Assessment of soil surface BRDF using an imaging spectrometer

Wang, Z.; Coburn, Craig A.; Ren, Xiaomeng; Mazumdar, Deepayan Dutta; Myshak, Stephen; Mullin, A.; Teillet, P. M.

doi:10.1117/12.865099

Cited by 4 publications

(5 citation statements)

References 12 publications

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“…has been observed as a bell curve with the maximum occurring where the sample is sensed at nadir. 25,27 Signal drops off fairly uniformly as the sensing zenith angle increases, because shadowing changes very little when the sensor is moved along the azimuthal axis perpendicular to the sun. This can be observed in Fig.…”

Section: Resultsmentioning

confidence: 99%

“…[24][25][26] This preferential scattering is due to an absence of particle shadowing and occlusion within the line of sight between the sensor and the sample. Unique reflectance features also arise from the intimate mixing of grains, scattering albedo, grain transmittance, and sample density.…”

Section: Resultsmentioning

confidence: 99%

“…This sensor configuration matches that of the University of Lethbridge goniometer system version 2.5 (ULGS-2.5). 25 Prior to simulation, the total scene irradiance, E, is specified by the user. The solar illumination source was initially positioned with a zenith angle of 30 deg from nadir.…”

Section: Radiometrymentioning

confidence: 99%

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Soil signature simulation of complex mixtures and particle size distributions

2015

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Abstract. Soil reflectance signatures were modeled using the digital imaging and remote sensing image generation model and Blender three-dimensional (3-D) graphic design software. Using these tools, the geometry, radiometry, and chemistry of quartz and magnetite were exploited to model the presence of particle size and porosity effects in the visible and the shortwave infrared spectrum. Using the physics engines within the Blender 3-D graphic design software, physical representations of granular soil scenes were created. Each scene characterized a specific particle distribution and density. Chemical and optical properties of pure quartz and magnetite were assigned to particles in the scene based on particle size. This work presents a model to describe an observed phase-angle dependence of beach sand density. Bidirectional reflectance signatures were simulated for targets of varying size distribution and density. This model provides validation for a phenomenological trade space between density and particle size distribution in complex, heterogeneous soil mixtures. It also confirms the suggestion that directional reflectance signatures can be defined by intimate mixtures that depend on pore spacing. The study demonstrated that by combining realistic target geometry and spectral measurements of pure quartz and magnetite, effects of soil particle size and density could be modeled without functional data fitting or rigorous analysis of material dynamics. This research does not use traditional function-based models for simulation. The combination of realistic geometry, physically viable particle structure, and first-principles ray-tracing enables the ability to represent signature changes that have been observed in experimental observations. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Soil signature simulation of complex mixtures and particle size distributions

2015

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“…Over the years, a number of different designs have been developed for measurement of hyperspectral HCRF. These have included the Swiss Field-Goniometer System (FIGOS), 37 , 38 dual-view FIGOS, 39 the European Goniometric Facility, 38 the University of Lethbridge Goniometer System (ULGS) 40 , 41 and ULGS-II, 5 , 42 the Automated Spectro-Goniometer (ASG), 7 the Compact Laboratory Spectro-Goniometer, 43 a robotic laboratory goniometer system, 44 the Manual Transportable Instrument platform for ground-based Spectro-Directional observations, 45 the Mobile Unit for Field Spectroradiometric Measurements, 46 and systems based on unmanned aerial vehicles, 47 among others 48 – 50 While some systems have been designed primarily for the laboratory, 38 , 43 , 44 others are primarily field instruments 37 , 40 , 45 , 46 .…”

Section: Instrumentationmentioning

confidence: 99%

Flexible field goniometer system: the Goniometer for Outdoor Portable Hyperspectral Earth Reflectance

Bachmann

Abelev

Montes

et al. 2016

J. Appl. Remote Sens

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

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“…Second, the substrate under the canopy layer is assumed to be a Lambertian surface. Field studies have observed the effects of bidirectional reflectance distribution function (BRDF) for soils (Liang and Townshend, 1996;Wang et al, 2010), and coupled soil and vegetation models (Ni and Li, 2000;Verhoef and Bach, 2007) should be tested to understand the effects of soil BRDF on canopy photosynthesis. Third, we assume maximum constant leaf stomatal conductance over the growing season.…”

Section: Assumptions and Future Improvementsmentioning

confidence: 99%

Modeling photosynthesis of discontinuous plant canopies by linking the Geometric Optical Radiative Transfer model with biochemical processes

Xin

Gong

2015

Biogeosciences

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Abstract. Modeling vegetation photosynthesis is essential for understanding carbon exchanges between terrestrial ecosystems and the atmosphere. The radiative transfer process within plant canopies is one of the key drivers that regulate canopy photosynthesis. Most vegetation cover consists of discrete plant crowns, of which the physical observation departs from the underlying assumption of a homogenous and uniform medium in classic radiative transfer theory. Here we advance the Geometric Optical Radiative Transfer (GORT) model to simulate photosynthesis activities for discontinuous plant canopies. We separate radiation absorption into two components that are absorbed by sunlit and shaded leaves, and derive analytical solutions by integrating over the canopy layer. To model leaf-level and canopylevel photosynthesis, leaf light absorption is then linked to the biochemical process of gas diffusion through leaf stomata. The canopy gap probability derived from GORT differs from classic radiative transfer theory, especially when the leaf area index is high, due to leaf clumping effects. Tree characteristics such as tree density, crown shape, and canopy length affect leaf clumping and regulate radiation interception. Modeled gross primary production (GPP) for two deciduous forest stands could explain more than 80 % of the variance of flux tower measurements at both near hourly and daily timescales. We demonstrate that ambient CO 2 concentrations influence daytime vegetation photosynthesis, which needs to be considered in biogeochemical models. The proposed model is complementary to classic radiative transfer theory and shows promise in modeling the radiative transfer process and photosynthetic activities over discontinuous forest canopies.

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Assessment of soil surface BRDF using an imaging spectrometer

Cited by 4 publications

References 12 publications

Soil signature simulation of complex mixtures and particle size distributions

Soil signature simulation of complex mixtures and particle size distributions

Flexible field goniometer system: the Goniometer for Outdoor Portable Hyperspectral Earth Reflectance

Modeling photosynthesis of discontinuous plant canopies by linking the Geometric Optical Radiative Transfer model with biochemical processes

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