Photometric properties of Mars soils analogs

Abstract

[1] We have measured the bidirectional reflectance of analogs of dry, wet, and frozen Martian soils over a wide range of phase angles in the visible spectral range. All samples were produced from two geologic samples: the standard JSC Mars-1 soil simulant and Hawaiian basaltic sand. In a first step, experiments were conducted with the dry samples to investigate the effects of surface texture. Comparisons with results independently obtained by different teams with similar samples showed a satisfying reproducibility of the photometric measurements as well as a noticeable influence of surface textures resulting from different sample preparation procedures. In a second step, water was introduced to produce wet and frozen samples and their photometry investigated. Optical microscope images of the samples provided information about their microtexture. Liquid water, even in relatively low amount, resulted in the disappearance of the backscattering peak and the appearance of a forward-scattering peak whose intensity increases with the amount of water. Specular reflections only appeared when water was present in an amount large enough to allow water to form a film at the surface of the sample. Icy samples showed a wide variability of photometric properties depending on the physical properties of the water ice. We discuss the implications of these measurements in terms of the expected photometric behavior of the Martian surface, from equatorial to circum-polar regions. In particular, we propose some simple photometric criteria to improve the identification of wet and/or icy soils from multiple observations under different geometries.

On the effect of emergence angle on emissivity spectra: application to small bodies

“…Beck et al (2012) measured the bidirectional reflectance phase function of several meteorite samples in the VIS spectral range. Pommerol et al (2013) measured the bidirectional reflectance of Martian analogues in dry, wet, and frozen conditions over a wide range of phase angles in the visible spectral range. Visible/near-infrared reflectance measurements of lunar soil simulants, Apollo soils, and Martian analogue samples as functions of illumination and emission angles were described in Johnson et al (2013).…”

Realistic uncertainties on Hapke model parameters from photometric measurement

“…It characterizes the angular distribution of energy for an average particle. We used the empirical 2-term Henyey-Greenstein function (Henyey and Greenstein, 1941) (hereafter referred to as HG2) for studying planetary surfaces (Cord et al, 2003;Jehl et al, 2008;Johnson et al, 2006b,a;Souchon et al, 2011;Beck et al, 2012;Pommerol et al, 2013):…”

“…Please note that this method is somehow similar to genetic algorithms (Cord et al, 2003) and Particle Swarm Optimization (Beck et al, 2012;Pommerol et al, 2013), already used to solve this inverse problem empirically. Nevertheless, those previous methods, although much faster, are only heuristic since no convergence proof of the algorithms have been proposed.…”

“…The b and c couple can be correctly evaluated with a data uncertainty lower than 5%. Such uncertainty level can often be obtained in laboratory measurements (Pommerol et al, 2013;Johnson et al, 2013) but sometimes also in spaceborne measurements . Finally with 1% data uncertainty, the solution is well constrained close to the expected solutions.…”

“…Mishchenko, 1994;Hapke, 1996;Shepard and Helfenstein, 2007;Shkuratov et al, 2012;Hapke, 2013) but due to its relative simplicity and fast computation, many authors have been using it to analyze laboratory data (e.g. Cord et al, 2003;Souchon et al, 2011;Beck et al, 2012;Pommerol et al, 2013;Johnson et al, 2013), telescopic observation (e.g. Hapke et al, 1998), in situ data (e.g.…”