Spelling suggestions: "subject:"La solar"" "subject:"La polar""
241 |
Seasonal and inter-annual changes in the computation of Aura MLS HCl depletion and PSC-induced areas in the Antarctic polar stratosphere: 2005-2010 climate-chemistry assessment: the role of clouds in the Antarctic middle atmosphereArevalo Torres, Andolsa January 2012 (has links)
An examination of the seasonal and spatial distribution of Polar Stratospheric Clouds (PSCs) inferred from standard temperature profiles in the lower-middle atmosphere above Antarctica, as derived from the Earth Observing System (EOS) Aura Microwave Limb Sounder (MLS) satellite observations and NCEP/NCAR assimilations, is provided. Chemical volume mixing ratio (VMR) observations of EOS Aura MLS v2.2 hydrogen chloride (HCl) were used to show the interannual variability of PSC formation with respect to stratospheric chlorine partitioning during five Southern Hemisphere Antarctic seasons from 2005 to 2009. A remarkable first set of results, obtained from an algorithm developed for modelling HCl depletion areas in the Antarctic polar vortex region, and based on satellite observations, is presented. In particular, the analysis of HCl concentration data obtained from 2006 indicated that the area processed for HCl was larger than the area of PSC during some periods of Antarctic winter, and that this result was robust with respect to the various PSC formation and HCl depletion thresholds utilized. The results suggest that an underestimation in chlorine activation area can occur when temperature thresholds for PSC formation thresholds are employed. The work presented here also evaluated chlorine activation via sulfate aerosol (SA) in the Southern Hemisphere 2006 stratosphere, based on satellite measurements of water vapor (H2O) and constant values of SA, by implementing the TACL formula of Drdla and Müller [2010] in contrast to the TNAT formula of Hanson and Mauersberger [1988]. The results indicated that the former formula was not completely sufficient for accurately modeling areas of depleted HCl and chlorine deactivation for all pressure surfaces in the Antarctic stratosphere.
Based on the results of this study, the role of SA in chlorine activation appears to be more important at lower altitudes than for areas higher in the stratosphere.
|
242 |
Satellite observations of auroral acceleration processesEliasson, Lars January 1994 (has links)
Measurements with satellite and sounding rocket borne instruments contain important information on remote and local processes in regions containing matter in the plasma state. The characteristic features of the particle distributions can be used to explain the morphology and dynamics of the different plasma populations. Charged particles are lost from a region due to precipitation into the atmosphere, charge exchange processes, or convection to open magnetic field lines. The sources of the Earth’s magnetospheric plasma are mainly ionization and extraction of upper atmosphere constituents, and entry of solar wind plasma. The intensity and distribution of auroral precipitation is controlled in part by the conditions of the interplanetary magnetic field causing different levels of auroral activity. Acceleration of electrons and positive ions along auroral field lines play an important role in magnetospheric physics. Electric fields that are quasi-steady during particle transit times, as well as fluctuating fields, are important for our understanding of the behaviour of the plasma in the auroral region. High-resolution data from the Swedish Viking and the Swedish/German Freja satellites have increased our knowledge considerably about the interaction processes between different particle populations and between particles and wave fields. This thesis describes acceleration processes influencing both ions and electrons and is based on in-situ measurements in the auroral acceleration/heating region, with special emphasis on; processes at very high latitudes, the role of fluctuating electric fields in producing so called electron conics, and positive ion heating transverse to the geomagnetic field lines. / <p>Diss. (sammanfattning) Umeå : Umeå universitet, 1994, härtill 6 uppsatser.</p> / digitalisering@umu.se
|
243 |
Tomographic views of the middle atmosphere from a satellite platformHultgren, Kristoffer January 2014 (has links)
