1,720,960 research outputs found
Downscaling of American National Aeronautics and Space Administration (NASA) daily air temperature in Sicily, Italy, and effects on crop reference evapotranspiration
No full textAir temperature (Ta) is one of the key factors in agro-hydrological studies including estimation of crop reference evapotranspiration (ET0), which is crucial for irrigation water management and sustainability of agro-ecosystem productivity. Because direct measurements of ET0are difficult, expensive and time consuming, the use of physically based or empirical approaches linked to meteorological information is often preferred. The Prediction of Worldwide Energy Resource project developed by the American National Aeronautics and Space Administration (POWER-NASA) provides daily meteorological information on a 1° latitude by 1° longitude grid. Despite the poor spatial resolution characterizing this archive, the data is global and continuous in time, so that it can be used in particular regions of the globe where weather measurements are not well spatially distributed and/or there are some missing weather data to fill. Procedures for downscaling and spatial disaggregation of daily air temperatures retrieved from the POWER-NASA archive were proposed and validated for the climate of Sicily, Italy. In particular, a cosine function with three empirical parameters derived from ground elevation was suggested to estimate the spatial and temporal variability of a lapse rate adjustment factor used to downscale and to disaggregate POWER-NASA air temperature. Model calibration was carried out over three years (2006–2008), whilst validation regarded the measurements acquired over the following six years (2009–2014). Downscaled daily air temperature results were consistent and comparable with local ground measurements. The spatial disaggregation technique, aimed to map the distributions of Ta, was then tested by the joint use of the Digital Elevation Model (DEM) and the proposed model. Finally, in order to assess the suitability of downscaled air temperatures, two simplified empirical equations to estimate daily reference evapotranspiration (ET0) from air temperature and solar radiation (Turc, 1961; Hargreaves, 1975) were applied. To this aim, daily ET0estimated by introducing native and downscaled POWER-NASA air temperature values into Turc and Hargreaves equations were compared to the corresponding estimations obtained with FAO 56 Penman Monteith (FAO 56 PM) equation and climate data measured on ground
Assessing HYDRUS-2D model to estimate soil water contents and olive tree transpiration fluxes under different water distribution systems
Full text linkIn Mediterranean countries characterized by limited water resources for agricultural and societal sectors, irrigation
management plays a major role to improve water use efficiency at farm scale, mainly where irrigation systems are
correctly designed to guarantee a suitable application efficiency and the uniform water distribution throughout the
field.
In the last two decades, physically-based agro-hydrological models have been developed to simulate mass and
energy exchange processes in the soil-plant-atmosphere (SPA) system. Mechanistic models like HYDRUS 2D/3D
(Šimunek et al., 2011) have been proposed to simulate all the components of water balance, including actual crop
transpiration fluxes estimated according to a soil potential-dependent sink term. Even though the suitability of
these models to simulate the temporal dynamics of soil and crop water status has been reported in the literature
for different horticultural crops, a few researches have been considering arboreal crops where the higher gradients
of root water uptake are the combination between the localized irrigation supply and the three dimensional root
system distribution.
The main objective of the paper was to assess the performance of HYDRUS-2D model to evaluate soil water
contents and transpiration fluxes of an olive orchard irrigated with two different water distribution systems.
Experiments were carried out in Castelvetrano (Sicily) during irrigation seasons 2011 and 2012, in a commercial
farm specialized in the production of table olives (Olea europaea L., var. Nocellara del Belice), representing the
typical variety of the surrounding area. During the first season, irrigation water was provided by a single lateral
placed along the plant row with four emitters per plant (ordinary irrigation), whereas during the second season a
grid of emitters laid on the soil was installed in order to irrigate the whole soil surface around the selected trees.
The model performance was assessed based on the comparison between measured and simulated soil water content
and actual transpiration fluxes, under the hypothesis to neglect the contribute of the tree capacitance. Moreover,
two different crop water stress functions and in particular the linear model proposed by Feddes et al. (1978) and
the S-shape model suggested by van Genuchten et al. (1987), were considered.
