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LRO Mini-RF Bistatic Observations of Cabeus Crater Revisited

Presentation #101.08 in the session Moon & Earth I (Oral Presentation)

Published onOct 23, 2023
LRO Mini-RF Bistatic Observations of Cabeus Crater Revisited

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 has collected data in a bistatic architecture – a supporting ground-station transmits and Mini-RF/LRO receive the backscattered signal – since 2011. These data provide a means to characterize the scattering properties of the upper meter of the surface, in particular as a function of bistatic angle, and have been collected to address a variety of LRO science objectives. For example, water ice can exhibit a strong response at radar wavelengths in the form of a Coherent Backscatter Opposition Effect (CBOE) and the circular polarization ratio (CPR) of the returned data can be a useful indicator of such a response. Although this effect has been observed using ground-based radar observatories on the floor of some Mercurian polar craters, icy moons, and the Martian South Polar Layered Deposits, it has not been observed in the lunar south polar region. This result was supported by initial Mini-RF and Mini-SAR (Chandrayaan-1) monostatic observations of Cabeus crater (84.9°S, 35.5°W; 98 km dia.). However, later Mini-RF S-band bistatic observations showed an opposition response is present in the crater floor that is distinct from what is observed for the floors of nearby, similar-sized craters. A similar response has not been observed, though, with Mini-RF X/C-band bistatic data of the floor of Cabeus. This could indicate that, if water ice is present in Cabeus crater floor materials, it is buried beneath ~0.5 m of regolith that does not include radar-detectible deposits of water ice.

Since these observations were acquired, the Mini-RF instrument has completed an extensive campaign to better understand the calibration of its X/C-band channel and is nearing completion of a similar effort at S-band. In addition, recent work to account for the influence of geometric effects related to local topography on the returned signal for Mini-RF monostatic data have yielded new data products that reduce non-geologic systematic influences on the returned radar power and polarimetry (1). Here we re-examine observations of Cabeus crater, in light of these developments.

(1) Fassett, C.I. et al. (2023) LPSC 54, abs. no. 1564

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