6 results on '"Rivard, Benoit"'
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2. Effects of Season and Successional Stage on Leaf Area Index and Spectral Vegetation Indices in Three Mesoamerican Tropical Dry Forests
- Author
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Kalacska, Margaret E. R., Sánchez-Azofeifa, G. Arturo, Calvo-Alvarado, Julio C., Rivard, Benoit, and Quesada, Mauricio
- Published
- 2005
- Full Text
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3. Using visible-near-infrared spectroscopy to classify lichens at a Neotropical Dry Forest
- Author
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Guzmán, J. Antonio, Laakso, Kati, López Rodríguez, Jose Carlos, Rivard, Benoit, Sanchez-Azofeifa, G.A., and López Rodríguez, José Carlos
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0106 biological sciences ,General Decision Sciences ,Mineralogy ,Context (language use) ,010501 environmental sciences ,010603 evolutionary biology ,01 natural sciences ,ESPECTROSCOPÍA ,Genus ,LICHEN SPECTROSCOPY ,Ecosystem ,Taxonomic rank ,Lichen ,SPECTRAL CLASSIFICATION ,Ecology, Evolution, Behavior and Systematics ,0105 earth and related environmental sciences ,Ecology ,LÍQUENES ,15. Life on land ,WAVELET ANALYSIS ,Substrate (marine biology) ,VNIR ,REFLECTANCE ,SPECIES DISCRIMINATION ,visual_art ,visual_art.visual_art_medium ,Environmental science ,Bark - Abstract
The optical properties of lichens have been traditionally explored in the context of geological mapping where the encrustation of lichens on rocks may influence the detection of minerals of interest. As of today, few studies have looked into the potential of using the optical properties of lichens to classify them; however, none has investigated the classification of tropical lichens using spectroscopy. Here we explore the use of the visible-near infrared reflectance (VNIR; 450–1000 nm) to discriminate Neotropical corticolous lichens; the most abundant lichens in tropical forests. Reflectance measurements on lichens and their bark substrate were performed on 282 lichens samples of 32 species attached to their host's bark. Using these measurements, we first explored the degree of spectral mixing of bark and lichens by linear unmixing each lichen spectrum with the corresponding average species spectrum and bark spectrum. Overall, the results reveal that the lichen signatures tend to mask the spectral contributions from bark; however, there are some specific groups of species with high bark mixing probably due to their nature and the similarities between the lichen and bark spectra. Next, we classified the lichen spectra based on growth forms and taxonomic ranks (i.e., family, genus, species) using five machine learning classifiers. This analysis was conducted on raw reflectance spectra and wavelet-transformed spectra to enhance the absorption features prior to classification. As expected, the classification of lichen spectra is less accurate at species-specific levels, rather than higher taxonomic ranks. The wavelet transformation was found to enhance the general performance of classification; however, the accuracy of the classification depends on the classifier. Of the classifiers used in this study, linear discrimination applied to reflectance spectra presents the highest performance at the species level. Our results reveal the potential of using the VNIR reflectance as a method to discriminate Neotropical lichens. The introduced methodology may be conducted in the field, thus allowing the monitoring of lichen communities in forests; thereby furthering the current understanding of the role of lichens in ecosystem functioning. Las propiedades ópticas de los líquenes se han explorado tradicionalmente en el contexto del mapeo geológico donde la incrustación de líquenes en las rocas puede influir en la detección de minerales de interés. Hasta la fecha, pocos estudios han examinado el potencial de utilizar las propiedades ópticas de los líquenes para clasificarlos; sin embargo, ninguno ha investigado la clasificación de los líquenes tropicales mediante espectroscopia. Aquí exploramos el uso de la reflectancia del infrarrojo cercano visible (VNIR; 450–1000 nm) para discriminar líquenes cortícolas neotropicales; los líquenes más abundantes en los bosques tropicales. Las mediciones de reflectancia en líquenes y su sustrato de corteza se realizaron en 282 muestras de líquenes de 32 especies adheridas a la corteza de su huésped. Usando estas medidas, primero exploramos el grado de mezcla espectral de la corteza y los líquenes mediante la desmezcla lineal de cada espectro de líquenes con el espectro de especies promedio correspondiente y el espectro de corteza. En general, los resultados revelan que las firmas de los líquenes tienden a enmascarar las contribuciones espectrales de la corteza; sin embargo, existen algunos grupos específicos de especies con una alta mezcla de corteza probablemente debido a su naturaleza y las similitudes entre los espectros de líquenes y corteza. A continuación, clasificamos los espectros de líquenes según las formas de crecimiento y los rangos taxonómicos (es decir, familia, género, especie) utilizando cinco clasificadores de aprendizaje automático. Este análisis se realizó en espectros de reflectancia sin procesar y espectros transformados por ondículas para mejorar las características de absorción antes de la clasificación. Como era de esperar, la clasificación de los espectros de líquenes es menos precisa a niveles específicos de especies, en lugar de rangos taxonómicos más altos. Se descubrió que la transformación de ondículas mejora el rendimiento general de la clasificación; sin embargo, la precisión de la clasificación depende del clasificador. De los clasificadores utilizados en este estudio, la discriminación lineal aplicada a los espectros de reflectancia presenta el rendimiento más alto a nivel de especie. Nuestros resultados revelan el potencial de utilizar la reflectancia VNIR como método para discriminar líquenes neotropicales. La metodología introducida podrá realizarse en el campo, permitiendo así el seguimiento de las comunidades de líquenes en los bosques; fomentando así la comprensión actual del papel de los líquenes en el funcionamiento de los ecosistemas. Universidad Nacional, Costa Rica University of Minnesota Twin Cities, USA University of Alberta, Canada Escuela de Ciencias Biológicas
- Published
- 2020
4. Visible and short-wave infrared reflectance spectroscopy of selected REE-bearing silicate minerals.
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Turner, David J., Rivard, Benoit, and Groat, Lee A.