The middle atmosphere is a very important part of the Earth system. Until recently, we did not realize the importance of the structure of this vaporous shell and of the fundamental role it plays in both creating and sustaining life on the planet. Thanks to the development and improvement of new sounding methods and techniques, our knowledge of the composition of the atmosphere has become more detailed than ever before. We have also learned how to reveal complex interactions between different species and how they react to the incoming solar radiation. The middle part of the Earth’s atmosphere serves as a host for the Polar Mesospheric Clouds. These clouds consist of a thin layer of water-ice particles, only exsisting during the summer months and only close to the poles. There are indications that the occurrence of Polar Mesospheric Clouds may be linked to climate change. It has been pointed out that the first sightings coincide with the industrial revolution. Satellite observations have shown that Polar Mesospheric Clouds have become brighter and possibly more widely distributed during the 20th century. The clouds might therefore be suited as indicators of the variability of the climate - a good reason for studying this night-shimmering phenomena. The clouds can also be used as a proxy for middle atmospheric dynamics. In order to fully utilize Polar Mesospheric Clouds as tracers for atmospheric variability and dynamics, we need to better understand their local properties. The Optical Spectrograph and Infra-Red Imager System (OSIRIS) is one of two instruments installed on the Odin satellite. The optical spectrograph of this instrument observes sunlight scattered by the atmosphere and thus the Polar Mesospheric Clouds. This thesis deals with a tomographic technique that can reconstruct both horizontal and vertical structures of the clouds by using observations from various angles of the atmospheric region. From this information, microphysical properties such as particle sizes and number densities are obtained. The tomographic technique presented in this thesis also provides a basis for a new satellite concept - MATS. The idea behind the MATS satellite mission is to analyze wave activity in the atmosphere over a wide range of spatial and temporal scales, based on the scientific heritage from Odin/OSIRIS and the tomographic algorithms presented in this thesis. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper3: Submitted. Paper 4: Manuscript.</p>
|
244 |
Modelling of galactic and jovian electrons in the heliosphere / Daniel M. MoeketsiMoeketsi, Daniel Mojalefa January 2004 (has links)
A three-dimensional (3D) steady-state electron modulation model based on Parker (1965) transport
equation is applied to study the modelling of – 7 MeV galactic and Jovian electrons in the inner
heliosphere. The latter is produced within Jupiter's magnetosphere which is situated at - 5 AU in the
ecliptic plane. The heliospheric propagation of these particles is mainly described by the heliospheric
diffusion tensor. Some elements of the tensor, such as the diffusion coefficient in the azimuthal direction,
which were neglected in the previous two-dimensional modulation studies are investigated to account for
the three-dimensional transport of Jovian electrons. Different anisotropic solar wind speed profiles that
could represent solar minimum conditions were modelled and their effects were illustrated by computing
the distribution of 7 MeV Jovian electrons in the equatorial regions. In particular, the electron intensity
time-profile along the Ulysses spacecraft trajectory was calculated for these speed profiles and compared
to the 3-10 MeV electron flux observed by the Kiel Electron Telescope (KET) on board the Ulysses
spacecraft from launch (1990) up to end of its first out-of-ecliptic orbit (2000). It was found that the
model solution computed with the solar wind profile previously assumed for typical solar minimum
conditions produced good compatibility with observations up to 1998. After 1998 all model solutions
deviated completely from the observations. In this study, as a further attempt to model KET observations
more realistically, a new relation is established between the latitudinal dependence of the solar wind
speed and the perpendicular polar diffusion. Based on this relation, a transition of an average solar wind
speed from solar minimum conditions to intermediate solar activity and to solar maximum conditions
was modelled based on the assumption of the time-evolution of large polar coronal holes and were
correlated to different scenarios of the enhancement of perpendicular polar diffusion. Effects of these
scenarios were illustrated, as a series of steady-state solutions, on the computed 7 MeV Jovian and
galactic electrons in comparison with the 3-10 MeV electron observed by the KET instrument from the
period 1998 up to the end of 2003. Subsequent effects of these scenarios were also shown on electron
modulation in general. It was found that this approach improved modelling of the post-1998 discrepancy
between the model and KET observations but it also suggested the need for a time-dependent 3D
electron modulation model to describe modulation during moderate to extreme solar maximum
conditions. / Thesis (M.Sc.)--North-West University, Potchefstroom Campus, 2004.
