1,721,012 research outputs found
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
Recent Ice Wastage on the Tasman Glacier, Southern Alps, New Zealand, Obtained from Geodetic Elevation Changes
No full textThe Tasman Glacier is New Zealand’s largest body of ice comprising several tributary glaciers. Since the early 1990s it has undergone a rapid frontal retreat associated with the expansion of a proglacial lake. In this study, digital photogrammetric processing of vertical aerial photographs were used to derive two high-resolution Digital Elevation Models (DEM) of the Tasman Glacier. Additionally, in order to account for the volume loss due to lake expansion, the subaqueous lake topography was generated from a recent bathymetric survey and appended to the latest DEM. Detailed analysis of the multitemporal DEM enabled the quantification of geodetic surface elevation and mass balance changes. Calculations show that the main Tasman Glacier and its tributaries have lost 19.72 ± 0.05 × 10^8 m^3 of ice between 1986 and 2008. The proglacial Tasman Lake occupied ca. 28% of this volume loss. The glacier-wide volume loss corresponds to a geodetic balance of 0.87 ± 0.002 m w. eq. yr^-1. Differential DEM analysis revealed diverse spatial patterns of thickness and volume change, varying between the tributaries and within and between elevation bins. Furthermore, reworked and transported material from recent rockfall deposits produced localised areas of apparent positive elevation changes. Previous ice volume change estimates may have underestimated mass loss from the Tasman Glacier, partly due to a lack of bathymetric data to account for the glacier-wide volume variation and omission of the tributary glaciers. The methods developed in this study offer a potential way forward for glacier monitoring in New Zealand, where old aerial photographs are available but have not previously been processed in this manner to obtain accurate assessment of geodetic mass balance
Recent Ice Wastage on the Tasman Glacier, Southern Alps, New Zealand, Obtained from Geodetic Elevation Changes
No full textThe Tasman Glacier is New Zealand’s largest body of ice comprising several tributary glaciers. Since the early 1990s it has undergone a rapid frontal retreat associated with the expansion of a proglacial lake. In this study, digital photogrammetric processing of vertical aerial photographs were used to derive two high-resolution Digital Elevation Models (DEM) of the Tasman Glacier. Additionally, in order to account for the volume loss due to lake expansion, the subaqueous lake topography was generated from a recent bathymetric survey and appended to the latest DEM. Detailed analysis of the multitemporal DEM enabled the quantification of geodetic surface elevation and mass balance changes. Calculations show that the main Tasman Glacier and its tributaries have lost 19.72 ± 0.05 × 10^8 m^3 of ice between 1986 and 2008. The proglacial Tasman Lake occupied ca. 28% of this volume loss. The glacier-wide volume loss corresponds to a geodetic balance of 0.87 ± 0.002 m w. eq. yr^-1. Differential DEM analysis revealed diverse spatial patterns of thickness and volume change, varying between the tributaries and within and between elevation bins. Furthermore, reworked and transported material from recent rockfall deposits produced localised areas of apparent positive elevation changes. Previous ice volume change estimates may have underestimated mass loss from the Tasman Glacier, partly due to a lack of bathymetric data to account for the glacier-wide volume variation and omission of the tributary glaciers. The methods developed in this study offer a potential way forward for glacier monitoring in New Zealand, where old aerial photographs are available but have not previously been processed in this manner to obtain accurate assessment of geodetic mass balance
The role of control network in the accuracy of underground laser scanning surveys
No full textTerrestrial laser scanning is used in various fields with numerous applications, one being the documentation of heritage sites. Often scans will be georeferenced with respect to a real-world coordinate system. This is done using either direct or indirect georeferencing techniques. The indirect georeferencing method was used in this research, which uses coordinated targets, referred to as Ground Control Points (GCPs), that are captured in the scan scene. Manufacturers suggest a minimum of three GCPs are used, should the z-axis not be vertical, with additional GCPs for redundancy. Ideally GCPs should be placed evenly around the extent of the scan scene. For heritage site documentation, this is not always feasible given the unique and complex nature of each site. This research investigates the quantity and spatial variability of GCPs used in a scan scene, and the subsequent effect on the point cloud accuracy. A control test network was established at the School of Surveying (SoS), where variations of GCP scenarios were investigated, which was then applied to a case study in Arras, France. The case study being a network of underground World War One tunnels that were excavated by the New Zealand Engineering Tunnelling Company (NZETC), known as the Ronville Tunnels. The results from the SoS test network show, in this particular instance, that there is little benefit in using additional GCPs in a scan scene, should the minimum (three) be placed evenly around the extent of the area being captured. Low redundancy solutions may reduce the accuracy and robustness of georeferencing solutions, as seen with the case where large errors were present where the minimum number of GCPs were used. Geometrically poor placement of GCPs shows an increased correlation between the check points root mean square errors and range from the GCP centroid. The case study results, where the scan scene extents were hundreds of metres long, showed that it is necessary to supplement the minimum number of GCPs to mitigate uncertainties in the point cloud dataset. Similar to a least squares estimation adjustment where there are less fixed stations, there is more uncertainty for an unknown position. GCPs should therefore, be placed spatially around the extents of the scan scene and where scan scene extents increase so should the number of GCPs
Changing landscapes: Compositional and phenological shifts in New Zealand's natural grassland
No full textVegetation in a wide range of ecosystems across the globe is responding to recent anthropogenic climate change. There are two key ecological responses in plants associated with recent anthropogenic climate change: shifts in species’ geographic distributions (range shifts) and shifts in the timing of key life cycle events (phenological shifts). These shifts can lead to temporal and spatial changes in vegetation composition and growth activity and hence ecosystem function. Understanding the patterns and processes of these shifts is crucial for the successful management of natural ecosystems under ongoing anthropogenic environmental change.