The result of the study evidenced that for the investigated crop and under the examined conditions, HYDRUS-
2D model reproduces fairly well the dynamic of soil water contents at different distances from the emitters (RMSE<0.09 cm3
cm−3) and actual crop transpiration fluxes (RMSE<0.11 mm d−1), whose estimations can be slightly improved by assuming a S-shape crop water stress function
Inverse modelling to estimate the profile of conductivity at saturation. A case study for a shallow layered soil
No full textAssessment of the Water Balance in an Alpine Climate: Setup of a Micrometeorological Station and Preliminary Results
No full textAn experimental field campaign was performed during summer 2012 in an Alpine environment (Cividate Camuno, Oglio river basin, 274 m a.s.l.) in order to assess the water balance of an anthropized soil at the local scale. A micrometeorological station equipped with traditional sensors coupled with eddy covariance apparatus and TDR was installed in order to measure precipitation, evapotranspiration and soil—water content at different depths. The soil water properties were determined after field and laboratory investigations. Here the preliminary results of the campaign are presented and discussed, focusing on the assessment of the evapotranspiration and of the water exchanges in the vadose zone as ones of the major problems of water imbalance
Assessing the performance of different model-based techniques to estimate water content in the upper soil layer
Full text linkThe knowledge of soil water content (SWC) of the upper soil layer is important for most hydrological processes
occurring over vegetated areas and under dry climate. Because direct field measurements of SWC are difficult, the
use of different type of sensors and model-based approaches have been proposed and extensively used during the
last decade.
The main objective of this work is to assess the performance of two models estimating SWC of the upper soil
layer: the transient line heat source method and the physically based Hydrus-1D model. The models’ performance
is assessed using field measurements acquired through a Time Domain Reflectometer (TDR).
The experiment was carried out on an olive orchard located near the town of Castelvetrano (South-West of Sicily
- latitude 37.6429◦
, longitude 12.8471◦
). The temporal dynamic of topsoil water content was investigated in two
samplers, under wet and dry conditions. The samplers were opened at the upper boundary and inserted into the
soil to ensure the continuity of the soil surface.
A K2D Pro sensor allowed to measure the soil thermal properties allowing to estimate soil thermal inertia and
then SWC. The physically based Hydrus-1D model was also used to estimate SWC of both samples. Hourly
records of soil water contents, acquired by a TDR100 probe, were used to validate both the considered models.
The comparison between SWCs simulated by Hydrus-1D and the corresponding values measured by the TDR
method evidenced a good agreement. Similarly, even SWCs derived from the thermal diffusion model resulted
fairly close to those measured with the TDR
Assessing the Performance of Thermal Inertia and Hydrus Models to Estimate Surface Soil Water Content
Full text linkThe knowledge of soil water content (SWC) dynamics in the upper soil layer is important for several hydrological processes. Due to the difficulty of assessing the spatial and temporal SWC dynamics in the field, some model-based approaches have been proposed during the last decade. The main objective of this work was to assess the performance of two approaches to estimate SWC in the upper soil layer under field conditions: the physically-based thermal inertia and the Hydrus model. Their validity was firstly assessed under controlled laboratory conditions. Thermal inertia was firstly validated in laboratory conditions using the transient line heat source (TLHS) method. Then, it was applied in situ to analyze the dynamics of soil thermal properties under two extreme conditions of soil-water status (well-watered and air-dry), using proximity remote-sensed data. The model performance was assessed using sensor-based measurements of soil water content acquired through frequency (FDR) and time domain reflectometry (TDR). During the laboratory experiment, the Root Mean Square Error (RMSE) was 0.02 m3 m−3 for the Hydrus model and 0.05 m3 m−3 for the TLHS model approach. On the other hand, during the in situ experiment, the temporal variability of SWCs simulated by the Hydrus model and the corresponding values measured by the TDR method evidenced good agreement (RMSE ranging between 0.01 and 0.005 m3 m−3). Similarly, the average of the SWCs derived from the thermal diffusion model was fairly close to those estimated by Hydrus (spatially averaged RMSE ranging between 0.03 and 0.02 m3 m−3)
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
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