[X] My Assistant

[PDP8E]

Back to the Backshell

SUMMARY - I will present a super-resolved image of the Opportunity backshell/parachute and make a very initial analysis of the state of the backshell

INTRO - On Sol 66 of the Opportunity mission, the rover took 33 pictures of the backshell and parachute from a distance of about 1440 meters. I obtained the radiometrically calibrated IMG files and converted them to the lossless, large, but easy to manipulate BMP format. The original image sizes were 100x200 pixels.

IMAGE STACKER - In order to super resolve at the sub-pixel level (and not just merely improve the signal to noise ratio) then I needed to stack the images onto a finer background matrix. To do this I wrote a stacker in C++. I used one photo as the master that all others would be stacked against. I projected the master onto the finer backgound pixel grid that was nine times finer than the original image size; that is, the 100x200 pixel images [20,000 bytes] became 300x600 [180,000 bytes]).

I identified a 16x64 rectangle (1024 bytes) on the background projected master that contained high contrast (both bright and dark pixels; part of the backshell and part of the ground). The stacker moved the new image around the master and subtracted one image from the other in the ‘alignment rectangle’ area (we are left with 1024 ‘differences’). I took the mean of the 1024 differences, subtracted the mean from each of the 1024 diffs, and found the standard deviation of the whole rectangle (after each pixel by pixel nudge). The program registered each picture to the master by looking for the smallest standard deviation in that rectangle, 32 images were sub-pixel aligned in this manner.

I then used a cheap commercial deblur software package to tweak the soft edges (FixerLabs). The result are Images 1, 2, 3 (2 and 3 are just increased brightness, contrast)

FIRST APPROXIMATION ANALYSIS – The backshell is broken.

HiRise indicates that the backshell slammed onto the surface and created a persistent crater as seen from orbit. The backshell has a checkerboard pattern of light and dark areas. The dark areas are open seams of the backshell.

If you look at Opportunity’s ‘heatshield’ from HiRise it also has light areas with one dark stripe. From ground truth we know that is where the heatshield is broken open.

By contrast, Spirit’s backshell is homogenously light, there is no apparent or persistent impact crater and the parachute appears to have gently settled out of the sky in an inflated configuration. The Spirit backshell is not broken.

In the super resolved image of Opportunity’s backshell you can see ripped open seams (top left side of the backshell), that appear as dark points. The resulting open seam correlates to one of the seams on the HiRise image of the backshell.

In the super resolved image there is a faint circular pattern on the camera facing surface of the backshell. It appears to be either (1) a massive inward dent, (2) we are looking inside the backshell through another (larger) ripped seam, (3) this is debris from inside the backshell flopped outward (maybe the internal plate that holds the parachute canister).

Opportunity’s backshell in the HiRise image is distinctly ‘out of round’ (by contrast see Spirit’s backshell).

When you vertically exaggerate the super resolved image of Opportunity’s backshell, you will see the result of the impact on the hull. The triangular shape of the backshell should just be steeper but still remain distinctly triangular. The top of the hull has been broken open and the panels have been ripped outward. It is almost as if the circular plate near the top of the backshell (that holds the parachute canister and the lowering bridle for the rover) has been wrench out (or around) by the impact.

There is a small rock that has been super resolved, just to the right of the backshell. The parachute correlates well to the HiRise image (especially the bright white lump). The dark spots near the parachute are shadows or maybe rocks/debris thrown up by the impact. The dark areas appear as shadows in the HiRise image

The impact crater has also been resolved. It starts as the dark streak to the left of the backshell (which is not a long backshell shadow, since it is only 2:30 in the afternoon). The crater ends at the light triangular pattern under the left side of the backshell hull. That pattern is the crater wall.


Compare these images to the PanCam site super-res:
http://marswatch.astro.cornell.edu/pancam_...superres_4x.tif


Cheers!

 SR_OPBS_IMG_1.bmp ( 176.84K ) Number of downloads: 1050
 SR_OPBS_IMG_2.bmp ( 176.84K ) Number of downloads: 881
 SR_OPBS_IMG_3.bmp ( 176.84K ) Number of downloads: 962

[djellison]

I think the assumption is that in the case of MERB - the residual RAD firing at bridal cut flung the backshell and chute in a westerly direction, but the chute did not re-inflate. They followed an arc, impacting at very high speed, thus breaking the backshell and creating quite an impact. Whereas, if you look at the HiRISE imagery of both MERA and Pathfinder, you can see that the backshell is sat, upright, on the surface, with the chute to one side suggestive of the chute reinflating (at least partially) between that residual RAD impulse, and impact.

GREAT results - there were a LOT of super-res images taken while Opportunity was parked up with IDD trouble around Olympia (West end of Erebus) - if you're looking for food for your process, that's the place to go


Doug