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Dissertations / Theses on the topic 'Earth gravity'
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1
Rachel, Zammett Rachel Zammett. "Gravity Currents on Earth and Mars." Thesis, University of Oxford, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.491681.
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In this thesis we ~nvestigate three problems in the earth sciences where gravity currents play an important role. In the first part we consider two types of terrestrial gravity current: kata- . batic winds and submarine turbidity currents. We derive and solve the classical Prandtl model for katabatic wind flow in which the vertical wind profile is resolved. We show that this model breaks down when the slope becomes small, and pose a~ improved model which removes this singularity. Solutions of the improved model are compared with observations and output from a numerical model. We then investigate two layer-averaged models that are used to describe the flow of submarine turbidity currents. We find that both models predict that in some circumstances 'ignition' can occur, in which the current velocity becomes unbounded. We show that the only way this phenomenon can be prevented is by a decrease in the underlying slope. In the second part, we consider the unusual morphology of the Martian north polar ice cap. We use a model for the sublimation kinetics at the ice-atmosphere interface and include an explicit description of dust, both suspended in the atmosphere and frozen within the ice cap. Thansport of dust and ice are then included, and the model is investigated analytically and numerically. We find that this model can have multiple steady states, and that troughs may form during a transition between steady states. In this model, such a transition may be caused by obliquity-induced climate change.
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Rothleitner, Christian. "Ultra-high precision, absolute, earth gravity measurements." kostenfrei, 2008. http://www.opus.ub.uni-erlangen.de/opus/volltexte/2008/994/.
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Wu, Lichuan. "Introducing Surface Gravity Waves into Earth System Models." Doctoral thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-314760.
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Surface gravity waves alter the turbulence of the bottom atmosphere and the upper ocean. Accordingly, they can affect momentum flux, heat fluxes, gas exchange and atmospheric mixing. However, in most state-of-the-art Earth System Models (ESMs), surface wave influences are not fully considered or even included. Here, applying surface wave influences into ESMs is investigated from different aspects. Tuning parameterisations for including instantaneous wave influences has difficulties to capture wave influences. Increasing the horizontal resolution of models intensifies storm simulations for both atmosphere-wave coupled (considering the influence of instantaneous wave-induced stress) and stand-alone atmospheric models. However, coupled models are more sensitive to the horizontal resolution than stand-alone atmospheric models. Under high winds, wave states have a big impact on the sea spray generation. Introducing a wave-state-dependent sea spray generation function and Charnock coefficient into a wind stress parameterisation improves the model performance concerning wind speed (intensifies storms). Adding sea spray impact on heat fluxes improves the simulation results of air temperature. Adding sea spray impact both on the wind stress and heat fluxes results in better model performance on wind speed and air temperature while compared to adding only one wave influence. Swell impact on atmospheric turbulence closure schemes should be taken into account through three terms: the atmospheric mixing length scale, the swell-induced momentum flux at the surface, and the profile of swell-induced momentum flux. Introducing the swell impact on the three terms into turbulence closure schemes shows a better performance than introducing only one of the influences. Considering all surface wave impacts on the upper-ocean turbulence (wave breaking, Stokes drift interaction with the Coriolis force, Langmuir circulation, and stirring by non-breaking waves), rather than just one effect, significantly improves model performance. The non-breaking-wave-induced mixing and Langmuir circulation are the most important terms when considering the impact of waves on upper-ocean mixing. Accurate climate simulations from ESMs are very important references for social and biological systems to adapt the climate change. Comparing simulation results with measurements shows that adding surface wave influences improves model performance. Thus, an accurate description of all important wave impact processes should be correctly represented in ESMs, which are important tools to describe climate and weather. Reducing the uncertainties of simulation results from ESMs through introducing surface gravity wave influences is necessary.
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Joodaki, Gholamreza. "Earth Mass Change Tracking Using GRACE Satellite Gravity Data." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for bygg, anlegg og transport, 2014. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-23969.
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This project is dealing with the estimation of present-day Earth’s mass transport and its redistribution by using observations from Gravity Recovery and Climate Experiment (GRACE) satellite mission. GRACE measures the gravity fluctuations which are primarily related to redistribution of water around the globe. GRACE data has yield profound new insights into melting rates of ice sheets and mountain glaciers, land hydrology, ocean circulation, and sea level rise. In this project, first, the ice melting rate in the Greenlandic ice sheet is studied. This is done by analyzing the time series of monthly GRACE release 04 gravity field solutions from three different data sets, CSR (Center for Space Research), GFZ (Geoforschungszentrum), and JPL (Jet Propulsion Laboratory) with respect to their long-term temporal changes. The data are de-striped by applying a non-isotropic filter. Also, a method for reducing the leakage effects is developed. As an example, the ice mass balance is estimated of -163 ± 20 Gt/yr based on the CSR release 04 and smoothing by a parameter of a =1013 during April 2002 to February 2010. The results also show that the spatial distribution of the ice mass loss is changing with time and the ice mass loss is accelerating. For example, its acceleration is a rate of -32±6 Gt/yr2 during 2002 to 2011. The second part of this project is concern with the determination of water mass changes in the Nordic Seas. It is determined by analyzing the time series of monthly GRACE level 2 release 04 data from GFZ during October 2002 to October 2010. The striping errors are reduced by using a non-isotropic filter and the data are smoothed by a parameter of a =1014 according to Gaussian smoothing radius of 530 km. The time series of water mass changes are used to study the steric sea height variations over the Nordic Seas during the same period of study. This is done by analyzing the time series of monthly sea level anomaly from ENVISAT (Environmental Satellite) altimetry data, cycles 10 to 93, among the time series of water mass changes. The results show that the interdisciplinary nature of the GRACE measurements have opened up the unique opportunity to enhance our knowledge on the interaction between Earth system components and their response to climate variability. In the last part of this project, variations of the continental total water storage, total groundwater storage, and anthropogenic contributions across the Middle East are studied. By using a mascon analysis method and GRACE level 2 release 05 data from CSR during February 2003 to December 2012, the time series of total water storage, total ground water storage and anthropogenic contributions are estimated over this region. The region is subdivided to seven mascons including Iran, Iraq, Syria, eastern Turkey (east of 35º longitude), northern and southern Saudi Arabia (north and south of 25º latitude), and the region immediately west of Caspian Sea. The total groundwater storage, and anthropogenic contributions are separated from the total water storage by using the CLM4.5 (version 4.5 of the Community Land Model) hydrological model. The results show that Iran with a rate of 25±6 Gt/yr has the most groundwater loss rate during February 2003 to December 2012 in this region. The Iran’s rate of groundwater loss from the GRACE data is supported by an analysis of in situ well data from across Iran. The results also show that the GRACE mission is able to monitor monthly water storage changes within river basins and aquifers that are 200,000 km2 or larger in area, and, can contribute to water management at regional and national scales, and to international policy discussions as well.<br><p> </p><p> </p><p> </p>
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Anjasmara, Ira Mutiara. "Validating methods to infer mass changes from satellite gravity measurements using Synthetic Earth Gravity Modelling." Thesis, Curtin University, 2013. http://hdl.handle.net/20.500.11937/2379.
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Leakage properties of isotropic and anisotropic filters used to recover mass changes from space gravity observations are studied. These are done through the use of gravity induced by simulated mass changes within a closed-loop validation procedure. Results show that the use of filter techniques can introduce significant errors introducing distortions between recovered and simulated mass. Previously not well known, the study revealed that leakage is dependent on the geographic location if the mass change considered.
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Huang, Ou. "Terrain Corrections for Gravity Gradiometry." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1339698991.
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Regalado, Levi R. "Finite element analyses of gravity earth retaining structures founded on soil." Diss., Virginia Tech, 1992. http://hdl.handle.net/10919/40142.
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Fellner, Johannes Josef. "Numerical study on orthometric heights using a synthetic Earth gravity model." Thesis, Curtin University, 2011. http://hdl.handle.net/20.500.11937/1047.
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The fundamental problem of orthometric heights is that the mean gravity value cannot be determined due to the lack of precise topographical mass information. This thesis employs a global synthetic Earth gravity model, based on known and simulated global masses, in order to circumvent this problem. Applying forward gravity modelling techniques, the behaviour of gravity inside the topography as well as orthometric heights are studied in detail.
