1,720,993 research outputs found
Identification of homogeneous phenological patterns for the characterization of vegetation recovery times on climatic scales
No full textAssessment of spatially distributed values of Kc using vegetation indices derived from medium resolution satellite data
No full textIn the last years, the theme of suitable assessment of irrigation water supply has been raised relevant interest
for both general principles of sustainable development and optimization of water resources techniques and
management. About 99% of the water used in agriculture is lost by crops as evapotranspiration (ET). Thus, it
becomes crucial to drive direct or indirect measurement in order to perform a suitable evaluation of water loss by
evapotranspiration (i.e. actual evapotranspiration) as well as crop water status and its effect on the production.
The main methods used to measure evapotranspiration are available only at field scale (Bowen ratio, eddy
correlation system, soil water balance) confined to a small pilot area, generally due to expense and logistical
constraints. This led over the last 50 years to the development of a large number of empirical methods to estimate
evapotranspiration through different climatic and meteorological variables as well as combining models, based
on aerodynamic theory and energy balance, taking into account both canopy properties and meteorological
conditions. Among these, the Penman-Monteith equation seems to give the best results providing a robust and
consistent method world wide accepted.
Such conventional methods only provide accurate evapotranspiration assessment for a homogeneous region nearby
the meteorological gauge station and cannot be extrapolated to other different sites; whereas remote sensing
techniques allow for filling up such a gap. Some of these satellite techniques are based on the use of thermal band
signals as inputs for energy balance equations. Another common approach is mainly based on the FAO method
for estimating crop evapotranspiration, in which evapotranspiration data are multiplied by crop coefficients, Kc,
derived from satellite multispectral vegetation indices obtained. The rationale behind such a link considers that Kc
and vegetation indices are sensitive to both leaf area index and fractional ground cover.
Thermal-based energy balance models are more suitable than the FAO-Kc model for estimating crop ET, especially
under moisture stress conditions, but they require many inputs and detailed theoretical background knowledge;
so they can be only used in regions where high quality, hourly agricultural weather data are readily available
providing instantaneous values of heat fluxes corresponding to the time of the satellite overpass. Thus, FAO-Kc
approach is widely used in research activities and real-time irrigation scheduling for several water applications
since it does not require temporal upscaling for obtaining daily values and satellite imagery in the reflective bands
used for vegetation index computation are more readily available at higher spatial resolution than thermal band
data.
There is no simple way to compute crop coefficients because they depend on climate, soil type, crop and its
varieties, irrigation method, soil water, nutrient content and plant phenology. Consequently, specific calibrations
of crop coefficient are required in various climatic regions. Many authors suggested a linear relationship between
Kc and vegetation indices, but non-linear relationships have been proposed too. However, according to the
radiative transfer theory, the nature of such relationships depends on the crop architecture and the definition of
the adopted vegetation index, but the linear assumption can be adopted as first. Such studies, mainly investigated
the possibility to use high resolution satellite data, such as Quickbird, Ikonos, TM, which are not suitable for
operational purposes since in spite of the high spatial sampling they have an inadequate revisiting time over a
given area. To obtain adequate temporal sampling, some authors proposed the use of a virtual constellation made
by all currently available high-resolution satellites (e.g., DEMETER project). However the joint use of data from
different satellites requires a carefully inter-satellite cross-calibration and co-registration.
In order to avoid such problems and to generate spatially distributed values of Kc capturing field-specific crop
development, the employment of vegetation indices derived from medium resolution MODIS data having a
higher temporal sampling has been investigated. The spatial and temporal correlation between NDVI (Normalized
Difference Vegetation Index) and crop coefficients for different herbaceous and arboreal cultivations has been
investigated to define their relationships. Through this approach site-specific crop coefficients were derived taking
into account the effective ground coverage and status. The analysis has been applied on the 2005-2008 time series
for the Basilicata region, Southern Italy
Indicators of land degradation vulnerability due to anthropic factors: tools for an efficient planning
No full textLand degradation is one of the most impacting phenomena on natural resource availability, both in quantitative and qualitative terms. In order to provide efficient tools for territorial sustainable management in areas affected by land degradation, it is important to define suitable models and indicators able to identify exposed areas and their vulnerability level, so as to provide an effective support for decision makers in identifying intervention priorities and planning mitigation/adaptation strategies. This work is focused on the evaluation at high spatial detail of land degradation vulnerability due to anthropic factors, which is a crucial issue in areas devoted to farming practices. Vulnerability is evaluated by integrating a new indicator of the mechanization level the authors recently developed, with a set of census based indicators of land management. The new indicator is independent of census data being based on land cover data; thus, it can provide a better spatial characterization and a more frequent updating compared to commonly adopted indices that are evaluated at municipal scale. By analyzing data for the whole Southern Italy, such an indicator was integrated for the first time at full spatial resolution to obtain a final vulnerability index of land management. This comprehensive index enabled a more accurate estimation of the land degradation vulnerability due to anthropic factors allowing the discrimination of priority areas within the municipal areas
Development of environmental indicators for estimating vulnerability to land degradation
No full textGoing 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
Landscape-scale characterization of vegetation phenology by using AVHRR-NDVI and Landsat-TM data
No full textVariations 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
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