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ENGINEERING (1163 journals)            First | 2 3 4 5 6 7 8 9 | Last

International Journal of Hypersonics     Full-text available via subscription   (Followers: 3)
International Journal of Imaging Systems and Technology     Hybrid Journal   (Followers: 2)
International Journal of Impact Engineering     Hybrid Journal   (Followers: 7)
International Journal of Information Acquisition     Hybrid Journal   (Followers: 1)
International Journal of Innovation and Applied Studies     Open Access   (Followers: 2)
International Journal of Innovation Science     Full-text available via subscription   (Followers: 6)
International Journal of Innovative Technology and Research     Open Access  
International Journal of Integrated Engineering     Open Access   (Followers: 1)
International Journal of Intelligent Engineering Informatics     Hybrid Journal  
International Journal of Intelligent Systems and Applications in Engineering     Open Access  
International Journal of Lifecycle Performance Engineering     Hybrid Journal   (Followers: 1)
International Journal of Machine Tools and Manufacture     Hybrid Journal   (Followers: 5)
International Journal of Manufacturing Research     Hybrid Journal   (Followers: 5)
International Journal of Manufacturing Technology and Management     Hybrid Journal   (Followers: 7)
International Journal of Materials and Product Technology     Hybrid Journal   (Followers: 4)
International Journal of Mathematical Education in Science and Technology     Hybrid Journal   (Followers: 7)
International Journal of Mathematics in Operational Research     Hybrid Journal   (Followers: 1)
International Journal of Medical Engineering and Informatics     Hybrid Journal   (Followers: 5)
International Journal of Micro Air Vehicles     Full-text available via subscription   (Followers: 4)
International Journal of Microwave and Wireless Technologies     Hybrid Journal   (Followers: 1)
International Journal of Microwave Science and Technology     Open Access   (Followers: 2)
International Journal of Mobile Network Design and Innovation     Hybrid Journal   (Followers: 3)
International Journal of Multiphase Flow     Hybrid Journal   (Followers: 2)
International Journal of Nanomanufacturing     Hybrid Journal   (Followers: 1)
International Journal of Nanoscience     Hybrid Journal   (Followers: 1)
International Journal of Nanotechnology     Hybrid Journal   (Followers: 5)
International Journal of Nanotechnology and Molecular Computation     Full-text available via subscription   (Followers: 3)
International Journal of Navigation and Observation     Open Access   (Followers: 8)
International Journal of Network Management     Hybrid Journal  
International Journal of Nonlinear Sciences and Numerical Simulation     Full-text available via subscription  
International Journal of Numerical Methods for Heat & Fluid Flow     Hybrid Journal   (Followers: 7)
International Journal of Optics     Open Access   (Followers: 1)
International Journal of Organisational Design and Engineering     Hybrid Journal   (Followers: 10)
International Journal of Pattern Recognition and Artificial Intelligence     Hybrid Journal   (Followers: 6)
International Journal of Pavement Engineering     Hybrid Journal   (Followers: 2)
International Journal of Physical Modelling in Geotechnics     Hybrid Journal   (Followers: 3)
International Journal of Plasticity     Hybrid Journal   (Followers: 6)
International Journal of Plastics Technology     Hybrid Journal  
International Journal of Polymer Analysis and Characterization     Hybrid Journal   (Followers: 5)
International Journal of Polymer Science     Open Access   (Followers: 16)
International Journal of Precision Engineering and Manufacturing     Hybrid Journal   (Followers: 5)
International Journal of Precision Engineering and Manufacturing-Green Technology     Hybrid Journal  
International Journal of Precision Technology     Hybrid Journal  
International Journal of Pressure Vessels and Piping     Hybrid Journal   (Followers: 3)
International Journal of Production Economics     Hybrid Journal   (Followers: 13)
International Journal of Quality and Innovation     Hybrid Journal   (Followers: 4)
International Journal of Quality Assurance in Engineering and Technology Education     Full-text available via subscription   (Followers: 2)
International Journal of Quality Engineering and Technology     Hybrid Journal   (Followers: 2)
International Journal of Quantum Information     Hybrid Journal  
International Journal of Rapid Manufacturing     Hybrid Journal   (Followers: 1)
International Journal of Reliability, Quality and Safety Engineering     Hybrid Journal   (Followers: 7)
International Journal of Renewable Energy Technology     Hybrid Journal   (Followers: 8)
International Journal of Robust and Nonlinear Control     Hybrid Journal   (Followers: 3)
International Journal of Science Engineering and Advance Technology     Open Access  
International Journal of Sediment Research     Full-text available via subscription   (Followers: 1)