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Krishnamurthy, Venkataramanaiah. "The slow manifold and the persisting gravity waves." Thesis, Massachusetts Institute of Technology, 1985. http://hdl.handle.net/1721.1/54304.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1985.<br>Microfiche copy available in Archives and Science.<br>Bibliography: leaves 144-146.<br>by Venkataramanaiah Krishnamurthy.<br>Ph.D.
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Morgen, Brian A. "Virginia Gravity Flow Winery: A Transformative Journey." Thesis, Virginia Tech, 2018. http://hdl.handle.net/10919/83895.
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This thesis is embodied by the design of a new gravity flow winery on the eastern slopes of the Blue Ridge Mountains in Northern Virginia. The 100 acre site is home to an existing winery with grape vines aged over a decade.
From its initial inception, this thesis has been in part a response to the rapidly growing wine industry in Virginia and the typical ad hoc architecture associated with the wineries serving the state. The swelling interest in the culture of wine has sparked an evolution of the role of wineries. The winery of today is both an establishment for the production of wine as well as a venue for the enjoyment of its product and the delight of its natural setting. Creating a dialogue between site and visitor via thoughtful engagement of earth, air and sky is key for establishing a sense of place. The winery at the heart of this thesis is the quintessence of these ideals.
The architecture of this winery embraces the steps of gravity flow winemaking, which aims to preserve the integrity of the grapes by utilizing gravity instead of electric pumps. The design seeks to make these steps perceivable and understandable, taking a visitor from the wind swept heights of the mountainside to the cool air of the winery's subterranean vaults and back again. From vine to glass and from layperson to student of wine, this shared journey engenders a transformation of both grape and visitor.<br>Master of Architecture
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Rye, Maria del Carmen. "Dynamics and Control of a Tensegrity System in Low-Earth Orbit." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/77584.
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Tensegrity is the name given to a system of interconnected bars and tendons that can form a flexible self-standing structure. Its flexibility is due to the ability of the bars to move near-independent to each other, movement that can be caused by controlled tension forces in the tendons or external forces such as gravity. However, a balance of sorts must be maintained - if a tendon were to go slack, the entire structure could become unstable and collapse on itself.
This thesis looks at placing a tensegrity structure in orbit around the Earth. As a spacecraft's orbit is moved further away from the Earth, the strength of the Earth's gravity field lessens. Ideally, such a flexible structure would be placed far enough away from the Earth so that the gravity field would have too weak an impact on its individual elements to cause major distortions. However, the author recognizes that altitudes below 2,000 km, where the Earth's gravity field is still very prevalent, are the most common altitudes used by orbiting spacecraft today. The goal of this thesis is to analyze the distortions of the tensegrity structure at these lower altitudes, and also look at methods for controlling these distortions.<br>Ph. D.
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Wood, Stephanie. "Gravitational Potential Modeling of Near-Earth Contact Binaries." ScholarWorks @ UVM, 2017. http://scholarworks.uvm.edu/graddis/753.
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A significant component of recent space exploration has been unmanned mission to comets
and asteroids. The increase in interest for these bodies necessitates an increase in demand
for higher fidelity trajectory simulations in order to assure mission success. Most available
methods for simulating trajectories about asymmetric bodies assume they are of uniform
density. This thesis examines a hybrid method that merges a mass concentration ("mascon")
model and a spherical harmonic model using the "Brillouin sphere" as the interface. This
joint model will be used for simulating trajectories about variable density bodies and, in
particular, contact binary asteroids and comets.
The scope of this thesis is confined to the analysis and characterization of the spherical
harmonic modeling method in which three bodies of increasing asymmetrical severity are
used as test cases: Earth, asteroid 101955 Bennu, and asteroid 25143 Itokawa. Since the
zonal harmonics are well defined for Earth, it is used as the initial baseline for the method.
Trajectories in the equatorial plane and inclined to this plane are simulated to analyze the
dynamical behavior of the environment around each of the three bodies. There are multiple
degrees of freedom in the spherical harmonic modeling method which are characterized as
follows: (1) The radius of the Brillouin sphere is varied as a function of the altitude of
the simulated orbit, (2) The truncation degree of the series is chosen based upon the error
incurred in the acceleration field on the chosen Brillouin sphere, and (3) The gravitational
potential and acceleration field are calculated using the determined radial location of the
Brillouin sphere and the truncation degree.
An ideal Brillouin sphere radius and truncation degree are able to be determined as a
function of a given orbit where the error in the acceleration field is locally minimized. The
dual-density model for a contact binary is found to more accurately describe the dynamical
environment around Asteroid 25143 Itokawa compared to the single density model.
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Eshagh, Mehdi. "On Satellite Gravity Gradiometry." Doctoral thesis, Stockholm : Skolan för arkitektur och samhällsbyggnad, Kungliga Tekniska högskolan, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-10429.
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Crosby, A. G. "Aspects of the relationship between topography and gravity on the earth and moon." Thesis, University of Cambridge, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.598177.
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The thermal and mechanical structure of the lithosphere is the primary control on a planet’s geology, and is most commonly investigated using global or regional topography and gravity data. In this dissertation, the relationship between the two is used to investigate the lithosphere on the Moon and under the Earth’s ocean basins. Analysis of the relationship between gravity and topography on the nearside of the Moon, using line-of-sight accelerations from Doppler tracking of the Lunar Prospector spacecraft, indicates that <i>T<sub>e</sub></i> increased from less than 7 km to greater than 40 km between the time the oldest terrain formed and the most recent giant impacts. The increase is most simply interpreted in terms of the cooling and thickening of the lunar lithosphere, although the variation of <i>T<sub>e</sub></i><sub> </sub>is not well-described using simple thermal history models. Modelling of sometimes sparse topographic measurements above large seamounts using grids of satellite-derived sea-surface gravity indicates that, in the Earth’s oceans, <i>T<sub>e</sub></i> coincides roughly with the depth to the 300 ± 100°C isotherm at the time of loading. However, there is considerable scatter, and the interpretation is complicated by viscous relaxation, breaks in the plate, and uncertainty about the density of the load. The cooling thermal plate model has been used for the last 30 years to describe the subsidence of the ocean floor. However, an analysis of the average seafloor depth as a function of age shows that, in the absence of thickened crust and dynamic topography generated by mantle convection, the plate model does not provide a good description of the average topography of the ocean floor at ages greater than approximately 85 million years. There is evidence for a slight, temporary swallowing between the ages of 85-130 million years in the Pacific and Atlantic oceans, which is consistent with the outcome of early numerical experiments on the instability of a cooling thermal boundary layer. Nevertheless, the thermal plate model, with a plate thickness of approximately 90 km, does appear to provide a good description of the average subsidence of, and heat flux through, the oldest sea floor. An analysis of the relationship between gravity and topography over dynamic swells and depressions in the Pacific Ocean, Atlantic Ocean, and Central Africa indicates that gravity and topography are highly coherent at intermediate and long wavelengths, and that the admittance does not vary significantly with wavelength. This is in contrast to the predictions of early theoretical calculations. The long-wavelength admittance over marine dynamic topography is 30 ± 5 mGal km<sup>-1</sup>, and the admittance over dynamic topography in central Africa is approximately 40 mGal km<sup>-1</sup>. An analysis of the results of asthenospheric seismic tomography under the Pacific Ocean, using a recently-published parameterisation of SV-velocity in terms of temperature and depth, indicates that the intermediate and long-wavelength gravity field does not result primarily from temperature anomalies within the lower part of the asthenosphere.
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Lyon-Caen, Hélène. "Deep structure of the Himalaya and Tibet from gravity and seismological data." Thesis, Massachusetts Institute of Technology, 1985. http://hdl.handle.net/1721.1/54953.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1986.<br>Microfiche copy available in Archives and Science<br>Includes bibliographies.<br>by Hélène Lyon-Caen.<br>Ph.D.
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Yang, Hyo Jin. "Geoid Determination based on a Combination of Terrestrial and Airborne Gravity Data in South Korea." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1388677708.
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Ermakov, Anton. "Geophysical investigation of Vesta, Ceres and the Moon using gravity and topography data." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/108901.
