Phase angle dependence of sand density observable in hyperspectral reflectance

• Published in: Remote sensing of environment 2014-07, Vol.150, p.53-65
• Main Authors: Bachmann, Charles M., Philpot, William, Abelev, Andrei, Korwan, Dan
• Format: Article
• Language: English
• Subjects: Angle of reflection; Animal, plant and microbial ecology; Applied geophysics; Bidirectional Reflectance Distribution Function (BRDF); Biological and medical sciences; Constituents; Density; Earth sciences; Earth, ocean, space; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; General aspects. Techniques; Goniometer; Hyperspectral; Internal geophysics; Optimization; Phase angle; Radiative transfer; Reflectance; Reflectivity; Sand; Sand density; Scattering; Teledetection and vegetation maps
• ISSN: 0034-4257; 1879-0704
• DOI: 10.1016/j.rse.2014.03.024

This paper describes measurements of the phase angle dependence of sand density observable in hyperspectral reflectance. Bi-directional reflectance distribution measurements in the principal scattering plane were recorded for sand samples prepared near minimum and maximum relative densities. Radiative transfer theory for granular media of a single constituent would predict increased reflectance with increased density. However, sands are usually composite materials, and we observed that reflectance can actually decrease with increasing density when the dominant constituents of the sand are semi-translucent, and a darker fraction with typically smaller grains is also present. We postulate that under these circumstances, as density increases, multiple scattering modes are being suppressed as the darker absorbing fraction occupies more optimally the available pore space. •BRDF of mixed translucent and dark mineral grains decreases with increasing density.•Effect is strongest in the SWIR.•Effect may stem from suppressed multiple scattering.•Effect is reduced, dependent on λ and phase-angle in olivine sand with dark inclusions.•Weakest effect in semi-translucent to opaque sand, limited wavelengths/phase angles.