1,721,026 research outputs found
Surface and subsurface water from space: On the integration of microwave remote sensing observations with flood prediction systems
No full textThe technique of active microwave remote sensing has made much progress toward its high potential to monitor water storage changes in terrestrial surface and subsurface water bodies at various spatial and temporal scales. The number of studies demonstrating the support these data can offer in hydrological and hydraulic model building, model calibration and model updating is growing rapidly. While there is no doubt that this technological progress has already brought new insights into hydrology and hydraulics, there are still several issues that require attention. The questions to answer are: (1) How to add value to ‘raw’ remote sensing data for hydrological applications, (2) how to combine remote sensing techniques with hydrologic-hydraulic models for improved predictions, and (3) how to evolve irregular and intermittent remote sensing-based applications into systematic services? The first question deals with the adequate data processing to retrieve meaningful information about hydrological/hydraulic variables. Further, remote sensing-derived data are characterized by considerable uncertainty, which needs to be evaluated and clearly communicated to the users of such data. The second question deals with the effective integration of remote sensing-derived information and in situ data with adequate models, either offline for model building and calibration or online via assimilation for model updating. The third question focuses on an efficient production, processing and distribution of satellite data and the development of new services that may help to advance operational water resources management. This thesis deals with all three questions, with a clear focus on active microwave remote sensing and hydrological/hydraulic modeling.Water ResourcesCivil Engineering and Geoscience
Practical method for flow velocity measurements in ungauged sections
No full textThe river flow forecasting represents a crucial point to employ for improving a management policy addressed to the right use of water resources as well as for conjugating prevention and defence actions against environmental degradation. Indeed, for that the European directive 2000/60/CEE states the relevance of the monitoring and control activities as support to define the whole of protection measures to adopt for achieving the “good state” of the water body. Thus, the quantitative monitoring of rivers is an essential step for environmental purposes both for addressing middle and long term surveillance and control activities, and for civil protection purposes in terms of flood forecasting and risk mitigation. In such cases, a focal point is mainly represented by a continuous updating of flow depth/discharge ratio in each gauged section. This update relies on intense field activities not to easily carry out because of several factors mainly related to weather conditions and high costs. Thus, the aim of the present work is the development and implementation of quick and efficient sampling methods for discharge assessment in order to reduce the data acquisition time and processing maintaining a good level of accuracy and precision. This is of great interest in the chain of environmental monitoring for both gauged and ungauged river sections.
In according with ISO rules, the choice of measurement verticals and velocity points has been derived by an optimization tolerance analysis proposing sampling procedures based on a set of discrete velocity measures collected following a fixed geometric pattern and grid (verticals and points). The backbone of the proposed methodology deals with the rationale that in a river flow the large amount of the moving fluid volume (discharge) is generally concentrated in about 30% up to 50% of the whole cross section and in this area the maximum velocity usually occurs. Three main verticals (i.e., placed at 1/3, 1⁄2 and 2/3 of the total observed width) are fixed for the field measurement considering the points velocities in 30% of the area below the free surface. Thus, the assessment of maximum and average velocities is available and the entropy velocity profile can be derived. The reliability of such method has been tested to gauged river sites located along the Alzette natural channel, in Grand-Duchy of Luxembourg. The results show a good “technical” agreement among observed and estimated water discharges with errors not exceeding 25%, overall
Setting Up a Sentinel 1 Based Soil Moisture-Data Assimilation System for Flash Flood Risk Mitigation
No full text
Sentinel-1 InSAR coherence to detect floodwater in urban areas: Houston and hurricane harvey as a test case
Full text linkThis paper presents an automatic algorithm for mapping floods. Its main characteristic is that it can detect not only inundated bare soils, but also floodwater in urban areas. The synthetic aperture radar (SAR) observations of the flood that hit the city of Houston (Texas) following the landfall of Hurricane Harvey in 2017 are used to apply and validate the algorithm. The latter consists of a two-step approach that first uses the SAR data to identify buildings and then takes advantage of the Interferometric SAR coherence feature to detect the presence of floodwater in urbanized areas. The preliminary detection of buildings is a pre-requisite for focusing the analysis on the most risk-prone areas. Data provided by the Sentinel-1 mission acquired in both Strip Map and Interferometric Wide Swath modes were used, with a geometric resolution of 5 m and 20 m, respectively. Furthermore, the coherence-based algorithm takes full advantage of the Sentinel-1 mission's six-day repeat cycle, thereby providing an unprecedented possibility to develop an automatic, high-frequency algorithm for detecting floodwater in urban areas. The results for the Houston case study have been qualitatively evaluated through very-high-resolution optical images acquired almost simultaneously with SAR, crowdsourcing points derived by photointerpretation from Digital Globe and Federal Emergency Management Agency's (FEMA) inundation model over the area. For the first time the comparison with independent data shows that the proposed approach can map flooded urban areas with high accuracy using SAR data from the Sentinel-1 satellite mission
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
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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