181 research outputs found
Optimum Currency Areas Structural Changes and the Endogeneity of the OCA Criteria: Evidence from Six New EU Member States
No full textThe present paper has two aims. The first aim is to test whether six new member states of the European Union (the six Central and Eastern European Countries) form an optimum currency area (OCA) with the eurozone, in an attempt to assess their readiness for euro adoption. The second aim is to examine whether the introduction of the euro in 1999 and the decision of the countries to seek to join the euro area created any forces fostering their convergence, evidence which would be in line with the theory on the endogeneity of the OCA criteria. Our findings indicate that the introduction of the euro did promote integration of the six new member states and that, at present, they are quite well aligned with the eurozone.EU enlargement; OCA; real exchange rates; cointegration; GPPP.
Chloride threshold values for corrosion in concrete – a myth ?
No full textThis paper reviews the established conceptual approach of predicting initiation of chloride induced corrosion of reinforcing steel in concrete. The low predictive power of the current approach is illustrated with help of recent field data for the chloride threshold value. Limitations and particular gaps of knowledge are highlighted, and issues urgently needing further research are identified. This includes the production process and the resulting microstructure of the reinforcing steel. Most of our practical long-term experience from real structures relates to systems, where cold worked steel and Portland cement were used. During the last few decades, however, a transition to thermomechanically strengthened reinforcing steels and to blended cements occurred. There is indication that this drastically affects the corrosion behavior
Analysis of GPS data from an Antarctic ice stream
No full textTemporal variations in the flow of an active ice stream are analyzed using GPS data collected over a period of two months at six different locations. The diameter of the network is about 60 km. The ice stream moves with a velocity of about one meter per day. The kinematic data are processed using three different strategies: zero-difference network solution, Precise Point Positioning, and double-difference network solution with resolved carrier phase ambiguities. The solutions are compared with regard to the quality of the resulting coordinate time series. Special attention is paid to the positional accuracy as a function of temporal frequency for these different analysis methods as the overall aim of the measurements is to estimate temporal variability in ice flow
Global and Local Gravity Field Recovery from Satellite-to-Satellite Tracking
No full textThe main objective of this thesis is the gravity field recovery using satellite-to-satellite tracking methods. Based on new technologies like the global positioning system and accelerometers satellite-to-satellite tracking yields a dramatic improvement in the de- termination of the Earth gravity field. Two dedicated satellite missions, namely the CHAllenging Minisatellite Payload (CHAMP) and the Gravity Recovery And Climate Experiment (GRACE) are underway. This work describes the processing of the satel- lite data from CHAMP and GRACE based on the energy balance approach. The first part discusses the global gravity field recovery from CHAMP. Specifically, it aims at a reprocessing of kinematic position data and at a refinement of the data processing strategies. Although the energy balance approach is theoretically simple, its imple- mentation proved to be quite challenging. By refining the processing techniques an improvement of up to 30\% is reached for the low degree spherical harmonic coefficients. Nevertheless, the solutions still depend strongly on the variability of the groundtrack. The quality of the monthly solutions can vary up to one order of magnitude. To ad- dress this challenge, an in-depth analysis gives new insight into the phenomenon, and a new and unique combination method with GRACE data is presented, which yields a more homogeneous set of solutions and reaches the edge of the recoverability of a time-variable gravity signal from high-low satellite-to-satellite tracking missions. In the second part the energy balance approach is applied to the GRACE mission. Pre- vious attempts of expressing the kinetic energy in terms of the K-band measurement make use of an approximation. In this work, an exact representation is introduced and is validated by simulations. In the third part, the aim is to make optimal usage of the data distribution in the high latitude area. For this, interpolation and downward continuation techniques are investigated and an improvement, compared to the global solutions, is achieved. Overall, the analysis provides new and valuable insight into the data processing of satellite-to-satellite tracking data using the energy balance approach
Numerical solutions to altimetry-gravimetry boundary value problems in coastal regions
No full textBibliography: p. 202-209Some pages are in colour.This thesis presents novel solutions of altimetry-gravimetry boundary value problems (AGBVPs) with compatibility (smoothness) conditions along the coastline for geoid determination. After an analysis of the state of the art for AGBVPs it was found that a lot of work has already been done in terms of theoretical problem formulation and solution investigation of AGBVPs. The conditions under which the solutions of different AGBVPs exist and are unique have been provided. It has been shown that without additional compatibility conditions along the coastline a solution with higher level of regularity does not exist. This was the starting point of this work and, after three preliminary experiments, it was found that the effect of smoothness along the coast line is significant for cm-geoid determination. Further theoretical investigations by the author resulted in the following achievements and contributions to local and regional determination of the geoid. The theory of spherical pseudo-differential operators (PDOs), spherical wavelets and spherical harmonics