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Leaf area index estimation with MODIS reflectance time series and model inversion during full rotations of Eucalyptus plantations

MAIRE, Guerric le; MARSDEN, Claire; VERHOEF, Wouter; PONZONI, Flavio Jorge; SEEN, Danny Lo; BEGUE, Agnes; STAPE, Jose-Luiz; NOUVELLON, Yann
Fonte: ELSEVIER SCIENCE INC Publicador: ELSEVIER SCIENCE INC
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
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The leaf area index (LAI) of fast-growing Eucalyptus plantations is highly dynamic both seasonally and interannually, and is spatially variable depending on pedo-climatic conditions. LAI is very important in determining the carbon and water balance of a stand, but is difficult to measure during a complete stand rotation and at large scales. Remote-sensing methods allowing the retrieval of LAI time series with accuracy and precision are therefore necessary. Here, we tested two methods for LAI estimation from MODIS 250m resolution red and near-infrared (NIR) reflectance time series. The first method involved the inversion of a coupled model of leaf reflectance and transmittance (PROSPECT4), soil reflectance (SOILSPECT) and canopy radiative transfer (4SAIL2). Model parameters other than the LAI were either fixed to measured constant values, or allowed to vary seasonally and/or with stand age according to trends observed in field measurements. The LAI was assumed to vary throughout the rotation following a series of alternately increasing and decreasing sigmoid curves. The parameters of each sigmoid curve that allowed the best fit of simulated canopy reflectance to MODIS red and NIR reflectance data were obtained by minimization techniques. The second method was based on a linear relationship between the LAI and values of the GEneralized Soil Adjusted Vegetation Index (GESAVI)...

Análise histopatológica de lesões leucoqueratósicas da mucosa oral avaliadas pelos exames de luminescência, cromoscopia e microscopia confocal reflectante; Histological analysis identified and assessed by tests of luminescence, chromoendoscopy and confocal reflectance leukokeratosis lesions

Bezerra, Ana Patricia Carneiro Gonçalves
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 12/08/2014 PT
Relevância na Pesquisa
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O câncer de mucosa oral é um problema de saúde pública, com maior incidência em homens acima de 50 anos. Uma das manifestações clínicas mais precoces do câncer da mucosa oral são as lesões leucoqueratósica. O aspecto clínico não homogêneo e o tamanho maior de 200mm2, em mucosa não queratinizada como a do assoalho da boca e ventre da língua, são aspectos que implicam na possibilidade de evolução da lesão. A dificuldade do diagnóstico das lesões precoces está na seleção do local a ser biopsiado principalmente frente a lesões extensas e heterogêneas. O objetivo desta pesquisa é avaliar se a utilização do exame clínico juntamente com os métodos auxiliares de diagnóstico das lesões leucoqueratósica da mucosa oral (VELscope®, Azul de toluidina e Solução de lugol) contribui para uma maior precisão do diagnóstico de displasias nestas lesões quando comparado ao histopatológico. E, identificar os padrões morfológicos destas lesões quando avaliadas por meio da microscopia confocal reflectante. Foram selecionados 30 pacientes, maiores de 18 anos, portadores de lesão clínica compatível com leucoplasia oral triados no ambulatório da disciplina de Estomatologia Clínica da Faculdade de Odontologia da Universidade de São Paulo e que precisavam ser submetidos à biópsia para o estabelecimento do diagnóstico final. Foram realizados os testes de Azul de Toluidina...

