1,721,008 research outputs found
Assessing landscape changes associated to anthropic disturbances by means of the application of Structure from Motion photogrammetry using historical aerial imagery
No full textIn this paper we present a methodological workflow to obtain planimetric and topographic data from historical aerial photos using photogrammetric methods through Structure from Motion (SfM) and Multi-View Stereo (MVS) algorithms. This methodology is applied in two case studies located in the Upper Cinca River catchment (Southern Pyrenees). These sites have suffered a series of direct anthropogenic disturbances that have modified landscape topography. Specifically, topographic changes associated with the construction of a road and the extraction of materials from a pit quarry have been analysed. The resultant products extracted by the application of SfM-MVS are orthomosaics with a root mean square error (RMSE) between 0.5 and 1 m, and points clouds (topography) with a RMSE between 1 and 2 m. The topography before and after each of the impacts was compared with the objective to analyse the changes attributed to these disturbances. A simple minimum Level of Detection (minLoD) was estimated based on the RMSEs in order to distinguish potential real changes from those due to the noise ascribable to the uncertainty of the topographic data sets. The significance of both impacts is relevant in terms of topographic changes (from -20 to +15 m). The dominant topographic change (in extension) in the case of the road construction (51% of the surface) is extraction (i.e. erosion). In the case of the pit quarry, the dominant process is deposition (i.e. sedimentation; 27% of the area). The extension below the minLoD is around the 23% and 48%, respectively, indicating that the magnitude of the changes is substantially higher in the case of the road construction. In both cases the net volume is negative (-913,710 and -16,197 m3 in the case of the road and the quarry, respectively), that show the differences in terms of the extension of the processes and their magnitude in each case study. Finally, both impacts had a direct effect on landscape morphometry (e.g. changes in the slope and flow direction). The developed approach provides an opportunity to analysed and quantify landscape changes that may help to improve our understanding of the long-term evolution of the transfer of water and sediment through landscapes
The Role of Storm Movement in Controlling Flash Flood Response: An Analysis of the 28 September 2012 Extreme Event in Murcia, Southeastern Spain
No full textFlash flooding is strongly modulated by the spatial and temporal variability in heavy precipitation. Storm motion prompts a continuous change of rainfall space–time variability that interacts with the drainage river system, thus influencing the flood response. The impact of storm motion on hydrological response is assessed for the 28 September 2012 flash flood over the semiarid and medium-sized Guadalentín catchment in Murcia, southeastern Spain. The influence of storm kinematics on flood response is examined through the concept of ‘‘catchment-scale storm velocity.’’ This variable quantifies the interaction between the storm system motion and the river drainage network, assessing its influence on the hydrograph peak. By comparing two hydrological simulations forced by rainfall scenarios of distinct spatial and temporal variability, the role of storm system movement on the flood response is effectively isolated. This case study is the first to (i) show through the catchment-scale storm velocity how storm motion may strongly affect flood peak and timing and (ii) assess the influence of storm kinematics on hydrological response at different basin scales. In the end, this extreme flash flooding provides a valuable case study of how the interaction between storm motion and drainage properties modulate hydrological response
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
Toward the development of a stand-alone application for the assessment of sediment connectivity
No full textThe role of sediment connectivity in controlling sediment fluxes, in particular between sediment sources and downstream areas, is a key issue in the study of sediment transfer processes. In mountain catchments, in which the degree of hillslope-channel coupling and decoupling is controlled by the rugged morphology and the distribution of sediment sources, the assessment of connectivity patterns is especially useful for giving watershed management priorities. In this work, the authors present the ongoing development and the first-stage testing phase of a free, open source and stand-alone application for the computation of the Index of Connectivity (IC), as expressed in Cavalli et al. (2013). The tool is intended to have a wide variety of users, both from the scientific community and from the authorities involved in the environmental planning. Due to its open source nature, the tool can be modified and/or integrated according to the users requirements. Being also a stand-alone, easy-to-use application, the tool can help management authorities in the quantitative estimation of sediment connectivity in the framework of hazard and risk assessment. First results of the testing phase are encouraging since the modelled connectivity appears suitable to detect the potential for the sediment to reach specific targets areas such as the main channel network
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
The effects of land use and topographic changes on sediment connectivity in mountain catchments
Full text linkUnderstanding the evolution of sediment connectivity associated with different land use and topographic changes is a prerequisite for a better understanding of sediment budgets and sediment transport processes. We used the Index of Sediment Connectivity (IC) developed by Cavalli et al. (2013) based on the original approach by Borselli et al. (2008) to study the effects of decadal-scale land use and topographic changes on sediment connectivity in mountain catchments. The input variables of the IC (i.e. land cover and topography) were derived from historical aerial photos using Structure from Motion-Multi View Stereo algorithms (SfM-MVS). The method was applied in different sub-catchments of the Upper River Cinca Catchment (Central Pyrenees), representative of three scenarios: (a) Land cover changes; (b) Topographic changes in agricultural fields (terracing); and (c) Topographic changes associated with infrastructure (road construction). In terms of land cover changes, results show that although connectivity is increased in some areas due to the establishment of new field crops, for most of the study area connectivity decreased due to afforestation caused by rural abandonment. Topographic changes due to the establishment of agricultural terraces affected connectivity to a larger degree than land cover changes. Terracing generally reduced connectivity due to the formation of flat areas in step-slopes, but in certain points, an increase in connectivity caused by the topographic convergence produced by terraces was observed. Finally, topographic changes associated with road construction greatly modified surface flow directions and the drainage network, resulting in changes in connectivity that may affect erosional processes nearby. The methodology used in this paper allows to study the effects of real decadal-scale land use and topographic changes on sediment connectivity and also evaluating and disentangling those changes. Furthermore, this approach can be a useful tool to identify potential risks associated with morphological and land use changes, involving road infrastructures
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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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