This thesis investigates recent spatiotemporal compositional and phenological shifts in New Zealand’s natural grassland ecosystems and identifies potential topographical and climatic drivers of these shifts. Three grassland types in New Zealand are investigated (Alpine, Tall Tussock and Low Producing grasslands). They are characterised by high levels of indigenous endemic plant biodiversity and cover a wide elevation range. This thesis primarily utilises remote sensing information for quantifying growth dynamics and vegetation patterns in these grasslands over the last 16 years and across large spatial scales, i.e., the catchment of the river Clutha/Mata-Au River in South Island, New Zealand.
Shrub encroachment in grassland ecosystems is a globally observed example of compositional shifts in ecosystems associated with recent anthropogenic climate change. In New Zealand, where extensive area of current grassland habitats exist because of anthropogenic deforestation, shrub encroachment into grasslands has two distinct facets: firstly the invasion of non-native shrub species into native grasslands (i.e., exotic shrub invasion) and secondly the dispersal of native woody and shrub species into native grasslands (i.e., native shrub recovery). Propagule pressure is a measurement of species’ seed source size in neighbourhood of a focal area, and it is a key determinant of the degree to which a location gets colonised by individuals from species present in the neighbourhood. The spatial patterns of potential native and exotic shrub propagule pressure on three grassland types in New Zealand were quantified with the assumption that proximity of higher shrub coverage indicates higher shrub propagule availability. Results show that Alpine grasslands are mostly surrounded by native shrublands, while Low producing grassland are most at risk from exotic shrub invasion from neighbouring areas. High native and exotic shrub propagule pressure does not generally coincide spatially, however, it occurs in very similar climates for Low Producing grassland but not for Alpine and Tall Tussock grassland. The analysis of recent shrub encroachment over the last five years in a tussock grassland area in the central South Island showed a 0.35% year-1 increase in shrub cover in grassland area located in immediate neighbourhood of shrub. Shrub encroachment speed was strongly correlated with shrub cover in the neighbourhood. Recent shrub encroachment into grasslands was most pronounced in areas with neighbouring shrub cover of greater than 40%.
A wide range of species and ecosystems worldwide have shown changes in the timing of life cycle events and growing seasons in a direction congruent with recent anthropogenic climate changes. In this study, temporal trends over the last 16 years in the start, peak and end dates of the growing season were analysed using remotely sensed data on the Normalised Difference Vegetation Index (NDVI) in New Zealand’s three main grassland types. Overall, 90% of Alpine, 86% of Tall Tussock and 89% of Low Producing grassland areas showed an advancing start of the growing season over the last 16 years. In these areas start of the growing advanced by 7.2, 6.0 and 8.8 days per decade in Alpine, Tall Tussock and Low Producing grassland, respectively. Only small changes in timing of the end of the growing season were observed in the three grassland types. The length of growing season extended by 3.2, 5.2 and 7.1 days per decade in three grassland types.
Landscape topography (elevation and aspect) played an important role in particular in alpine grasslands: the start of the growing season was strongly correlated with elevation (later start with increasing elevation), while the end of the growing season was strongly correlated with aspect (later end of season on more south-facing slopes). The start of season was delayed by 7.5, 5.1 and 3.7 days/100 m elevation increase in Alpine, Tall Tussock and Low producing grassland, separately. The end of season was advanced by 1.7 (Alpine), 1.3 (Tall Tussock) and delayed by 0.3 (Low Producing) days/10-degree-south on the slopes in these three grassland types.
