• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 634
  • 527
  • 257
  • 3
  • 2
  • 1
  • Tagged with
  • 3084
  • 734
  • 245
  • 234
  • 233
  • 233
  • 131
  • 126
  • 120
  • 115
  • 113
  • 113
  • 109
  • 109
  • 99
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

The Swansea Valley disturbance

Weaver, J. D. 1972 (has links)
No description available.

Novel applications of airborne LiDAR and multispectral data for high-resolution geological mapping of vegetated ophiolitic rocks and sedimentary cover, Troodos Range, Cyprus

Grebby, Stephen Robert 2011 (has links)
Practical and financial constraints associated with traditional field-based mapping are often responsible for the production of coarse-scale geological maps that lack detail and have inaccurately defined lithological contacts. Although remote sensing offers potential solutions to these constraints, conventional use of remotely sensed data is only effective when applied to barren terrain because just small amounts of vegetation cover can obscure or mask the underlying geological materials and structures. In this thesis, novel algorithms that utilise airborne Light Detection And Ranging (LiDAR) data and airborne multispectral imagery are applied to high-resolution geological mapping of vegetated ophiolitic rocks and sedimentary cover in the northern Troodos Range (Cyprus) with the aim of demonstrating their potential application to any geological setting. These novel algorithms involve quantification of geobotanical and topographical characteristics that are generally distinct for different lithological units, followed by automated image classification based upon these characteristics. Whilst the algorithms that individually exploit the geobotanical associations and the correlation between lithology and topography are capable of generating maps that are more detailed and have more accurately defined contacts than the existing geological maps of the study area, an integrated approach was found to significantly enhance the lithological mapping performance. Moreover, despite widespread vegetation cover, it is also shown that airborne LiDAR data and airborne multispectral imagery can be utilised to extract detailed and accurate structural information that is consistent with field-based data. Overall, the novel application of airborne spectral imagery and airborne LiDAR data has significant potential to aid accurate and high-resolution 1:5000-scale geological mapping over large areas of vegetated or non-vegetated terrain.

Reconstruction and motion estimation of sparsely sampled ionospheric data

Foster, Matthew 2009 (has links)
This thesis covers two main areas which are related to the mapping and examination of the ionosphere. The first examines the performance and specific nuances of various state-of-the-art interpolation methods with specific application to mapping the ionosphere. This work forms the most widely scoped examination of interpolation technique for ionospheric imaging to date, and includes the introduction of normalised convolution techniques to geophysical data. In this study, adaptive-normalised convolution was found to perform well in ionospheric electron content mapping, and the popular technique, kriging was found to have problems which limit its usefulness. The second, is the development and examination of automatic data-driven motion estimation methods for use on ionospheric electron content data. Particular emphasis is given to storm events, during which characteristic shapes appear and move across the North Pole. This is a particular challenge, as images covering this region tend to have a very-low resolution. Several motion estimation methods are developed and applied to such data, including methods based on optical flow, correlation and boundarycorrespondence. Correlation and relaxation labelling based methods are found to perform reasonably, and boundary based methods based on shape-context matching are found to perform well, when coupled with a regularisation stage. Overall, the techniques examined and developed here will help advance the process of examining the features and morphology of the ionosphere, both during storms and quiet times.

2-day planetary waves in the stratosphere, mesosphere and lower thermosphere

Tunbridge, Victoria 2011 (has links)
This thesis presents observations of the 2-day planetary wave in the stratosphere, mesosphere and lower thermosphere. These observations were made using two ground-based meteor radars at polar latitudes and the satellite-borne microwave limb sounder (MLS) on the NASA Aura satellite. There have been relatively few observations of the 2-day wave at polar latitudes made using ground-based radars. This is particularly so in the Antarctic. Measurements of summertime and wintertime polar 2-day waves in the mesosphere and lower thermosphere (MLT) region were made using identical meteor radars at the conjugate geographical latitudes of Rothera (68!S, 68!W) in the Antarctic and Esrange (68!N, 21!E) in Arctic Sweden. This allows accurate quantification of the differences in the nature and seasonal variability of the 2day wave between the two polar regions. A clear seasonal variability is evident with the maximum amplitudes occurring during the summer months in both hemispheres. However, significant differences are found in the behaviour of the summertime wave between the two polar regions. In particular, wave activity is shorter lived but of larger amplitude in the Antarctic. These differences are suggested to be partly due to the different background winds of the two polar regions and possible differences in the component zonal wavenumbers in the northern and southern hemispheres. These radar studies have excellent spatial, height and time resolution but cannot resolve the component zonal wavenumbers of the 2-day wave. Therefore, Earth Observing System (EOS) Aura Microwave Limb Sounder (MLS) measurements of atmospheric temperature were used to investigate the climatology and interhemispheric differences of the different zonal wavenumbers (westward propagating zonal wavenumbers 2, 3 and 4) that compose the 2-day wave “complex”. This study demonstrates that the wave is dominated by different wavenumbers in the northern and southern hemisphere and that some of the interhemispheric differences observed in ground-based studies can be explained by the seasonal variability of these different zonal wavenumbers. These satellite studies led to participation in a multi-technique international collaboration to study the short-term variability of the summertime 2-day wave. Observations made in the northern hemisphere at mid-latitudes revealed that there are typically three peaks of enhanced 2-day wave amplitude during the summer, probably originating from a combination of baroclinic instability and critical wind speed.