International Journal of Self-Propagating High-Temperature Synthesis     Hybrid Journal   (Followers: 2)
International Journal of Signal and Imaging Systems Engineering     Hybrid Journal  
International Journal of Six Sigma and Competitive Advantage     Hybrid Journal  
International Journal of Social Robotics     Hybrid Journal   (Followers: 2)
International Journal of Software Engineering and Knowledge Engineering     Hybrid Journal   (Followers: 1)
International Journal of Space Science and Engineering     Hybrid Journal   (Followers: 2)
International Journal of Speech Technology     Hybrid Journal   (Followers: 4)
International Journal of Spray and Combustion Dynamics     Full-text available via subscription   (Followers: 6)
International Journal of Superconductivity     Open Access  
International Journal of Surface Engineering and Interdisciplinary Materials Science     Full-text available via subscription   (Followers: 1)
International Journal of Surface Science and Engineering     Hybrid Journal   (Followers: 7)
International Journal of Sustainable Engineering     Hybrid Journal   (Followers: 7)
International Journal of Sustainable Manufacturing     Hybrid Journal   (Followers: 4)
International Journal of Systems and Service-Oriented Engineering     Full-text available via subscription  
International Journal of Systems Assurance Engineering and Management     Hybrid Journal  
International Journal of Systems, Control and Communications     Hybrid Journal   (Followers: 2)
International Journal of Technoethics     Full-text available via subscription   (Followers: 1)
International Journal of Technology Management and Sustainable Development     Hybrid Journal   (Followers: 1)
International Journal of Technology Policy and Law     Hybrid Journal   (Followers: 5)
International Journal of Telemedicine and Applications     Open Access   (Followers: 2)
International Journal of Thermal Sciences     Hybrid Journal   (Followers: 7)
International Journal of Thermodynamics     Open Access   (Followers: 2)
International Journal of Turbo & Jet-Engines     Full-text available via subscription  
International Journal of Ultra Wideband Communications and Systems     Hybrid Journal  
International Journal of Vehicle Autonomous Systems     Hybrid Journal   (Followers: 1)
International Journal of Vehicle Design     Hybrid Journal   (Followers: 6)
International Journal of Vehicle Information and Communication Systems     Hybrid Journal   (Followers: 2)
International Journal of Vehicle Noise and Vibration     Hybrid Journal   (Followers: 3)
International Journal of Vehicle Safety     Hybrid Journal   (Followers: 5)
International Journal of Vehicular Technology     Open Access   (Followers: 2)
International Journal of Virtual Technology and Multimedia     Hybrid Journal   (Followers: 4)
International Journal of Wavelets, Multiresolution and Information Processing     Hybrid Journal  
International Journal on Artificial Intelligence Tools     Hybrid Journal   (Followers: 4)
International Nano Letters     Open Access   (Followers: 9)
International Review of Applied Sciences and Engineering     Full-text available via subscription  
International Scholarly Research Notices     Open Access   (Followers: 222)
Inverse Problems in Science and Engineering     Hybrid Journal   (Followers: 2)
Ionics     Hybrid Journal  
IPTEK The Journal for Technology and Science     Open Access  
IRBM News     Full-text available via subscription  
Ironmaking & Steelmaking     Hybrid Journal   (Followers: 2)
Irrigation and Drainage Systems     Hybrid Journal  
ISA Transactions     Full-text available via subscription   (Followers: 1)
IT Professional     Full-text available via subscription   (Followers: 3)
Johnson Matthey Technology Review     Open Access   (Followers: 2)

  First | 2 3 4 5 6 7 8 9 | Last

Journal Cover   Journal of Electronic Imaging
  [SJR: 0.367]   [H-I: 46]   [4 followers]  Follow
   Partially Free Journal Partially Free Journal
   ISSN (Print) 1017-9909 - ISSN (Online) 1560-229X
   Published by SPIE - International Society for Optical Engineering Homepage  [7 journals]
  • Empirical mode decomposition of long-term polar motion observations
    • Abstract: Abstract We use the Empirical Mode Decomposition (EMD) method to study the decadal variations in polar motion and its long-term trend since year 1900. The existence of the so-called “Markowitz wobble”, a multidecadal fluctuation of the mean pole of rotation whose nature has long been debated since its discovery in 1960, is confirmed. In the EMD approach, the Markowitz wobble naturally arises as an empirical oscillatory term in polar motion, showing significant amplitude variations and a period of approximately 3 decades. The path of the time-averaged, non-cyclic component of polar motion matches the results of previous investigations based on classical spectral methods. However, our analysis also reveals previously unnoticed steep variations (change points) in the rate and the direction of secular polar motion.
