VIS-NIR reflectance of water ice/regolith analogue mixtures and implications for the detectability of ice mixed within planetary regoliths

• Published in: Geophysical research letters Vol. 42; no. 15; pp. 6205 - 6212
• Main Authors: Yoldi, Zuriñe, Pommerol, Antoine, Jost, Bernhard, Poch, Olivier, Gouman, Julien, Thomas, Nicolas
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 16.08.2015; John Wiley & Sons, Inc
• Subjects: Bidirectional reflectance; Coefficients; Errors; Estimating; Estimation; Grains; Ice; Infrared signatures; Laboratories; Mathematical models; Measurement; Mercury; Mercury surface; mixture; Moon; Near infrared radiation; Nonlinear systems; Nonlinearity; Particle size; Photometry; Poles; Reflectance; Reflectivity; Regolith; Saturn; Shape; Signatures; Spectra; surface; Water; Water ice
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/2015GL064780

Permanently shadowed regions at the poles of the Moon and Mercury have been pointed out as candidates for hosting water ice at their surface. We have measured in the laboratory the visible and near infrared spectral range (VIS‐NIR) bidirectional reflectance of intimate mixtures of water ice and the JSC‐1AF lunar simulant for different ice concentrations, particle sizes, and measurement geometries. The nonlinearity between the measured reflectance and the amount of ice in the mixture can be reproduced to some extent by the mixing formulas of standard reflectance models, in particular, those of Hapke and Hiroi, which are tested here. Estimating ice concentrations from reflectance data without knowledge of the mixing coefficients—strongly dependent on the size/shape of the grains—can result in large errors. According to our results, it is possible that considerable amounts of water ice might be intimately mixed in the regolith of the Moon and Mercury without producing noticeable photometric signatures. Key Points Bidirectional reflectance of ice/lunar regolith simulant binary mixtures measured in the laboratory Strong VIS‐NIR signature of ice at high phase angle could be used to detect ice on the surface The effect of particle size in common reflectance models is tested