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Thesis: Ph. D. in Planetary Science, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2017.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 236-262).<br>The shape and gravity field are fundamental properties of a planetary body. Combining gravity and topography data sets is, arguably, the most powerful tool to study planetary interiors from orbit. However, even when gravity and topography data are in hand, typically, a wide range of possible geophysical structures is possible. The reader will find that this problem of non-unique solutions permeates all chapters of this thesis. The general strategy to reduce non-uniqueness is to find ways to use additional observations that are sensitive to the interior structure but are not degenerate with gravity and/or topography. In this work, we study three Solar System bodies: asteroid Vesta, dwarf planet Ceres and the Earth's Moon. Using the data from the Dawn spacecraft, we find that once hot and hydrostatic, Vesta is no longer either. It was despun by two giant collisions. We use the Dawn gravity/topography data along with meteoritic data to provide constraints on Vesta's internal structure. Unlike Vesta, Ceres is close to hydrostatic equilibrium. Based on Ceres' topographic spectrum, we conclude that it has experienced limited viscous relaxation. Contrary to the pre-Dawn expectations, we find that the cerean crust is mechanically rock-like. We provide constraints on Ceres' rheology and density structure by combining gravity/topography data with finite-element modeling of lithospheric relaxation. Additionally, we find that Ceres' obliquity undergoes large oscillations, which has important implications for volatile transport. The GRAIL mission has produced gravity models of the Moon with an unprecedented accuracy. We study the spectral content of gravity models and characterize their effective resolution to provide users of these models with the information necessary to understand the model limitations.<br>by Anton Ermakov.<br>Ph. D. in Planetary Science
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Shang, Kun. "GRACE Time-Variable Gravity Field Recovery Using an Improved Energy Balance Formalism." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1437393586.
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Ågren, Jonas. "Regional Geoid Determination Methods for the Era of Satellite Gravimetry : Numerical Investigations Using Synthetic Earth Gravity Models." Doctoral thesis, KTH, Infrastructure, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-55.
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<p>It is the purpose of this thesis to investigate different regional geoid determination methods with respect to their feasibility for use with a future GOCE satellite-only Earth Gravity Model (EGM). This includes investigations of various techniques, which involve different approximations, as well as the expected accuracy. Many, but not all, of these tasks are tested by means of Synthetic Earth Gravity Models (SEGMs). The study is limited to remove-compute-restore methods using Helmert condensation and to Sjöberg's combined approach (method with additive corrections).</p><p>First, a number of modifications of Stokes' formula are tested with respect to their compatibility with a GOCE EGM having negligible commission error. It is concluded that the least squares modification method should be preferred.</p><p>Next, two new point-mass SEGMs are constructed in such a way that the resulting models have degree variances representative for the full and topographically reduced gravity fields, respectively. These SEGMs are then used to test different methods for modified Stokes' integration and downward continuation. It is concluded that the combined method requires dense observations, obtained from the given surface anomalies by interpolation using a reduction for all known density anomalies, most notably the topography. Examples of other conclusions are that the downward continuation method of Sjöberg (2003a) performs well numerically.</p><p>To be able to test topographic corrections, another SEGM is constructed starting from the reduced point-mass model, to which the topography, bathymetry and isostatic compensation are added. This model, which is called the Nordic SEGM, is then applied to test one strict and one more approximate approach to Helmert's condensation. One conclusion here is that Helmert's 1st method with the condensation layer 21 km below sea level should be preferred to Helmert's 2nd condensation strategy.</p><p>The thesis ends with a number of investigations of Sjöberg's combined approach to geoid determination, which include tests using the Nordic SEGM. It is concluded that the method works well in practice for a region like Scandinavia. It is finally shown how the combined strategy may preferably be used to estimate height anomalies directly.</p>
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Schiek, Cara Gina. "Characterizing the deformation of reservoirs using interferometry, gravity, and seismic analyses." To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2009. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
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Yale, Mara M. "Modeling upper mantle rheology with numerical experiments and mapping marine gravity with satellite altimetry /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1997. http://wwwlib.umi.com/cr/ucsd/fullcit?p9823700.
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Ebeling, Robert M. "Methods of evaluating the stability and safety of gravity earth retaining structures founded on rock." Diss., Virginia Polytechnic Institute and State University, 1989. http://hdl.handle.net/10919/54351.
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The objective of this study was to investigate the accuracy of the procedures employed in the conventional equilibrium method of analysis of gravity-earth-retaining structures founded on rock, using the finite element method of analysis. This study was initiated because a number of existing large retaining structures at various navigation lock sites in the United States that show no signs of instability or substandard performance have been found not to meet the criteria currently used for design of new structures.
The results of following load analyses show that when the loss of contact along the base of a wall is modeled in the finite element analysis, the calculated values of effective base contact area and maximum contact pressure are somewhat larger than those calculated using conventional equilibrium analyses. The values of the mobilized base friction angle calculated using both methods are in precise agreement.
Comparisons between the results of backfill placement analyses using the finite element method and the conventional equilibrium analyses indicate that conventional analyses are very conservative. The finite element analyses indicate that the backfill exerts downward shear loads on the backs of retaining walls. These shear forces have a very important stabilizing effect on the walls. Expressed in terms of a vertical shear stress coefficient (Kᵥ - r<sub>xy</sub>/σᵥ), this shear loading was found to range in value from 0.09 to 0.21, depending on the geometrical features and the values of the material parameters involved in the problem.
Another important factor not considered in the conventional equilibrium method is that the displacements of the wall have a significant influence on the distribution of both the stabilizing and destabilizing forces exerted on the wall. In general, as the wall moves away from the backfill, the lateral forces exerted on the wall by the backfill decrease, and the lateral forces exerted on the front of the wall by the toe fill increase.<br>Ph. D.
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Lee, Sang-Mook. "Tectonics of the East Pacific rise : studies of faulting characteristics and magnetic and gravity anomalies." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/54403.
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Simons, Mark. "Localization of gravity and topography : constraints on the tectonics and mantle dynamics of Earth and Venus." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/58356.
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Mazarico, Erwan Matías Alexandre 1981. "Precise orbit determination of the Mars Odyssey spacecraft and geodetic inversion for the Martian gravity field." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/28611.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2004.<br>Includes bibliographical references (leaves 73-75).<br>Remote sensing techniques are widely used in planetary science for acquiring precise, global inforniation about an object. One of these techniques consists of the study of the radio signals emitted by a spacecraft, from which it is possible to derive the forces acted upon it. For this project, we used the radio science data from the Mars-orbiting spacecraft "IMars Odyssey". Launched in April 2001, more than two years of daily radio tracking of this satellite are now available, allowing for Precision Orbit Determination. Using the program Geodyn, the position of the spacecraft with respect to the centre of mass of Mars is typically determined down to a few meters, while the velocity precision is better than 1 mm/s. Once a large number of orbits have been calculated, it is possible to use the residuals (misfits of the data to the modeled trajectory) to solve for some of the model parameters. Here, we determine the coefficients of the spherical harmonic expansion of the gravity field, as well as the drag coefficient of the satellite (a proxy for atmospheric density). To obtain such results, many high-precision data sets and models are combined: electromagnetic wave propagation, with tropospheric and ionospheric corrections; tracking station positions, including tidal and tracking station corrections; solar and thermal radiation; ephemerides of all the major bodies in the Solar System, plus the Martian moons. The inputs of the orbit determination program are the radio signals (Doppler and range), the angular momentum desaturations t.inings, the attitude (of the main bus of course, but also of the high-gain antenna and the solar panels), and a model of the spacecraft. Some results of this radio science experiment are pre-sented here, in the form<br>(cont.) of gravity field spherical harmonic expansions sensed by the spacecraft.<br>by Erwan Matías Alexandre Mazarico.<br>S.M.
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Jin, Yu 1959. "State-of-stress and rheology of Tibet and its vicinity from gravity anomalies and numerical models." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/54429.
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Rosales, de Cáceres José J. "On the effect of the Sun's gravity around the Earth-Moon L1 and L2 libration points." Doctoral thesis, Universitat de Barcelona, 2020. http://hdl.handle.net/10803/670809.
