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Search Results: 1 - 10 of 465349 matches for " Santiago Beguería "
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Identification of Mangrove Areas by Remote Sensing: The ROC Curve Technique Applied to the Northwestern Mexico Coastal Zone Using Landsat Imagery
Luis C. Alatorre,Raquel Sánchez-Andrés,Santos Cirujano,Santiago Beguería,Salvador Sánchez-Carrillo
Remote Sensing , 2011, DOI: 10.3390/rs3081568
Abstract: In remote sensing, traditional methodologies for image classification consider the spectral values of a pixel in different image bands. More recently, classification methods have used neighboring pixels to provide more information. In the present study, we used these more advanced techniques to discriminate between mangrove and non?mangrove regions in the Gulf of California of northwestern Mexico. A maximum likelihood algorithm was used to obtain a spectral distance map of the vegetation signature characteristic of mangrove areas. Receiver operating characteristic (ROC) curve analysis was applied to this map to improve classification. Two classification thresholds were set to determine mangrove and non-mangrove areas, and two performance statistics (sensitivity and specificity) were calculated to express the uncertainty (errors of omission and commission) associated with the two maps. The surface area of the mangrove category obtained by maximum likelihood classification was slightly higher than that obtained from the land cover map generated by the ROC curve, but with the difference of these areas to have a high level of accuracy in the prediction of the model. This suggests a considerable degree of uncertainty in the spectral signatures of pixels that distinguish mangrove forest from other land cover categories.
Recurrencias en el infarto cerebral
Pérez Nellar,Jesús; Beguería Santos,Ramón;
Revista Cubana de Medicina , 1996,
Abstract: one hundred and thirty one patients presenting with cerebral infarction were systematically observed during the first year following ictus with the aim of studying recurrences. the frequency of recurrence was 9.2 %. the presence of arterial hypertension associated with other predisposing factors, mainly age, was found to be the main predictor of a new ischemic episode.
Trends in rainfall erosivity in NE Spain at annual, seasonal and daily scales, 1955–2006
M. Angulo-Martínez ,S. Beguería
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2012,
Abstract: Rainfall erosivity refers to the ability of precipitation to erode soil, and depends on characteristics such as its total volume, duration, and intensity and amount of energy released by raindrops. Despite the relevance of rainfall erosivity for soil degradation prevention, very few studies have addressed its spatial and temporal variability. In this study the time variation of rainfall erosivity in the Ebro Valley (NE Spain) is assessed for the period 1955–2006. The results show a general decrease in annual and seasonal rainfall erosivity, which is explained by a decrease of very intense rainfall events whilst the frequency of moderate and low events increased. This trend is related to prevailing positive conditions of the main atmospheric teleconnection indices affecting the West Mediterranean, i.e. the North Atlantic Oscillation (NAO), the Mediterranean Oscillation (MO) and the Western Mediterranean Oscillation (WeMO).
Diversidad espacial de la actividad vegetal en campos abandonados del Pirineo Central espa ol: análisis de los procesos de sucesión mediante imágenes Landsat (1984-2001)
Vicente-Serrano, S. M.,Beguería, S.,Lasanta, T.
