Spring at Cape York, Sol 2947 (after Greeley Haven) - sol 3040 Options

[Stu]

...and another nice chunka gypsum...

[brellis]

Stu, in that gorgeous pic from your Post 270 -- fascinating that some of the layered rock is vertical, and some looks smeared or shaved horizontally.

[Stu]

Seriously, have you guys found anything on Mars that is uninteresting?

Paolo

Yep..

http://qt.exploratorium.edu/mars/opportuni...FFBRQ2P2935M2M1

[Phil Stooke]

Astro0, I'm going to go out on a limb here and say I don't think your features are arches. This looks like the famous case of O'Neill's Bridge on the Moon. An arcing shadow with an illuminated lump in front of it looks very much like an arch with illuminated terrain behind it. I think the arch shadow should be more forward in the image than it is if it were real.

Phil

[algorimancer]

...how about all those Cal Target? Any ideas on what we can do with them (besides their intended use)?

A bit late to the party (I was on vacation last week), but some time back I realized that, if you use pancam photogrammetry to measure the various linear distances among the corners of the square aluminum base plate of the calibration target, you can use these distances as a means of estimating the changes in temperature of the plate. I even did a quick validation check of this using AlgorimancerPG, but decided that it would take more time than I was willing to spend to do anything of interest with this notion, though it was clear that the changes in dimension predicted due to fairly small changes in temperature were quite accessible with this method, and the fact that you can measure between combinations of corners provides a foundation for some good statistics on the estimates. Is the temperature of the base plate of any real interest to anyone? Considering that it is affected by solar irradiation effects moderated by dust?

[RoverDriver]

That's a good one. I would have to look at what is the actual resolution you can get from the PANCAM. The pointing of the PMA is not very accurate. For example when we do RAT activities we point the PMA to the turret but we do not repoint until all the RAT activity is complete because when we blink the images we do not want to be distracted by the pointing inaccuracies. Another source of error would be the changing sistance from the CalTarget plate and the PMA due to thermal dilation/contraction. Recovering the footprint of the caltarget automatically would be quite difficult but not impossible. For starters one could analyze a few selected images taken early in the morning or late in the afternoon and compare the plate size to images taken at noon. I'm going to leave this exercise to the reader ;-)

Paolo

[djellison]

The Sundial base is 8cm across, and about 215 pixels across at its nearest side. Roughly 0.37mm/pixel - but at this range it's out of focus - the PSF is probably a couple of pixels across.

Aluminium's thermal expansion is about .023mm/meter per degree K. So 0.00184 mm / degree.

Given a 100 degree change - you might see something like 0.2mm change

I would doubt, very much, that it would be visible.

[jamescanvin]

Slipped out of the habit of doing these again, especially seeing how good and how quick Stu is these days.

Need to get back to it ready for MSL, so her is my take of Veladero:

[algorimancer]

I would doubt, very much, that it would be visible.

The trick here is that you can take advantage of measurements along each edge and diagonal of the base, then do pairwise comparisons between these measurements on different dates. So it is not so critical to observe the change on a single edge -- let's say you measure the 4 edge lengths and the 2 diagonals, then scale the diagonal lengths to match the edges (divide by sqrt(2)), so you've essentially got 6 samples of the edge length of this square base on that occasion. Do the same thing on a different occasion. Perform a paired t-test by pairing the equivalent measurements from the 2 occasions. From this you've got a mean change in the edge length, and you can get an associated confidence interval and p-value. The "noise" in the measurements is essentially averaged out, and since you can quantify the noise (since you can get a standard deviation) you can do some good statistics; handily, this sort of measurement error should be very "normal".

Paolo, the pointing of the pancam need only be such that the target is included in both L & R images taken on that occasion, the exact orientation of the pancam is not critical, we're depending on the camera model to identify the xyz coords of each vertex on the plate, then finding the 3D distances between those vertices. Where this gets potentially complicated is if you stop to consider whether the change in temperature also changes the camera model enough to be a problem.

My back-of-envelope estimates at the time I first looked at this suggest that a 100 degree C change in temperature should be easily measurable, and likely even a 20 degree change. Below that it looked "iffy".

[Phil Stooke]

Sharp edges can be located to significantly better than a pixel by appropriate modelling, as is routinely done in astronomy by limb-fitting routines. I don't know the details but they must be readily available. Measuring along the edge, you would be taking advantage of lots of pixels, not just the end points of an edge or diagonal. Every pixel on the edge would contribute to fixing the position.

Phil

[Astro0]

Astro0, I'm going to go out on a limb here and say I don't think your features are arches. This looks like the famous case of O'Neill's Bridge on the Moon. An arcing shadow with an illuminated lump in front of it looks very much like an arch with illuminated terrain behind it. I think the arch shadow should be more forward in the image than it is if it were real.
Phil

One of the reasons I was going with a natural arch was because of the rock feature immediately to the right in that pan of Stu's.
The next rock has hollows in it. So assuming that the 'arch rock' is a piece of that same rock type, then the arches may well be there.
I guess unless they take something higher res and perhaps a different angle (unlikely), we'll never know.
Maybe we'll luck out and get another shot of the area under different lighting conditions.
But it is interesting to look at this area and try to interpret what we are seeing without having the benefit of actually being there.

That's the fun part!

[CosmicRocker]

If you look at it in a false color composite, it seems clear that we are seeing the "blue" soil through two holes in the rock.

[Guest_Oersted_*]

Very convincing Cosmicrocker: definitely looks like arches to me. The rightmost arch even seems to be composed partially of vein material, doesn't it?

[Phil Stooke]

The one on the left is more convincing, certainly. I might believe in that one, eventually! The one on the right looks like it's casting its shadow backwards if it's an arch. I don't find that one very convincing.

Phil

[algorimancer]

Sharp edges can be located to significantly better than a pixel by appropriate modelling

Quite true, and I have seen this used elsewhere in photogrammetry, so in principal the dimensions of the base plate can be determined rather precisely, and its changes in temperature estimated likewise. Estimating temperature changes is a neat trick -- would this be of value in the absence of an external thermometer on the MER rovers, or would it just be a neat thing to do?

Incidentally, if anyone is curious to try this using distances between the corners of the plate (as described in an earlier post) with the AlgorimancerPG application, one difficulty I encountered when I initially looked into this (December 2010) was that many of the images of the calibration target were sub-frame images, rather than the full-frame 1024x1024 images required by the software in its current incarnation. If this is important, the software could be modified to handle sub-frame images in conjunction with the pancam tracking database.

This brings up another issue -- in the absence of an available camera model for MSL, there will likely be a lengthy post-landing delay in revising AlgorimancerPG for MSL.