      PubDate: 2014-12-12
  • Prediction of porosity in crystalline rocks using artificial neural
           networks: An example from the Chinese Continental Scientific Drilling Main
    • Abstract: Abstract Porosity plays an important part of understanding permeability and fluid flow within the continental, crystalline rocks. Geophysical well logs are presently the most consistent means of providing continuous information for porosity estimation. However, it is difficult to interpret geophysical well logs data in crystalline rocks due to their complex geological features and the difficulty in understanding and using the complex and intensive information content in these data. Motived by the successful prediction abilities of artificial neural networks (ANN) to solve different problems in geophysics, this study explore the applicability of using ANNs to predict porosity in continental, crystalline rocks. This ANN technique is calibrated on Chinese Continental Scientific Drilling Main Hole (CCSD-MH) data, which provides core porosity data combined with four geophysical well logs (density, neutron porosity, sonic and resistivity). The data from CCSD-MH is utilized to train feed-forward backpropagation (FFBP) neural network and radial basis function (RBF) neural network to derive a relationship between geophysical well logs and porosity, and hence predict porosity accurately. The findings demonstrate that ANNs provide better performances with sets of three geophysical well logs (density, sonic and resistivity) than regression technique. Comparison of FFBP to RBF showed that RBF reveals better stability and more accurate performances than FFBP. Based on the success achieved in this study, this intelligence artificial technique can be a very advantageous tool in facilitating the task of geophysicists in the framework of research drillings in continental crust.
      PubDate: 2014-11-26
  • Limits of out-of-phase susceptibility in magnetic granulometry of rocks
           and soils
    • Abstract: Abstract Frequency-dependent magnetic susceptibility enables the amount of newly created ultrafine superparamagnetic particles to be assessed, being therefore important tool for environmental and palaeoclimatologic research. It was shown recently that the out-of-phase susceptibility is also able to provide this information. In the present paper we investigate the accuracy of the measurement of the out-of-phase susceptibility at all three frequencies of the MFK1-FA Kappabridge as well as accuracy in the determination of the XON parameter, which is the microscopic equivalent of the XFN parameter characterizing the frequency-dependent susceptibility. The method is tested on samples of cave sediments, a loess/palaeosoil sequence, and artificial specimens. The detection limit in determining the XON parameter is about 3%, which is only slightly worse than the reproducibility of the XFN parameter (about 1%). A new measuring technique is proposed making the accuracy in determination of the XON parameter comparable to that in determining XFN parameter. The main advantage of the out-of-phase susceptibility is that it is measured simultaneously with the in-phase susceptibility during one measuring process. This is very useful in working with large specimen collections as in palaeoclimatology and environmental magnetism.
      PubDate: 2014-11-26
  • Application of P-wave Mwp magnitude to earthquakes for tsunami early
           warning in and around South-Western Turkey
    • Abstract: Abstract Tsunami warning centres inform the population who are located near and around coastal areas by determining the size and location of an earthquake. The Pacific Tsunami Early Warning System has used P-wave moment magnitude (Mwp) for the warning system for many years. A moment magnitude determination from the P-wave arrivals has the advantage of estimating the size of an earthquake within a couple of minutes, compared to other estimation procedures. The Eastern Mediterranean region is tectonically active area and has experienced many tsunami earthquakes in history. In this paper, the moment magnitude determination technique was used to calculate the moment magnitudes of events that occurred in the Eastern Mediterranean and near the coasts of Turkey with magnitudes between 5.5 and 6.8 and epicentral distance between about 100 and 1700 km. Mwp was calculated using seismic stations that were installed in the area and the number of stations used changed event by event. Their numbers were in the range of 11 to 71. Calculated Mwp values showed good compatibility with Global Centroid Moment Tensor Mw. The results of this study are encouraging for the early warning system that will be set up in the near future in the region.
