Quantification of shape and texture for wind abrasion studies: Proof of concept using analog targets

The surface topology, surface area, and volume of rock simulant targets abraded in a boundary layer wind tunnel are quantified using results from a laser scanner with a spatial resolution of ~300 µm, an order of magnitude improvement over previous measurement techniques. Laplacian smoothing enables delineation of topography at even finer scale. The surface area to volume ratio generally increases at a rate greater than log (2/3), indicating roughening with time. Sub-millimeter- to millimeter-scale changes provide information on the relationships between natural abrasion and the resulting textures. Pit size frequency statistics reflect a balance between pit production from fresh impacts and net loss when two or more pits merge into a single pit. Most targets show a rollover in curves, whereby the number of pits smaller than a few hundred µm in size decrease with continuing abrasion whereas the abundance of larger pits increases. This is evidence that smaller pits merge into larger ones over time. There is a weak correspondence between elongation and diameter, with larger pits tending to have a more elliptical shape, especially among more abraded samples. For angled front faces and with increasing abrasion, pits tend to dig into the targets at an angle greater than that of the facet. Most facets have a greater fraction of elongated pits aligned downwind at the conclusion of abrasion compared to the start, with variable trends at intermediate stages. Profiles of layered targets show a progressive retreat of the front face, with angled targets developing stair-stepped topography, with 60° angles showing the greatest development and 30° the least. Natural abraded rocks in terrestrial desert environments and probably on Mars show many of the textural characteristics documented in the wind tunnel rock simulants. Correlation of these parameters promises to provide information on integrated abrasion duration, offering a new tool for constraining weathering history on Earth and Mars.