Abstract
We compare field hyperspectral bidirectional reflectance distribution function (BRDF) measurements acquired by a hyperspectral goniometer system known as the goniometer of the Rochester Institute of Technology (GRIT) during an experiment in the Algodones Dunes system in March 2015 with NASA Goddard’s light detection and ranging, hyperspectral, and thermal imagery of the site acquired during the experiment. We augment our field spectral data collection with laboratory hyperspectral BRDF measurements of samples brought back from the Algodones Dunes site using GRIT and our second-generation goniometer GRIT-two (GRIT-T). In these laboratory experiments, we vary geophysical parameters such as sediment density and grain size distribution of the sediments that would typically impact observed BRDF with the goal of extending the range of applicability of our resulting BRDF spectral libraries. Geotechnical measurements on site confirm the variability of geophysical parameters such as density and grain size distributions within the dune system, and measurements with GRIT and GRIT-T demonstrate the impact on observed spectral variation. By augmenting field spectral libraries with laboratory BRDF, we show that a greater proportion of the dune system is more faithfully represented in the expanded spectral library. Beyond developing appropriate calibration data for airborne and satellite imagery of the Algodones Dunes, laboratory and field studies also support goals to develop reliable retrieval methods for geophysical quantities such as sediment density directly from spectral imagery. We consider approaches based on the Hapke model. Our approaches use the invariance of the observed functional forms of the single scattering phase function, which must be invariant to differences in the illumination geometry. Fill factor is retrieved and correlates with expected direct measurements of sediment density in a laboratory setting.
Highlights
In March 2015, a joint field experiment and airborne measurement campaign was conducted in the Algodones Dunes, California
This fact, combined with natural variations anticipated within a large dune system, such as Algodones, made the direct measurement of the bidirectional reflectance distribution function (BRDF), which characterizes the angular variation in scattered light from the surface for a given illumination geometry, of paramount importance
We have seen that field-measured hemispherical conical reflectance factor (HCRF) with the goniometer of the Rochester Institute of Technology (GRIT) hyperspectral goniometer system is well matched to the hyperspectral imagery collected during the Algodones Dunes campaign
Summary
In March 2015, a joint field experiment and airborne measurement campaign was conducted in the Algodones Dunes, California. The experiment was a multiinstitutional effort involving NASA, South Dakota State University, the University of Arizona, the University of Lethbridge, and the Rochester Institute of Technology (RIT). This fact, combined with natural variations anticipated within a large dune system, such as Algodones, made the direct measurement of the bidirectional reflectance distribution function (BRDF), which characterizes the angular variation in scattered light from the surface for a given illumination geometry, of paramount importance. Within the context of the larger team effort, our goals were to provide representative hyperspectral BRDF measurements at a number of sites within the dune system and to characterize the geophysical properties of the surface that might influence observed variations in BRDF at these locations and throughout the dune system.
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