Alteration of soil properties through a weathering sequence as evaluated by spectral reflectance

Demattê, José Alexandre M.; Garcia, Gilberto J.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 327-342
ENG
Relevância na Pesquisa
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In the study of physical, chemical, and mineralogical data related to the weathering of soils and the quantification of their properties, remote sensing constitutes an important technique that, in addition to conventional analyses, can contribute to soil survey. The objectives of this research were to characterize and differentiate soils developed from basaltic rocks that occur in the Parana state, Brazil and to quantify soil properties based on their spectral reflectance. These observations were used to verify the relationship between the soils and reflectance with regard to weathering, organic matter (OM), and forms of Fe. From the least to the most weathered soil, we used a Typic Argiudoll (Reddish Brunizem), Rhodudalf (Terra Roxa Estruturada), and Rhodic Hapludox (Very Dark Red Latosol). The spectral reflectances between 400 and 2500 nm were obtained in the laboratory from soil samples collected at two depth increments, 0- to 20- and 40- to 60-cm, using an Infra Red Intelligent Spectroradiometer (IRIS). Correlation, regression, and discriminant estimates were used in analyzing the soil and spectral data. Results of this study indicated that soils could be separated at the soil-type level based on reflectance intensity in various absorption bands. Soil collected in the 40- to 60-cm depth appeared to have higher reflectance intensities than those from the 0- to 20-cm depth. Removal of OM from soil samples promoted higher reflectance intensity in the entire spectrum. Amorphous and crystalline Fe influenced reflectance differently. Weathering of basaltic soils was correlated with alterations in the reflectance intensities and absorption features of the spectral curves. Multivariate analysis demonstrated that this technique was efficient in the estimation of clay...

Metodos FIA para analise de niquel e de sulfato por refletancia difusa na região do visivel; Flow injection analysis methods for nickel and sulphate analysis by diffuse reflectance in visible region

Carlos Alberto da Rocha Queiroz
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 16/09/2008 PT
Relevância na Pesquisa
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Neste trabalho foram desenvolvidos dois procedimentos de análise quantitativa em fluxo, um para níquel e o outro para sulfato, usando a refletância difusa na região do visível. O primeiro sistema químico estudado faz uso da clássica reação de níquel (II) com dimetilglioxima em meio alcalino amoniacal, formando o precipitado de cor rosa forte, Ni(DMG)2. Este precipitado, como se sabe, é bastante volumoso e adere facilmente às paredes do recipiente onde se encontra. Também, coagula rapidamente formando aglomerados. Estas características já desqualificam, em princípio, este precipitado para uso em sistemas de fluxo, por anunciarem problemas de entupimento nas tubulações e problemas de aderência nas janelas da cela de medida colorimétrica, se esta for a técnica usada. No presente trabalho logrou-se contornar todos estes problemas utilizando-se um sistema de fluxo muito simples. A cela desenvolvida para medidas de refletância foi construída em PTFE branco, sendo nela inseridos o detector (LDR) e emissor de luz (LED verde). O LED foi alimentado com uma fonte com voltagem adequada e o LDR foi introduzido numa ponte de Wheatstone que forneceu as medidas analíticas. Dentro desta cela foi colocado um tudo de vidro, conectado à tubulação do sistema de fluxo...

Quantificação de nitrofurazona e de nitrofurantoína em medicamentos por espectrofotometria de refletância difusa e de transmissão; Measurement of nitrofurazone and nitrofurantoin drugs in spectrophotometric diffuse reflectance and transmittance

Marcio das Neves Palumbo
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 12/09/2011 PT
Relevância na Pesquisa
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A nitrofurazona e a nitrofurantoína são substâncias derivadas dos nitrofuranos e comercializadas em preparações farmacêuticas com ação bactericida, antifúngica e antimicrobiana com um amplo espectro de aplicação. Apresentam coloração amarela e comprimento de onda de máxima absorção em 370 nm. A maior parte das substâncias pertencentes ao grupo dos nitrofuranos, tem baixíssima solubilidade em água o que dificulta o desenvolvimento de métodos analíticos, sem o uso de solventes orgânicos. Neste trabalho foi desenvolvida metodologia para a determinação do teor de nitrofurazona e de nitrofurantoína em medicamentos por refletância difusa. Para a nitrofurantoína a medida é direta no fármaco, sem uso de qualquer solvente, enquanto que, para nitrofurantoína dissolve-se o fármaco em polietilenoglicol e mede-se a refletância em seguida. A técnica de refletância envolveu, para fins de comparação, a utilização de dois equipamentos distintos: (I) um espectrofotômetro Shimadzu UV-2450 com assessório de refletância e; (II) um refletômetro portátil construído em nosso laboratório. Também foram desenvolvidos duas metodologias para a análise quantitativa dos dois fármacos por transmissão em solução aquosa. Ambos os métodos na região uv-visível do espectro. Os resultados dos dois procedimentos foram comparados entre si e também com aqueles obtidos pela método oficial em high performance liquid cromatagraphy (HPLC)...

