Lunar mare single-scattering, porosity, and surface-roughness properties with SMART-1 AMIE

Abstract

A novel shadowing and coherent-backscattering model is utilized in the analysis of the single-scattering albedos and phase functions, local surface roughness, and regolith porosity of specific lunar mare regions imaged by the AMIE camera (Advanced Moon micro-Imager Experiment) onboard ESA SMART-1 mission. Shadowing due to the regolith particles is accounted via ray-tracing computations for densely-packed particulate media with a fractional-Brownian-motion interface with free space. The shadowing modeling allows us to derive the scattering phase function for a ∼100-μm volume element of the lunar mare regolith. The volume-element phase function is explained by coherent-backscattering modeling, where the fundamental single scatterers are the wavelength-scale particle inhomogeneities or the smallest fraction of the particles on the lunar surface. The phase function of the fundamental scatterers is expressed as a sum of two Henyey-Greenstein terms, accounting for increased backward scattering as well as increased forward scattering. Based on the modeling of the AMIE lunar photometry, we conclude that most of the lunar mare opposition effect is caused by coherent backscattering within volume elements comparable in size to typical lunar particles, with only a small contribution from shadowing effects.

Lunar opposition effect as inferred from Chandrayaan‐1 M3 data

“…[5] Recent analysis of the LRO data for highland regions by Hapke et al [2012] showed that the coherent backscatter enhancement contributes nearly 40% in the UV, increasing to over 60% in the red. A significant contribution of this enhancement to the BOE at a < 10 is also assessed in Muinonen et al [2011]. Thus, several authors concluded that the BOE contains a large component of coherent backscattering.…”

“…A significant contribution of this enhancement to the BOE at α < 10° is also assessed in Muinonen et al . []. Thus, several authors concluded that the BOE contains a large component of coherent backscattering.…”

“…[2] The brightness dependence on phase angle a (phase function f(a)) carries information about the surface composition and microstructure, and therefore photometry is used to study the Moon with telescopic and orbital spectrophotometric surveys [Muinonen et al, 2011;Shkuratov et al, 2011;Hapke et al, 2012]. Among the remarkable photometric properties of the Moon is the strong backscattering or brightness opposition effect (BOE).…”

The Far Ultraviolet Wavelength Dependence of the Lunar Phase Curve as Seen by LRO LAMP

“…To compare the same area covered from multiple observations with different observation geometries and to compare data taken from different instruments, photometric corrections are needed to normalize the reflectance as if it is measured in the same observation geometry. Numerous photometric analyses have been performed on the Moon using the spectral data from ground-based, orbital (i.e., Lunar Orbiter, SMART-1, Kaguya, Chang'E, Chandrayann-1, and LRO itself), and in situ (e.g., the Yutu Rover of the Chang'E-3 lunar mission) observations, covering wavelengths from UV, visible (VIS), and near infrared (NIR; Besse et al, 2013;Buratti et al, 2011;Hapke et al, 2012;Hicks et al, 2011;Hillier et al, 1999;Jin et al, 2015;Kieffer & Stone, 2005;McEwen, 1996;Muinonen et al, 2011;Robinson & Jolliff, 2002;Sato et al, 2014;Wilkman et al, 2014;Wu et al, 2013;Yokota et al, 2011). Notable FUV observations in particular, prior to LRO, have been performed by Apollo-17 Ultraviolet Spectrometer, Hopkins Ultraviolet Telescope, and Galileo-Ultraviolet Spectrometer (Hendrix, 1996;Henry et al, 1995;Lucke et al, 1976).…”

Asteroid Photometry

“…Further numerical modeling techniques were developed by Muinonen et al (2011) and Wilkman et al (2014a) with the lunar mare data acquired by SMART-1/AMIE. They employed a numerical approach to solve for the shadowing function resulted from the surface roughness using ray-tracking technique with the LS sphere as the auxiliary tool.…”