1,721,187 research outputs found
Retrieval of vegetation properties using Top of Atmosphere radiometric data: A multi-sensor approach
No full textVegetation is the main source of primary production and plays an important role inmodeling the exchanges of energy and mass of carbon, oxygen and water between the earth and the atmosphere. Mapping andmonitoring of vegetation canopies are crucial for various applications including agro-ecosystem models, climatology modeling, crop growth modeling and vegetation productivity modeling. The reflected radiance from vegetation carries information about chemical and bio-geophysical vegetation characteristics. Leaf area index (LAI), chlorophyll content and fraction of vegetation cover (fCover) are among the most important vegetation properties that can be retrieved from satellite observations. Over the past decades, considerable effort has been given toward improving vegetation properties retrieval fromremotely sensed data. A number of satellite observations are currently being utilized to retrieve vegetation characteristics in a diverse range of spatial and temporal resolutions and new ones will become available soon with an unprecedented capacity to quantify vegetation properties. The accurate vegetation variable retrieval depends on three issues: radiometric data quality, forward radiance modeling and parametrization and regularization. The major goal of this contribution is to improve vegetation properties retrieval from top of atmosphere optical satellite observations, given the richness of current and near-future sources of optical remote sensing data. The first part of this contribution deals with model parameterization for variable retrieval and determining retrievable variables through sensitivity analysis. The sensitivity of top of atmosphere radiance and surface reflectance of a soil-vegetation systemto input biophysical and biochemical variables is estimated using the coupled Soil-Leaf-Canopy radiative transfer model SLC and MODTRAN. This study also proposes an improvement to the design and sampling of screening methods for efficient sensitivity analysis of computationally expensive models. The results demonstrated high correlation between the proposed improvement (with only modest computational demands) against variance-based global sensitivity analysis in determining the most influential and non-influential variables. The second part of this contribution provides a proof of concept for a multi–temporal, multi–sensor approach to retrieve biophysical and biochemical vegetation variables using spectral–directional radiometric data. The approach is designed for the exploitation of a temporal sequence constructed by combining data acquired by different sensors over time. Focus is given to the retrieval of three important vegetation variables; LAI, fCover and chlorophyll content over the agricultural test site in Barrax, Spain. A variety of different satellite observations including, CHRIS–Proba, Landsat TM and ASTER are used to invert the coupled surface–atmosphere SLC–MODTRAN radiative transfer model. This thesis presents an overview of the results and challenges in utilizing the multi–temporal, multi–sensor approach and the Bayesian inversion technique in the retrieval of terrestrial vegetation properties. It was shown that the approach is capable of dealing with a diversity of optical sensors by exploiting heterogeneous radiometric data and allows for having frequent updates of vegetation biophysical and biochemical products over time. Moreover, the results showed that integrating information from different sensors improves the retrieval of vegetation variables compared to the case of single sensor retrievals. The last part of this contribution is devoted to the investigation of the topographic effects on top of atmosphere radiance modeling and variable retrieval. To account for such effects, this study presents an extension of “the four-stream radiative transfer theory” previously proposed by Verhoef and Bach (2003b, 2007, 2012). The extension is mainly focused on two aspects in top of atmosphere radiance modeling. First, the study gives a detailed account of themain topography-induced effects on top of atmosphere radiance modeling and the relevant equations are given. Second, a new formulation is proposed for the derivation of the six atmospheric coefficients using MODTRAN in order to make it more computationally efficient, as well as to avoid using zero surface albedo which causes some miscalculations in the results. It was demonstrated that the topographic effect has to be taken into account in variable retrieval and the approach presented in this thesis can be used tomodel such effects on top of atmosphere radiance over rugged terrain.Geoscience & Remote SensingCivil Engineering and Geoscience
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Een automatische procedure ter verkrijging van corresponderende punten in Caesar-beelden
No full textThis report describes an automatic procedure in finding corresponding points in CAESAR-images. CAESAR is a multispectral scanner jointly developed by the Nationaal Lucht- en Ruimtevaartlaboratorium (National Aerospace Laboratory) and Technisch-Physische Dienst. First, the ' CAESAR-images are geometrically corrected by the software-package OPTIPARES, using inertial system data and a geometrical analysis is performed. These images are then used in an automatic procedure to calculate the geometrical transformation-model between these images. This is done in order to use the spectral information as good as possible. Correlation-techniques are used within this procedure. By using two images, in the first image interesting points are found by using the Moravec-operator. The corresponding points in the second image are determined by a ~2D-cross-correlation. From the -two point-lists the geometrical transformation-model can be calculated. In the opinion of the NLR, a shift is sufficient in this model. The results show that this assumption can not hold. Higher-order polynomals give better results. When the geometrical transformation-model is known, a resampling takes place to match the imagesCivil Engineering and GeosciencesFotogrammetrie en remote sensin
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