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In this thesis we explored some aspects of the dynamics around the Earth-Moon L1 and L2 points in the context of two Restricted Four Body Problems: the Bicircular Problem (BCP) and the Quasi-bicircular Problem (QBCP). Both the BCP and QBCP model the dynamics of a massless particle moving under the influence of the Sun, Earth, and Moon. Although these two models focus on the same system, it is relevant to study both because their behavior around the L2 is qualitatively different.Ðhese two models can be written in the Hamiltonian formalism as periodic time-dependent perturbations of the RTBP. To study these Hamiltonians, we used numerical tools tailored to these type of models to get an insight on the phase space. These two techniques are the reduction to the center manifold, and the computation and continuation of 2D tori.ßor the BCP, the analysis focused around the L2 point. The results obtained showed that the reduction to the center manifold, and the non-autonomous normal form computed in this thesis do not provide useful information about the neutral motion around L2. The approach taken was to compute families of 2D tori, and explore any connections and their stability. As a summary of this effort we identified a total of six families of 2D tori: two Lyapunov-type planar quasi-periodic orbits, and four vertical. One of the vertical families was obtained by direct continuation of Halo orbits from the RTBP. This showed that the family of Halo orbits from the RTBP survive in the BCP, with the understanding that this new family is Cantorian. It was also shown that one of the other vertical families is Halo-like. Hence, members of this family may be potential candidates for future space missions. However, these tori are hyperbolic, as opposed the ones coming directly from the RTBP Halo obits, which are partially elliptic. It was also shown that this family of Halo-like tori comes from a family of quasi-periodic orbits in the RTBP that are resonant with the frequency of the Sun. Hence, these family of Halo-like orbits in the BCP have their counterparts in the RTBP.ßor the QBCP, the focus of the analyses was there Earth-Moon L1 and L2 points. In this model, the reduction to the center manifold provided relevant qualitative information about the dynamics around L1 and L2. The main takeaway was that L1 and L2 had a similar qualitative behavior. In both cases there were two families of quasi-periodic Lyapunov orbits, one planar and one vertical. It was also shown that the quasi-periodic planar Lyapunov family underwent a (quasi-periodic) pitchfork bifurcation, giving rise to two families of quasi-periodic orbits with an out-of-plane component. Between them, there was a family of Lissajous quasi-periodic orbits, with three basic frequencies. Qualitatively, the phase space of the center manifold, as constructed in this thesis, resembled the phase space of the center manifold of the RTBP around L1 and L2. In the QBCP we also continued families of invariant 2D tori, and for both L1 and L2. In these cases, the quasi-periodic planar and vertical families were continued. The bifurcations of the quasi-periodic planar Lyapunov were identified. A conclusion from this numerical experiment was that the family of out-of-plane orbits born from the bifurcation seemed not to be the RTBP Halo counterparts in the QBCP. The RTBP Halo orbits do survive in the QBCP, but do not seem to be connected to the quasi-periodic planar Lyapunov family. ßinally, and also in the context of the BCP and the QBCP, numerical simulations to study transfers from a parking orbit around the Earth to a Halo orbit around the Earth-Moon L2 point were studied. The main conclusion is that the invariant manifolds of the target orbits studied intersect with potential parking orbits around the Earth. The relevance of this result is that it shows that there are one-maneuver transfers from a vicinity of the Earth to Earth-Moon L2 Halo orbits. This is not case when using the RTBP as reference model. Experiments were done for both the BCP and the QBCP, and in all cases is it was shown that the total cost in terms of ∆V and transfer time is comparable to other techniques requiring two or more maneuvers.<br>En aquesta tesi explorem alguns aspectes de la dinàmica al voltant dels punts L1 i L2 Terra-Lluna en el context de dos problemes restringits de quatre cossos: el problema bicircular (PBC) i el problema quasi-circular (PQBC). Tant el PBC com el PQBC modelen la dinàmica d’una partícula sense massa que es mou sota la influència del Sol, la Terra i la Lluna. Tot i que aquests dos models es centren en el mateix sistema, és rellevant estudiar-los tots dos perquè el seu comportament al voltant de la L2 és qualitativament diferent. Aquests dos models es poden escriure en el formalisme hamiltonià com a pertorbacions periòdiques del problema restringit dels tres cossos (PRTC) dependents del temps. Per estudiar aquests hamiltonians, utlitzem eines numèriques adaptades a aquest tipus de models per obtenir una idea de l’espai de fases. Aquestes dues tècniques són la reducció a la variety central i el càlcul i la continuació de tors 2D.
Per al PBC, l'anàlisi es centra al voltant del punt L2. Els resultats obtinguts mostren que la reducció a la varietat central i la forma normal no autònoma calculada en aquesta tesi no proporcionen informació útil sobre el moviment neutre al voltant de L2. L'enfocament adoptat es calcular famílies de tors 2D, i explorar les seves connexions i estabilitat. Com a resum d’aquest esforç, s'identifiquen un total de sis famílies de tors 2D: dues famílies d'òrbites quasi-periòdiques planes tipus Lyapunov i quatre verticals. Una de les famílies verticals s'obté per continuació directa de les òrbites Halo del PRTC. Això demostra que la família de les òrbites Halo del PRTC sobreviuen al PBC, entenent que aquesta nova família és cantoriana. També es demostra que una de les altres famílies verticals és semblant a les Halo. Per tant, els membres d’aquesta família poden ser candidats potencials per a futures missions espacials. No obstant això, aquests tors són hiperbòlics, a diferència dels que provenen directament de les Halo del PRTC, que són parcialment el·líptics. També es mostra que aquesta família de tors semblants a les Halo prové d’una família d’òrbites quasi-periòdiques del PRTC que són ressonants amb la freqüència del Sol. Per tant, aquestes famílies d’òrbites semblants a les Halo al PBC tenen els seus homòlegs al PRTC.
Per al PQBC, el focus de les anàlisis es troba en els punts L1 i L2 Terra-Lluna. En aquest model, la reducció a la varietat central proporciona informació qualitativa rellevant sobre la dinàmica al voltant de L1 i L2. El principal resultat és que L1 i L2 tenen un comportament qualitatiu similar. En ambdós casos hi ha dues famílies d’òrbites quasi-periòdiques tipus Lyapunov, una plana i una vertical. També es demostra que la família plana quasi-periòdica tipus Lyapunov sobrevé una bifurcació tipus pitchfork (quasi-periòdica), donant lloc a dues famílies d’òrbites quasi periòdiques amb un component vertical. Entre ells, hi havia una família d’òrbites quasi-periòdiques tipos Lissajous, amb tres freqüències bàsiques. Qualitativament, l’espai de fase de la varietat central, tal com es construeix en aquesta tesi, s’assembla a l’espai de fase del la varietat central del PRTC al voltant de L1 i L2. Al PQBC també es continuen famílies de tors 2D invariants, tant per a L1 com per a L2. En aquests casos, es continuen les famílies planes i verticals quasi-periòdiques. Durant aquest procés es troben bifurcacions a les families d'òrbites quasi-periòdiques planes. Una conclusió d’aquest experiment numèric és que la família d’òrbites amb component vertical nascudes de la bifurcació no són les contraparts de les Halo de PRTC. Les òrbites Halo de PRTC sobreviuen en el PQBC, però no semblen estar connectades a la família plana quasi-periòdica.
Finalment, i també en el context del PBC i el PQBC, es s'estudien simulacions numèriques per estudiar les transferències des d’una òrbita d’estacionària al voltant de la Terra fins a una òrbita Halo al voltant del punt L2 Terra-Lluna. La principal conclusió és que les varietats invariants de les òrbites objectiu estudiades passen molt a prop de la Terra. La rellevància d’aquest resultat és que mostra que hi ha transferències d’una maniobra des de d'una òrbita al voltat de Terra a les òrbites L2 Halo Terra-Lluna. No és així quan s’utilitza el PRTC com a model de referència. Es fan experiments tant per al BCP com per al QBCP, i en tots els casos es demostra que el cost total en termes de ∆V i temps de transferència és comparable a altres tècniques que requereixen dues o més maniobres.
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Hodgart, M. S. "Gravity gradient and magnetorquing attitude control for low-cost low earth orbit satellites : the UOSAT experience." Thesis, University of Surrey, 1989. http://epubs.surrey.ac.uk/844220/.
