Icarus 202 (2009) 393–413 Contents lists available at ScienceDirect Icarus www.elsevier.com/locate/icarus Photometric anomalies of the lunar surface studied with SMART-1 AMIE data V. Kaydash a,* , M. Kreslavsky b , Yu. Shkuratov a , S. Gerasimenko a , P. Pinet c , J.-L. Josset d , S. Beauvivre d , B. Foing e , and the AMIE SMART-1 Team a Astronomical Institute of Kharkov National University, Sumskaya 35, Kharkov 61022, Ukraine b Earth and Planetary Sciences, University of California - Santa Cruz, 1156 High St., Santa Cruz, CA 95064, USA c UMR 5562/CNRS/Toulouse III University, OMP (Midi-Pyrenees Observatory), 14 Av. E. Belin, 31400 Toulouse, France d Space Exploration Institute, Case postale, CH-2002 Neuchâtel, Switzerland e ESA/ESTEC, Keplerlaan 1, 2201 Noordwijk, The Netherlands article info abstract Article history: Received 31 October 2008 Revised 12 March 2009 Accepted 15 March 2009 Available online 19 March 2009 Keywords: Moon, surface Photometry Cratering Regoliths We present new results from the mapping of lunar photometric function parameters using images acquired by the spacecraft SMART-1 (European Space Agency). The source data for selected lunar areas imaged by the AMIE camera of SMART-1 and the data processing are described. We interpret the behavior of photometric function in terms of lunar regolith properties. Our study reveals photometric anomalies on both small (sub-kilometer) and large (tens of kilometers) scales. We found the regolith mesoscale roughness of lunar swirls to be similar in Mare Marginis, Mare Ingenii, and the surrounding terrains. Unique photometric properties related to peculiarities of the millimeter-scale regolith structure for the Reiner Gamma swirl are confirmed. We identified several impact craters of subkilometer sizes as the source of photometric anomalies created by an increase in mesoscale roughness within the proximal crater ejecta zones. The extended ray systems reveal differences in the photometric properties between proximal and distant ejecta blankets. Basaltic lava flows within Mare Imbrium and Oceanus Procellarum indicate higher regolith porosity for the redder soils due to differences in the chemical composition of lavas.  2009 Elsevier Inc. All rights reserved. 1. Introduction The observable optical properties of the lunar surface are formed in the uppermost layers of the regolith. The interaction of light with the regolith includes several physical phenomena such as single scattering, incoherent multiple scattering between parti- cles, mutual shadowing of particles, coherent multiple backscatter enhancement at opposition, and effects of macroscopic roughness (e.g., Hapke, 1993). For given illumination/observation geometry, the relative contribution of all those effects is controlled by the physical properties of the regolith, such as the transparency of re- golith particles, the shape and compaction of them, everything that governs the regolith structure at different scales from comparable to the wavelength of the incident light to the spatial resolution of observations. Therefore, observable variations of photometric prop- erties contain some information about the regolith structure. To describe the bidirectional reflectance variations R on the lunar surface at arbitrary observation/illumination geometry, the photometric function F , given by R (i , ε, ϕ) = R 0 F (i , ε, ϕ), is used. In this equation i is the incidence angle, ε is the emission or view- * Corresponding author. E-mail address: vgkaydash@gmail.com (V. Kaydash). ing angle, ϕ is the azimuth angle (the angle between the plane of incidence and the plane of emergence), and R 0 is the reflectivity determined at a specific angle geometry, e.g., R 0 = R (0, 0, 0) (e.g., Hapke, 1993). For some applications another set of angles (photo- metric coordinates) are more convenient to use: the photometric longitude γ , the photometric latitude β , and the phase angle α. For the Earth-based observations of the Moon at large or moderate phase angles, β , γ are close to the selenographic latitude and lon- gitude. The relationships between (i , ε, ϕ) and (α,β, γ ) are (e.g., Hapke, 1993): cos α = cos ε cos i + sin ε sin i cos ϕ cos γ = cos ε/ cos β cos β =  (sin(i+ε)) 2 -(cos ϕ 2 ) 2 sin 2ε sin 2i (sin(i+ε)) 2 -(cos ϕ 2 ) 2 sin 2ε sin 2i+(sin ε) 2 (sin i) 2 (sin ϕ) 2        (1) and cos i = cos β cos(γ - α) cos ε = cos β cos γ cos ϕ = cos α - cos i cos ε sin i sin ε        . (2) The dependence of the photometric function F on the photo- metric coordinates can be presented as follows (e.g., Hapke, 1993): F (α,β, γ ) = f (α) · D(α,β, γ ), where f (α) is the phase function 0019-1035/$ – see front matter  2009 Elsevier Inc. All rights reserved. doi:10.1016/j.icarus.2009.03.018