tim.

I would say that effect is too small to be really worth considering - how far apart are the CCD's - a cm, an inch - not much more than that....over a distance of 250km We're talking .000002 to .000011 degrees ( for 1 to 5 centimetre offset...if my very old Trig isn't letting me down)

I agree that the colour fringing is there - but it's down to downsampling imho. I agree with Tim - Tuvas et.al. should be able to fill us in on tha tone.

Doug

I think your reasoning might be wrong. Let's say the camera has a 1 degree FOV (yes, I know HiRISE is a fraction of this) projected on a 10 cm diameter image area at focus. If the two detectors were 5 cm apart, would that not imply around 0.5 degree look difference? It is small (gives around 0.6 meters ground parallax for topography at 70 meters height), but it's still vastly larger an angle than what your simple trigonometric method neglecting camera projection gives. I wonder what the real numbers for HiRISE are.
That said, color binning on the other two filters is a real possibility and quite likely to make things harder. Sojourner won't be resolvable with 1x1 binning and its spectral signature can only be further diluted in 2x2 binning. Assuming they even get the color portion of the swath over the rover. It's definitely possible some of the color fringes in other color images are due to binning, but the fringes do look a bit stereo-ish to me.

EDIT: Okay, I did a quick calculation based on the layout of the CCDs as seen in this document. The greatest stereo separation would be between the blue-green and NIR detectors. Visually, they seem to be separated by about 1 CCD width. Given that the CCD width is 2048 pix and with an IFOV of 1 microrad, that means the stereo look angles should differ by 2 millirad. Applied to Victoria crater depth of 70 meters that gives a parallax shift of 70*0.002 or 0.14 meters. This is well below the HiRISE minimal pixel size of 0.25 m/pix so in this case the color fringing probably was due to binning alone. Severe topography would be noticeably affected, however.

I don't know much about how the camera works, but if the color layers are taken sequentially would the movement of the spacecraft not account for a wider separation? Anyone know the timing of the image sequence? The speed of MRO relative to the ground track? Willing to do the calculations (I'm not. Y'all have made me lazy here).

Doug:

Wasn't it you who posted a pic of what the various hardware components would look like in hirise images?

I'll keep looking, but if you can point me to it before I find it...

Happy holidays, troops!

-Tim.

Yup - 'twas I...

http://www.unmannedspaceflight.com/index.php?showtopic=3495

Specifically

http://www.unmannedspaceflight.com/index.p...ost&id=8409


I was quite pleased how the Viking back-shells turned out.

Doug

Any chance of getting an answer this week?

By my best estimate - Sojourner is estimated to be at...

1,-6...ish...

Rounding to .25 metres....

Mizarkey 1.5m
Rahkir 1.75m
Nix 2.0m
SL 2.5m
AM 3.0m
AlexB 3.5m
ME 3.5m
Tuvas 4.25m
James 5m

Nico the only person with a pin that got bent by Sojourner

Kudos to Mizar and Rahkir.....both damned close

The image is a bit of a mess - a combo of lots of different photoshop layers - but I'm open to interpretation at this stage - it's certainly between Mizar and Rahkir - that's for sure.

Doug

So who won the pool?

See also this release.

This may help a little with your map, Doug -- an unannotated image of the landing site at 300 percent, with a white dot in Sojourner's proposed position.

--Emily

See Emily's blog entry, too.

Doug,

I'd have gone with 2, -6.5, but I guess it's hard to say exactly... I can't beleive how close I was with just using some wierd thing like pi... Congrats to everyone for their close guesses! I didn't know until yesterday where it was myself the location where the little rover was supposed to be, so...

I've tried putting the new topo map over the top of the pool 'sheet'....tried the HiRISE image on the sheet, and the overhead projections from the Pathfinder era just don't match up very well at all.

I always said I'd take just the numbers from the HiRISE imagery and consider the image on the Pool image to just be a 'guide' and not an actual reference..... but it's much harder than I expected to match them up.

Every overlay I've done has put it with Mizar JUST ahead of Rakhir.

If you look at the background image from the Pool itself - (which we said we wouldn't) Mizar got it bloody SPOT ON with Rakhir 2nd, SL 3rd.

I think Mizar gets it - Rakhir very very closely second.
Doug