1,720,970 research outputs found
Independent Digital Elevation Model of Greenland from GNSS-R data from TechDemoSat-1
No full textSGR-ReSI, TechDemoSat-1,Improved Digital Elevation Model (DEM) of the Greenland Ice Sheet derived from Global Navigation Satellite Systems-Reflectometry (GNSS-R). This builds on a previous study (Cartwright et al., 2018) using GNSS-R to derive an Antarctic DEM but uses improved processing and an additional 13 months of measurements. A median bias of under 10 m and root-mean-square (RMS) errors of under 166 m are obtained, as compared to existing DEMs. Funding was provided by NERC grant NE/L002531/1.,Gridded group delay altimetry from TechDemoSat-1's GNSS-R data collected between September 2014 and December 2018. For full details see Cartwright et al., 2020.,A median bias of under 10 m and root-mean-square (RMS) errors of under 166 m are obtained, as compared to existing DEMs.</span
Independent Digital Elevation Model of Antarctica from GNSS-R data from TechDemoSat-1 - VERSION 2.0
No full textSGR-ReSI, TechDemoSat-1,Gridded group delay altimetry from TechDemoSat-1's GNSS-R data collected between September 2014 and December 2018. For full details see Cartwright et al., 2020.,Improved Digital Elevation Model (DEM) of the Antarctic Ice Sheet derived from Global Navigation Satellite Systems-Reflectometry (GNSS-R). This builds on a previous study (Cartwright et al., 2018) using GNSS-R to derive an Antarctic DEM but uses improved processing and an additional 13 months of measurements. A median bias of under 10 m and root-mean-square (RMS) errors of under 53 m are obtained, as compared to existing DEMs. Funding was provided by NERC grant NE/L002531/1.,A median bias of under 10 m and root-mean-square (RMS) errors of under 53 m are obtained, as compared to existing DEMs. This represents, compared to the earlier study, a halving of the median bias to 9 m, an improvement in coverage of 18 %, and a four times higher spatial resolution (now gridded at 25 km). These are the first published satellite altimetry measurements of the region surrounding the South Pole. Comparisons south of 88° S yield RMS errors of less than 33 m when compared to NASA's Operation IceBridge measurements.</span
Novel applications of GNSS-R data from TechDemoSat-1 to monitoring the cryosphere
No full textAs conditions in the cryosphere are expected to change rapidly, it is important to understand the characteristics of these dynamic regions if we are to fully account for their current and future role in the physical systems of the planet. The monitoring of the cryosphere through satellite remote sensing ensures maximum coverage and reliability of measurements otherwise affected by temporal and spatial sampling biases. Here I exploit signals of opportunity in the form of Global Navigation Satellite Systems-Reflectometry (GNSS-R) for this purpose. These signals allow low-cost observation of global systems, using only a receiver and existing navigation satellites in orbit. Data from the SGR-ReSI onboard TechDemoSat-1 (TDS-1) are exploited through the satellite’s initial (November 2014 - July 2017) and extended (August2017 - December 2018) missions. I use the Level 1B data to measure both sea ice and glacial ice in order to assess the potential of these signals for understanding these regions. I produce Digital Elevation Models over the Antarctic and Greenland Ice Sheets. These results demonstrate that when compared with existing products, application of GNSS-R to glacial ice altimetry is possible, acquiring comparable measurements(within 40 cm median difference) to dedicated satellites (eg. CryoSat-2), despite having many fewer measurements, a shorter temporal span and fewer corrections applied. As a multi-static configuration, GNSS-R is in the unique position to be able to obtain measurements at the geographic South Pole itself where traditional altimeters cannot. Use of GNSS-R for the detection of sea ice in both the Northern and Southern Hemispheres demonstrates the potential for future monitoring of sea ice extent using GNSS-R and shows the benefit of the small footprint of such measurements. Seasonal patterns are visible over the extent of the time series, and high agreement is found with four external products. Overall, this thesis finds that GNSS-R holds great potential for use over the cryosphere, with the ability to increase spatial resolution of measurements oversea ice and provide data where current altimeters cannot. The use of a multiplatform system for GNSS-R in a constellation configuration would allow increased temporal resolution of measurements and frequency of sampling, and through this higher accuracie
Improved GNSS-R bi-static altimetry and independent digital elevation models of Greenland and Antarctica from TechDemoSat-1
Full text linkImproved digital elevation models (DEMs) of the Antarctic and Greenland ice sheets are presented, which have been derived from Global Navigation Satellite Systems-Reflectometry (GNSS-R). This builds on a previous study (Cartwright et al., 2018) using GNSS-R to derive an Antarctic DEM but uses improved processing and an additional 13 months of measurements, totalling 46 months of data from the UK TechDemoSat-1 satellite. A median bias of under 10 m and root-mean-square errors (RMSEs) of under 53 m for the Antarctic and 166 m for Greenland are obtained, as compared to existing DEMs. The results represent, compared to the earlier study, a halving of the median bias to 9 m, an improvement in coverage of 18 %, and a 4 times higher spatial resolution (now gridded at 25 km). In addition, these are the first published satellite altimetry measurements of the region surrounding the South Pole. Comparisons south of 88∘ S yield RMSEs of less than 33 m when compared to NASA's Operation IceBridge measurements. Differences between DEMs are explored, the limitations of the technique are noted, and the future potential of GNSS-R for glacial ice studies is discussed
Sea ice detection using GNSS‐R data from TechDemoSat‐1
Full text linkA new method for the detection of sea ice using GNSS‐R (Global Navigation Satellite Systems Reflectometry) is presented and applied to 33 months of data from the U.K. TechDemoSat‐1 mission. This method of sea ice detection shows the potential for a future GNSS‐R polar mission, attaining an agreement of over 98% and 96% in the Antarctic and Arctic, respectively, when compared to the European Space Agency's Climate Change Initiative sea ice concentration product. The algorithm uses a combination of two parameters derived from the delay‐Doppler Maps to quantify the spread of power in delay and Doppler. Application of thresholds then allows sea ice to be distinguished from open water. Differences between the TechDemoSat‐1 sea ice detection and comparison data sets are explored. The results provide information on the seasonal and multiyear changes in sea ice distribution of the Arctic and Antarctic. Future potential and applications of this technique are discussed
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
Independent Digital Elevation Model of Antarctica from GNSS-R data from TechDemoSat-1
No full textDigital Elevation Model (DEM) of the Antarctic Ice Sheet derived from Global Navigation Satellite Systems-Reflectometry (GNSS-R) data from the UK TechDemoSat-1 satellite. This is obtained using all available data from the mission (32 months). It has a median bias under 18 metres and Root Mean Square Difference under 91 metres when compared to the CryoSat-2 1 km v1.0 DEM (Slater et al., 2017).,Median bias under 18 metres and Root Mean Square Difference under 91 metres when compared to the CryoSat-2 1 km v1.0 Digital Elevation Model (Slater et al, 2017). 'NaN' denotes no data available.,See Cartwright et al. (2018) for further information.</span
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
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