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SILICATE minerals , *RARE earth metals , *NEAR infrared reflectance spectroscopy - Abstract
Natural samples of the rare earth element (REE)-bearing silicate minerals cerite, mosandrite, kainosite, zircon, and eudialyte were studied using reflectance spectroscopy in the visible to short-wave infrared regions (500 to 2500 nm) and further characterized by scanning electron microscopy and electron microprobe analysis. Spectral features of these minerals are driven primarily by 4
f -4f intraconfigurational electronic transitions of trivalent lanthanides, as well as 5f -5f electronic transitions of uranium and vibrational overtones and combinations of H2O and OH–. Spectra of eudialyte are also impacted by relative amounts of IVFe2+ and VFe2+. Respective spectra of these REE-bearing silicate minerals are sufficiently distinct to enable spectral classification. Spectral variability (e.g., band depths and locations) of some specific REE-related absorptions, such as an Er3+- and Yb3+-related absorption near 978 nm and Nd3+-related absorptions near 746, 803, and 875 nm, are interpreted to be driven by cation site differences in the crystal structures. This work adds to the growing understanding of REE-bearing mineral reflectance spectroscopy, which facilitates detection, identification, and quantification of REE-bearing silicate minerals in remote sensing applications. This is especially relevant for hyperspectral imaging spectroscopy with high spatial resolutions where the spectral response of a pixel becomes increasingly dominated by mineralogy rather than lithology. [ABSTRACT FROM AUTHOR]- Published
- 2018
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5. Visible and short-wave infrared reflectance spectroscopy of REE phosphate minerals.
- Author
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TURNER, DAVID J., RIVARD, BENOIT, and GROAT, LEE A.
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NEAR infrared reflectance spectroscopy , *XENOTIME , *MONAZITE , *RARE earth metals , *FLUORAPATITE - Abstract
Reflectance spectroscopy in the visible to short-wave infrared regions (500 to 2500 nm) was carried out using natural samples of the rare earth element (REE) phosphate minerals monazite, xenotime, and britholite. Samples were characterized by scanning electron microscopy and electron microprobe analysis. Absorption band positions were recorded with their probable origins, and spectral variability among the samples is discussed. Spectral features of these minerals are driven primarily by 4f-4f intraconfigurational electronic transitions of trivalent lanthanides. The distinct REE distributions of monazite, xenotime, and britholite drive their bulk spectral patterns, which in turn are sufficiently distinct to enable spectral classification. Spectral variability of some specific REE-related absorptions are interpreted to be driven by differences of the coordination polyhedra for the lanthanide cations between the crystal structures. Spectra of these minerals were also compared against carbonatitehosted REE bearing fluorapatite. The work presented here strengthens the growing foundation for the interpretation of reflectance spectra of these REE phosphate minerals and enables exploitation of the observed features by the remote sensing community for detection, identification, and quantification of REE phosphate minerals. This is especially relevant for hyperspectral imaging spectroscopy with high spatial resolution, where the spectral response of a pixel becomes increasingly dominated by mineralogy. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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6. Foliar spectral properties following leaf clipping and implications for handling techniques
- Author
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Foley, Sheri, Rivard, Benoit, Sanchez-Azofeifa, G. Arturo, and Calvo, J.
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REFLECTANCE , *LEAVES , *SPECTRUM analysis , *OPTICAL reflection - Abstract
Abstract: After leaves are clipped their reflectance properties change over time at variable rates. Spectral change can in part be attributed to the changing water content of the leaf, which affects absorption in the VIS, NIR and the SWIR. Maintaining water volume within samples has been the motivation behind many leaf handling techniques. This study has assessed the time constraints between leaf collection and spectral measurement. Specifically the relationship between leaf water content and foliar spectra (350–2500 nm) was examined over time for five tropical trees (common guava (Psidium guajava), purple guava (Psidium littorale), weeping fig (Ficus benjamina), floss silk (Chorisia speciosa), and coffee (Coffea arabica)). This investigation was carried for leaves wrapped with moist gauze around their petiole (treatment leaves) and leaves with no treatment. Spectral measurements and mass measurements were repeated for each leaf once every hour for the first 12 h, then every 4–6 h for 18 h, followed by one measurement after 12 h, and finally once a day until the control samples became air-dry. Foliar reflectance in the visible spectrum was not immediately responsive to water content changes and did not change until wilting of the leaf was observed. The NIR and SWIR wavelength regions were affected immediately by small changes in water content. Thus, by the time wilting was first observed the NIR and SWIR foliar reflectance differed considerably from corresponding fresh leaf reflectance. No common time limit could be observed for leaf clipping and reflectance measurement. Leaves have a variety of water contents and dehydration rates hence measurement time constraints are dependent on the properties of the leaf or species. Rather than using a time limit it is recommended that leaf handling techniques be based upon managing leaf water content and leaf structure. The results of this study indicate that leaves with petioles wrapped in moist paper towel and placed within plastic bags will maintain leaf reflectance longer than equivalent leaves without treatment; samples tested here lasted a minimum of 7 days. θ and D indices (“angle difference” and “root mean square difference”, respectively) revealed a stronger relationship between leaf water content and spectral shape than between leaf water and raw reflectance magnitude. The ratio of 1187/1096 nm, when compared with θ and D indices and individual reflectance bands, showed the highest coefficient of determination with leaf water content (r 2 =0.952). [Copyright &y& Elsevier]
- Published
- 2006
- Full Text
- View/download PDF
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