Fully automated laboratory and field-portable goniometer used for performing accurate and precise multiangular reflectance measurements

Abstract

, "Fully automated laboratory and field-portable goniometer used for performing accurate and precise multiangular reflectance measurements," J. Appl. Remote Sens. 11(4), 046014 (2017), doi: 10.1117/1.JRS.11.046014. Abstract. Field-portable goniometers are created for a wide variety of applications. Many of these applications require specific types of instruments and measurement schemes and must operate in challenging environments. Therefore, designs are based on the requirements that are specific to the application. We present a field-portable goniometer that was designed for measuring the hemispherical-conical reflectance factor (HCRF) of various soils and low-growing vegetation in austere coastal and desert environments and biconical reflectance factors in laboratory settings. Unlike some goniometers, this system features a requirement for "target-plane tracking" to ensure that measurements can be collected on sloped surfaces, without compromising angular accuracy. The system also features a second upward-looking spectrometer to measure the spatially dependent incoming illumination, an integrated software package to provide full automation, an automated leveling system to ensure a standard frame of reference, a design that minimizes the obscuration due to self-shading to measure the opposition effect, and the ability to record a digital elevation model of the target region. This fully automated and highly mobile system obtains accurate and precise measurements of HCRF in a wide variety of terrain and in less time than most other systems while not sacrificing consistency or repeatability in laboratory environments.

Retrieval of Sediment Fill Factor by Inversion of a Modified Hapke Model Applied to Sampled HCRF from Airborne and Satellite Imagery

“…The models of our experiments described in this paper ignore the CBOE since our BCRF and HCRF measurements do not include sufficiently small phase angles. GRIT-T can not measure at phase angles this small due to the finite extent of the sensor chassis; GRIT-T self-shading occurs for phase angles ≤5 • [41]. The IMSA model in Equation (1) also excludes factors of 1/π and µ i as the measurements described are typically BCRF and HCRF.…”

“…The goniometer of the Rochester Institute of Technology-Two (GRIT-T) is a second-generation system designed to obtain BRDF measurements in both laboratory and field settings [3,41,58]. Figure 2 illustrates the different components of the GRIT-T system, deployed in various settings.…”

“…The NASA Goddard LiDAR, hyperspectral, and thermal (G-LiHT) sensor suite [39,40] collected airborne imagery during the field campaign, and the field team collected sediment samples from various sites across the dune system, capturing the variation in its geophysical properties [3,39]. During the campaign, Hyperspectral hemispherical conical reflectance factor (HCRF) measurements of sediments were collected on site using the Goniometer of the Rochester Institute of Technology (GRIT), and later from samples returned to RIT in a laboratory setting using GRIT and a second generation instrument, the Goniometer of the Rochester Institute of Technology Two (GRIT-T) [3,39,41].…”

Retrieval of Sediment Filling Factor in a Salt Panne from Multi-View Hyperspectral Imagery

“…What sets our particular study apart is the fact that this is the first analysis, to our knowledge, in which sediment bulk density measured in situ in a field setting has been compared directly to sediment filling factor obtained from inversion of the Hapke model using input hyperspectral imagery of the validation locations. Even our own past analyses using this inversion scheme had used either inputs from laboratory-based hyperspectral BCRF measurements obtained from goniometer systems [39] with carefully controlled densities [8,9] or had been based on field hyperspectral imagery, but without ground truth directly within the field of view of the hyperspectral imaging system, but instead only in close proximity to the hyperspectral scenes [9]. While the latter retrieval was consistent with nearby ground truth [9], it was nevertheless not a direct test from ground truth.…”

“…In past work, we have developed methods to invert both the Hapke model and a modified form of the Hapke model that we developed [8,9] in order to specifically retrieve the sediment filling factor from multi-view hyperspectral data. Initially, we had focused on laboratory studies, using hyperspectral bi-conical reflectance factor (BCRF) [35][36][37][38] data derived from the Goniometer of the Rochester Institute of Technology-Two (GRIT-T) [8,39] to demonstrate the feasibility of the approach. Our method relied on the observation that single particle properties such as the single scattering phase function are intrinsic properties of particles with a distribution depending only on the phase angle g, i.e., the relative angle between illumination and observation direction [8].…”