      PubDate: 2014-11-26
  • Comparison of least-squares and simulated annealing to estimate fault
           parameters from airborne gravity gradiometry
    • Abstract: Abstract The inverse problem of estimating parameters (e.g., size, depth) of subsurface structures can be considered as an optimization problem where the parameters of a constructed forward model are estimated from observations collected on or above the Earth’s surface by minimizing the difference between the predicted model and the observations. Traditional solutions based on gradient-based approaches applied to nonlinear and non-unique problems basically depend on the initial conditions and may not always converge to the global minimum of the cost function if the starting model is far away from the true model. Alternatives to these straightforward approaches are innovative methods such as random search techniques that operate directly on the nonlinear models. This study compares a Monte-Carlo optimization method called Simulated Annealing (SA) to the Least-Squares Solution (LESS) within the general Gauss-Helmert formulation to estimate the parameters of a dip-slip fault from gravity gradient measurements as might be collected on profiles surveyed by an airborne system. It is shown that the SA algorithm is a more robust technique with respect to initial conditions in that it proceeds more comprehensively in parameter space and converges to their true values and thus the global minimum of the cost function. The SA algorithm is able to estimate the parameters of the fault as well as or better than LESS, and in the presence of significant background geologic and observation noise.
      PubDate: 2014-11-18
  • New evidence on an episode of geomagnetic instability, recorded in Middle
           Miocene lava flows in Northwest Iceland
    • Abstract: Abstract Information on the character of paleomagnetic polarity transitions and major excursions is important to understanding of the generation of the geomagnetic field. The main aim of this study was to extend previous observations on a complex excursion event at around 13 Ma, recorded in lava flows south of the Ísafjarðardjúp fjord in the Northwest peninsula of Iceland. Core samples were collected in four short hillside profiles, for measurement of their remanence vectors after conventional alternating-field treatment. Despite minor hydrothermal alteration in the area, reliable estimates of primary geomagnetic directions were obtained in 49 of the 51 sites sampled. It is shown that large directional variations were taking place between at least 25 successive flows. Judging from the overall rate of buildup of the local lava pile, the duration of this event may reach 100 kyr. The results support findings in the literature on the occurrence of other episodes of geomagnetic instability in the Neogene. The excursion sequence in Ísafjarðardjúp will also be of value for stratigraphic correlation in the Northwest peninsula (and even farther afield), as it is probably contemporaneous with an excursion found 30 km away.
      PubDate: 2014-11-18
  • Comparison of the performances of different spring and superconducting
           gravimeters and STS-2 seismometer at the Gravimetric Observatory of
           Strasbourg, France
    • Abstract: Abstract Since 1973, the Gravimetric Observatory of Strasbourg (France) is located in an old fort named J9 and has been the place for various gravity experiments. We present a comparison of the noise levels of various instruments that are or were continuously recording at J9, including the LaCoste&Romberg Earth-Tide Meter ET-5 (1973–1985), the GWR Superconducting Gravimeter TT-T005 (1987–1996), the Superconducting Gravimeter C026 (since 1996), the STS-2 seismometer (since 2010) and the LaCoste&Romberg ET-11 (continuously since October 2010). Besides these instruments, the J9 Observatory has hosted temporary gravity experiments with the Micro-g LaCoste Inc. gPhone-054 (May–December 2008 and May–September 2009) and the Micro-g LaCoste Inc. Graviton-EG1194 (June–October 2011). We include also in the comparison the absolute gravimeter Micro-g FG5 #206 which is regularly performing absolute gravity measurements at J9 since 1997 and a spring gravimeter Scintrex CG5 which recorded at J9 between March 2009 and February 2010. We present the performances of these various instruments in terms of noise levels using a standardized procedure based on the computation of the residual power spectral densities over a quiet time period. The different responses to atmospheric pressure changes of all the instruments are also investigated. A final part is devoted to the instrumental self-noise of the SG C026, STS-2 and L&R ET-11 using the three channel correlation analysis method applied to 1-Hz data.
