1,720,962 research outputs found
Western Alaska Lake Database
No full textThis vector data layer covers 6 major lake districts (Baldwin Peninsula, Kobuk Delta, Selawik Lowland, Northern Seward Peninsula, Central Seward Peninsula, and Yukon-Kuskokwim Delta) in the northern and central sub-regions of the Western Alaska Landscape Conservation Cooperative (WALCC) region and consists of polygons of lakes with areas equal or greater than 1.0 ha. More than 58000 Lakes were mapped from Landsat TM and ETM+ imagery acquired between 1972 and 1975, 2002 and 2009, and 2013 and 2014 using Object-Based Image Analysis (OBIA) techniques with an classification accuracy of 96%. The spatial image resolution of Landsat TM and ETM+ is 30 m. Permafrost characteristics and surficial geology associated with lake polygons were determined from the Alaska permafrost map (Jorgenson et al. 2008)
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
Remote sensing of lake dynamics in Alaska
Get PDFDissertation (Ph.D.) University of Alaska Fairbanks, 2016Lakes are abundant in high northern latitude permafrost regions. They are important ecosystem components forming a complex and dynamic landscape with repeated cycles of lake formation and drainage affecting regional hydrological and terrestrial characteristics, biogeochemical processes and carbon cycling, wildlife habitats, and human communities living in the permafrost region. Remote sensing is a useful tool to map the spatial distribution of lakes and assess its change, understand lake dynamics, and to extract useful information to study their associated feedbacks in a changing climate. In this dissertation, I focused on remote sensing studies associated with (1) methane ebullition from a thermokarst lake, (2) post-drainage succession patterns in drained thermokarst lake basins, and (3) lake change dynamics. I developed a semi-automatic classification method based on an Object-based Image Analysis (OBIA) framework to detect methane ebullition bubbles trapped in a snow-free ice-covered lake using high-resolution airborne images of Goldstream lake, Fairbanks, Alaska acquired following freeze up in October of 2011 and 2012. This study showed that remote sensing is a valuable tool to map ebullition bubbles (bubble patches) on the entire lake surface with an accuracy of > 95%, a task that is difficult to achieve through field-based survey alone. The image analysis performed by combining the mapping results from the OBIA and field-based observations showed a relationship between bubble patch brightness and ground-measured methane flux, which was then used to estimate the whole-lake methane flux. A strong inverse exponential relationship (R2 >= 0.79) was found between the percent of the surface area of lake ice covered with bubble patches and distance from the active thermokarst lake margin, indicating high methane production as a response to thermokarst activity that released labile organic-rich carbon along the eroding lake margin. Despite the influence of atmospheric pressure conditions on distribution of ebullition bubble patches following the lake freeze-up events, the spatiotemporal regularity of bubble patches revealed that a larger number of seeps are stable over at least annual timescales. This remote sensing technique is applicable to other regions for mapping ebullition bubbles trapped in snow-free ice-covered lakes, identifying their relative flux, and assessing their spatiotemporal dynamics. By using TerraSAR-X (TSX) Synthetic Aperture Radar (SAR) backscatter data and the Normalized Difference Vegetation Index (NDVI) derived from a Landsat-5 image from the year 2009, I characterized drained thermokarst lake basins (DTLBs) of various age ranging between 0 to 10,000 years since drainage in the northern Seward Peninsula, Alaska. In the study I found logarithmic relationships of basin age from 0 to 10,000 years with mean basin TSX backscatter (R2 = 0.36) and with mean basin NDVI (R2 = 0.53). However, TSX data performed much better to discriminate older basins in the age class 50–10,000 years with R2 = 0.58, while no significant relationship was found between NDVI and basin age. Results of this study demonstrated the potential application of X-band SAR data in combination with NDVI data to enhance differentiation of soil moisture and vegetation status on drained basins for mapping long-term succession dynamics of DTLBs. Finally, I demonstrated the utility of Landsat imagery to identify lake distribution patterns and changes between 1972 and 2014 in six major lake-rich study regions across various permafrost zones covering an area of 68,830 km2 in western Alaska. Even though lake area change was found to be positive (increase by less than 4%) in some study areas while negative (decrease by 4-15%) in others, there was a widespread drainage of mainly large lakes in all regions creating remnant ponds that increased the abundance of lakes <10 ha in all study regions by 2-27%. The average lake area decline observed in various permafrost zones did not represent the trend of individual sites due to spatial heterogeneity in lake characteristics. While lake drainage dominated the non-continuous permafrost zones, areas of continuous permafrost showed both trends of negative and positive lake area change accompanied by major lake drainage events that led to a regional lake area loss in the continuous permafrost zone. This remote sensing technique proved to be useful in identifying ongoing lake drainage and expansion events within study regions and a regional shift in lake distribution (i.e. lake area loss) that is happening in western Alaska. Based upon my research, there is an immense opportunity to use and combine various remote sensing tools to study lake dynamics and to evaluate associated environmental changes. Future work should be directed towards collaborative research for combining field-based observations and remote sensing tools to improve the understanding of how lakes and drained lake basins change in a changing climate as well as extend the scale of observations of methane ebullition features by covering many lakes in an environmentally diverse set of regions. This will guide us to understanding the feedback of lake dynamics to the surrounding ecosystem, global carbon budget, and to upscale the response of lakes to changing climate and permafrost environments to larger regions.Chapter 1. Introduction -- Chapter 2. An object-based classification method to detect methane ebullition bubbles in early winter lake ice -- Chapter 3. Detection and spatiotemporal analysis of methane ebullition on thermokarst lake ice using high-resolution optical aerial imagery -- Chapter 4. Characterizing post-drainage succession in thermokarst lake basins on the Seward Peninsula, Alaska with TerraSAR-X backscatter and Landsat-based NDVI data -- Chapter 5. Landsat-based lake distribution and changes in western Alaska between 1972 and 2014 -- Chapter 6. Summary
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
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