Espectroscopia de refletância e emissividade de rochas fosfáticas ígneas e sedimentares do centro-oeste do Brasil : estudos de caso nos depósitos de Catalão I (GO), Tapira (MG), Rocinha e Lagamar (MG) = Reflectance and emissivity spectroscopy of igneous and sedimentary rocks from Midwest Brazil: case study of the Catalão I (GO), Tapira (MG), Rocinha and Lagamar deposits; Reflectance and emissivity spectroscopy of igneous and sedimentary rocks from Midwest Brazil : case study of the Catalão I (GO), Tapira (MG), Rocinha and Lagamar deposits

Emanuel Amorer Hernández
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 05/07/2013 PT
Relevância na Pesquisa
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A pesquisa compreende estudos sobre a assinatura ultraespectral e multiespectral de fosfatos de origem ígnea e sedimentar contidos, respectivamente, nos depósitos de Catalão I (GO), Tapira (MG) e Rocinha-Lagamar (MG), centro-oeste do Brasil. Medidas de reflectância e emissividade (focadas na faixa de 8-12µm) foram analisadas em conjunto com dados de Difração de Raios X e Fluorescência de Raios X visando a determinação da mineralogia e quimismo das rochas envolvidas nas áreas de estudo. Os fosfatos ígneos de Catalão I e Tapira, inseridos na Província Ígnea do Alto Paranaíba, encontram-se hospedados em complexos carbonatíticos. Apresentam Elementos de Terras Raras em sua composição e feições de absorção intrínsecas em espectros de reflectância em torno de 0,75µm. A profundidade e forma das feições auxiliam na identificação e qualificação de monazita, fluoroapatita e cloroapatita como minerais de minério. Associações comuns nas zonas mineralizadas e que apresentam assinaturas espectrais características incluem fluoroapatite-ajoita-vermiculita; fluoroapatita-vermiculita-calcita e fluoroapatita-calcita-monazita. Teores anômalos de fosfato ocorrem na presença de vermiculita, flogopita, calcita, dolomita...

Surface Reflectance Estimation and Natural Illumination Statistics

Dror, Ron O.; Adelson, Edward H.; Willsky, Alan S.
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Formato: 22 p.; 7750699 bytes; 706071 bytes; application/postscript; application/pdf
EN_US
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Humans recognize optical reflectance properties of surfaces such as metal, plastic, or paper from a single image without knowledge of illumination. We develop a machine vision system to perform similar recognition tasks automatically. Reflectance estimation under unknown, arbitrary illumination proves highly underconstrained due to the variety of potential illumination distributions and surface reflectance properties. We have found that the spatial structure of real-world illumination possesses some of the statistical regularities observed in the natural image statistics literature. A human or computer vision system may be able to exploit this prior information to determine the most likely surface reflectance given an observed image. We develop an algorithm for reflectance classification under unknown real-world illumination, which learns relationships between surface reflectance and certain features (statistics) computed from a single observed image. We also develop an automatic feature selection method.

