Multiply overlapping Mars imagery, Looking for 5 or more images of same spot Options

[elakdawalla]

A reader (Bill Green, a retired JPL guy who helped develop MIPL) alerted me to a recent article in IEEE Computer, "Aerial Computer Vision for a 3D Virtual Habitat" (subscription only, I'm afraid) that describes a method that they refer to as the "high overlap paradigm" for developing extremely high-resolution digital elevation models by using many aerial photos from many look angles. I contacted the paper's first author, Franz Leberl, to see if he was interested in attempting to apply his method to images from Mars, and the answer was: Yes, he's very interested. So my question is, where on Mars do we have sets of highly overlapping images? Here's what Leberl said he needed:

For a fully automated process that associates a surface elevation with each pixel, we need 5 or so images of each terrain point. If it is more, that is even better. If you have a focal length and location of the principal point, that would be helpful also. We do not need any data about the camera positions; but if you had such data, we would want to compare our results to those you have. And if you also had previous results in the form of a digital surface model created by traditional two-image stereo, we could use this as well for an analysis and comparison.

Can the hivemind of UMSF help me connect Leberl with the data he would need to make some seriously detailed DTMs?

[tharrison]

CTX images the Spirit and Opportunity landing sites about once a month, baring unforeseen complications like safe mode, so there are about 30 overlapping images of each of them in the PDS at the moment. We also have about 800 sites that we monitor at a frequency from weekly to every few months for things like changes in surface features (i.e. dust devil tracks), gullies, dust-raising events, etc., so if a site that is more diverse topographically than the MER landing sites would be better for Leberl's method, I can look for one.

EDIT: Completely forgot about MSL—there are a bunch of overlapping CTX images of the candidate MSL landing sites, particularly of Gale.

If most/all of the images were obtained with the spacecraft directly (or close to directly) above the landing site the viewing geometry might not be different enough from image to image. For traditional stereo I have found that as an absolute minimum the angles must differ by ~5 degrees with ~30 degrees being optimal for the software I'm using (example: subspacecraft longitude 0 degrees in one image and 30 degrees in another one). The lighting probably needs to be similar as well.

For CTX, we've found that the minimum roll angle difference needs to be 9° for anaglyphs, but for DEMs, the larger the roll is, the better. HiRISE prefers angles >15°. When we acquire stereopairs, we try to get both images in the pair within ~4 months of each other (or at the same time the following Mars year) to make sure the illumination conditions are similar. Of course, both the illumination conditions and angle difference needed for optimal DEMs depends on the topography of that area.

Hmm. MRO got just the one image of Phoenix' descent, right? Too bad there wasn't another taken a couple of seconds later. Lots of relative motion/look angle change happening there. I wonder if this method could generate a really detailed look at the chute, which would presumably be useful for future chute engineering.

With CTX we can't command images less than 15 seconds apart (I'm not sure if this is the same for HiRISE, but I think they require more time between images due to the sheer file size). Taking an image of the same place on the same orbit would also require some special maneuvering of the spacecraft, because we typically only slew rather than pitch and yaw (although every so often MRO is pitched for some CRISM observations).