1,720,956 research outputs found
Using ground-based thermography to analyse surface temperature distribution and estimate debris thickness on Gran Zebrù glacier (Ortles-Cevedale, Italy)
No full textIn this paper we used ground-based thermal infrared imaging to investigate the spatial variability of surface temperatures on a mountain glacier at high spatial resolution and to estimate the supraglacial debris thickness distribution. The surveyed area is the eastern tongue of Gran Zebrù glacier, a small mountain glacier of the Ortles-Cevedale group (Italy). A FLIR E85 Thermal Camera was used to obtain a panoramic thermal image of the glacier surface on 30 September 2019 that was calibrated and georeferenced in order to obtain surface temperatures. Based on field data, debris thickness and debris surface temperature were correlated by using an exponential equation. The equation was used to estimate debris thickness on the glacier from the temperature data. The results show a spatial variability of surface temperatures, with the lowest temperatures found on snow and ice surfaces, and the highest on supraglacial debris. The estimated debris thicknesses show an inhomogeneous distribution, with a calculated mean debris thickness of 0.09 m in the areas of continous debris coverage. We found a good correspondence between measured and estimated debris thickness at 30 validation points (RMSE = 0.04 m and r = of 0.92). We demonstrated that ground-based thermal imaging can provide very high resolution maps of glacier surface temperatures and of debris thickness that can be used for the estimation of glacier ablation, with a spatial resolution more suitable than that offered by satellite data, especially for glaciers with a small area and with a heterogeneous surface
Evolution of the sparse debris cover during the ablation season at two small Alpine glaciers (Gran Zebrù and Sforzellina, Ortles-Cevedale group)
No full textDespite the increase of sparse debris on many glaciers in the world and its undisputed impact on glacier ablation, both its evolution and its detailed effect have been poorly investigated yet. In this study we evaluated the evolution of the sparse debris cover during the ablation season at two small glaciers of the Ortles-Cevedale group (Central Italian Alps, Italy), the eastern tongue of Gran Zebra glacier and Sforzellina glacier. We investigated the different effects of the sparse debris on albedo, on the glacier surface temperatures (using ground-based thermal imaging) and on ablation. The supraglacial debris cover increased three times faster at Sforzellina glacier, both in terms of mass and percentage debris cover, with a mean debris coverage rate of 621 g/m2 per day and a percentage of 2.07% per day, with respect to Gran Zebra glacier. As debris accumulates on the surface mainly by melt out of englacial debris, the debris coverage rates depend both on the ablation and on the englacial debris concentration, which was found to be higher at Sforzellina glacier (mean 10,810 g/m3) as compared to Gran Zebra glacier (mean 6131 g/m3). Debris is mainly composed by clasts coarser than 25 mm at both glaciers (ca 90%), with subangular sedimentary rocks prevailing at Gran Zebra and angular metamorphic rocks at Sforzellina glacier, suggesting a debris supply from the rockwalls surrounding the glaciers, with a longer englacial transport at Gran Zebra. Albedo decreases at increasing percentage of debris covering the surface, linearly at Sforzellina and logarithmically at Gran Zebra and surface temperatures are positively correlated with the mass of debris present on the glacier surface. The influence of the percentage of debris on the mean ablation rate is explained by a quadratic function, with the ablation rate increasing at increasing debris cover for moderate debris covers, due to the decreasing albedo, and decreasing ablation rates with high percentages of debris cover (>80%), due to the insulation effect of clasts
Using PlanetScope images to investigate the evolution of small glaciers in the Alps
No full textSmall glaciers (having an area smaller than 1 km2) dominate in terms of total number in the Alps and it is important to study their evolution. In this study we assessed the potential of daily, high resolution (3 m pixel size) PlanetScope images for investigating small Alpine glaciers. We compared the evolution of five small glaciers, covering an area lower or slightly higher than 1 km2, located in different areas of the Alps and having different characteristics and meteorological conditions. The investigated glaciers are: Bors (0.645 km2, Piedmont, Italy), Seewjinen (1.339 km2, Valais, Switzerland), Pizzo Ferrè (0.442 km2, Lombardy, Italy), Gran Zebrù (0.579 km2, Lombardy, Italy) and Solda Orientale (0.829 km2, South Tirol, Italy). We manually mapped the glacier outline and the highest position of the transient snowline (TSL) through PlanetScope images from the end of the ablation season for each year from 2017 to 2021 and each glacier. The snow cover area ratio (SCAR) was retrieved using the TSLs. We found that the glaciers lost between 4 and 14% of their area between 2017 of 2021, with a mean area loss of −1.5% per year. The strongest shrinkage (14%) is recorded at the smallest glacier (Pizzo Ferrè). The highest TSL showed a variability from year to year. For two glaciers, a supervised classification of the surface facies (snow, ice and supraglacial debris) was performed on all the available cloud-free images from the 2017–2021 ablation seasons. PlanetScope images, with their high spatial and temporal resolution proved to be a valuable tool for studying small glaciers. They permitted to map small glaciers with small uncertainties (between 2.2 and 5.1% of the glacier area), much lower than with medium resolution satellite data (e.g. Landsat 15/30 m, Sentinel 10 m) and to increase the number of images available for analysis. The daily repeat cycle is well suited for increasing the probability to find images from the end of the ablation season with minimum snow cover, in order to identify the real end-of-summer snowline
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
Small-scale spatial-temporal variability in snow cover and relationships with vegetation and climate in maritime Antarctica
No full textSnow cover changes can have important effects on ecosystems, especially where spatial variability in cover is high, influencing the biogeochemical conditions of the underlying soil as well as the vegetation. In this study, snow thickness and areal distribution were monitored using a time lapse camera over a grid of 15 x 20 m between 2009 and 2017 at Signy Island (60 degrees S, South Orkney Islands, maritime Antarctica). The data obtained confirmed high spatial and temporal variability in snow cover. Over the study period, the mean annual snow depth ranged between 5.6 cm (2017) and 11.1 cm (2012) while the maximum of the mean daily snow depth across the entire grid ranged between 17.1 cm (2017) and 50.1 cm (2015). No temporal trend was apparent but there was a strong correlation with mean annual air temperature, suggesting that possible future warming could decrease snow depth in the area. A negative correlation was identified between the winter Southern Oscillation Index (SOI) and mean annual snow depth, indicating an influence of El Nino-Southern Oscillation (ENSO) on snow cover in this part of Antarctica. There was considerable small-scale spatial variability in snow depth at each individual stake, with mean values between 3.9 and 25.3 cm and maximum values between 27 and 85 cm. Snow depth variability was influenced primarily by microtopography and wind direction, but also by the land cover type (vegetation). Our data highlight that spatial monitoring of snow accumulation is required at small physical scale to predict future effects of climatic changes on these sensitive maritime Antarctic terrestrial ecosystems
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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