Detection and Characterization of Rocks and Rock Size-Frequency Distributions at the Final Four Mars Science Laboratory Landing Sites

Background: Shadows cast from rocks in High-Resolution Imaging Science Experiment (HiRISE) images were used during Phoenix landing site selection to measure the diameter and height of rocks in the northern plains using an automated rock detector algorithm that fits ellipses to the shadows and cylinders to the rocks. Results show that the size-frequency distribution of rocks >1.5 m diameter are fully resolvable in HiRISE images and follow the same exponential models developed from lander measurements of smaller rocks distributions at the landing sites. Method: Greater image complexity at prospective Mars Science landing sites required improvements in shadow segmentation, which included 4 blind deconvolution steps to sharpen the rock shadows and sectional image processing. Shadows of non-rocks were removed by fitting model size-frequency distributions to rocks 1.5-2.25 m diameter in 450 m bins, all of which significantly improved the rock detection algorithm. Conclusion: Rock distributions measured from orbit and the ground for the Phoenix landing site follow the same exponential model size-frequency distribution (within 1% rock abundance), further validating accurate extrapolations of rock abundance using HiRISE images. Size-frequency distributions determined in 450 m HiRISE bins matched model distributions and indicates average rock abundances of 5.4±2.6%, 3.9±3.0%, 0.3±1.1% and 3.3±2.7% at the Mars Science Laboratory (MSL) Eberswalde, Gale, Holden and Mawrth final four landing sites, respectively. MSL landing simulations indicate the probability of failure due to landing on a rock higher than the rover belly pan is 0.30%, 0.17%, 0.03% and 0.08% at Eberswalde, Gale, Holden, and Mawrth, respectively. Because these probabilities are less than the engineering requirement of <0.5%, all sites are safe with respect to rocks and rocks were not a factor in landing site selection.

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