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An important concern in spacecraft engineering is attitude determination control and stabilisation (ADCS) - the combination of applied mathematics, classical physics and modern technology which maintains the pointing direction of one or more axes of an Earth-orbiting satellite. This thesis is a detailed study of a particular type of ADCS which exploits the gravity-gradient effect, which is just the weak tendency for an appropriately shaped body to point naturally in preferred directions; reinforced by magnetorquing, which is the active interaction of the geomagnetic field with a switched current passing through coils in the spacecraft body. The advantages of this technology is that it is low-cost, non-consumable and has no moving parts - so constituting no limitation to the satellite's life. The thesis is a detailed study of this form of ADCS with specific application to low Earth polar-orbiting (LEO) satellites, for which it is particularly suitable. The work is also a study in attitude determination based solely on a 3-axis magneometer measurement of the geomagnetic field, which is in principle a simple way, in terms of technology, of determining the attitude of the spacecraft, and from this controlling the attitude, if mediated by an on-board computer implementing appropriate algorithms. The results are for the most part practically based on the author's involvement with two satellites over a six year period with the satellites UOSAT-1 and UOSAT-2, which were designed, built, and continue to be controlled from the University of Surrey. A practical innovation in 2-axis attitude control is described: the active 'delibration' by active damping of a gravity-gradient controlled LEO satellite in an attitude-stabilised state, using a threshold comparison algorithm. A new theory and algorithms are then developed for 3-axis attitude control, based on a complementary use of magnetorquing and gravity gradient. Subject to further development these could alter the general perception of the most effective way of controlling low Earth orbiting satellites.
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Chan, Mei-ki. "Gravity and aeromagnetic modelling of the Longmenshan Fold-and-Thrust Belt, SW China." Click to view the E-thesis via HKUTO, 2008. http://sunzi.lib.hku.hk/hkuto/record/b4020330x.
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Wang, Lei. "Coseismic Deformation Detection and Quantification for Great Earthquakes Using Spaceborne Gravimetry." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1331098701.
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Rosenburg, Margaret Anne. "Predicted and observed free-air gravity anomalies for delamination models of the formation of the Siberian Flood Basalts." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/114338.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2007.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (page 30).<br>The mechanism responsible for the formation of the Siberian Flood Basalts (SFB) has yet to be discovered and adequately quantified. One theory proposes that thinning of the lithosphere due to delamination triggered the eruption. This model is characterized by a drip of denser material within the mantle, and because it involves a density-driven process, calculations of predicted gravity at the surface can be used to test the model. Temperature, composition, and stress output from the delamination model presented in Elkins-Tanton (2007) were used to calculate predicted gravity measurements at the surface. These predictions were then compared to gravity observations of the SFB, focusing on the potential eruptive center at Noril'sk. Model runs in both Cartesian and axisymmetric coordinates were analyzed, and each run predicted a negative anomaly over the site of the drip with a magnitude ranging from 20 to 50 mGal. In the observations, an average radial gravity profile centered on Noril'sk also contained a slight negative anomaly at the center, suggesting partial agreement with the delamination theory. Because the amplitude of the observed gravity anomaly is substantially smaller than the predicted amplitude, the qualitative agreement is encouraging, but not definitive.<br>by Margaret A. Rosenburg.<br>S.B.
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Panasyuk, Svetlana Valeryevna 1965. "The effect of compressibility, phase transformations, and assumed density structure on mantle viscosity inferred from earth's gravity field." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/55056.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1998.<br>Includes bibliographical references (p. 147-148).<br>by Svetlana, Valeryevna Panasyuk.<br>Ph.D.
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Ågren, Jonas. "Regional geoid determination methods for the era of satellite gravimetry : numerical investigations using synthetic earth gravity models /." Stockholm, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-55.
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Beiki, Majid. "New Techniques for Estimation of Source Parameters : Applications to Airborne Gravity and Pseudo-Gravity Gradient Tensors." Doctoral thesis, Uppsala universitet, Geofysik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-143015.
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Gravity gradient tensor (GGT) data contains the second derivatives of the Earth’s gravitational potential in three orthogonal directions. GGT data can be measured either using land, airborne, marine or space platforms. In the last two decades, the applications of GGT data in hydrocarbon exploration, mineral exploration and structural geology have increased considerably. This work focuses on developing new interpretation techniques for GGT data as well as pseudo-gravity gradient tensor (PGGT) derived from measured magnetic field. The applications of developed methods are demonstrated on a GGT data set from the Vredefort impact structure, South Africa and a magnetic data set from the Särna area, west central Sweden. The eigenvectors of the symmetric GGT can be used to estimate the position of the causative body as well as its strike direction. For a given measurement point, the eigenvector corresponding to the maximum eigenvalue points approximately toward the center of mass of the source body. For quasi 2D structures, the strike direction of the source can be estimated from the direction of the eigenvectors corresponding to the smallest eigenvalues. The same properties of GGT are valid for the pseudo-gravity gradient tensor (PGGT) derived from magnetic field data assuming that the magnetization direction is known. The analytic signal concept is applied to GGT data in three dimensions. Three analytic signal functions are introduced along x-, y- and z-directions which are called directional analytic signals. The directional analytic signals are homogenous and satisfy Euler’s homogeneity equation. Euler deconvolution of directional analytic signals can be used to locate causative bodies. The structural index of the gravity field is automatically identified from solving three Euler equations derived from the GGT for a set of data points located within a square window with adjustable size. For 2D causative bodies with geometry striking in the y-direction, the measured gxz and gzz components of GGT can be jointly inverted for estimating the parameters of infinite dike and geological contact models. Once the strike direction of 2D causative body is estimated, the measured components can be transformed into the strike coordinate system. The GGT data within a set of square windows for both infinite dike and geological contact models are deconvolved and the best model is chosen based on the smallest data fit error.<br>Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 730
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Hancock, Craig Matthew. "Degree-2 spherical harmonics of the Earth's gravity field from Earth rotation parameters and SLR measurements to LAGEOS." Thesis, University of Newcastle Upon Tyne, 2012. http://hdl.handle.net/10443/1413.
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The gravity field of the Earth is fundamental to subjects such as geodesy and geophysics. Many observations within geodesy refer directly or indirectly to gravity. Geodetic techniques provide information regarding the Earth and the processes that act on it. Mass and angular momentum are, according to physics, conserved in a closed system. The Earth interacts very little with components outside of it and can be thought of as a closed system. Mass components in one reservoir of the Earth system are exchanged with others. Mass redistribution within the Earth system is caused by geophysical processes. This movement of geophysical fluid (mass) causes variations in the Earth’s rotation, gravity field and geocentre. The improvement of geodetic techniques over the last few decades allows us to measure the effects of these processes on the Earth to an unprecedented accuracy. Earth rotation parameters (ERPs) are excited by variations in the mass distribution on the Earth’s surface and the exchange of angular momentum between the atmosphere and oceans and the solid Earth. The same mass redistribution causes temporal changes in the gravity field coefficients with the second degree harmonics related to the rotational deformation and hence to changes in the Earth’s inertial tensor. If precise models of the atmospheric and oceanic angular momentum are available solution for polar motion and degree-2 Stokes harmonics can be unified. In this study we utilise SLR tracking of LAGEOS to compare (i) degree-2 harmonics from ERPs and gravitation, and (ii) LAGEOS excitation functions and geophysical data (mass + motion). To what extent a unified approach is possible with current models for AM data and gravity mass change estimated from ERP within orbit determinations is investigated. Finally, the ability of SLR to calculate the motion of the Earth’s geocentre is also investigated.
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Jordan, Tom A. R. M. "Gravity anomalies, flexure, and the long-term rigidity of the continental lithosphere." Thesis, University of Oxford, 2007. http://ora.ox.ac.uk/objects/uuid:9f803b42-522e-442b-9849-bb8e6c2a5494.
