Photoclinometry Measurements of Meter-Scale Slopes in Support of the 2003 Mars Exploration Rovers

Details Photoclinometry Measurements of Meter-Scale Slopes in Support of the 2003 Mars Exploration Rovers Photoclinometry Measurements of Meter-Scale Slopes in Support of the 2003 Mars Exploration Rovers

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.p22a0393b&link_type=abstract

American Geophysical Union, Fall Meeting 2002, abstract #P22A-0393

Other

5464 Remote Sensing, 5470 Surface Materials And Properties, 5494 Instruments And Techniques, 6225 Mars, 6297 Instruments And Techniques

Scientific paper

Evaluating meter-scale slopes on the Martian surface is an important activity for ascertaining the safety of potential landing sites and for characterizing terrains and their formation and modification processes. Our efforts to date have concentrated on candidate ellipses for the 2003 Mars Exploration Rovers (MER). Qualitative assessments of meter-scale roughnesses from Mars Orbital Camera (MOC) images can be misleading. MOC images tend to be stretched to maximize contrast, so depending on the overall scene content any area may or may not look rough. MOC stereo provides quantitative slope data, but covers only narrow slivers of the surface. The photoclinometry technique that we use, in spite of its limitations, is the only way to quantify slopes at meter-scales over a large number of MOC NA images. Although often limited by uncertainties in atmospheric contributions and albedo variations, it offers excellent upper limits to the slopes. Our technique measures a slope (in the down-sun direction) for each pixel in an image. From these measurements we obtain an average slope and an RMS slope deviation. For landing sites the average slope should be zero, but the RMS slope deviation is a measure of the roughness of the surface and is a critical number used in MER lander survival simulations. To estimate the precision of our technique, we have applied it to MOC images of the Viking and Pathfinder landing sites. Our measurements yield an upper limit RMS slope between 4 and 8 degrees for all three sites at the 2 meter length scale, in agreement with other measurements. For the potential landing sites, the upper limit RMS slope is 2 to 8 degrees for Athabasca Valles, about 8 degrees at Elysium Planitia, 4 to 8 degrees for Eos Chasma, 4 to 10 degrees at Gusev Crater, 2 to 10 degrees for the Hematite Area, and 4 to 8 degrees in Isidis Planitia. Individual slope measurements are not very sensitive to the choice of photometric function, and do not suffer from cumulative errors (like extracting topographic profiles via photoclinometry). Slope values are very sensitive to the choice of offset correction (atmospheric haze plus scattered light in MOC). We can estimate the minimum offset value from the darkest values in an image, and lower-resolution topographic data can also provide a constraint.

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