Pirineos : Revista de Ecología de Monta?a , 2006,
Abstract: This paper analyses the evolution of the Normalized Difference Vegetation Index (NDVI) in the central Spanish Pyrenees. For this purpose, Landsat-TM and ETM+ were used. The selected images correspond to August of 1984, 1991 and 2001. The difference in days between the images was not very important to diminish the effects of phenology. The images were geometrically and atmospherically corrected by means of a mixed method based on physical and statistical procedures. Using the NDVI images we calculated coefficients of variation within a radius of 150 meters by means of a moving window procedure. This approach allows to analyse the spatial variability of the vegetation cover. The results show that the NDVI changes have not been important in the analysed period. Nevertheless, there are noticeable modifications in the spatial structure and variability of the NDVI, resulted in homogenization/heterogenisation processes. The forests located at high altitudes have suffered the most important homogenisation processes. On the contrary at low elevated areas the spatial diversity of the vegetation activity increases. Nevertheless, in these areas some spatial differences are found: the heterogenisation of the vegetation cover is less important in the forests than in areas dominated by sclerophyllous vegetation and those characterised by the transition from shrubs to forests. These areas show less mature successional phases after the land abandonment and they are characterised by an increase of the spatial heterogeneity of the NDVI. Se analiza la evolución temporal del índice de vegetación normalizado (Normalizad Difference Vegetation Index, NDVI), obtenido a partir de imágenes Landsat-TM y ETM+, en un sector del Pirineo central espa ol. Se han utilizado tres imágenes de agosto de los a os 1984, 1991 y 2001, con una escasa diferencia en días en la toma de las mismas para garantizar la homogeneidad en la fenología de la vegetación. Las imágenes fueron corregidas geométrica y atmosféricamente siguiendo un método mixto basado en un modelo físico y procedimientos estadísticos. A partir de las imágenes de NDVI se han calculado coeficientes de variación móviles en un radio de 150 metros, para analizar la variabilidad espacial en la actividad vegetal. Los cambios en el NDVI han sido poco importantes durante el periodo analizado, existiendo escasas diferencias entre las tres imágenes. Sin embargo, sí se han producido cambios apreciables en la variabilidad espacial de la actividad vegetal, como consecuencia de procesos de homogeneización/heterogeneización. Se ha comprobado que
Recurrencias en el infarto cerebral
Jesús Pérez Nellar,Ramón Beguería Santos
Revista Cubana de Medicina , 1996,
Abstract: Se observaron periódicamente 131 enfermos con infarto cerebral durante el primer a o que siguió al ictus, con el objetivo de estudiar las recurrencias. La frecuencia de recurrencias fue del 9,2 %. Se demostró que la presencia de hipertensión arterial asociada a otros factores predisponentes, fundamentalmente la edad, fue el principal predictor de un nuevo episodio isquémico. One hundred and thirty one patients presenting with cerebral infarction were systematically observed during the first year following ictus with the aim of studying recurrences. The frequency of recurrence was 9.2 %. The presence of arterial hypertension associated with other predisposing factors, mainly age, was found to be the main predictor of a new ischemic episode.
Trends in rainfall erosivity in NE Spain at annual, seasonal and daily scales, 1955–2006
M. Angulo-Martínez,S. Beguería
Hydrology and Earth System Sciences Discussions , 2012, DOI: 10.5194/hessd-9-6285-2012
Abstract: Rainsplash – the detachment and transport of soil particles by the impact of raindrops on a bare soil – is a major mechanism of soil degradation and erosion on semiarid areas and agricultural lands. Rainfall erosivity refers to the ability of precipitation to erode soil, and depends on the characteristics of the raindrops – size and velocity – and on the rainfall intensity and duration. Despite the relevance of rainfall erosivity for soil degradation prevention very few studies addressed its spatial and temporal variability. On this study the time variation of rainfall erosivity in the Ebro valley (NE Spain) is assessed for the period 1955–2006. The results show a general decrease in annual and seasonal rainfall erosivity, which is explained by a decrease of very intense rainfall events whilst the frequency of moderate and low events increased. This trend is related to prevailing positive conditions of the main atmospheric teleconnection indices affecting the West Mediterranean, i.e. the North Atlantic Oscillation (NAO), the Mediterranean Oscillation (MO) and the Western Mediterranean Oscillation (WeMO).
Hydrologic and landscape changes in the Middle Ebro River (NE Spain): implications for restoration and management
A. Cabezas, F. A. Comín, S. Beguería,M. Trabucchi
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2009,
Abstract: The changes of landscape (1927–2003), discharge regime and anthropic activities with the river-floodplain of one reach at the Middle Ebro River (NE Spain) were investigated with the objective to identify the factors that best explain the natural ecotope succession and propose a realistic restoration option with consideration of the landscape dynamics during the last century and the socio-economic context. Our results indicate that hydrological and landscape patterns have been dramatically changed during the last century as a consequence of human alteration of the fluvial dynamics within the studied reach. The magnitude and variability of river discharge events have decreased at the end of the last century, and flood protection structures have disrupted the river floodplain connectivity. As a result, the succesional pathways of riparian ecotopes have been heavily modified because natural rejuvenation no longer takes place, resulting in decreased landscape diversity. It is apparent from these data that floodplain restoration must be incorporated as a significant factor into river management plans if a more natural functioning wants to be retrieved. The ecotope structure and dynamics of the 1927–1957 period should be adopted as the guiding image, whereas current hydrologic and landscape (dykes, raised surfaces) patterns should be considered. Under the current socio-economic context, the more realistic option seems to create a dynamic river corridor reallocating dykes and lowering floodplain heights. The extent of this river corridor should adapt to the restored flow regime, although periodic economic investments could be an option if the desired self-sustained dynamism is not reached.