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The cause and distribution of spatial variations in the mechanical properties of the continental lithosphere are fundamental questions for modern geology. In this study variations in long-term lithospheric rigidity have been investigated. These investigations used profile- and grid-based flexural models of the lithosphere’s response to geologically imposed topographic, or buried, loads. These models were constrained by topographic and gravity data allowing recovery of best fitting rigidity values. In Oman a Cretaceous ophiolite acts as a significant load on the continental crust. Flexural models along profiles orthogonal to the ophiolite strike show that the observed gravity data can be best modelled by an elastic beam with standard thickness (T<sub>e</sub>) of 30 km. Along strike there is shown to be significant variation in the foreland shape and the observed gravity signal. This, it is proposed, relates to the complex tectonic processes which occurred as the ophiolite was obducted. The Himalayan foreland has been the focus of controversy over the recovered long-term rigidity of the continents, with recovered T<sub>e</sub> values ranging from 40 to over 90 km. Both profile- and grid-based techniques show that T<sub>e</sub> is high (>70 km) in the foreland region. Across the India-Eurasia collisional system as a whole T<sub>e</sub> values are variable. Beneath the Tibetan plateau recovered values are generally low (<10 km), while the plateau margins are marked by regions of higher rigidity. Recovered T<sub>e</sub> values across the Arabia-Eurasia collisional system range from over 60 km in the foreland region to close to zero beneath the high Zagros mountains. In the eastern part of the foreland, flexural models match the gravity data; however, they disagree with sediment thickness data for the material infilling the foreland. This discrepancy is interpreted in terms of de-coupling of the flexural lithosphere from the shallower crustal levels, caused by the presence of significant salt deposits in this region. Application of grid-based techniques to South America, North America and Europe recover a broad range of Te values from ∼0 to over 90 km. The low T<sub>e</sub> values are explained in active orogenic belts in terms of current processes acting to weaken the lithosphere, and in the continental interiors as the relics of past orogenic events. High T<sub>e</sub> values in the continental interiors correlate with ancient cratonic cores which have undergone little deformation since their formation in the Archean. This study shows that T<sub>e</sub> variations have a critical influence on the development of large compressional orogenic belts. In the Himalayan and Andean orogens there is a correlation between the over-thrusting of the orogenic belt and high T<sub>e</sub> foreland regions. Where lower T<sub>e</sub> regions are seen, less over thrusting is apparent, and in the case of the India-Eurasia collisional system out-flow of lower crustal material may be occurring.
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Georgiopoulos, Andreas Xenophon. "Models for the upper crust of the Chaleston, South Carolina, seismic zone based on gravity and magnetic data." Thesis, Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/25861.
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Ryttberg, Mattias. "Introducing Lantmäteriet’s gravity data in ArcGIS with implementation of customized GIS functions." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-203137.
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Gravity is measured and used by Lantmäteriet to calculate a model of the geoid to get accurate reference heights for positioning. Lantmäteriet are continuously measuring new gravity and height data across Sweden to both complement, replace and to add new data points. This is mainly done by measurements in the field at benchmark points. One of the major reasons for continued measurements on e.g. benchmark points is that the measuring always moves forward which makes the measurements more accurate. More accurate data leads to a more accurate calculation of the geoid due to the more accurate gravity values. A more accurate geoid gives the possibility of more precise positioning across Sweden, due to the more precise height values. Lantmäteriet is in the process of updating their entire database of gravity data. They are also measuring at locations where there are none or sparse with measurements. As a stage in the renewing of their database and other systems the Geodesy department wishes to get an introduction to the ArcGIS environment. By customizations of several ArcGIS functions, Lantmäteriet’s work with the extensive data will get easier and perhaps faster. Customized tools will help make e. g. adding and removing data points easier, as well as making cross validation and several other functions only a click of a button away.
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Cai, Zhiyuan. "Global Mohorovicic Discontinuity Estimates Based on Isostatic Theories Using Gravity Data and Seismic Models." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu159455139426099.
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van, den Bremer T. S. "The induced mean flow of surface, internal and interfacial gravity wave groups." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:e735afe7-a77d-455d-a560-e869a9941f69.
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Although the leading-order motion of waves is periodic - in other words backwards and forwards - many types of waves including those driven by gravity induce a mean flow as a higher-order effect. It is the induced mean flow of three types of gravity waves that this thesis examines: surface (part I), internal (part II) and interfacial gravity waves (part III). In particular, this thesis examines wave groups. Because they transport energy, momentum and other tracers, wave-induced mean flows have important consequences for climate, environment, air traffic, fisheries, offshore oil and other industries. In this thesis perturbation methods are used to develop a simplified understanding of the physics of the induced mean flow for each of these three types of gravity wave groups. Leading-order estimates of different transport quantities are developed. For surface gravity wave groups (part I), the induced mean flow consists of two compo- nents: the Stokes drift dominant near the surface and the Eulerian return flow acting in the opposite direction and dominant at depth. By considering subsequent orders in a separation of scales expansion and by comparing to the Fourier-space solutions of Longuet-Higgins and Stewart (1962), this thesis shows that the effects of frequency dis- persion can be ignored for deep-water waves with realistic bandwidths. An approximate depth scale is developed and validated above which the Stokes drift is dominant and below which the return flow wins: the transition depth. Results are extended to include the effects of finite depth and directional spreading. Internal gravity wave groups (part II) do not display Stokes drift, but a quantity analogous to Stokes transport for surface gravity waves can still be developed, termed the “divergent- flux induced flow” herein. The divergent-flux induced flow it itself a divergent flow and induces a response. In a three-dimensional geometry, the divergent-flux induced flow and the return flow form a balanced circulation in the horizontal plane with the former transporting fluid through the centre of the group and the latter acting in the opposite direction around the group. In a two-dimensional geometry, stratification inhibits a balanced circulation and a second type of waves are generated that travel far ahead and in the lee of the wave group. The results in the seminal work of Bretherton (1969b) are thus validated, explicit expressions for the response and return flow are developed and compared to numerical simulations in the two-dimensional case. Finally, for interfacial wave groups (part III) the induced mean flow is shown to behave analogously to the surface wave problem of part I. Exploring both pure interfacial waves in a channel with a closed lid and interacting surface and interfacial waves, expressions for the Stokes drift and return flow are found for different configurations with the mean set-up or set-down of the interface playing an important role.
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Chan, Mei-ki, and 陳美琪. "Gravity and aeromagnetic modelling of the Longmenshan Fold-and-Thrust Belt, SW China." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B4020330X.
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Putra, Muhammad Ansyar Rafi. "Trajectory Optimization of Round Trip to Arjuna-type Near-Earth Asteroids from a Lunar Distant Retrograde Orbit Using Lunar Gravity Assist." Thesis, Luleå tekniska universitet, Rymdteknik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-76222.
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Asteroid mining is rapidly becoming a popular topic amongst space community, primarily due to the potential resources that the asteroids can provide for future spacefaring. One of the interesting resources that can be obtained from asteroids is water, which can also be processed into oxygen and fuel. An intriguing concept would be to process fuel from asteroid, and establish a fuel depot in an Earth-centered orbit. This thesis considers a mission concept consisting of travelling to an Arjuna near-Earth asteroid from a lunar distant retrograde orbit as a depot orbit, processing fuel in-situ from the water on the asteroid, and bringing back 100 tons of fuel to the depot orbit. In order to minimize fuel consumption for such a trip, the thesis develops an optimization method that can obtain the best trajectory for different phases of the round trip, given certain constraints to ensure the spacecraft successfully reaches the asteroid and comes back to the Earth system. The optimization model consists of four steps, i.e., the outbound trip, the first phase of the return trip, the second phase of the return trip, and the optimization for the combined phases of return trip. The outbound trip is the trajectory from the depot orbit to the asteroid. After at least three months of mining, the spacecraft brings back the processed fuel to the vicinity of the Moon. This phase is called the first phase of the return trip. The spacecraft is then captured without an insertion burn to an Earth-centered orbit by a lunar gravity assist maneuver, and travels to the point where the insertion maneuver to the depot orbit begins. This is the second phase of the return trip. The last step of the optimization is the combination of the two phases of return trip, in addition to the final maneuver for entering the lunar distant retrograde orbit. The optimization method uses MATLAB fmincon solver, and it was applied to 29 synthetic asteroids. There were 19 converged solutions, but for 10 asteroids the optimizations was not able to converge. The lowest minimum fuel consumption for a trip is 19965.5 kg, and the highest minimum fuel consumption is 61821.4 kg. For the lowest minimum fuel consumption, the duration of the trip is nearly 7 years, and the duration for the highest minimum fuel consumption is about 2.6 years.
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Asgharzadeh, Mohammad Forman. "Geodynamical analysis of the Iranian Plateau and surrounding regions." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1173126914.
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Werth, Susanna. "Calibration of the global hydrological model WGHM with water mass variations from GRACE gravity data." Phd thesis, Universität Potsdam, 2010. http://opus.kobv.de/ubp/volltexte/2010/4173/.
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Since the start-up of the GRACE (Gravity Recovery And Climate Experiment) mission in 2002 time dependent global maps of the Earth's gravity field are available to study geophysical and climatologically-driven mass redistributions on the Earth's surface. In particular, GRACE observations of total water storage changes (TWSV) provide a comprehensive data set for analysing the water cycle on large scales. Therefore they are invaluable for validation and calibration of large-scale hydrological models as the WaterGAP Global Hydrology Model (WGHM) which simulates the continental water cycle including its most important components, such as soil, snow, canopy, surface- and groundwater. Hitherto, WGHM exhibits significant differences to GRACE, especially for the seasonal amplitude of TWSV. The need for a validation of hydrological models is further highlighted by large differences between several global models, e.g. WGHM, the Global Land Data Assimilation System (GLDAS) and the Land Dynamics model (LaD).