The results from this thesis show that recent shrub invasion into New Zealand grasslands is highest near shrub areas once a threshold of shrub cover in the neighbourhood is reached. Shrub encroachment was highest at lower elevations and on north-facing slopes. It also highlighted a measurable shift to an earlier start and extended length of the growing season in New Zealand’s main grassland types over the last 16 years, but the magnitude of these shifts showed considerable geographic variation. Importantly, this study has shown a high degree of topographical control on the timing of the growing in New Zealand’s grasslands with elevation and aspect acting differentially on start and end of the growing season. This highlights the importance of landscape heterogeneity and microclimates for ecosystem responses to climate change. This study shows that remotely sensed data can be successfully used to elucidate ecosystem-level shifts in temporal dynamics and spatial patterns of vegetation growth in grassland ecosystems
The role of control network in the accuracy of underground laser scanning surveys
Full text linkTerrestrial laser scanning is used in various fields with numerous applications, one being the documentation of heritage sites. Often scans will be georeferenced with respect to a real-world coordinate system. This is done using either direct or indirect georeferencing techniques. The indirect georeferencing method was used in this research, which uses coordinated targets, referred to as Ground Control Points (GCPs), that are captured in the scan scene. Manufacturers suggest a minimum of three GCPs are used, should the z-axis not be vertical, with additional GCPs for redundancy. Ideally GCPs should be placed evenly around the extent of the scan scene. For heritage site documentation, this is not always feasible given the unique and complex nature of each site. This research investigates the quantity and spatial variability of GCPs used in a scan scene, and the subsequent effect on the point cloud accuracy. A control test network was established at the School of Surveying (SoS), where variations of GCP scenarios were investigated, which was then applied to a case study in Arras, France. The case study being a network of underground World War One tunnels that were excavated by the New Zealand Engineering Tunnelling Company (NZETC), known as the Ronville Tunnels. The results from the SoS test network show, in this particular instance, that there is little benefit in using additional GCPs in a scan scene, should the minimum (three) be placed evenly around the extent of the area being captured. Low redundancy solutions may reduce the accuracy and robustness of georeferencing solutions, as seen with the case where large errors were present where the minimum number of GCPs were used. Geometrically poor placement of GCPs shows an increased correlation between the check points root mean square errors and range from the GCP centroid. The case study results, where the scan scene extents were hundreds of metres long, showed that it is necessary to supplement the minimum number of GCPs to mitigate uncertainties in the point cloud dataset. Similar to a least squares estimation adjustment where there are less fixed stations, there is more uncertainty for an unknown position. GCPs should therefore, be placed spatially around the extents of the scan scene and where scan scene extents increase so should the number of GCPs
Measuring Sperm whales via Acoustics and Photogrammetry
Full text linkThe most common vocalisations heard from sperm whales are short, broadband clicks which often display a decaying, evenly spaced, multi-pulse structure. The time between these pulses (inter-pulse interval: IPI) represents the two-way time for a pulse to travel between the air sacs located at either end of the sperm whale‟s head. The IPI therefore, is measure of head length and via an allometric relationship, total length. In order to compare IPIs of known individuals to an independent measure of length, a new, boat-based fully digital stereo photogrammetric system was developed and its measurement accuracy assessed. A field test was conducted measuring objects of known length throughout a distance/angle network. Mean measurement error over the entire network was 0.82% and it was found that the largest contributor to measurement error was the repeated manual selection of conjugate points in stereo images. IPIs were measured using a newly developed software plugin1 for Pamguard, an open-source software package for passive acoustic monitoring. The plug-in was based on the recently developed “bent horn” theory of sound production in sperm whales. Previous studies relating IPI to an independent measure of length have suffered from very small sample sizes. Therefore, this study measured 21 sperm whales off Kaikoura, New Zealand using the new photogrammetric and acoustic method. Both measurement methods produced results which were repeatable and more accurate than previously published studies (mean C.V = 1.57% and 0.63%, respectively). A new equation describing the relationship between IPI and total length was proposed. To further boost sample size, the IPI plugin was also used to measure IPIs from archived recordings of whales that had been measured with a previous photogrammetric system. This brought the total sample size of different whales with both IPI measurements and stereo photogrammetric measurements to 33. Finally the IPI plugin was used to estimate acoustically the growth rates of 29 seasonal resident sperm whales which had been repeatedly recorded between 1991 and 2009. Most whales showed an increase in IPI over time representing growth. For individuals that were recorded many times over several years von Bertalanffy growth curves fitted the data well (mean r2 = 0.83; range = 0.13- 0.99). This is the first time growth has been estimated using an acoustic method and because it is non-lethal it has the potential to allow different types of questions related to growth to be investigated
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