Surface Reflectance Recognition and Real-World Illumination Statistics

Dror, Ron O.
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Formato: 195 p.; 7366082 bytes; 3656634 bytes; application/postscript; application/pdf
EN_US
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Humans distinguish materials such as metal, plastic, and paper effortlessly at a glance. Traditional computer vision systems cannot solve this problem at all. Recognizing surface reflectance properties from a single photograph is difficult because the observed image depends heavily on the amount of light incident from every direction. A mirrored sphere, for example, produces a different image in every environment. To make matters worse, two surfaces with different reflectance properties could produce identical images. The mirrored sphere simply reflects its surroundings, so in the right artificial setting, it could mimic the appearance of a matte ping-pong ball. Yet, humans possess an intuitive sense of what materials typically "look like" in the real world. This thesis develops computational algorithms with a similar ability to recognize reflectance properties from photographs under unknown, real-world illumination conditions. Real-world illumination is complex, with light typically incident on a surface from every direction. We find, however, that real-world illumination patterns are not arbitrary. They exhibit highly predictable spatial structure, which we describe largely in the wavelet domain. Although they differ in several respects from the typical photographs...

Identification of mineral components in tropical soils using reflectance spectroscopy and advanced spaceborne thermal emission and reflection radiometer (ASTER) data.

VICENTE, L. E.; SOUZA FILHO, C. R. de
Fonte: Remote Sensing of Environment, v. 115, p. 1824-1836, 2011. Publicador: Remote Sensing of Environment, v. 115, p. 1824-1836, 2011.
Tipo: Artigo em periódico indexado (ALICE)
EN
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Soil characteristics provide important support for understanding transformations that occur in environmental systems. Physical characteristics and chemical compositions of soils controlled by pedogenetic processes, climatic changes and land use imply different types of environmental transformations. Reflectance spectroscopy is an alternative soil mapping technique that uses spectral absorption features between visible (VIS) and short-wave infrared (SWIR) wavelengths (0.3?2.5 μm) for determining soil mineralogy. Soil analysis by means of reflectance spectroscopy and orbital optical sensors have provided favorable results in mapping transformation processes in environmental systems, particularly in arid and semiarid climates in extra-tropical terrains. In the case of inter-tropical environments, these methods cannot be readily applied due to local factors such as lack of exposed regolith, high amounts of soil moisture and the presence of dense vegetation. This study uses Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and reflectance spectroscopy data to map mineral components of soils covering a part of the state of São Paulo, Brazil, which could be linked to key aspects of environmental transformations in this tropical area (e.g....

Patterns of Spectral Reflectance in Metriaclima zebra

Tremblay, Maude
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado Formato: 486400 bytes; application/msword
EN
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The study of spectral reflectance patterns in African cichlids is essential to understanding the explosive radiation of this family, as well as to understanding the maintenance of species barriers to preserve biodiversity. However, little research has gone into determining the best methods for studying such patterns. The present study aims to determine whether elapsed time, intensity of ambient light and choice of anaesthetic method affect spectral reflectance measurements in Metriaclima zebra, a Lake Malawi rock-dwelling cichlid. Using a spectroradiometer, fish were measured at a sample of patches 1) consecutively over a period of time, 2) at varying light intensities, and 3) under various anaesthetic methods. Ambient light intensity was found to have significant effects on spectral reflectance patterns, such that increasing light intensity increased maximum percent reflectance. The method of anaesthetization (i.e. Clove Oil, MS-222, ice water bath), also influenced the spectral reflectance of the measured patches in terms of maximum percent reflectance and the proportion of UV reflectance. Future studies examining spectral reflectance in M. zebra will require a careful consideration of methodology and potentially standardization of these methods.

