S-band Observations of the Aristarchus Plateau from the LRO Mini-RF Instrument

Abstract:

The Aristarchus Plateau on the lunar nearside is characterized by a variety of interesting geological features. The plateau itself is surrounded by flood basalts of Oceanus Procellarum, is oddly shaped, and has extreme high and low reflectance areas. The rille, Vallis Schröter, cuts through the plateau, which is also nearly covered by a large pyroclastic deposit thought to be between 20-30m thick and dominated by low-Ti glass spheroids. A set of streaks, which are generally radial to Aristarchus crater, have been observed in multiple wavelengths (e.g., optical, radar) across the plateau.

The Mini-RF instrument aboard NASA’s Lunar Reconnaissance Orbiter (LRO) is a hybrid-polarized, dual-frequency synthetic aperture radar (SAR) that operates in cooperation with the Arecibo Observatory (AO) to collect S-band (12.6 cm wavelength) bistatic radar measurements of the lunar nearside and poles. For each observation, the surface is illuminated with a circularly polarized, chirped signal that tracks the Mini-RF antenna boresight intercept on the surface of the Moon. The Mini-RF receiver operates continuously, separately receiving the horizontal and vertical polarization components of the signal backscattered from the lunar surface. In this architecture, the incidence angle varies as a function of the observation geometry and the data have a spatial resolution of ~100 m in range and ~2.5 m in azimuth. This can vary from one observation to another as a function of the viewing geometry. The data are coherently processed onto grids with a spacing of 4 m along track and 25 m cross track. For analysis, they are then incoherently reduced to a uniform 100 m grid yielding approximately a 25-look average for each sampled location.

Four Mini-RF S-band bistatic observations of the Aristarchus Plateau, spanning a range of bistatic angles, have been acquired over the course of 2 different observation campaigns. These data are providing unique insights into the local geology, related to cratering and volcanic processes.