1,720,956 research outputs found
Statistical characterisation of COSMO Sky-Med X-SAR retrieved precipitation fields by scale-invariance analysis
No full textCOSMO Sky-Med (CSK) is an important programme of the Italian Space Agency aiming at supporting environmental monitoring and management of exogenous, endogenous and anthropogenic risks through X-band Synthetic Aperture Radar (X-SAR) on board of 4 satellites forming a constellation. Most of typical SAR applications are
focused on land or ocean observation. However, X-band SAR can be detect precipitation that results in a specific signature caused by the combination of attenuation of surface returns induced by precipitation and enhancement
of backscattering determined by the hydrometeors in the SAR resolution volume. Within CSK programme, we conducted an intercomparison between the statistical properties of precipitation fields derived by CSK SARs and those derived by the CNR Polar 55C (C-band) ground based weather radar located in Rome (Italy).
This contribution presents main results of this research which was aimed at the robust characterisation of rainfall
statistical properties across different scales by means of scale-invariance analysis and multifractal theory. The
analysis was performed on a dataset of more two years of precipitation observations collected by the CNR Polar
55C radar and rainfall fields derived from available images collected by the CSK satellites during intense rainfall events.
Scale-invariance laws and multifractal properties were detected on the most intense rainfall events derived from
the CNR Polar 55C radar for spatial scales from 4 km to 64 km.
The analysis on X-SAR retrieved rainfall fields, although based on few images, leaded to similar results and
confirmed the existence of scale-invariance and multifractal properties for scales larger than 4 km. These outcomes
encourage investigating SAR methodologies for future development of meteo-hydrological forecasting models based on multifractal theory
Retention performance of green roofs in representative climates worldwide
No full textThe ongoing process of global urbanization contributes to an increase in stormwater runoff from impervious surfaces, threatening also water quality. Green roofs have been proved to be innovative stormwater management measures to partially restore natural states, enhancing interception, infiltration and evapotranspiration fluxes. The amount of water that is retained within green roofs depends not only on their depth, but also on the climate, which drives the stochastic soil moisture dynamic. In this context, a simple tool for assessing performance of green roofs worldwide in terms of retained water is still missing and highly desirable for practical assessments.
The aim of this work is to explore retention performance of green roofs as a function of their depth and in different climate regimes. Two soil depths are investigated, one representing the intensive configuration and another representing the extensive one. The role of the climate in driving water retention has been represented by rainfall and potential evapotranspiration dynamics. A simple conceptual weather generator has been implemented and used for stochastic simulation of daily rainfall and potential evapotranspiration. Stochastic forcing is used as an input of a simple conceptual hydrological model for estimating long-term water partitioning between rainfall, runoff and actual evapotranspiration. Coupling the stochastic weather generator with the conceptual hydrological model, we assessed the amount of rainfall diverted into evapotranspiration for different combinations of annual rainfall and potential evapotranspiration in five representative climatic regimes. Results quantified the capabilities of green roofs in retaining rainfall and consequently in reducing discharges into sewer systems at an annual time scale. The role of substrate depth has been recognized to be crucial in determining green roofs retention performance, which in general increase from extensive to intensive settings. Looking at the role of climatic conditions, namely annual rainfall, potential evapotranspiration and their seasonality cycles, we found that they drive green roofs retention performance, which are the maxima when rainfall and temperature are in phase.
Finally, we provide design charts for a first approximation of possible hydrological benefits deriving from the implementation of intensive or extensive green roofs in different world areas. As an example, 25 big cities have been indicated as benchmark case studies
Retention performances of green roofs worldwide at different time scales
No full textUrbanization process is rapidly converting forested areas and grasslands to residential, commercial, or industrial spaces, triggering soil degradation and significantly increasing impervious surfaces. Consequently, man-made environments experience significant decrease of infiltration and groundwater recharge, enhancing the problems related to the management and protection from increased stormwater runoff. Green roofs are structural measures able to mitigate these negative drawbacks due to anthropic transformation, retaining and detaining stormwater runoff, with the main advantage of reducing hydraulic loads on combined storm sewer systems. Hydrological performance of green roofs have been studied in different parts of the world under different climatic conditions, but a comprehensive study that provides global responses, even in an approximate way, is still missing. The aim of this work is to assess the convenience and the feasibility of installing green roofs in any target area of the world, providing a rough indication of geographic regions where green roof installation is possible with good hydrological performance, and feasible in rainfed conditions with low vegetation water stress. To do that, we explored in silico green roofs' hydrological performance worldwide, using climatological forcings from ERA-Interim database as input for a simple conceptual hydrological model to estimate green roof outputs, in terms of evapotranspiration and runoff
Extreme rainfall regime characterization in Sardinia using daily rainfall data
Get PDFFor the design of hydraulic structures for flood conveyance and discharge, or
protection of territory against flood is fundamental the knowledge of the ``extreme
rainfall regime'' in the area where the hydraulic structures must be set up.
Indeed the design flood is commonly evaluated as output of rainfall-runoff models that
receive as input the quantitative description of a rainfall extreme event with a given
exceedance probability.
This dissertation assesses the performance of different statistical approaches in
characterizing extreme rainfall in the island of Sardinia (Italy).
After a detailed review of the theoretical bases of existing methodologies, we compare
the results obtained from the use of:
a) a Generalized Extreme value (GEV) distribution model, and a Two component
Extreme Value (TCEV) distribution model, both applied to yearly maxima of daily
rainfall, and b) a Generalized Pareto (GP) distribution model applied to rainfall
excesses above a properly specified threshold. For the latter purpose, we use the
Multiple Threshold Method (MTM) developed by Deidda(2010), which demonstrate
good performance also in the case of quantized records.
In order to describe the spatial variation of TCEV, GEV and GP model parameters a
regional approach based on homogeneous regions, and two versions of Kriging (a
commonly used geostatistical approach) i.e. ordinary Kriging (OK), and Kriging for
uncertain Data (KUD), are compared.
The obtained results are very promising, pointing towards the use of: a)a GEV
distribution model for yearly rainfall maxima, and a KUD model to describe the spatial
variation of model parameters, and b)a GP model for rainfall excesses and either an OK
or a KUD model for the spatial variation of model parameters. The reason why the OK
and KUD approaches lead to the same results in the GP case, is attributed to the
robustness of the MTM method
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
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