Radiative transfer in vegetation canopies with anisotropic scattering

Shultis, J. Kenneth; Myneni, Ranga B.

doi:10.1016/0022-4073(88)90079-9

Cited by 137 publications

(64 citation statements)

References 14 publications

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“…Plant leaves, however, represent a dense packaging of optically active material, which violates the single-scattering assumptions of these exact solutions. Consequently, models of irradiance distribution in plant canopies must rely on more empirical relationships between leaf optical properties and light attenuation by the bulk canopy (Goudriaan 1988;Shultis and Myneni 1988;Ganapol and Myneni 1992).…”

Section: Acknowledgmentsmentioning

confidence: 99%

A biooptical model of irradiance distribution and photosynthesis in seagrass canopies

Zimmerman

2003

Limnology & Oceanography

123

133

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Although extremely vulnerable to coastal eutrophication, seagrasses represent important structuring elements and sources of primary production in shallow waters. They also generate an optical signature that can be tracked remotely. Accurate knowledge of light absorption and scattering by submerged plant canopies permits the calculation of important plant-and ecosystem-level properties, including rates of photosynthesis, vegetation abundance, and distribution. The objectives of this study were to develop a realistic, yet simply parameterized two-flow model of plane irradiance distribution through a seagrass canopy submerged in an optically active water column, to evaluate its performance against in situ measurements, and to explore the impacts of variations in canopy architecture on irradiance distribution and photosynthesis within the canopy. Allometric functions derived from leaf length-frequency data enabled simple parameterization of canopy architecture. Model predictions of downwelling spectral irradiance distributions in seagrass canopies growing in both oligotrophic and eutrophic waters were within 15% of field measurements. Thus, the model provides a robust tool for investigating photosynthetic performance of seagrass canopies as functions of water quality, depth distribution, canopy architecture, and leaf orientation. Model predictions of upwelling irradiance were less reliable, particularly in the upper half of the canopies. The model was more sensitive to leaf orientation than leaf optical properties, seabed reflectance, or the average cosine of downwelling irradiance. Better knowledge of leaf orientation appears to be a fruitful avenue for improving our understanding of the interaction between seagrasses and the submarine light environment.

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Section: Acknowledgmentsmentioning

confidence: 99%

A biooptical model of irradiance distribution and photosynthesis in seagrass canopies

Zimmerman

2003

Limnology & Oceanography

123

133

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“…Tais modificações devem tornar possível o cálculo de reflectância especificamente para vegetações, bem como absorção da radiação (transmitância) pelo solo [12]. A formulação básica aqui desenvolvidaé fundamental e necessária na abordagem (via ADO) destes modelos mais específicos de transporte de fótons em copas de vegetações (nos dosséis), acrescida do tratamento de termos de fonte e da variável azimutal.…”

Section: Conclusõesunclassified

“…Especificações na elaboração dos modelos consideram formulações em meio homogêneo, unidimensional, com espalhamento anisotrópico e com invariância rotacional do elemento de dispersão básico (folha do dossel) [7]. Outros autores consideram que no transporte de fótons em dosséis, além de se admitir que a direcionalidade do elemento de dispersão básico torna o meio inerentemente anisotrópico, também há que se procurar introduzir características especiais na definição do núcleo de espalhamento [11,10,12].…”

Section: Introductionunclassified

Avaliação de Propriedades Radiativas em Meios Homogêneos Unidimensionais: Reflectância e Transmitância

Cromianski

Camargo²,

Rodrigues³

et al. 2018

Tend. Mat. Apl. Comput.

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Recebido em 12 janeiro, 2017 / Aceito em 27 agosto, 2017 RESUMO. Neste trabalhoé derivada uma solução para a equação de transferência radiativa em meio homogêneo unidimensional, buscando avaliar propriedades como reflectância e transmitância do meio, que podem, por exemplo, estar associadasà caracterização de uma vegetação. Resultados numéricos obtidos com o método analítico de ordenadas discretas (ADO), para diferentes formulações das condições de contorno do problema, são discutidos e comparados aos de outros trabalhos disponíveis na literatura. A análise dos resultados mostra que a formulação ADOé rápida e precisa.Palavras-chave: método de ordenadas discretas, reflectância, transmitância. INTRODUÇÃOO entendimento das formas de interação da radiação solar com vegetaçõesé fundamental para a interpretação de dados de sensoriamento remoto, para o desenvolvimento de metodologias de análise das informações de monitoramentos quantitativos e qualitativos e para a criação de novos sensores. A parte do organismo vegetal envolvida nessas interaçõesé denominada dossel, formado por um conjunto estruturado de folhas, caules, espigas e flores, conforme o tipo e as condições da vegetação. Um determinado dosselé caracterizado pela sua constituição, pelo comportamento espectral de seus componentes, sua estrutura interna e sua organização no espaço [13].Estudos buscam modelar a transferência radiativa em copas de vegetações densas, utilizando a equação linear de Boltzmann particularmente para avaliação de propriedades como reflectância e transmitância nos dosséis. Especificações na elaboração dos modelos consideram formulações *Autor correspondente: Patricia Rodrigues

