1,720,961 research outputs found
Global Composites of the MERIS Terrestrial Chlorophyll Index
No full textFrom the year 2006, the European Space Agency (ESA) supported the production of the global composite (Level 3) of a unique terrestrial chlorophyll product called the MERIS Terrestrial Chlorophyll Index (MTCI) (Dash and Curran 2004). The MTCI is calculated using three red/near infrared bands of Envisat MERIS data (Rast et al. 1999). This index estimates the relative location of the reflectance 'red edge' of vegetation and is more sensitive than red edge position to canopy chlorophyll content, notably at high chlorophyll contents. This product effectively combines information on leaf area index and the chlorophyll concentration of leaves to produce an image of chlorophyll content (i.e. the amount of chlorophyll per unit area of ground). Chlorophyll content plays an important role in determining the physiological status of a plant, is related to photosynthetic rate and varies temporarily and spatially. MTCI global composites can be used to estimate relative and land cover specific, chlorophyll content in space and time and this in turn can be a key input to models of terrestrial productivity, gas exchange and vegetation health.Two global monthly MTCI composites for March and August 2003 are presented on the cover. These images display the MTCI on a nominal scale of 0 to 6, with higher values indicating higher chlorophyll content. These images clearly capture the phenology of global vegetation. In March, a major part of the southern hemisphere (e.g. South Africa, South America) had high MTCI values during the peak of their growing season, whereas a major part of the northern hemisphere had low MTCI values in March. In August, the situation was reversed. A major part of the northern hemisphere (e.g. Europe, North America) had high MTCI values when the coverage of green leaves was at a maximum. In both images the tropical rain forests had relatively high MTCI values. It is interesting to note that even at the centre of these forests there is a change in MTCI values between March and August.This global MTCI product will be produced as weekly and monthly composites and is the only terrestrial chlorophyll product available from space. The MTCI along with oceanographic chlorophyll concentration estimates, also from MERIS, can be used to generate a 'global chlorophyll map' for the estimation of global productivity.<br/
Signal-to-noise ratio for MTCI and NDVI time series data,
No full textThe Phenology of vegetation varies with climate and variability in phenology is a powerful measure of climate change. Remotely-sensed data can be used to produce phenology curves that capture ‘green-up’, maturity and senescence from local to global scales. These curves are usually produced with Normalised Difference Vegetation Index (NDVI) data but are notoriously noisy. The MERIS Terrestrial Chlorophyll Index (MTCI) is related to the chlorophyll content, does not suffer from some of the limitations of NDVI (e.g., saturation at high biomass) and should, it was hypothesised, produce a less noisy phenological curve. Two methods were used to determine the phenological curve (signal) and Variability in the curve (noise); iterative polynomial fitting and discrete Fourier transformation.
The signal-to-noise ratio (SNR) for MTCI curves was significantly higher than for the NDVI curves and this difference was largest for high green biomass areas. This was probably the result of the compositing techniques typically used for MTCI data. However, the two methods of SNR calculation produced different results for the NDVI but not the MTCI, thus suggesting that there was bias in the less noisy NDVI curve
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
A comparison of two phenological variables derived from vegetation NDVI and MERIS MTCI: A feasibility study in the context of global monitoring for environment and security (GMES)
No full textDispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
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