Availability of LRO Mini-RF S- and X/C-band Data for Landing Site Characterization

NASA’s Mini-RF instrument on the Lunar Reconnaissance Orbiter (LRO) is a hybrid-polarized, dual-frequency synthetic aperture radar (SAR) that operates at S- (12.6 cm) and X/C-band (4.2 cm) . Mini-RF initially operated as a monostatic system – i.e., the instrument antenna transmitter and receiver co-located. A transmitter anomaly led to Mini-RF transitioning to a bistatic architecture – i.e., transmitting from Arecibo Observatory (AO) or the Goldstone deep space communications complex antenna DSS-13 and receiving at the LRO spacecraft. These data can be used to characterize the radar scattering properties of the lunar surface and near subsurface at depth scales < 1 cm to > 3 m and are valuable for identifying landing site hazards and constraining the dielectric properties (including volatile content) of regolith within landing regions of interest.

Monostatic data include both 150 m (baseline) and 30 m (zoom) resolution modes. The majority of these data were collected at S-band in zoom mode and cover >95% of the poles. Controlled mosaics of derived Stokes products for both poles have been produced and allow characterization of permanently shadowed regions (PSRs) at a resolution of 30 m. Where available, monostatic coverage in X/C-band zoom and S- and X/C-band baseline modes provide additional wavelength coverage and sensitivity.

Bistatic data include both S- and X/C-band observations and have a processed resolution of ~100 m in range and 2 m in azimuth. The range resolution can vary from one observation to another, as a function of the viewing geometry, and the data are averaged in azimuth to provide a spatial resolution of 100 m, yielding a 50-look statistical average for each pixel. This architecture allows examination of the scattering properties of a target surface for a variety of bistatic angles. Laboratory data and analog experiments have shown that the scattering properties of lunar materials can be sensitive to variations in bistatic angle. Although Mini-RF is not currently collecting S-band bistatic data, X/C-band acquisition is ongoing.

The ability of radar to interrogate the lunar subsurface provides a unique perspective with which to explore geologic processes and their influence on regolith development (including volatile content). Recent and ongoing Mini-RF research that can be leveraged to support the characterization landing sites include: production of orthorectified monostatic S-band data that provide improved understanding of surface scattering properties; development of modeled, meter-scale radar rock abundance data at S-band zoom resolutions (i.e., 30 m); characterization of volatile potential associated with polar craters and PSRs (including on seasonal timescales); identification of secondary crater populations within polar craters of interest; and direct analyses of NASA Artemis III landing zones and other sites of interest. These data provide fundamental information on the structure and dielectric properties of the lunar surface and buried materials within the penetration depth of the system(s) and have the advantage of being sensitive to the physical form of water ice. The continued operation of Mini-RF provides unique capabilities for addressing science and engineering objectives of the Artemis, CLPS, and international missions supporting the continued exploration of the Moon.