EPSC Abstracts Vol. 9, EPSC2014-63, 2014 European Planetary Science Congress 2014 EEuropeaPn PlanetarSy Science CCongress c Author(s) 2014

Mini-RF Bistatic Observations of Cabeus Crater

G. W. Patterson (1), D. B. J. Bussey (1), A. M. Stickle (1), J. T. S. Cahill (1), L. M. Carter (2), and the Mini-RF Team (1) 1Johns Hopkins University Applied Physics Laboratory, Laurel, MD ([email protected]), (2) NASA Goddard Space Flight Center, Greenbelt, MD

Abstract received at another. The former provides information on the scattering properties of a target surface at zero Observations of the south polar crater Cabeus phase. The latter provides the same information but indicate anomalous scattering behavior associated over a variety of phase angles. NASA’s Mini-RF with crater floor materials (behavior not observed instrument on the Lunar Reconnaissance Orbiter and with monostatic data). We interpret this behavior to the Arecibo Observatory in Puerto Rico are currently be indicative of the presence of water ice. It is operating in a bistatic architecture (the Arecibo probable that the incidence angle at which the data Observatory serves as the transmitter and Mini-RF was acquired plays a role in the differences observed serves as the receiver). This architecture maintains between bistatic images and with the monostatic data. the hybrid dual-polarimetric nature of the Mini-RF instrument [8] and, therefore, allows for the calculation of the Stokes parameters (S1, S2, S3, S4) 1. Introduction that characterize the backscattered signal (and the The Mini-RF instrument aboard NASA’s Lunar products derived from those parameters). Reconnaissance Orbiter (LRO) is currently acquiring bistatic radar data of the lunar surface in an effort to 3. Observations understand the scattering properties of lunar terrains as a function of bistatic (phase) angle. Previous work, A common product derived from the Stokes at optical wavelengths, has demonstrated that the parameters is the Circular Polarization Ratio (CPR), material properties of lunar regolith can be sensitive S − S ( 1 4 ) (1). to variations in phase angle [1-3]. This sensitivity µC = gives rise to the lunar opposition effect and likely (S1 + S4 ) involves contributions from shadow hiding at low CPR information is commonly used in analyses of phase angles and coherent backscatter near zero planetary radar data [4-7], and is a representation of phase [1]. Mini-RF bistatic data of lunar materials surface roughness at the wavelength scale of the indicate that such behavior can also be observed for €radar (i.e., surfaces that are smoother at the lunar materials at the wavelength scale of an S-band wavelength scale will have lower CPR values and radar (12.6 cm). Among the terrains observed thus surfaces that are rougher will have higher CPR far, we have found the response of materials values). High CPR values can also serve as an associated with the floor of the crater Cabeus to be indicator of the presence of water ice [9]. particularly interesting. Data for the south polar crater Cabeus has been acquired on four occasions and these data cover a 2. Bistatic Operations phase angle range of 0° to 18°. When viewed at near zero phase (Fig. 1), the floor of Cabeus crater shows Radar observations of planetary surfaces provide an enhancement in CPR with respect to surrounding important information on the structure (i.e., materials. This is not apparent in data acquired of roughness) and dielectric properties of surface and Cabeus crater when Mini-RF operated in a buried materials [4-7]. These data can be acquired monostatic mode [10]. Further, when viewed at phase using a monostatic architecture, where a single angles of several degrees, the floor of Cabeus crater antenna serves as the signal transmitter and receiver, shows a suppression of CPR with respect to or they can be acquired using a bistatic architecture, surrounding materials. where a signal is transmitted from one location and 4. Summary References

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