The northern boundary of the Ikertoq shear belt, west Greenland

Grocott, John 1977 (has links)
No description available.

Fracture mechanics of volcanic eruptions

Matthews, C. 2009 (has links)
Seismology is a key tool in the forecasting of volcanic eruptions. The onset of an eruption is often preceded and accompanied by an increase in local seismic activity, driven by fracturing within the edifice. For closed systems, with a repose interval of the order of a century or more, this fracturing must occur in order to create a pathway for the magma to reach the surface. Time-to-failure forecasting models have been shown to be consistent with seismic acceleration patterns prior to eruptions at volcanoes in subduction zone settings. The aim of this research is to investigate the patterns in seismic activity produced by a failure model based on fundamental fracture mechanics, applied to a volcanic setting. In addition to the time series of earthquake activity, statistical measures such as seismic b-value are also analysed and compared with corresponding data from the field and laboratory studies. A greater understanding of the physical factors controlling fracture development and volcano-tectonic activity is required to enhance our forecasting capability. The one dimensional, fracture mechanics grid model developed in this work is consistent with the theory of growth and coalescence of multi-scale fractures as a controlling factor on magma ascent. The multi-scale fracture model predicts an initial exponential increase in the rate of seismicity, progressing to a hyperbolic increase that leads to eruption. The proposed model is run with variations in material and load properties, and produces exponential accelerations in activity with further development to a hyperbolic increase in some instances. In particular, the model reproduces patterns of acceleration in seismicity observed prior to eruptions at Mt. Pinatubo (1991) and Soufriere Hills (1995). The emergence of hyperbolic activity is associated with a mechanism of crack growth dominated by interaction and coalescence of neighbouring cracks, again consistent with the multi-scale fracture model. The model can also produce increasing sequences of activity that do not culminate in an eruption; an occurrence often observed in the field. Scaling properties of propagating fractures are also considered. The seismic bvalue reaches a minimum at the time of failure, similar to observations from the field and measurements of acoustic emissions in the laboratory. Similarly, the fractal dimension describing the fracture magnitude distribution follows trends consistent with other observations for failing materials. The spatial distribution of activity in the model emerges as a fractal distribution, even with an initially random location of fractures along the grid. Significant shifts in the temporal or spatial scaling parameters have been proposed as an indication of change in controlling factors on a volcanic system, and therefore represent a relatively unexplored approach in the art of eruption forecasting.

Reconstructing Buried Alluvial Landscapes : The Application of Multiple Geophysical and Geoarchaeological Techniques

Mansfield, Carol 2007 (has links)
No description available.

Sedimentary studies in Lake Windermere

Holmes, P. W. 1964 (has links)
Late Quaternary sediments, soils,and parent rocks in and around the Windermere North Basin are studied by modern sedimentological techniques. Tho data obtained is examined statistically. Till points, scattered randomly on the Sand/silt/clay triangle, were redistributed into a "still later group", glaciolacustrine clays and main Windermere sediments; and a coarse fluvioglacial group which is better sorted and more rounded than the till. Fine sands, negatively skewed due to finer admixtures, typify certain lake environments. Beach deposits are better sorted and more rounded than the till from which they were partly derived; they are more rounded and coarser on the eastern exposed beaches than on sheltered ones; they are positively skewed due to inefficient fluviatile saltation. Three assumptions: a. Flocculation caused real mechanical bimodality of organic sediments. b. Spasmodic sedimentation was by underflowing "turbidity" currents during storms. c. Deposition occurred when settling (discrete or flocculated) overcame mechanical dispersal. Loss of river water impetus, and organic content and biological activity, controlled Poet Glacial sed1mentation. The relative importance of the two main rivers has alternated. Two basic mineralogical populations formed Late Quaternary material: a)Pink Late Glacial form, non hydrated. Post Glacial form, illite and aluminosilicates, hydrated and flocculated due to organic content and acidic environment (occurs up to 0.020 mm). b) Silt. Chloritic rock fragments (magnesium rich ripidolite, iron rich thuringite); calcite was removed from all but buried varves by Post Glacial acid corrosion. A marked change in lake sedimentation occurred with the spread of plant growth at the end of Late Glacial times 11,000 years ago. Controlled erosion, flocculation, and a high organic content characterised Post Glacial reddish gyttja sedimentation. Human settlement in the last 200 years caused further changes: accelerated erosion due to forest removal, reducing lakewater conditions due to sewage caused stronger flocculation in the blackish surface ooze.

The analysis of seismic attenuation spectra in rock mass characterisation : a case study at Acklington opencast coal site

Young, R. P. 1981 (has links)
No description available.

Seismic hazard assessment in Pakistan

Rehman, Khaista 2010 (has links)
No description available.

Page generated in 0.0356 seconds