1,721,101 research outputs found
Iterative deconvolutions to compensate wavelet stretching on 4th order traveltime kinematic
Full text linkSource to receiver distances employed in seismic data acquisition have been steadily increasing and it is now common to work with data acquired with more than 10 km of offset. Sub-basalt exploration and seismic undershooting are just two applications where long-offset reflections are valuable. However, such reflections are often subjected to muting to avoid NMO stretch artifacts, thus causing a loss of valuable information. It is therefore of interest to find ways to avoid the distortions caused by the standard NMO correction and to retrieve these portions of the recorded wavefield for a better use in the processing. To this end we develop a non-stretch NMO correction based on a wavelet estimation and on a iterative procedure of partial NMO correction and deconvolution. To drive the corrections we make use of 4th order traveltime curves, that further extend the offset range of usable reflections. Then we estimate time and space variant wavelets, by means of SVD along the sought traveltimes, that become the desired output for the deconvolution trying to retrieve the original shapes of the partially stretched wavelets. We test our method on a synthetic gather presenting time and offset varying wavelets and noise. This example demonstrate that our new algorithm effectively limits the stretching associated with the NMO correction and enables the recovery of those portions of the stacked sections which are typically ruled out by the mute function in the standard NMO correction
Design of crustal acquisitions: Vibroseis vs. Explosive and Expanding Spread experiments
No full text
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
Normal Moveout through partial corrections
No full textIn seismic data processing, Normal Moveout (NMO) correction is applied to common mid
point (CMP) gathers to simulate a zero-offset trace from traces recorded at variable source to
receiver offset x. Then, properly NMO corrected CMP gathers can be the input for a number
of different tasks: AVO analysis, residual statics computation, and most commonly, stacking
to produce a seismic image with higher S/N ratio and with attenuated multiple reflections.
The NMO correction in exploration seismology is a common practice. The wavelet stretching
and the event duplication resulting from this procedure are removed from the seismic data by
the application of mute functions, computed on the basis of the maximum stretch threshold
allowed. Usually, enough data are still available after the mute, because stretching and event
superposition have a limited influence at depths of interest in exploration seismic.
This is not the case in near surface seismic, where the NMO stretch and the corresponding
mute constitute a major problem especially for shallow reflections. Indeed, not only the mute
limits the stack potential in enhancing the S/N ratio, but sometime this effect is so severe that
all the recorded seismic data at shallow times are zeroed-out.
Various methods have been proposed in literature to overcome the problem of the NMO
stretching. Trickett (2003) made a synthetic and clear review of the different methodologies
that have been proposed since 1975, with an accurate description of the main drawbacks each
of the proposed algorithms is affected by. The stretch-free stacking proposed by Trickett
(2003) replaces the NMO correction and stacking with a single inversion step to zero-offset.
As pointed out by the author, no NMO corrected CMP gather is formed by this procedure,
limiting the method’s applicability. Our procedure tries to overcome this limitation
suggesting, at the same time, an alternative way to estimate the zero-offset stack trace.
This new algorithm was applied to synthetic and several field data-sets with satisfactory
results
- …