|
245 |
Application of translational addition theorems to electrostatic and magnetostatic field analysis for systems of circular cylindersMachynia, Adam 11 April 2012 (has links)
Analytic solutions to the static and stationary boundary value field problems relative to an arbitrary configuration of parallel cylinders are obtained by using translational addition theorems for scalar Laplacian polar functions, to express the field due to one cylinder in terms of the polar coordinates of the other cylinders such that the boundary conditions can be imposed at all the cylinder surfaces. The constants of integration in the field expressions of all the cylinders are obtained from a truncated infinite matrix equation.
Translational addition theorems are available for scalar cylindrical and spherical wave functions but such theorems are not directly available for the general solution of the Laplace equation in polar coordinates. The purpose of deriving these addition theorems and applying them to field problems involving systems of cylinders is to obtain exact analytic solutions with controllable accuracies, thereby, yielding benchmark solutions to validate other approximate numerical methods.
|
246 |
The Syntax of Korean polar alternative questions: A-not-A.Ceong, Hailey Hyekyeong 03 January 2012 (has links)
This thesis explores how question FORCE (Rizzi 1997) is represented and licensed in Korean polar alternative questions (Korean PAQs). The syntactic properties of polar alternative questions have not been fully discussed in the literature; this work seeks to address that gap. The thesis has two main components. First, I provide an initial detailed investigation into the syntactic structure of Korean polar alternative questions (Korean PAQs), also called A-not-A questions, such as ciwu-nun ca-ni an ca-ni? ‘Is Jiwoo sleeping or not?’ I argue that Korean PAQs consist syntactically of a single clause. In this respect, Korean PAQs are distinct from both alternative questions and polar questions. The second goal of this thesis is to account for the asymmetric behaviour of complementizers in main clauses and embedded clauses. Variant complementizers occur in main clauses in Korean PAQs, while neutralized ci is the only complementizer which is licensed to appear in embedded clauses. Furthermore, Korean PAQs are incompatible with constituent questions in main clauses, but compatible with them in embedded clauses. This asymmetry is explained by appealing to the notion of a unique illocutionary question force in main clauses. In main clauses, the syntactic constituent ForceP cannot carry more than one kind of illocutionary question force: it bears either constituent question force or polar alternative question force, but not both. In contrast, since embedded clauses contain non-question (non-answer-requiring) complementizers, separate question forms do not conflict with each other in this location. Based on a wide range of empirical data from Korean, this thesis proposes to distinguish Force (‘question’) complementizers in the main clauses from Type (‘interrogative’) complementizers in embedded clauses.
The novel data from Korean polar alternative questions require a major rethinking of the received view on the analysis of complementizers as expressed in Rizzi (1997). My analysis shows that the pragmatic categories of illocutionary force are highly significant for syntactic analysis in ways that have not been treated consistently in theoretical discussions of questions, in particular as regards the very distinct roles of main and embedded ‘questions’. / Graduate
|
247 |
Searching for Simple Symmetric Venn DiagramsAhmadi Mamakani, Abdolkhalegh 24 July 2013 (has links)
An n-Venn diagram is defined as a collection of n finitely intersecting closed curves dividing the plane into 2^n distinct regions, where each region is in the interior of a unique subset of the curves. A Venn diagram is simple if at most two curves intersect at any point, and it is monotone if it has some embedding on the plane in which all curves are convex. An n-Venn diagram has n-fold rotational symmetry if a rotation of 180 degrees about a centre point in the plane leaves the diagram unchanged, up to a relabeling of the curves. It has been known that rotationally symmetric Venn diagrams could exist only if the number of curves is prime. Moreover, non-simple Venn diagrams with rotational symmetry have been proven to exist for any prime number of curves. However, the largest prime for which a simple rotationally symmetric Venn diagram was known prior to this, was 7. In this thesis, we are concerned with generating simple monotone Venn diagrams, especially those that have some type(s) of symmetry. Several representations of these diagrams are introduced and different backtracking search algorithms are provided based on these representations. Using these algorithms we show that there are 39,020 non-isomorphic simple monotone 6-Venn diagrams in total. In the case of drawing Venn diagrams on a sphere, we prove that there exists a simple symmetric n-Venn diagram, for any n >= 6, with the following set(s) of isometries : (a) a 4-fold rotational symmetry about the polar axis, together with an additional involutional symmetry about an axis through the equator, or (b) an involutional symmetry about the polar axis together with two reflectional
