Influence of density on hyperspectral BRDF signatures of granular materials

Abstract

Recent hyperspectral measurements of composite granular sediments of varying densities have revealed phenomena that contradict what radiative transfer theory would suggest. 5 In high-density sands where dominant constituents are translucent and supplementary, darker grains are present, bidirectional reflectance distribution function (BRDF) measurements of high density sediments showed reduced intensity when compared to lower density counterparts. It is conjectured that this is due to diminished multiple scattering from the darker particles which more optimally fill pore space as density increases. The goal of these experiments is to further expand upon these earlier results that were conducted primarily in the principal scattering plane and only at minimum and maximum densities. In the present study, the BRDF of granular composites is compared along a gradient of densities for optically contrasting materials. Systematic analysis of angular and material dependence will be used to develop better models for multiple scattering effects of the granular materials. The measurements in this experiment used the recently constructed, laboratory and field-deployable Goniometer of the Rochester Institute of Technology (GRIT), which measures BRDF for geometries covering 360 degrees in azimuth and 65 degrees in zenith. In contrast to the previous studies limited to the principal scattering plane, GRIT provides a full hemispherical BRDF measurement.

A next generation field-portable goniometer system

“…This device is meant to replace the current system, the Goniometer of RIT, or GRIT, with a more automated and purpose-driven design. 7,8 The GRIT system, seen in figure 3, was able to capture reflectance functions in both field and laboratory settings and featured two stepper motors that allowed it to move in both azimuth and zenith directions. These motions were then measured using two VectorNav inertial measurement units (IMUs) to determine the position of the foreoptic with respect to Earth's gravity vector.…”