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“…Instantaneous foliar-fAPAR, the fraction of incoming PAR (PAR,) absorbed by photosynthetic plant tissues (green leaves), can be calculated using a RT model such as DISORD [Shultis and Myneni, 1988]. PAR, (given in J m -2 s-•) depends upon solar zenith angle and sky conditions, while foliar-fAPAR is a function of the variables described in equation (1) [Goward and Huemmrich, 1992] (2) where APARfonag c is the amount of incoming PAR absorbed by the foliage at time (t), and the integration occurs over the number of daylight hours.…”

Section: Modeling Carbon Uptakementioning

confidence: 99%

Estimating vegetation structural effects on carbon uptake using satellite data fusion and inverse modeling

Asner¹,

Bateson²,

Privette³

et al. 1998

J. Geophys. Res.

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Abstract. Regional analyses of biogeochemical processes can benefit significantly from observational information on land cover, vegetation structure (e.g., leaf area index), and biophysical properties such as fractional PAR absorption. Few remote sensing efforts have provided a suite of plant attributes needed to link vegetation structure to ecosystem function at high spatial resolution. In arid and semiarid ecosystems (e.g., savannas), high spatial heterogeneity of land cover results in significant functional interaction between dominant vegetation types, requiring new approaches to resolve their structural characteristics for regional-scale biogeochemical research. We developed and tested a satellite data fusion and radiative transfer inverse modeling approach to deliver estimates of vegetation structure in a savanna region of Texas. Spectral mixture analysis of Landsat data provided verifiable estimates of woody plant, herbaceous, bare soil, and shade fractions at 28.5 rn resolution. Using these subpixel cover fractions, a geometric-optical model was inverted to estimate overstory stand density and crown dimensions with reasonable accuracy. The Landsat cover estimates were then used to spectrally unmix the contribution of woody plant and herbaceous canopies to AVHRR multiangle reflectance data. These angular reflectances were used with radiative transfer model inversions to estimate canopy leaf area index (LAI). The suite of estimated canopy and landscape variables indicated distinct patterns in land cover and structural attributes related to land use. These variables were used to calculate diurnal PAR absorption and carbon uptake by woody and herbaceous canopies in contrasting land cover and land use types. We found that both LAI and the spatial distribution of vegetation structural types exert strong control on carbon fluxes and that intercanopy shading is an important factor controlling functional processes in spatially heterogeneous environments. IntroductionChanges in land use often lead to changes in vegetation structure, which significantly impact biosphere-atmosphere exchange processes and biogeochemical cycles (e.g., carbon fluxes, nutrient dynamics). However, structural differences (e.g., type and amount of tissue) between vegetation types also predispose different ecosystems to distinct functional responses to human disturbance and climate variability [e.g., Townsend et al. To analyze actual rather than potential ecosystem function at regional scales, especially under conditions of changing land use, observations of changing vegetation structure must be linked to functional processes. To date, our ability to connect function to structure has been limited because (1) the physiological and biogeochemical links between structure and function are highly complex and (2) observation of structure is often constrained to detailed ground studies over very small scales (e.g., meters). Studies focusing on structure at large scales (e.g., kilometers) often lack sufficient detail required for many analyses of e...

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Radiative transfer in vegetation canopies with anisotropic scattering

Cited by 137 publications

References 14 publications

A biooptical model of irradiance distribution and photosynthesis in seagrass canopies

A biooptical model of irradiance distribution and photosynthesis in seagrass canopies

Avaliação de Propriedades Radiativas em Meios Homogêneos Unidimensionais: Reflectância e Transmitância

Estimating vegetation structural effects on carbon uptake using satellite data fusion and inverse modeling

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