symmetries about orthogonal planes that intersect at the polar axis. Finally, we introduce a new type of symmetry of Venn diagrams which leads us to the discovery of the first simple rotationally symmetric Venn diagrams of 11 and 13 curves. / Graduate / 0984 / Khalegh@GMail.com
|
248 |
Greenhouse gas production and consumption in soils of the Canadian High Arctic2015 January 1900 (has links)
Micro-organisms living in the soils of the Canadian High Arctic produce and consume the greenhouse gases (GHGs) CO2, CH4, and N2O, contributing to global nutrient and GHG cycles; however, different vegetation and soil communities differ in their net productions of each gas and the total emissions from the ecosystem. The range of Arctic vegetation communities spans wetlands, tundras, and deserts differing in their soil water contents and other properties such as organic matter content. Previous estimates of total GHG emissions are often imprecise relative to the scale of microbial processes that result in these emissions. Deserts have extremely low levels of both water and organic matter, yet I found that deserts produce nearly as much GHGs as wetter, more fully vegetated tundras. To test the hypothesis that this unexpectedly strong source of GHGs in deserts was a consequence of recently-thawed, organic-rich permafrost, I measured GHG net production throughout the active layer of polar desert soils; both production and consumption of CH4 and N2O, as well as soil respiration were found throughout the profile, indicating no link to thawed permafrost and suggesting these high GHG activities are characteristic features of Arctic polar deserts rather than transient effects of recent warming.
I studied the community of microorganisms of the Arctic deserts by examining DNA from soil samples collected from three deserts on Ellesmere Island using DNA microarrays targeted for the functional genes AmoA and pmo. Using Structural Equation Modeling (SEM) I evaluated the hypotheses that the community of ammonia-oxidizers would be causally linked to the observed patterns of N2O net production, and that methane-oxidizers would be causally linked to CH4 net production. The SEM showed the expected link for CH4 production, but not N2O production. Available nitrogen in Arctic desert soils is primarily in the form of ammonia/ammonium, thus I find it surprising that no link could be found to the nitrifying community. Subsequent analysis of the occurence patterns of nitrous oxide reductase, a gene present in denitrifying bacteria and the only known biological sink for N2O, revealed only a weak association. Thus it remains unknown which organisms are responsible for the high levels of N2O emitted from Arctic polar desert soils. Furthermore, I observed several cases of unusual GHG processes, including a positive correlation between net CO2 and net N2O production in only some soils and some soil layers that consumed both CH4 and N2O.
|
249 |
Ecología trófica y áreas de forrajeo del escúa polar del sur, <i>Stercorarius maccormicki</i>, en dos localidades antárticas / Trophic ecology and foraging areas of South Polar skua <i>Stercorarius maccormicki</i> at two antarctic localitiesSantos, María Mercedes January 2014 (has links)
El escúa polar del sur Stercorarius maccormicki, es un predador tope, con una dieta amplia y es considerado como uno de los mejores representantes de especies oportunistas y generalistas entre las aves marinas antárticas. En la época reproductiva, se distribuye en el continente antártico, extendiéndose hacia el norte de la Península Antártica, islas Shetland del Sur e islas Orcadas del Sur. En esta zona se reproduce en simpatría con el escúa pardo S. lonnbergi. Aquí, el escúa pardo monopoliza las colonias de pingüinos, que representan una fuente de alimento predecible mientras que el escúa polar del sur se alimenta generalmente en el mar. Por el contrario, en áreas de alopatría, el escúa polar del sur se alimenta principalmente de pingüinos y aves voladoras, así como también de peces. Si bien se han realizado numerosos análisis de la dieta del escúa polar del sur en las Islas Shetland del Sur y Península Antártica, los resultados obtenidos han diferido notoriamente según la metodología utilizada, contribuyendo a la falta de consenso sobre la existencia y naturaleza de la competencia entre ambas especies. El propósito de esta tesis fue obtener información confiable de la ecología trófica del escúa polar del sur, utilizando distintas metodologías, en poblaciones que difieren en el número de parejas de escúa pardo, su potencial competidor. Esta información provee valiosos indicadores de los recursos en Antártida, necesarios para evaluar y establecer los planes de manejo de los predadores y sus presas.
