A next generation field-portable goniometer system

Abstract

Various field portable goniometers have been designed to capture in-situ measurements of a materials bidirectional reflectance distribution function (BRDF), each with a specific scientific purpose in mind. 1-4 The Rochester Institute of Technology's (RIT) Chester F. Carlson Center for Imaging Science recently created a novel instrument incorporating a wide variety of features into one compact apparatus in order to obtain very high accuracy BRDFs of short vegetation and sediments, even in undesirable conditions and austere environments. This next generation system integrates a dual-view design using two VNIR/SWIR spectroradiometers to capture target reflected radiance, as well as incoming radiance, to provide for better optical accuracy when measuring in non-ideal atmospheric conditions or when background illumination effects are non-negligible. The new, fully automated device also features a laser range finder to construct a surface roughness model of the target being measured, which enables the user to include inclination information into BRDF post-processing and further allows for roughness effects to be better studied for radiative transfer modeling. The highly portable design features automatic leveling, a precision engineered frame, and a variable measurement plane that allow for BRDF measurements on rugged, un-even terrain while still maintaining true angular measurements with respect to the target, all without sacrificing measurement speed. Despite the expanded capabilities and dual sensor suite, the system weighs less than 75 kg, which allows for excellent mobility and data collection on soft, silty clay or fine sand.

Modeling and intercomparison of field and laboratory hyperspectral goniometer measurements with G-LiHT imagery of the Algodones Dunes

“…5. 9 In these experiments, individual variables such as grain size distribution and density were manipulated, along with the illumination geometry, and used in a series of laboratory biconical reflectance factor (BCRF) 7,8,10 measurements. The primary sites where field HCRF measurements were taken with GRIT in tandem with geotechnical measurements were on the western side of the Algodones Dunes system (Fig.…”

“…For the laboratory studies, BRDF measurements were conducted using two different generations of the goniometer system, GRIT 5,6 and GRIT-T. 9 In a laboratory setting, BRDF measurements are sometimes referred to as BCRF 7,8,10 measurements when there is a finite aperture for both the single directional illumination source and the sensor. The term "factor" signifies the referencing of sample radiance data to the radiance of a Lambertian standard.…”

Observed Relationship Between BRF Spectral-Continuum Variance and Macroscopic Roughness of Clay Sediments

“…A novel goniometer system capable of obtaining very high accuracy BRF measurements of vegetation and soils was recently developed in the Chester F. Carlson Center for Imaging Science, Rochester Institute of Technology [14], [15], known as the goniometer of the Rochester Institute of Technology-two (GRIT-T). The GRIT-T provides an important tool for studying the surface materials, such as sediments and the impact of their geophysical properties on spectral BRF.…”

“…Laboratory tests showed that the sensor has an elevation measurement repeatability within 0.5 mm and an elevation measurement accuracy within 2 mm. It was shown that the laser sensor has an elliptical beam spot size of approximately 11 mm × 4.5 mm when operating at a typical target-to-sensor distance of 600 mm [14], [15].…”

Shaping the Color and Angular Appearance of Plasmonic Metasurfaces with Tailored Disorder

“…Another application is the characterization of surface albedo and vegetation patterns via satellite imaging. BRDF measurements at these size scales are typically done by goniometer-based setups, in which a light source and a detector are moved through a set of angles relative to a surface . At the sub-100 μm size scale of the work presented here, it is in principle possible to record BRDF measurements using goniometric ellipsometry setups (actually designed to determine the dielectric function of a material), but these typically suffer from a limited spatial resolution.…”