2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 290-2
Presentation Time: 8:30 AM


STICKLE, Angela M., Applied Physics Laboratory, Johns Hopkins Unviersity, 11100 Johns Hopkins Road, MS200-W230, Laurel, MD 20723, PATTERSON, G. Wesley, Applied Physics Laboratory, Johns Hopkins University, 11101 Johns Hopkins Rd, Laurel, MD 20723, BUSSEY, Ben, Applied Physics Laboratory, Johns Hopkins University, 11100 Johns Hopkins Rd, Laurel, MD 20723 and CAHILL, Joshua T.S., Space Department, The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723

The Miniature Radio Frequency (Mini-RF) instrument flown on NASA’s Lunar Reconnaissance Orbiter (LRO) is a Synthetic Aperture Radar (SAR) with a hybrid dual-polarimetric architecture. The returned information can be represented using the classical Stokes parameters (S1, S2, S3, S4), which can be used to derive a variety of useful products to characterize the radar scattering properties of the lunar surface. One such product, the circular polarization ratio (CPR), is commonly used in analyses of planetary radar data and is a representation of surface roughness on the order of the radar wavelength (e.g., ≤ meter scale features).

Comparing radar scattering properties as a function of radius reveals information about ejecta emplacement in mare craters. Here, we examined the scattering properties of the ejecta blankets for 10 young, fresh, mare craters with diameters ranging from 7–55 km. Average CPR profiles were calculated as a function of radius for each crater, beginning at the crater rim and extending 100-200 km. Observations reveal that CPR profiles adjacent to craters may provide insight regarding subsurface layering in mare regions. For many craters, the CPR drops rapidly near the crater rim, but then plateaus for a short distance before dropping again to the lunar background surface scattering levels; these shelves neither begin nor end at the same relative radius from the crater rim. These data suggest that measures of lunar crater ejecta CPR can isolate the surface expressions of discrete layering within mare terrain.

The ejecta blanket of Kepler crater provides a clear example. Hörz et al. [1983] estimate that the dominant source depth for primary ejecta within the continuous ejecta blanket is <0.01 times the crater diameter. To a first order, the depth from which material in the continuous ejecta blanket (within approximately 1 crater radius from the rim where a high CPR is seen) is excavated at Kepler crater would then be approximately 300 m, consistent with the approximate depth of the layering observed in LROC NAC images. Thus, a CPR profile of Kepler may reveal a discrete subsurface layer that was emplaced at the surface during the impact process.