Examinando por Materia "data processing"

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    Ítem
    Application of the continuous wavelet transform in the extraction of directional data on RTM imaging condition wavefields
    (Ecopetrol, 2018-01-01) Paniagua-Castrillón J.-G.; Quintero-Montoya O.-L.; Universidad EAFIT. Escuela de Ciencias; Modelado Matemático
    Low-frequency artifacts in reverse time migration result from unwanted cross-correlation of the source and receiver wavefields at nonreflecting points along ray-paths. These artifacts can hide important details in migrated models and increase poor interpretation risk. Some methods have been proposed to avoid or reduce the number of these artifacts, preserving reflections, and improving model quality, implementing other strategies such as modification of the wave equation, proposing other imaging conditions, and using image filtering techniques. One of these methods uses wavefield decomposition, correlating components of the wavefields that propagate in opposite directions. We propose a method for extracting directional information from the RTM imaging condition wavefields to obtain characteristics allowing for better, more refined imaging. The method works by separating directional information about the wavefields based on the continuous wavelet transform (CWT), and the analysis of the main changes on the frequency content revealed within the scalogram obtained by a Gaussian wavelet family. Through numerical applications, we demonstrate that this method can effectively remove undesired artifacts in migrated images. In addition, we use the Laguerre-Gauss filtering to improve the results obtained with the proposed method. © 2018 Ecopetrol S.A. All Rights Reserved.
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    Expanding level of coastal armouring: Case studies from different countries
    (COASTAL EDUCATION & RESEARCH FOUNDATION, 2011-01-01) Stancheva, M.; Rangel-Buitrago, N.; Anfuso, G.; Palazov, A.; Stanchev, H.; Correa, I.; Universidad EAFIT. Departamento de Ingeniería; Ciencias del Mar
    Concreting the natural shoreline by use of traditional hard protective structures, as well as by port/harbour developments is commonly known as coastal armouring. Over the recent decades the expanding level of coastline hardening and its adverse impacts on the environment has arisen as one of the most critical problems all over the world. Therefore, our goal in this study was to demonstrate the crucial issue of progressive extent of technogenous coastal occupation by two case studies from different countries in Europe and in South America: Bulgaria and Colombia. To assess direct impact of armouring on the coastline and adjacent areas two case areas were selected for detailed investigation: an 18 km long coastline of the large Varna Bay (Bulgarian Black Sea coast) and 349 km long littoral of the Cartagena municipality (Caribbean coastline of Colombia). An indicative coastal segmentation of the both case sites by geomorphologic and engineering criteria was first implemented in GIS environment. As well as, for quantitative assessment of the influence of all maritime structures (port and coast-protection) on the studied coasts the coefficient of technogenous impact K was explored. A GIS methodology was applied for data processing, mapping the natural landforms/structures and to evaluate the technogenous impact on the both coastlines. The identified high extent of impacts due to built hard defence structures along the selected study areas in Bulgaria and Colombia could be considered as indicative of the large technogenous occupation of the coasts and the increasing level of shoreline armouring as a global issue.
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    Sensitivity, uncertainty and identifiability analyses to define a dengue transmission model with real data of an endemic municipality of Colombia
    (Public Library of Science, 2020-01-01) Lizarralde-Bejarano, D.P.; Rojas-Díaz, D.; Arboleda-Sánchez, S.; Puerta-Yepes, M.E.; Lizarralde-Bejarano, D.P.; Rojas-Díaz, D.; Arboleda-Sánchez, S.; Puerta-Yepes, M.E.; Universidad EAFIT. Departamento de Ciencias; Matemáticas y Aplicaciones
    Dengue disease is a major problem for public health surveillance entities in tropical and subtropical regions having a significant impact not only epidemiological but social and economical. There are many factors involved in the dengue transmission process. We can evaluate the importance of these factors through the formulation of mathematical models. However, the majority of the models presented in the literature tend to be overparameterized, with considerable uncertainty levels and excessively complex formulations. We aim to evaluate the structure, complexity, trustworthiness, and suitability of three models, for the transmission of dengue disease, through different strategies. To achieve this goal, we perform structural and practical identifiability, sensitivity and uncertainty analyses to these models. The results showed that the simplest model was the most appropriate and reliable when the only available information to fit them is the cumulative number of reported dengue cases in an endemic municipality of Colombia. © 2020 Lizarralde-Bejarano et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.