El objetivo general de este trabajo fue analizar la ecología trófica y reproductiva del escúa polar del sur y estimar las áreas de alimentación en la Isla 25 de Mayo (islas Shetland del Sur) y en la Península Antártica, donde ambas especies se reproducen en simpatría aunque con distinto número de parejas reproductivas de escúa pardo. Los muestreos se realizaron durante 5 temporadas reproductivas (2003-04 a 2007-08) en dos localidades antárticas, Península Potter (Isla 25 de Mayo) y Punta Cierva (Península Antártica). Durante este periodo, en Pla. Potter, la colonia de escúa polar del sur era de 68-70 parejas y la de escúa pardo de 30-40 parejas, mientras que en Pt. Cierva, la colonia de escúa polar del sur era de 166 parejas y sólo dos de escúa pardo. Este es el primer estudio de dieta del escúa polar del sur realizado partir del análisis comparativo de recolección de egagrópilas, regurgitados y lavados estomacales, en varias temporadas y en dos localidades que difieren en el número de parejas reproductivas de escúa pardo.
Se caracterizó la dieta para ambas localidades y se determinó que está integrada por dos grandes categorías, peces y pingüinos, que se complementan con aves voladoras (principalmente petrel de las tormentas) y kril. Entre las presas consumidas los peces que presentaron mayor frecuencia fueron Pleuragramma antarcticum, particularmente en Pta. Cierva y Electrona antarctica en Pla. Potter. Durante los cuidados parentales, aumenta el número de ítems, aparecen además de peces y pingüinos, otras aves (restos de pichón de escúa y gaviota cocinera), kril, otros crustáceos y moluscos. Estos cambios podrían deberse al aumento en los requerimientos energéticos y/o cambios en la disponibilidad de alimento. Es interesante señalar que los resultados variaron en relación con la metodología utilizada. Si se consideran los resultados obtenidos mediante el análisis de las egagrópilas, el escúa polar del sur consume principalmente pingüinos en Pla. Potter y peces en Pta. Cierva, mientras que en base al análisis de regurgitados y lavados estomacales, para ambas localidades, los peces son el ítem principal en su dieta. En el análisis combinado de egagrópilas y regurgitados no se detectaron evidencias de competencia por el alimento entre ambas especies. En base a la comparación directa de metodologías en poblaciones que difieren marcadamente en el número de parejas reproductivas de escúa pardo, aquí se presenta una fuerte evidencia de una función no alimenticia para la ingesta de plumas, más que la explicación alternativa de los pingüinos como un importante ítem dietario, a pesar de la alta frecuencia de plumas hallada en las egagrópilas.
A partir de la ecología de estas presas y en base a la duración de los viajes de forrajeo se determinó que las áreas de alimentación del escúa polar del sur se extienden hasta 25 km en Pla. Potter y 32 km en Pta. Cierva, respecto de la costa. En ambos localidades, los escúas se alimentaron en zonas más resguardadas y evitaron los viajes en mar abierto. Se comprobó que el esfuerzo de alimentación de las parejas reproductoras fue variable entre años, entre periodos y entre fechas. Como era esperable, las parejas aumentan el tiempo de búsqueda y obtención de alimento cuando tienen pichones, debido a los requerimientos energéticos asociados, aunque las respuestas fueron diferentes entre temporadas. Asimismo, se observó que en fechas determinadas el esfuerzo se incrementó independientemente del estatus reproductivo, lo que sugiere fluctuaciones en la disponibilidad de alimento, particularmente al ser analizadas en conjunto con la información de dieta.