For this purpose, GRACE links geodetic and hydrological research aspects. This link demands the development of adequate data integration methods on both sides, forming the main objectives of this work. They include the derivation of accurate GRACE-based water storage changes, the development of strategies to integrate GRACE data into a global hydrological model as well as a calibration method, followed by the re-calibration of WGHM in order to analyse process and model responses.
To achieve these aims, GRACE filter tools for the derivation of regionally averaged TWSV were evaluated for specific river basins. Here, a decorrelation filter using GRACE orbits for its design is most efficient among the tested methods. Consistency in data and equal spatial resolution between observed and simulated TWSV were realised by the inclusion of all most important hydrological processes and an equal filtering of both data sets. Appropriate calibration parameters were derived by a WGHM sensitivity analysis against TWSV. Finally, a multi-objective calibration framework was developed to constrain model predictions by both river discharge and GRACE TWSV, realised with a respective evolutionary method, the ε-Non-dominated-Sorting-Genetic-Algorithm-II (ε-NSGAII).
Model calibration was done for the 28 largest river basins worldwide and for most of them improved simulation results were achieved with regard to both objectives. From the multi-objective approach more reliable and consistent simulations of TWSV within the continental water cycle were gained and possible model structure errors or mis-modelled processes for specific river basins detected. For tropical regions as such, the seasonal amplitude of water mass variations has increased. The findings lead to an improved understanding of hydrological processes and their representation in the global model. Finally, the robustness of the results is analysed with respect to GRACE and runoff measurement errors. As a main conclusion obtained from the results, not only soil water and snow storage but also groundwater and surface water storage have to be included in the comparison of the modelled and GRACE-derived total water budged data. Regarding model calibration, the regional varying distribution of parameter sensitivity suggests to tune only parameter of important processes within each region. Furthermore, observations of single storage components beside runoff are necessary to improve signal amplitudes and timing of simulated TWSV as well as to evaluate them with higher accuracy.
The results of this work highlight the valuable nature of GRACE data when merged into large-scale hydrological modelling and depict methods to improve large-scale hydrological models.<br>Das Schwerefeld der Erde spiegelt die Verteilung von Massen auf und unter der Erdoberfläche wieder. Umverteilungen von Erd-, Luft- oder Wassermassen auf unserem Planeten sind damit über eine kontinuierliche Vermessung des Erdschwerefeldes beobachtbar. Besonders Satellitenmissionen sind hierfür geeignet, da deren Umlaufbahn durch zeitliche und räumliche Veränderung der Schwerkraft beeinflusst wird. Seit dem Start der Satellitenmission GRACE (Gravity Recovery And Climate Experiment) im Jahr 2002 stellt die Geodäsie daher globale Daten von zeitlichen Veränderungen des Erdschwerefeldes mit hoher Genauigkeit zur Verfügung. Mit diesen Daten lassen sich geophysikalische und klimatologische Massenumverteilungen auf der Erdoberfläche studieren. GRACE liefert damit erstmals Beobachtungen von Variationen des gesamten kontinentalen Wasserspeichers, welche außerordentlich wertvoll für die Analyse des Wasserkreislaufes über große Regionen sind. Die Daten ermöglichen die Überprüfung von großräumigen mathematischen Modellen der Hydrologie, welche den natürlichen Kreislauf des Wassers auf den Kontinenten, vom Zeitpunkt des Niederschlags bis zum Abfluss in die Ozeane, nachvollziehbar machen. Das verbesserte Verständnis über Transport- und Speicherprozesse von Süßwasser ist für genauere Vorhersagen über zukünftige Wasserverfügbarkeit oder potentielle Naturkatastrophen, wie z.B. Überschwemmungen, von enormer Bedeutung.
Ein globales Modell, welches die wichtigsten Komponenten des Wasserkreislaufes (Boden, Schnee, Interzeption, Oberflächen- und Grundwasser) berechnet, ist das "WaterGAP Global Hydrology Model" (WGHM). Vergleiche von berechneten und beobachteten Wassermassenvariationen weisen bisher insbesondere in der jährlichen Amplitude deutliche Differenzen auf. Sehr große Unterschiede zwischen verschiedenen hydrologischen Modellen betonen die Notwendigkeit, deren Berechnungen zu verbessern. Zu diesem Zweck verbindet GRACE die Wissenschaftsbereiche der Geodäsie und der Hydrologie. Diese Verknüpfung verlangt von beiden Seiten die Entwicklung geeigneter Methoden zur Datenintegration, welche die Hauptaufgaben dieser Arbeit darstellten. Dabei handelt es sich insbesondere um die Auswertung der GRACE-Daten mit möglichst hoher Genauigkeit sowie um die Entwicklung einer Strategie zur Integration von GRACE Daten in das hydrologische Modell. Mit Hilfe von GRACE wurde das Modell neu kalbriert, d.h. Parameter im Modell so verändert, dass die hydrologischen Berechnungen besser mit den GRACE Beobachtungen übereinstimmen. Dabei kam ein multikriterieller Kalibrieralgorithmus zur Anwendung mit dem neben GRACE-Daten auch Abflussmessungen einbezogen werden konnten.
Die Modellkalibierung wurde weltweit für die 28 größten Flusseinzugsgebiete durchgeführt. In den meisten Fällen konnte eine verbesserte Berechnung von Wassermassenvariationen und Abflüssen erreicht werden. Hieraus ergeben sich, z.B. für tropische Regionen, größere saisonale Variationen. Die Ergebnisse führen zu einem verbesserten Verständnis hydrologischer Prozesse. Zum Schluss konnte die Robustheit der Ergebnisse gegenüber Fehlern in GRACE- und Abflussmessungen erfolgreich getestet werden. Nach den wichtigsten Schlussfolgerungen, die aus den Ergebnissen abgeleitet werden konnten, sind nicht nur Bodenfeuchte- und Schneespeicher, sondern auch Grundwasser- und Oberflächenwasserspeicher in Vergleiche von berechneten und GRACE-beobachteten Wassermassenvariationen einzubeziehen. Weiterhin sind neben Abflussmessungen zusätzlich Beobachtungen von weiteren hydrologischen Prozessen notwendig, um die Ergebnisse mit größerer Genauigkeit überprüfen zu können.
Die Ergebnisse dieser Arbeit heben hervor, wie wertvoll GRACE-Daten für die großräumige Hydrologie sind und eröffnen eine Methode zur Verbesserung unseres Verständnisses des globalen Wasserkreislaufes.
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Ohiwa, Mitchihiro 1977. "An experimental study on mixing induced by gravity currents on a sloping bottom in a rotating fluid." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/55068.
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Thesis (S.M.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences and the Woods Hole Oceanographic Institution), 2002.<br>Includes bibliographical references (p. 75-77).<br>Mixing induced by gravity currents on a sloping bottom was studied through laboratory experiments in a rotating fluid. The dense fluid on the sloping bottom formed a gravity current that could be in regimes where the flow was laminar or had waves. The mixing on a sloping bottom for gravity currents in the laminar and wave regimes was studied both qualitatively and quantitatively. The laboratory experiments were conducted on rotating tables in a tank with homogeneous ambient fluid. The slope angle, rotation rate, reduced gravity, and flow rate of the dense source water were changed for the experiments. The mixing was quantized by measuring the density of the ambient fluid, dense source water, and the bottom water collected at the end of the bottom slope and calculating the ratio of the source water in the bottom water. Comparing the mixing in the laminar regime and the wave regime by changing the slope angle and rotation rate showed that the waves in the gravity current increased the mixing due to the waves. Analysis of the ratio of source water based on the internal Froude number, the Ekman number, and the timescale of the experiments showed that diffusion was not the main mechanism for mixing. The Ekman layer solution was validated by the observation of a streak left by a grain of dye in the dense water layer. The values for the entrainment parameter for the laboratory experiments bracketed those calculated for the Denmark Strait overflow and the Mediterranean outflow, and the values based on observations in the ocean and those from the laboratory were similar for a nondimensional parameter defined using variables used in the laboratory experiments. This shows that the results from the experiments could be used to discuss the mixing in the ocean due to gravity currents along a slope in the ocean and that the waves observed in the laboratory might also be observed in the ocean.<br>by Mitchihiro Ohiwa.<br>S.M.
