1,721,012 research outputs found
Two-sample Kalman filter and system error modelling for storm surge forecasting
No full textTwo directions for improving the accuracy of sea level forecast are investigated in this study. The first direction seeks to improve the forecast accuracy of astronomical tide component. Here, a method is applied to analyze and forecast the remaining periodic components of harmonic analysis residual. This method is found to work reasonably well during calm weather, but poorly during stormy period. This finding has led to continue the study with the second direction, which is about data assimilation implemented into the operational two-dimensional storm surge forecast model. The operational storm surge forecast system in the Netherlands uses a steady-state Kalman filter to provide more accurate initial conditions for forecast runs. An important factor, which determines the success of a Kalman filter, is the specification of system error covariance. In the operational system, the system error covariance is modelled explicitly by assuming isotropy and homogeneity. In this study, we investigate the use of the difference between wind products of two similarly skillful atmospheric models as proxy to the unknown error of the storm surge forecast model. To accommodate this investigation, a new method for computing a steady-state Kalman gain, called the two-sample Kalman filter, is developed in this study. It is an iterative procedure for computing the steadystate Kalman gain of a stochastic process by using two samples of the process. A number of experiments have been performed to demonstrate that this algorithm produces correct solutions and is potentially applicable to different models. The two-sample Kalman filter algorithm is implemented by using the wind products from two meteorological centers: the Royal Dutch Meteorological Institute (KNMI) and UK Met Office (UKMO). Here, the investigation is focused on random component of the system error. Therefore, bias or systematic error is eliminated prior to the implementation of the wind products to the two-sample Kalman filter. The system error spatial correlation estimated from these two wind products is found to be anisotropic, in contrast to the one assumed in the operational system. The steady-state Kalman filter based on this error covariance estimate is found to work well in steering the model closer to the observation data. For the stations along the Dutch coast, the data assimilation is found to improve the forecast accuracy up to about 12 hours. Moreover, it is also demonstrated that this data assimilation system outperforms a steady-state Kalman filter based on isotropy assumption. To further improve the data assimilation system, the two-sample Kalman filter is extended to work with more samples. By using more samples, the computation of the error covariance can be done by averaging over shorter time. This relaxes the stationarity assumption and is expected to simulate better the state-dependence model error. In this study, this algorithm is implemented by using wind ensemble of the LAMEPS, which is operational at the Norwegian Meteorological Institute. This setup is found to perform similarly well as the steady-state Kalman filter during large positive surge. However, the steady-state Kalman filter is found to perform better than the ensemble system in forecasting negative surge. The resulting ensemble spread during negative surge is found to be narrower than the standard deviation assumed by the steady-state Kalman filter. A further investigation on the wind ensemble is required.Delft Institute of Applied MathematicsElectrical Engineering, Mathematics and Computer Scienc
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Global tide model with DFlow-FM
No full textThis thesis is about the beginning of a global tide model in DFlow-FM, a project by Deltares. The first focus lay on finding the best grid that can be used for this model. We tried to grids, a rotated lat-lon grid and a squarely grid with local refinement. After calculating the RMS-value it was found that the local refined grid gave the best results and should therefore be used. The second part of the thesis was about internal tide, how it should be included in the model. This needs future work to improve the results but the way it should be included was found to be a linear friction coefficient.Bachelor Applied Mathematics and Applied PhysicsEEMCS and Applied SciencesDelft University of Technolog
The impact of future sea-level rise on the global tides
Get PDFTides are a key component in coastal extreme water levels. Possible changes in the tides caused by mean sea-level rise (SLR) are therefore of importance in the analysis of coastal flooding, as well as many other applications. We investigate the effect of future SLR on the tides globally using a fully global forward tidal model: OTISmpi. Statistical comparisons of the modelled and observed tidal solutions demonstrate the skill of the refined model setup with no reliance on data assimilation. We simulate the response of the four primary tidal constituents to various SLR scenarios. Particular attention is paid to future changes at the largest 136 coastal cities, where changes in water level would have the greatest impact.Spatially uniform SLR scenarios ranging from 0.5 to 10 m with fixed coastlines show that the tidal amplitudes in shelf seas globally respond strongly to SLR with spatially coherent areas of increase and decrease. Changes in the M2 and S2 constituents occur globally in most shelf seas, whereas changes in K1 and O1 are confined to Asian shelves. With higher SLR tidal changes are often not proportional to the SLR imposed and larger portions of mean high water (MHW) changes are above proportional. Changes in MHW exceed ±10% of the SLR at ~10% of coastal cities. SLR scenarios allowing for coastal recession tend increasingly to result in a reduction in tidal range. The fact that the fixed and recession shoreline scenarios result mainly in changes of opposing sign is explained by the effect of the perturbations on the natural period of oscillation of the basin. Our results suggest that coastal management strategies could influence the sign of the tidal amplitude change. The effect of a spatially varying SLR, in this case fingerprints of the initial elastic response to ice mass loss, modestly alters the tidal response with the largest differences at high latitudes
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
A modified POD procedure with patterns in time for parameter estimation
No full textProper orthogonal decomposition (POD) is a well established model order reduction technique, however its efficiency is limited for advection dominated model. In this report, we explore a modified proper orthogonal decomposition procedure with patterns in time instead of the usual patterns in space. This modified procedure is more suitable for this kind of model. Its efficiency is studied in the context of parameter estimation.master programmeMathematical physicsElectrical Engineering, Mathematics and Computer Scienc
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