Distintos parámetros del éxito reproductivo pueden ser indicadores de las condiciones favorables o desfavorables durante la reproducción. Se determinaron dos temporadas con condiciones favorables y dos con condiciones desfavorables, inferidas a partir de la fecha de arribo y comienzo de la reproducción, del número de individuos anidantes, del tamaño de la nidada y del volumen de los huevos. En todas las temporadas, las condiciones favorables y desfavorables, fluctuaron durante el periodo de cuidados parentales de los pichones, que repercutió en el éxito reproductivo general y en el crecimiento de los pichones.
En síntesis, en este trabajo concluimos que en la región de la Península Antártica e islas Shetland del Sur, el escúa polar del sur es una especie piscívora y no se detectó competencia con el escúa pardo por el recurso terrestre. Por lo tanto, los cambios en el ecosistema marino y en particular la presencia de determinadas especies en la dieta, se reflejarán en el comportamiento de alimentación y repercutirán en el éxito reproductivo. Consideramos que esta especie puede ser un útil bioindicador de la presencia de P. antarcticum, especie clave en el ecosistema antártico y sensible al cambio climático regional registrado en el área. / The south polar skua Stercorarius maccormicki is a top predator with one of the most opportunistic and generalist diets of all Antarctic seabirds. In northerly parts of its range from the Antarctic Peninsula to South Shetland and South Orkney islands, south polar skua breeds in sympatry with brown skuas S. lonnbergi. Here, brown skua dominates terrestrial resources, particularly penguin colonies which provide a predictable source of food during the breeding season, while south polar skuas are reportedly almost wholly piscivorous. In allopatry, by contrast, this species reportedly feed principally on penguins and flighted birds as well as fish. Dietary studies of skuas on South Shetland Island and the Antarctic Peninsula have varied in their sampling methodologies, contributing to a lack of consensus on the existence and nature of competition between the two species. The aim of this study was to obtain reliable information on trophic ecology of south polar skua using methods designed to quantify diets at different levels of sympatry with BS. Unbiased data on seasonal diets of skuas provide valuable indicators of resource levels in the high Antarctic, with which to inform management policies for populations of both predators and prey.
The general objective of the thesis was to compare feeding and breeding ecology of south polar skua between two sites: Potter peninsula (Isla 25 de Mayo, South Shetland Island) and Point Cierva (Antarctic Peninsula) where their breeding colonies were sympatric with different numbers of brown skuas. The study covered five consecutive breeding seasons from 2003-04 to 2007-08. During this period, the colony at Potter peninsula of 68-70 south polar skua nests also contained 30-40 brown skua nests, while the colony at Point Cierva of 166 south polar skua nests contained only two brown skua nests. Diet was determined from comparative analysis of samples of pellets, chick regurgitate and adult stomach contents. This is the first dietary study of these species to compare the contents of pellets, stomach samples and regurgitates of South Polar Skuas, produced across years and localities that differ in the number of BS breeding pairs.
The diet of south polar skua was represented by two main groups: fishes and penguins, followed in importance by flighed birds and crustaceans. Fish predominated in the diet at both sites across years, with Pleuragramma antarcticum favoured at Point Cierva and Electrona antarctica at Potter peninsula. Dietary breadth varied with breading stage, in particular increasing during the guard stage to encompass penguins, skua chicks, seagulls, krill and other crustaceans, and molluscs. Such shifts in diet reflected increased energetic demand and changes in food availability during the breeding season. The combined analysis of pellets and regurgitates revealed strong dietary similarities between sites, despite the large numbers of brown skuas only at Potter peninsula. Evidence for the predominance of fish in south polar skua diet at both sites came from regurgitates. The pellets on their own would have suggested an almost exclusively fish-based diet at Point Cierva contrasting with a predominance of penguin over fish at Potter peninsula. The combined analysis revealed the major switch between sites, from a high representation of moss and low presence of penguin feathers at Point Cierva to a high representation of penguin feathers and little moss at Potter peninsula. This site difference reflects a scarcity of moss at Potter. It is consistent with feathers performing the same gut-cleaning function as moss. We suggest that pellet-based studies of diet may have over-represented bird prey taken by south polar skuas, and consequently overestimated competitive impacts from brown skuas.