Estimating Major Ion and Nutrient Concentrations in Mangrove Estuaries in Everglades National Park Using Leaf and Satellite Reflectance

Lagomasino, David; Price, René M.; Whitman, Dean; Campbell, Petya K.E.; Melesse, Assefa M.
Fonte: FIU Digital Commons Publicador: FIU Digital Commons
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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Coastal mangrove ecosystems are under duress worldwide because of urban development, sea-level rise, and climate change, processes that are capable of changing the salinity and nutrient concentration of the water utilized by the mangroves. This study correlates long-term water chemistry in mangrove environments, located in Everglades National Park, with mangrove spectral reflectance measurements made at both the leaf and canopy scales. Spectral reflectance measurements were collected using a handheld spectrometer for leaf-level measurements and Landsat 5TM data for regional coverage. Leaf-level reflectance data were collected from three mangrove species (i.e., red, black and white mangroves) across two regions; a tall mangrove (~ 18 m) and dwarf mangrove (1–2 m) region. The reflectance data were then used to calculate a wide variety of biophysical reflectance indices (e.g., NDVI, EVI, SAVI) to determine signs of stress. Discrete, quarterly water samples from the surface water, groundwater, and pore water (20 and 85 cm depths) and daily autonomous surface water samples were collected at each site and analyzed for major anions (Cl− and SO42−), cations (Na+, K+, Mg2 +, and Ca2 +), total nitrogen (TN) and total phosphorus (TP). Mangrove sites that exhibited the highest salinity and ionic concentrations in the surface and subsurface water also had the lowest near-infrared reflectance at both the leaf and satellite levels. Seasonal reflectance responses were measured in the near-infrared (NIR) wavelengths at both the leaf and canopy scales and were strongly correlated with nutrient and ionic concentrations in the surface and subsurface water...

Far infrared reflectance and optical properties of organic superconductor (TMTSF)2ClO4 /

Ellison, Rodica.
Fonte: Brock University Publicador: Brock University
Tipo: Electronic Thesis or Dissertation
ENG
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Polarized reflectance measurements of the quasi I-D charge-transfer salt (TMTSFh CI04 were carried out using a Martin-Puplett-type polarizing interferometer and a 3He refrigerator cryostat, at several temperatures between 0.45 K and 26 K, in the far infrared, in the 10 to 70 cm- 1 frequency range. Bis-tetramethyl-tetraselena-fulvalene perchlorate crystals, grown electrochemically and supplied by K. Behnia, of dimensions 2 to 4 by 0.4 by 0.2 mm, were assembled on a flat surface to form a mosaic of 1.5 by 3 mm. The needle shaped crystals were positioned parallel to each other along their long axis, which is the stacking direction of the planar TMTSF cations, exposing the ab plane face (parallel to which the sheets of CI04 anions are positioned). Reflectance measurements were performed with radiation polarized along the stacking direction in the sample. Measurements were carried out following either a fast (15-20 K per minute) or slow (0.1 K per minute) cooling of the sample. Slow cooling permits the anions to order near 24 K, and the sample is expected to be superconducting below 1.2 K, while fast cooling yields an insulating state at low temperatures. Upon the slow cooling the reflectance shows dependence with temperature and exhibits the 28 cm- 1 feature reported previously [1]. Thermoreflectance for both the 'slow' and 'fast' cooling of the sample calculated relative to the 26 K reflectance data indicates that the reflectance is temperature dependent...

Colour Change in Fish: Spectral Reflectance Characteristics in 'Melanochromis auratus'

Hart, Francine L.
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado Formato: 9603584 bytes; application/msword
EN
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African cichlid fishes represent one of the most diverse vertebrate assemblages on the planet. Cichlid evolution involves the diversification of male nuptial colouration, where males use their colour patterns to attract females during courtship behaviour. Measuring spectral reflectance can present some difficulties given that fish can undergo rapid colour changes that can be stimulated by social interactions, photic environment, and stress. This research focuses on the effect of time, ambient light intensity and anaesthetic conditions that could be affecting spectral reflectance properties. The purpose of this study is to develop sound methodological approaches for evaluating spectral reflectance of 'Melanochromis auratus', a rock-dwelling Lake Malawi cichlid. In three separate experiments, spectral reflectance measurements were gathered at varying time intervals, under varying ambient light conditions and using three common fish anaesthetics (MS222, clove oil and an ice water bath). Generally, spectral reflectance properties decreased over time and increased with increasing light intensities; the maximum percent reflectance increased with increasing light intensities, indicating that chromatophores respond to light and may perform maximally at high light intensities (i.e....