Debris flow characteristics and relationships in the Central Spanish Pyrenees
A. Lorente,S. Beguería,J. C. Bathurst,J. M. García-Ruiz
Natural Hazards and Earth System Sciences (NHESS) & Discussions (NHESSD) , 2003,
Abstract: Unconfined debris flows (i.e. not in incised channels) are one of the most active geomorphic processes in mountainous areas. Since they can threaten settlements and infrastructure, statistical and physically based procedures have been developed to assess the potential for landslide erosion. In this study, information on debris flow characteristics was obtained in the field to define the debris flow runout distance and to establish relationships between debris flow parameters. Such relationships are needed for building models which allow us to improve the spatial prediction of debris flow hazards. In general, unconfined debris flows triggered in the Flysch Sector of the Central Spanish Pyrenees are of the same order of magnitude as others reported in the literature. The deposition of sediment started at 17.8°, and the runout distance represented 60% of the difference in height between the head of the landslide and the point at which deposition started. The runout distance was relatively well correlated with the volume of sediment.
Soil erosion and sediment delivery in a mountain catchment under land use change: using point fallout 137Cs for calibrating a spatially distributed numerical model
L. C. Alatorre,S. Beguería,N. Lana-Renault,A. Navas
Hydrology and Earth System Sciences Discussions , 2011, DOI: 10.5194/hessd-8-11131-2011
Abstract: Soil erosion and sediment yield are strongly affected by land use/land cover (LULC). Spatially distributed erosion models are useful tools for comparing erosion resulting from current LULC with a number of alternative scenarios, being of great interest to assess the expected effect of LULC changes. In this study the soil erosion and sediment delivery model WATEM/SEDEM was applied to a small experimental catchment in the Central Spanish Pyrenees. Model calibration was carried out based on a dataset of soil redistribution rates derived from 137Cs inventories along three representative transects, allowing capture differences per land use in the main model parameters. Model calibration showed a good convergence to a global optimum in the parameter space. Validation of the model results against seven years of recorded sediment yield at the catchment outlet was satisfactory. Two LULC scenarios where then modeled to reproduce the land use at the beginning of the twentieth Century and a hypothetic future scenario, and to compare the simulation results to the current LULC situation. The results show a reduction of about one order of magnitude in gross erosion (3180 to 350 Mg yr 1) and sediment delivery (11.2 to 1.2 Mg yr 1 ha 1) during the last decades as a result of the abandonment of traditional land uses (mostly agriculture) and subsequent vegetation re-colonization. The simulation also allowed assessing differences in the sediment sources and sinks within the catchment.
Influence of the Yesa reservoir on floods of the Aragón River, central Spanish Pyrenees
J. I. López-Moreno,S. Beguería,J. M. García-Ruiz
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2002,
Abstract: The Yesa reservoir, the largest Pyrenean reservoir, was constructed in 1959 to supply water to new irrigated areas in the Ebro Depression, NE Spain. It is filled from October to May-June and then releases large quantities of water in the summer via the Bardenas Canal. The results confirm that the frequency of floods downstream of the dam decreased. The reduction mainly depends on two factors: i) the water storage level, and ii) the season of the year. Floods are very well controlled when the reservoir level is lower than 50%. Between 50 and 70%, only the highest floods are controlled. Finally, the reservoir retains mainly autumn and spring floods; most winter floods are released downstream to ensure the safety of the dam. Keywords: reservoir, flood control, flood seasonality, flood frequency, river regime, Pyrenees
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