1,723,230 research outputs found
Sea ice lead fractions from SAR-derived sea ice divergence in the Transpolar Drift during MOSAiC 2019/2020
No full textLeads and fractures in sea ice play a crucial role in the heat and gas exchange between the ocean and the atmosphere, impacting atmospheric, ecological, and oceanic processes. The precise knowledge of the aerial coverage, location, and formation history of leads is thus of great importance for polar research. Leads result from sea ice deformation processes. The breaking of the sea ice, followed by divergent ice motion, forms leads. Since the magnitude of divergence is directly proportional to the lead width, divergence is a powerful indicator of the location and width of leads. Divergence derived from satellite synthetic-aperture radar (SAR) data provides this information independent of the presence of clouds. We present here lead fractions from daily divergence fields in the Transpolar Drift along the drift of the Multidisciplinary Drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition in 2019/2020. The lead fractions have a spatial resolution of 700 m and are based on divergence from Sentinel-1 imagery with an original spatial resolution of 50 m ( doi:10.1594/PANGAEA.958449). Typically, the time between two scenes was one day, with a few exceptions of 2-3 days, and the size of the scenes was on average 200 x 200 km. Lead fractions are available from 7 October 2019 to 14 January 2020 and from 15 March 2020 to 1 June 2020. Lead fractions are regularly gridded in Polar Stereographic North projection (latitude of true scale: 70°N, center longitude: 45°W) within a bounding box corresponding to 180°/60°N: -3314693.24, -3314693.24, 3314693.24, 3314693.24. Divergence alone only detects leads when they form or continue to open. To determine if a lead is closed, opened further, or stayed open, we use the divergence and convergence fields of subsequent dates and accumulate them after adjusting lead fractions from different dates to a common location using sea ice drift data. With this dataset, the data user can study (accumulated) lead fractions (adjusted to a common location) for the last 10 time instances. The data user can choose the age of the leads (typically 1-11 days) they wish to include in their analysis. In addition, the user can understand when and where a lead has formed or closed. We evaluate the accumulated divergence-derived lead fractions against existing lead products along the MOSAiC drift track (von Albedyll, et al, in review)
Linear Kinematic Features (leads & pressure ridges) detected and tracked in Sentinel-1 drift and deformation data during the MOSAiC expedition
No full textLeads and pressure ridges are dominant features of the Arctic sea ice cover. Not only do they affect heat loss and surface drag, but also provide insight into the underlying physics of sea ice deformation. Due to their elongated shape they are referred as Linear Kinematic Features (LKFs). This data-set includes LKFs that were detected and tracked in sea ice deformation data obtained during the MOSAiC expedition from Sentinel-1 SAR data (von Albedyl & Hutter, 2023). The data-set spans the winter months between October 2019 and May 2020. A detailed description of the data-set and of the algorithms deriving it is provided in Hutter et al. (2019). We used the updated version of the algorithm for the data processing (Hutter, 2023). The dataset is closer described in Ringeisen et al. (2023)
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
High-resolution sea ice drift and deformation from sequential SAR images in the Transpolar Drift during MOSAiC 2019/2020
No full textSea ice deformation is a crucial process in the polar climate system and, thus, it is an important cross-cutting theme for all disciplines of the interdisciplinary research expedition MOSAiC. Because sea ice deformation is highly localized and intermittent, drift and deformation with a high spatial and temporal resolution and a large spatial coverage are required for a comprehensive description of the sea ice dynamics. We provide a regularly gridded, high-resolution drift and deformation dataset that can be used for several potential applications. Drift fields were obtained from Sentinel-1, HH polarization SAR images acquired in enhanced wide mode. These had a pixel resolution of 50 m in Polar Stereographic North projection (latitude of true scale: 70 N, center longitude: 45 W). We used an ice-tracking algorithm introduced by Thomas et al. (2008, 2011) and modified by Hollands and Dierking (2011) to derive drift from sequential pairs. Typically, the time between two scenes was one day, with a few exceptions of 2-3 days, and the size of the scenes was on average 200 x 200 km. Images are available for the entire study period, except for the time between 14 January and 15 March 2020, when the ship was north of the latitudinal coverage of the satellite. The resulting drift data set was defined on a regular grid with a spatial resolution of 700 m. Next, we calculate the spatial derivatives from the regularly spaced drift field following von Albedyll et al. (2021). Divergence, convergence, shear, and total deformation are then derived from the spatial derivatives of the velocity field. To reduce noise in the divergence fields, we filter the drift data with a directional filter that detects the direction with the smallest variation at each pixel and smooths along, but not across this orientation, with a 1-d kernel. The direction is chosen to minimize the standard deviation in a neighborhood of 7 pixels. This way, noise is reduced while preserving the strong gradients in the velocity field that are indicative of deformation. We provide the filtered divergence variable together with the unfiltered divergence values. For better distribution, the drift and deformation data were re-grided to one common grid in North Stereographic Projection (bounding box corresponding to 180/60°N: -3314693.24 -3314693.24 3314693.24 3314693.24) with 700 m resolution and combined into one per time step
EM-Bird ice thickness measurements in the Transpolar Drift during MOSAiC 2019/2020, part 1
No full textTotal (snow+ice) thickness measurements obtained during the international Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) campaign using the helicopters on board the research vessels Polarstern and Akademik Fedorov. The data was gathered during 14 flights between October 2019 and July 2020 in the Transpolar Drift on spatial scales up to 80 km distance from the position of the ships. Version 1.0. For details for the processing, please see Henricks & Rohde (2020), Haas et al. (2009) and von Albedyll et al. (2021)
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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