Water content estimation in vegetation with MODIS reflectance data and model inversion methods

Zarco-Tejada, Pablo J.; Rueda, C. A.; Ustin, S. L.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 4085 bytes; image/gif
ENG
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Statistical and radiative-transfer physically based studies have previously demonstrated the relationship between leaf water content and leaf-level reflectance in the near-infrared spectral region. The successful scaling up of such methods to the canopy level requires modeling the effect of canopy structure and viewing geometry on reflectance bands and optical indices used for estimation of water content, such as normalized difference water index (NDWI), simple ratio water index (SRWI) and plant water index (PWI). This study conducts a radiative transfer simulation, linking leaf and canopy models, to study the effects of leaf structure, dry matter content, leaf area index (LAI), and the viewing geometry, on the estimation of leaf equivalent water thickness from canopy-level reflectance. The applicability of radiative transfer model inversion methods to MODIS is studied, investigating its spectral capability for water content estimation. A modeling study is conducted, simulating leaf and canopy MODIS-equivalent synthetic spectra with random input variables to test different inversion assumptions. A field sampling campaign to assess the investigated simulation methods was undertaken for analysis of leaf water content from leaf samples in 10 study sites of chaparral vegetation in California...

Natural and stress-induced effects on leaf spectral reflectance in Ontario species

Mohammed, G. H.; Noland, T. L.; Irving, P. H.; Sampson, P. H.; Zarco-Tejada, Pablo J.; Miller, J. R.
Fonte: Ontario Ministry of Natural Resources Publicador: Ontario Ministry of Natural Resources
Tipo: Capítulo de libro Formato: 2925277 bytes; application/pdf
ENG
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This study explores some of the biological factors influencing leaf-based spectral reflectance, and endeavours to answer the questions: (1) Can Ontario plant species be satisfactorily distinguished by their leaf spectra? (2) Can spectral properties be used to identify physiological strain in plants before visual symptoms appear? and (3) How strongly do factors other than species and stress affect spectral properties? Forty-four species were examined for species effects. Some general patterns were revealed, including: low reflectance in the near infrared region for conifers compared to broadleaved species; higher reflectance in the blue wavebands for species with blue hues in their foliage; and more rapid decay of the green spectral peak in deciduous tree and shrub species. However, the influence of species was easily superceded by other factors, such as leaf age, leaf side, and stress status. The effects of stresses such as senescence and herbicide on leaf reflectance were evident prior to the appearance of visual symptoms such as chlorosis, browning, and reduced growth. The application of spectral indices was a useful means to quantify previsual changes in spectral reflectance. The red edge inflection point was well correlated with chlorophyll content...

Diffuse Reflectance Spectroscopy Characterization for Extraction of Tissue Physiological Parameters

Phelps, Janelle Elise
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Dissertação
Publicado em //2010
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Variations in hemoglobin concentration can be indicative of a number of serious complications, including blood loss and anemia. Rapid, noninvasive measurements of hemoglobin are important in applications where blood status is reflective of patient well-being, such as in the emergency room, operating room, or the battlefield. Probe-based diffuse reflectance spectroscopy is capable of noninvasively quantifying tissue optical properties, including hemoglobin concentration. The quantification of hemoglobin concentration using optical methods is complicated by tissue scattering and the robustness of the algorithm and instrumentation used to interrogate the tissue. The sensing depth of diffuse reflectance spectroscopy can be tailored by the wavelengths of light and probe design used.

In this thesis, the accuracy and clinical viability of different diffuse reflectance spectroscopy implementations are presented. The robustness of an inverse Monte Carlo model, in which tissue optical properties are determined from measured reflectance using ultraviolet-visible (UV-VIS) wavelengths and a steady-state instrument, was tested using laboratory measurements. From the laboratory measurements, a set of references was identified which provided accurate absorption and scattering measurements...

