SURFACE ROUGHNESS PATTERNS IN LUNAR SOUTH POLE-AKIN BASIN

Quantitative analysis of roughness reveals surface textures on the Moon. We use co-occurrence roughness textures, a method developed for analyzing volcanic deposits, to interrogate digital elevation models (DEMs) derived from the Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC). The Bhabha Eastern Plain is located in central South Pole-Akin Basin (SPA) near ancient volcanic deposits and units that may be related to the original impact-melt generated during the formation of the basin over 4 billion years ago.

To process the data, DEMs are converted to local roughness maps by fitting 6-meter planes to the surface in a grid. The standard deviation of the residuals (DEM elevations minus planer elevations) is our measure of surface roughness (i.e., a de-trended RMS roughness). Co-occurrence statistics are then used to identify patterns in roughness.

Or preliminary analysis of a small (10 km²) patch of this region reveals that plains have homogenous roughness distributions as do crater floors. Fresh crater rims have increased entropy (randomness) in the roughness data while comparatively older crater rims have more homogenous roughness distributions. This indicates that over time small impacts disrupt the morphology of impact crater rims adding order to the deposits. Furthermore, circular high-entropy regions are evident in the results that are not obvious in the original meter-scale NAC data. These regions are likely impact crater rims that have been near-completely erased but retain a subtle roughness signature. These signatures are likely the result of boulder rings that at the 6 m pixel scale appear random but taken together reveal an otherwise hidden crater.

This work indicates that roughness patterns, a tool developed for volcanic mapping on Earth, is a critical tool for mapping degraded impact structures on the Moon.