Lunar Photometry From Clementine Multiangular Data: Analysis Of Hapke Parameters Estimate And Im- plication For Upcoming Smart-1 Spot-Pointing DatA

Introduction: The analysis and interpretation of reflectance dependence on illumination / observation geometry is widely used in planetary research. Two main issues are generally addressed in this field: 1) the choice of an appropriate quantitative photometric model describing the physics of the scattering by regolithic surfaces; 2) when dealing with orbital observations, how extensive should the photometric orbital survey be for a reliable derivation of the photometric function parameters? In this study we explore how well constrained is the determination of photometric function parameters using: 1) the widely used Hapke photometric model and 2) extensive set of spotpointing observations provided by Clementine over the Reiner-Gamma region on the Moon. Reiner-Gamma spot-pointing photometry: The well-documented photometric phase function is derived from spot-pointing observations over the ReinerGamma formation [1, 2, 5] known as a photometrically unusual “swirl” feature. Here, we consider the southern bright part of the swirl and the adjacent dark mare basalts southward region (inset in Fig. 1). The diversity of phase curves (for wavelength 900 nm) is also shown on Fig. 1.: blue (for the brightest part of the swirl), green – for the darkest mare basalt area and red one for the swirl part with a lower reflectance. These data offers the possibility of deriving phase curves in the range 10-80 degrees, with observations made both in and out of the principal scattering plane.