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

¹ Department of Physics, PO Box 64, 00014 University of Helsinki, Finland
e-mail: karri.Muinonen@Helsinki.Fi
² Finnish Geodetic Institute, PO Box 15, 02431 Masala, Finland
³ Instituto de Astrofísica de Canarias, Calle vía Láctea, 38205 La Laguna (Tenerife), Spain
⁴ Space Exploration Institute, Case postale 774, 2002 Neuchâtel, Switzerland
⁵ Micro-cameras & Space Exploration, Puits-Godet 10a, 2000 Neuchâtel, Switzerland
⁶ IRAP/Observatoire Midi-Pyrénées/CNRS/Université Toulouse III, 14, Avenue Edouard Belin, 31400 Toulouse, France
⁷ European Space Agency ESA, ESTEC/SRE-S, postbus 299, 2200 AG Noordwijk, The Netherlands
⁸ European Space Agency ESA, ESAC/SRE-OS, Apdo. de correos 78, 28691 Villanueva de la Cañada, Madrid, Spain

Received: 10 November 2010
Accepted: 19 April 2011

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.