A model to predict the reflectance from a concrete surface as a function of the sun-object-image angular relationship

Grogan, George C.
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
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A study was made of the variation in the reflectance of a concrete sample as the sun-object-image angular relationship was varied. The research work was performed in the controlled conditions of a laboratory so that atmospheric effects could be neglected. Reflectance measurements were taken from a. concrete sample whose surface roughness had been measured. Both specular and diffuse illumination in the red (630 - 680nm) wavelength region of the visible spectrum were measured. A model which can be used to predict the reflectance value for a given sun-object-image angular relationship was developed. Actual reflectance measurements taken outdoors agreed to within one percent of the model's predicted reflectance values.

Comparison of methods for generation of absolute reflectance factor measurements for BRDF studies

Feng, Xiaofan
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
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For remote sensing applications, there is a need for knowledge concerning the reflectance properties of natural and man-made materials as a function of measurement geometry and wavelength. This information is used to determine the so-called bidirectional reflectance distribution function (BRDF). This study is intended to generate an absolute bidirectional reflectance factor for BRDF studies. This is accomplished by development of a goniospectroradiometer which can simulate any source-sensor-target geometry. The spectral range is from visible to near- infrared (2500 nm) with a spectral resolution of 10 nm. The study involves both theoretical and experimental work for calibration of BRDF by: (1) the directional hemispherical reflectance and (2) a NIST calibrated standard reflectance tile. A PTFE sample is calibrated using both methods, and a comparison test was conducted to verify the accuracy. This PTFE sample can be used as a reference standard material to transfer reflectance factor scale to all source-target-sensor geometries in the visible and infrared regions (400 nm to 2500 nm) of the spectrum.

Comparison of methods for generation of absolute reflectance factor values for bidirectional reflectance-distribution function studies

Feng, Xiaofan; Schott, John; Gallagher, Timothy
Fonte: Optical Society of America (OSA) Publicador: Optical Society of America (OSA)
Tipo: Artigo de Revista Científica
EN_US
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Currently, spectrophotometric standard reference materials are calibrated only by using the illumination and viewing geometries recommended by the Commission Internationale de l'Eclairage, and for some geometries the spectral range is limited to the visible wavelengths. A need exists for procedures that calibrate standards at many other geometries and for a broader spectral range. Two methods for calibrating the spectral bidirectional reflectance factor are described. The absolute bidirectional reflectance factor of a sintered polytetrafluoroethylene (PTFE) sample is determined for nearly all the possible illumination and viewing geometries from 400 nm to 2500 nm. The references are a 45/0 reflectance standard calibrated by the National Institute of Standards and Technology and a sintered PTFE sample with a directional, hemispherical reflectance factor traceable to the Institute. The results of the two methods agree to within 0.01 in reflectance factor values. With this PTFE sample as a transfer standard, the instrument described can also be used to measure the absolute bidirectional reflectance factor at nearly all the illumination and viewing geometries from 400 nm to 2500 nm.; RIT community members may access full-text via RIT Libraries licensed databases: http://library.rit.edu/databases/; n/a

Spectral Reflectance Analysis of the Caribbean Sea

Aguirre Gómez,Raúl
Fonte: Instituto de Geofísica, UNAM Publicador: Instituto de Geofísica, UNAM
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2014 EN
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Reflectance spectral curves were analysed by a derivative method. Derivative reflectance spectra revealed concealed peaks of both reflectance and absorption curves of Caribbean seawater and elements contained within it. Reflectance curves showed a predominant blue colour (400-500 nm) characteristic of Caribbean oligotrophic waters, conspicuous peaks result from the optical properties of chlorophyll a and seawater. Reflectance curves had a similar spectral response. This paper analyses reflectance spectra of surface seawater at 31 stations in the Caribbean Sea during the summer of 2001.