Global Mini-RF S-Band Observations of the Moon

The Lunar Reconnaissance Orbiter (LRO) carries with it NASA's Mini-RF instrument, which has returned high-quality radar of all regions of the Moon. Mini-RF is a hybrid-polarized, side-looking, synthetic aperture radar that showcases the power of radar science in a small package transmitting and receiving in both S-band (12.6 cm) and X-band (4.2 cm) [1, 3]. Unique observations Mini-RF has collected in S-band (sensitive to materials 0.1 to 1.26 meters in size and depth) include near complete coverage of the lunar North and South Poles (~99% coverage) and ~67% of the lunar globe with relatively unrestricted viewing geometries [2, 4]. This includes never before observed radar coverage of western Orientale and the farside Feldspathic Highlands and South Pole Aitken basin terranes (FHT and SPA, respectively). These regions are not visible from Earth-based radar observatories such as, Arecibo Radar and Green Bank Telescopes [2]. Here, we present orthorectified Mini-RF global S-band products at 100 m/pixel that augment previous Earth-based and orbital (i.e., Chandrayaan-1's Mini-SAR) radar data sets of the Moon [5-9]. An often-used radar analysis parameter is the circular polarization ratio (CPR), which is defined as the ratio of the same sense relative to the opposite sense polarized returns. Specular echoes from the lunar surface that are smooth at wavelength scales will return low CPR values, while scattering from rough surfaces generate CPR values approaching one or greater. Another analysis parameter employed by [5] and used here to corroborate CPR interpretations referred to as an m-chi decomposition, leverage three physical parameter measurements in a single RGB image for analyses. These paremeters include double bounce backscatter (db; e.g., dihedral, volume ice), randomly polarized materials (vs; i.e., volume scattering), and single bounce backscatter (bs; e.g., Bragg scattering). Mini-RF mapping of the global Moon suggest a wide range of CPR values (0 - 1.5). Some lunar terranes, such as the Procellarum KREEP Terrane (PKT), are easily differentiated by low backscatter and are spatially consistent with previous terrane designations based upon composition and topography [6, 7]. However, farside SPA and FHT are not as easily differentiated and have relatively similar scattering properties. Western hemisphere scattering analyses suggest relatively uniform Bragg scattering that suggest a regolith consisting of a high density of wavelength scale scatterers blanketing most features. Volumetric scatterers of this hemisphere dominantly reflect regolith depth and maturation and suggest thin, smooth, and Ti-rich mare-like scattering characteristics that reach beyond normal western-PKT boundaries and into eastern and southern Orientale Basin proper and extend to continuous and discontinuous ejecta deposits. Double bounce measurements, a low proportion of the global radar return, refine volumetric scattering interpretations of the western hemisphere suggesting wavelength scale blocks are dominantly confined to the western side of Orientale and Copernican craters of the FHT. [1] Nozette et al., SSR 150, 285 (2010); [2] Campbell et al., IEEE TGRS 45, 4032 (2007); [3] Chin, SSR, (2007); [4] Raney, GRSL. 3, 317 (2006); [5] Raney et al., in LPSC. (2012); [6] Jolliff et al., JGR-Planets 105, 4197 (2000); [7] Wieczorek, Phillips, JGR-Planets 105, 20417 (2000)