The foraging areas for breeding south polar skuas were estimated from trip durations combined with information on prey distributions. According to this, at Potter skuas forage up to 25 km at Potter peninsula and up to 33 km at Point Cierva. Skuas at both localities fed in sheltered areas and avoided the open sea. Feeding behaviour differed by sex, season and breeding stage. Breeding pairs increased their foraging effort when feeding chicks, reflecting their increased energy requirements at this stage. The timing of this response differed between seasons, however, suggesting changes in food availability at sea.
Conditions for breeding varied among seasons, from favourable in two seasons to unfavourable in two seasons, based on dates of arrival and initiation of reproduction, number of breeding birds, clutch size, and egg size. Across seasons, initial conditions fluctuated during the parent care stage. This impacted in the overall breeding success and chicks’ growth.
In summary, SPS was found to be a piscivorous species at the two study sites, not detectably competing for food with BS. Changes in the Antarctic ecosystem related to the abundance and distribution of fish prey are therefore likely to have observable impacts on SPS feeding behaviour and ultimately on breeding success. We consider that SPS is a useful indicator of P. antarcticum presence, a key species in the Antarctic ecosystem and sensitive to regional climate change recorded in this area.
|
250 |
Digital Video Watermarking Robust to Geometric Attacks and CompressionsLiu, Yan 03 October 2011 (has links)
This thesis focuses on video watermarking robust against geometric attacks and
video compressions. In addition to the requirements for an image watermarking algorithm,
a digital video watermarking algorithm has to be robust against advanced
video compressions, frame loss, frame swapping, aspect ratio change, frame rate change,
intra- and inter-frame filtering, etc. Video compression, especially, the most efficient
compression standard, H.264, and geometric attacks, such as rotation and cropping,
frame aspect ratio change, and translation, are considered the most challenging attacks
for video watermarking algorithms.
In this thesis, we first review typical watermarking algorithms robust against geometric
attacks and video compressions, and point out their advantages and disadvantages.
Then, we propose our robust video watermarking algorithms against Rotation,
Scaling and Translation (RST) attacks and MPEG-2 compression based on the logpolar
mapping and the phase-only filtering method. Rotation or scaling transformation
in the spatial domain results in vertical or horizontal shift in the log-polar mapping
(LPM) of the magnitude of the Fourier spectrum of the target frame. Translation has
no effect in this domain. This method is very robust to RST attacks and MPEG-2
compression. We also demonstrate that this method can be used as a RST parameters
detector to work with other watermarking algorithms to improve their robustness to
RST attacks.
Furthermore, we propose a new video watermarking algorithm based on the 1D
DFT (one-dimensional Discrete Fourier Transform) and 1D projection. This algorithm
enhances the robustness to video compression and is able to resist the most advanced video compression, H.264. The 1D DFT for a video sequence along the temporal domain
generates an ideal domain, in which the spatial information is still kept and the
temporal information is obtained. With detailed analysis and calculation, we choose
the frames with highest temporal frequencies to embed the fence-shaped watermark
pattern in the Radon transform domain of the selected frames. The performance of the
proposed algorithm is evaluated by video compression standards MPEG-2 and H.264;
geometric attacks such as rotation, translation, and aspect-ratio changes; and other
video processing. The most important advantages of this video watermarking algorithm
are its simplicity, practicality and robustness.
|
Page generated in 0.0464 seconds