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Abt, Tin Lian. "Detection of a Local Mass Anomaly in the Shallow Subsurface by Applying a Matched Filter." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1313154731.
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Hernandez, Orlando. "Tectonic analysis of northwestern South America from integrated satellite, airborne and surface potential field anomalies." Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1158512351.
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Amarante, Rogério Rodrigues 1972. "Sistematização do processamento de dados gravimétricos aplicados a determinação do modelo geoidal." [s.n.], 2012. http://repositorio.unicamp.br/jspui/handle/REPOSIP/258364.
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Orientador: Jorge Luiz Alves Trabanco<br>Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e Urbanismo<br>Made available in DSpace on 2018-08-21T16:53:48Z (GMT). No. of bitstreams: 1
Amarante_RogerioRodrigues_D.pdf: 8479306 bytes, checksum: c6760b22f8c1f110ad1b61e48c59508b (MD5)
Previous issue date: 2012<br>Resumo: Com o uso de métodos adequados, receptores GNSS podem determinar coordenadas com acurácia suficiente para aplicação em projetos de engenharia. Porém a altitude elipsoidal obtida não utiliza o mesmo sistema de referência da engenharia de transportes. A altitude elipsoidal pode ser transformada em ortométrica com a utilização de modelos geoidais que são gerados a partir de dados gravimétricos. Neste trabalho são apresentados alguns conceitos introdutórios sobre a geração de modelo geoidais. Em seguida mostra o desenvolvimento de uma nova sistematização do tratamento de dados gravimétricos com objetivo de facilitar a detecção de erros, aumentar a produtividade e melhorar a organização de resultados obtidos. Dentro deste desenvolvimento, são revisadas as teorias utilizadas para transformar medições feitas com gravímetros diferenciais em aceleração da gravidade. Apresenta também técnicas de ajustamento de observações com intuito tratar erros aleatórios. A nova abordagem sugerida foi utilizada para o desenvolvimento de um software objetivando validar as idéias propostas, permitir a comparação com outras soluções existentes e também servir como uma contribuição tecnológica. Dados gravimétricos reais foram testados dentro da abordagem proposta tendo sido observados mais organização, ganho de produtividade e principalmente a detecção de erros grosseiros e aleatórios. Com a revisão do cálculo da correção da maré, percebeu-se que programas e equipamentos atualmente em uso não possuem configuração do fator gravimétrico, fato que pode influenciar em até 0; 007mGals no processamento das observações<br>Abstract: With the use of appropriate methods, GNSS receivers can determine coordinates with sufficient accuracy for use in projects. The ellipsoidal height obtained, however, does not use the same reference system as the one used in transportation engineering. The ellipsoidal height can be transformed to orthometric height using geoid models that are generated from gravimetric data. In this work some introductory concepts on the generation of geoid model are presented. Then it shows the development of a new approach in systematization of gravimetric data processing aiming to facilitate the detection of errors, increase productivity and improve the organization of the results obtained in the gravimetric surveys. Within this development, the theories used to convert measurements of the differences in gravity acceleration are revised. It also features adjustment techniques of observations in order to deal with random errors. The new suggested approach was used to develop software in order to validate the proposed ideas, allow comparison with other existing solutions, and also serves as a technological contribution. Gravimetric data were tested within the suggested approach. It was observed better organization, productivity gains and mainly detection of gross errors and random. With the review of the tide correction calculation, it was realized that programs and equipments now widely used have no gravimetric factor setting, a fact that can influence up to 0; 007mGals in processing the readings<br>Doutorado<br>Transportes<br>Doutor em Engenharia Civil
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Yildiz, Ersan. "A Numerical Study On The Dynamic Behaviour Of Gravity And Cantilever Retaining Walls With Granular Backfill." Phd thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/2/12608145/index.pdf.
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Dynamic behaviour of gravity and cantilever retaining walls is investigated by finite element method, incorporating the nonlinear elasto-plastic material properties of soil and seperation of the wall and backfill. Two dimensional finite
element models are developed employing the finite element software ANSYS. The wall is modelled to rest on a soil layer allowing translational and rotational movements of the wall. Soil-wall systems are subjected to harmonic and real earthquake motions with different magnitude and frequency characteristics at the base. The maximum lateral force and its application point durinG dynamic loading are determined for each case. It is observed that the frequency content of the base motion has a significant influence on the dynamic lateral soil pressures and the lateral forces considerably increase as the base motion frequency approaches the fundamental frequency of the soil layer. The maximum lateral thrusts calculated by finite element analyses are generally found to be greater than those suggested by Mononobe-Okabe method and experimental findings. Nevertheless, the locations of the application point obtained by finite element method are found to be in good agreement with the results of experimental studies.
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Couhert, Alexandre. "Amélioration des références massiques de la Terre par synergie entre différentes mesures de géodésie spatiale : Application à l'océanographie par altimétrie spatiale." Thesis, Toulouse 3, 2019. http://www.theses.fr/2019TOU30242.
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Dans le contexte du changement climatique mondial et la nécessité d'étudier les conséquences de l'ampleur de la fonte des glaces continentales sur le niveau des mers ainsi que sur la répartition des masses fluides à l'échelle du globe, notre travail de thèse s'intéresse aux phénomènes à très grande échelle qui modifient la forme de la Terre, son champ de gravité et l'équilibre de sa rotation. Il se focalise sur la stratégie à mettre en place pour observer et modéliser des variations très fines sur des termes géodynamiques (coefficients de bas degrés) qui sont encore aujourd'hui mal connus, et pourtant déterminants dans l'établissement des références terrestres fondamentales. La première partie de la thèse concerne l'observation du mouvement du géocentre par différentes techniques de mesures géodésiques. Ces travaux débouchent, par une meilleure maîtrise des sources d'erreurs, sur une explication des écarts entre les séries de mesures laser du mouvement du géocentre obtenues sur les satellites LAGEOS (référence actuelle pour l'origine du repère international, ITRF) et celles obtenues indépendamment sur le satellite altimétrique Jason-2 à partir d'observations DORIS/laser/GPS. La deuxième partie de la thèse s'intéresse à la détermination cohérente des coefficients de degrés 0 (coefficient gravitationnel GM), 1 (géocentre), et 2 (inertie/orientation) du champ de pesanteur terrestre. Nous utilisons pour cela les mesures de télémétrie laser disponibles depuis les années 1970 (par exemple, Starlette lancé en précurseur par le CNES dès 1975), car ce sont les seules mesures à caractère absolu qui donnent accès à ces trois premiers degrés. Nos analyses menées sur près de 35 ans aboutissent à une nouvelle valeur de la constante gravitationnelle géocentrique et la détection d'une réponse viscoélastique du manteau de notre planète aux échelles de temps décennales, par combinaison des termes de degré 2 et paramètres d'orientation de la Terre avec les équations d'Euler-Liouville<br>In the context of the overall climate change and the need to analyze the implications of the record ice-sheet melting for the sea level and global fluid mass redistribution budgets, our PhD work focuses on large-scale phenomena impacting the shape of the Earth, its gravity field, and the stability of its rotation pole. We explore strategies for the observation and modeling of subtle variations in geodynamic parameters (lowermost degree coefficients), which are still poorly constrained, despite their importance in determining fundamental terrestrial references. The first part of this PhD is dedicated to the observation of the geocenter motion, using different geodetic technics. The outcomes of this work provided explanations, through a correct handling of the dominant error sources, for the discrepancies between the reference laser-based LAGEOS geocenter time series (defining the origin of the international frame, ITRF) and independent solutions using DORIS/laser/GPS observations from the Jason-2 altimeter satellite. The second part of this PhD presents a self-consistent determination of the degrees 0 (gravitational coefficient GM), 1 (geocenter motion), and 2 (Earth's figure axis orientation) of the geopotential. To this end, we use the available laser data since the 1970s (e.g., the first geodetic satellite Starlette launched by CNES in 1975), as they are the only absolute measurements making possible the monitoring of the first three degree terms. Based on 35 years of satellite laser tracking, an updated value of the geocentric gravitational coefficient was obtained, and a viscoelastic behavior of the Earth's mantle manifesting at decadal time scales was exhibited, combining the derived figure axis variations of the Earth and polar motion observations with the Euler-Liouville equations