1,721,064 research outputs found
Interbed demultiple using Marchenko redatuming on 3D field data of the Santos basin
No full textWe apply Marchenko redatuming using an adaptive double-focusing method to 3D field data of the Santos basin, Brazil. This method was already successfully applied to 2D field data and we now study the acquisition geometry and preprocessing requirements in 3D. We start from 3D synthetic data modeled on a dense grid of colocated sources and receivers and decimate down to a realistic NAZ streamer acquisition. The synthetic tests show that the sail line spacing and the missing outer cables are the acquisition parameters with the strongest effect on Marchenko redatuming. We can interpolate for the sail line spacing and the near offsets, but the missing outer cables are unfortunately a limitation of the acquisition. After applying the proposed interpolation to 3D field data, interbed multiples are successfully predicted and subtracted from the target area, resulting in a significant improvement in the geological interpretation. Naturally, the pre-processing requirements and challenges strongly depend on the acquisition geometry and the geology of the area under investigation (e.g. water depth, shape of the overburden, maximum dip). Hence, these tests only give a general idea about the limitations of 3D Marchenko redatumingAccepted author manuscriptApplied Geophysics and PetrophysicsImPhys/Acoustical Wavefield Imagin
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
Adaptive Marchenko internal multiple attenuation
No full textCuriosity regarding what we cannot see has always driven research. Science has helped us to uncover many of those hidden secrets. In particular, geophysics has helped us to image the inside of the Earth. By sending a seismic signal into the Earth and recording the signal that comes back, geophysicists can characterize the layers of the subsurface. Nowadays, geophysics is used for many purposes, for example, the localization of fossil fuels, the characterization of the subsurface for the construction of wind farms and the evaluation of reservoirs for geothermal energy. In order to decrease the risk and cost involved in these activities, we need images of the subsurface that are as accurate as possible. These images can only be obtained if we fully understand the propagation of the seismic signal in the subsurface. A long-standing problem in geophysical imaging is the presence of internal multiple reflections. When imaging the subsurface, we assume that the signal only reflects once when there is a contrast in velocity and/or density (for example, when changing from sand to rock). However, in reality, the signal can reflect many times inside the subsurface before being recorded at the surface. When treating the arrivals that have reflected many times as arrivals that have only reflected once, we incorrectly image the subsurface and create ghost reflectors that do not exist. This problem is particularly strong in geological settings that have a complex structure with many strong velocity and/or density contrasts above an area of interest. This may happen, for example, when there is a reservoir of oil below a thick stratified salt layer. In such cases, the image of the area of interest is unreliable due to the presence of many ghost reflectors. Therefore, we have to use knowledge of wave propagation to predict and attenuate the internal multiples in the data prior to imaging.In this thesis, I further develop the data-driven and wave-equation-based Marchenko method to make it suitable for the attenuation of internal multiples in seismic field data. In addition, I evaluate the performance of suitable methods by applying them to field datasets recorded in different geological settings. I start this evaluation by demonstrating that what we call the conventional Marchenko method is perhaps not the most suitable Marchenko method for the application to field data. I develop an alternative Marchenko method instead: the adaptive double-focusing method. I show that this method indeed produces improved results compared to the conventional Marchenko method when applying it to a line of 2D data of the Santos Basin, Brazil. Since the 2D results show promise, I continue with the extension to 3D applications. I first identify the key acquisition parameters that affect the result of our Marchenko method on 3D synthetic data and conclude that the limited crossline aperture and the coarse sail line spacing have the strongest effect on the quality of the result. Based on this evaluation, I interpolate the sail line spacing on 3D field data acquired in the Santos Basin and use the adaptive double-focusing method to predict and subtract internal multiples. I conclude that 3D Marchenko internal multiple attenuation seems to be sufficiently robust for the application to narrow azimuth streamer data in a deep marine setting, provided that there is sufficient aperture in the crossline direction and that the sail lines are interpolated. In addition, the adaptive double-focusing method is suitable for the attenuation of internal multiples generated by a complex overburden and for simultaneously redatuming to a level below this overburden. Next, I modify the adaptive double-focusing method to obtain an adaptive double dereverberation method that is suitable when only aiming to attenuate internal multiples generated in an overburden without redatuming. Moreover, this method does not require a velocity model. I apply this method to a 2D line of data acquired in the very shallow Arabian Gulf. Also, I assess how to meet the data requirements for the Marchenko method in shallow water environments (e.g., the removal of surface-related multiples, the deconvolution of the source signature) and demonstrate that the state-of-the-art Robust Estimation of Primaries by Sparse Inversion (R-EPSI) method is capable of producing the correct input data for the Marchenko method in such settings. Subsequently, I discuss the role of the adaptive filter in the application of the Marchenko method to field data. I argue that developments in seismic data processing allow us to predict internal multiples with more accuracy, such that only a conservative adaptive filter is needed to correct for the unavoidable minor amplitude and phase discrepancies between the internal multiples in the data and the predicted internal multiples. I demonstrate this by using a conservative adaptive filter to subtract internal multiples that were predicted by applying an adaptive Marchenko multiple elimination method to a 2D line of field data acquired in the Norwegian North Sea. Finally, based on the results presented in this thesis, I conclude that the Marchenko method is an effective, data-driven and robust method for the prediction of internal multiples in marine seismic data. Different Marchenko methods are suitable for different purposes. There are two key elements for the successful application of a Marchenko method to field data: 1) the acquisition geometry needs to be sufficiently dense and 2) a careful processing workflow needs to be constructed that accounts for the specifics of the geological setting at hand, with significant emphasis on amplitude and phase preservation.Applied Geophysics and Petrophysic
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
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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