was combined for local and regional geoid determination in coastal areas. Using the theory of PDOs, it has been proven that the fixed AGBVP II has a unique solution and different methods applied to solve this problem yield the same solution. It has been shown that the compatibility conditions given by Svensson (1988) are equivalent to the condition that the data and their first and second order gradients coincide with each other along the coastline. It has been proven that PDOs are uniformly Lipschitz α in this case, they can be combined with wavelets that are locally Lipschitz α to increase the regularity (smoothness) of the solution along the coastline. A modified algorithm for reconstruction of a signal using wavelet modulus maxima points is suggested to detect and to smooth existing discrepancies and irregularities along the coastline. Any kind of functionals of disturbing potential is presented in a discrete form, which allows spherical PDOs and wavelets to be applied numerically; even the compatibility conditions are expressed in an explicit form in discrete form as a sum of two functionals described above. Final numerical solution with spherical HShannon wavelets was proposed and conclusions are drawn about its advantages from an application point of view. Finally, as a result of the proposed procedure a smooth transition of the geoid from land to sea can be achieved, which will result in an improved geoid model in coastal areas
Detection of industrial machinery looseness by vibration analysis
No full textBibliography: p. 159-165
GNSS carrier phase ambiguity resolution: challenges and open problems
No full textInteger carrier phase ambiguity resolution is the key to fast and high-precision global navigation satellite system (GNSS) positioning and application. Although considerable progress has been made over the years in developing a proper theory for ambiguity resolution, the necessary theory is far from complete. In this contribution we address three topics for which further developments are needed. They are: (1) Ambiguity acceptance testing; (2) Ambiguity subset selection; and (3) Integer-based GNSS model validation. We will address the shortcommings of the present theory and practices, and discuss directions for possible solution
A dynamic geoid model for Canada
No full textBibliography: p. 209-232Some pages are in colour.The main objective of this research is to develop a methodology that can be used to optimally combine geodetic data for empirical modelling of the temporal variations of the geoid caused by the slow dynamic process of glacial isostatic adjustment of the Earth. A dynamic geoid model is needed for establishing a modem dynamic geoid-based vertical datum for Canada. By correcting the geoid for the secular temporal variations, a reference surface for orthometric heights free from systematic effects due to geodynamics will be maintained. To provide a centimetre level of accuracy for precise surveying activities, corrections should be applied generally at a ten-year time interval. Models of the temporal variations of orthometric heights are another important outcome required for ensuring consistency between the dynamic vertical reference surface and gravity related heights. The sub-objectives of this research are (i) developing a general framework for combining terrestrial and space-borne data including GRACE, GPS, tide gauge/altimetry, and absolute gravimetry data, (ii) implementing data-driven statistical approaches for modelling temporal variations of the geoid and heights, and (iii) delineating practical considerations for implementing the dynamic geoid model as a dynamic vertical reference surface. The developed methodology is applied, for the first time, to combine GRACE-observed rates of vertical deformation with terrestrial data. The modeled temporal variations of the geoid agree within 0.1 - 0.2 mm/yr with glacial isostatic model predictions based on the ICE-4G model in the areas with a peak geodynamic signal. Making use of robust leastsquares procedures combined with variance component estimation, reliable constraints for geodynamic modelling free from the influence of erroneous observations and reliably estimated error bounds of the empirical rates of crustal displacement are provided. An important outcome of this research is the use of the developed statistical tools as a necessary step towards combining geodynamic modelling of glacial isostatic adjustment with the empirical statistical approach in a rigorous dynamic-based procedure
Geopotential of the Geoid-Based North American Vertical Datum
No full textThe European Space Agency’s dedicated satellite gravity field mission the Gravity Field and Steady-state Ocean Circulation Explorer (GOCE) will at the end of its lifespan achieve 1-2 cm geoid accuracy at a spatial resolution of 100 km. This thesis attempts to answer the question: is a GOCE satellite-only global geopotential model (GGM) sufficient for geodetic applications such as datum unification in North America? The main research objectives that were investigated in order to answer this question include: GOCE GGM evaluation, estimation of height datum offsets for regional vertical datums, and the estimation of the gravity potential for a geoid-based vertical datum. Based on the research objective outcomes, it can be concluded that using only a GOCE satellite-based GGM is not sufficient for geodetic applications such as datum unification in North America. Thus, a GOCE GGM should be rigorously combined with gravity and topography data in a remove-compute-restore geoid modelling scheme
Application of Computer Algebra System to Geodesy
No full textThis contribution extends the previous work of (2005). Using Groebner basis and Dixon resultant as the engine behind Computer Algebra Systems (CAS). The authors demonstrate how 3D GPS positioning, 3D intersection, as well as datum transformation problems are solved ‘live’ in Mathematica, thanks to modernization in CAS. Mathematica notebooks containing these ‘live’ computational models and examples are available at http://library.wolfram.com/infocenter/ MathSource/665
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