      PubDate: 2014-11-18
  • Numerical modeling of borehole-surface electromagnetic responses with 3-D
           finite difference method and comparison with physical simulations
    • Abstract: Abstract Borehole-surface electromagnetic method (BSEM) is a high-accuracy electromagnetic prospecting method that uses AC-powered vertical finite line source as the excitation source. The observed surface electromagnetic field is inverted for the subsurface conductivity structure. In this paper, the total field is separated into a primary part, due to a horizontally layered host medium, and a secondary part due to 3-D heterogeneities. After solving for the primary field with an analytical method, the frequency-domain second-order differential equation for the secondary field is discretized by finite differences. A sparse matrix storage scheme is employed and a BiCGSSTAB(m) method with a diagonal matrix preconditioner is used to obtain the secondary field as well as the 3-D BSEM response of the model. We compare the result of anomalous responses of three-layered medium derived by 3-D forward modeling with the result of semi-analytical solution. We also perform physical simulation and 3-D numerical forward modeling based on similarity criterion. As a result, the shape of both anomalous response curves are the same, which validates the 3-D numerical simulation method. The anomalous fields of 3-D numerical forward and physical simulation share similar anomalous feature of symmetric bimodal structure that is consistent with its harmonic response curve. It demonstrates that borehole-surface electromagnetic method can be used not only for prospection by employing a multi-frequency response, but also can provide multi-angle information about subsurface anomaly by varying relative depths of vertical finite line source in the borehole.
      PubDate: 2014-11-18
  • The secondary indirect topographic effect in physical geodesy
    • Abstract: Abstract The use of Stokes’ integral by the remove-compute-restore technique is the most common way to determine the geoid today. The method includes direct, primary and secondary indirect topographic effects. This article is mainly devoted to the secondary indirect topographic effect (SITE), which reaches the extreme values of 265 mGal and −0.6 mGal for the uncompensated and Helmert condensation compensated gravity anomalies, respectively. The corresponding effects on the geoid height reach the magnitudes of 328 m and −0.5 m, respectively. Here we emphasize that the SITE is a direct effect, needed in a rigorous gravity anomaly. For surface as well as for classical gravity anomalies, located at the geoid, the SITE can be interpreted as a shift in the normal gravity along the ellipsoidal normal to the point where the normal potential equals the topographically reduced geopotential at the computation point. We show that it may yield a bias of the order of −0.9 m in the Himalayas if not properly considered in the surface anomaly. This bias does not change when using a topographic compensation model, e.g., by Helmert condensation of the topography. The problem is avoided when using the no-topography gravity anomaly with or without compensation.
      PubDate: 2014-11-18
  • Heat wave of August 2012 in the Czech Republic: comparison of two
           approaches to assess high temperature event
    • Abstract: Abstract We present an analysis of a period of high air temperature that occurred in the second half of August 2012 in the Czech Republic (CZ). We use and compare the results of two different approaches for the evaluation of high air temperature events. The Weather Extremity Index (WEI) evaluates the extremity and spatial extent of the meteorological event of interest. The second method is based on the duration of daily maximum air temperature above specific thresholds. In 2012, the high air temperature in the CZ lasted from 18 August to 24 August (18/8 to 24/8). It was connected with the inflow of hot air from northern Africa between the low pressure trough over the eastern Atlantic and the region of high pressure in central Europe. The high air temperature culminated on 20/8 when its maximum was greater than 30°C across the whole of the CZ. The highest daily maximum air temperature on record in the CZ with a value of 40.4°C was observed at the Dobřichovice station. Our results demonstrate that the studied period was quite extraordinary, occurring so late in the summer with a relatively large areal extent and extremity of detected maximum air temperature. Furthermore, the WEI was found useful for identification of very extreme high air temperature events and facilitated intercomparison in terms of extremity and spatial extent. However, WEI cannot be used for detection of periods with a persistent relatively high air temperature that could have severe impacts on both human activities and natural ecosystems but during which the extremity of observed air temperature values is not very high.
      PubDate: 2014-10-30
  • Reproducing kernel and Neumann’s function for the exterior of an
           oblate ellipsoid of revolution: application in gravity field studies
    • Abstract: Abstract The purpose of this paper is to discuss the construction of the reproducing kernel of Hilbert’s space of functions that are harmonic in the exterior of an oblate ellipsoid of revolution. The motivation comes from the weak solution concept applied to Neumann’s problem for Laplace’s partial differential equation in gravity field studies. The use of the reproducing kernel enables the construction of a function basis that is suitable for the approximation representation of the solution and offers a straightforward way leading to entries in Galerkin’s matrix of the respective linear system for unknown scalar coefficients. The serious problem, however, is the summation of the series that represents the kernel. It is difficult to reduce the number of summation indices since in the ellipsoidal case there is no straightforward analogue to the addition theorem known for the spherical situation. This makes the computation of the kernel and the set of the entries in Galerkin’s matrix rather demanding, even by means of high performance computer facilities. Therefore, the reproducing kernel and its series representation are analyzed. The apparatus of hypergeometric functions and series is used. The kernel is split into parts. Some of the resulting series may be summed relatively easily, except for some technical tricks. For the remaining series, however, the summation needs more complex tools. In particular, the summation was converted to elliptic integrals. This approach leads to an effective numerical treatment of the kernel. The results are presented. Finally, the relation of the reproducing kernel to Green’s function of the second kind (Neumann’s function) is discussed with a special view to physical geodesy applications.
      PubDate: 2014-10-01
  • On the effect of planar approximation in the Geodetic Boundary Value
    • Abstract: Abstract In the framework of the analytical treatment of the Geodetic Boundary Value Problem (GBVP) various approximations are necessary in order to end up with a solution in a “closed” form. Besides linearization and isotropic (“spherical”) approximation the socalled planar approximation has been introduced in the case of a non-spherical, topographic boundary surface. In this context the term “planar approximation” refers to neglecting terms proportional to the quotient of elevation and mean Earth radius in the respective kernel functions, not to confuse with approximating the boundary surface by a plane. In this paper the effect of planar approximation on the boundary condition of the fixed GBVP and on the disturbing potential is estimated. A global study is presented on the basis of synthesized gravity disturbances computed from the global geopotential model EGM2008 and the topography model DTM2006.0. A regional densification is carried out for the area of the Andes; therefore the gravity disturbances are refined by RTM-effects on the basis of the SRTM3 topography model. This analysis which is valid for the scalar free and the fixed versions of the GBVP simultaneously, is based on high-resolution digital elevation models (DEM) and shows that the numerical estimates of the effects of planar approximation depend on the resolution of the DEMs. The numerical investigations confirm the assumed relative error of the order 0.1%. This assumption implies a maximum effect of approximately 0.5 mGal for the boundary values and 10 cm for the quasigeoidal heights.
      PubDate: 2014-10-01
  • The gravity field due to a homogeneous triaxial ellipsoid in generalized
    • Abstract: Abstract The exterior gravity potential and its derivative induced by a homogeneous triaxial ellipsoid are presented in generalized coordinates. The variant of the ellipsoidal coordinates, which is used in the formulations, is presented in some detail along with its geometrical interpretation. Some expressions, which are used for the representation of the exterior gravitational potential, are mentioned. Subsequently, the mathematical framework is derived by means of the generalized coordinates. In this case, the gravitational potential includes elliptic integrals which can be computed by a numerical integration method. From the gravity potential, the gravity vector components are consequently obtained. The novel general expressions can be applied to a triaxial ellipsoid, oblate spheroid and sphere. Also, the gravity field due to a homogeneous oblate spheroid is obtained as a degenerate case. Numerical examples are given in order to illustrate the validity of the general expressions.
      PubDate: 2014-10-01
  • Regional quasigeoid from GOCE and terrestrial measurements
    • Abstract: Abstract Results obtained as a solution to the geodetic boundary-value problem, where two different sources of input boundary data are combined together, are presented. On the upper part of the boundary defined by the Earth surface and separated from the Earth masses, the gravity anomalies are derived from GOCE gravity gradiometry data using a transformation and downward continuation procedure. On the bottom part of the boundary, the gravity anomalies derived from the terrestrial or marine gravity measurements are used. The boundary-value problem is then solved numerically by the finite element method. In some cases an independency of our solution from the highdegree global gravity models (e.g. EGM2008) can be considered as the advantage. The standard deviation of our model tested by GNSS/leveling method in Auvergne area is 10 cm.
      PubDate: 2014-10-01
  • A concept for the estimation of high-degree gravity field models in a high
           performance computing environment
    • Abstract: Abstract The determination of global gravity field models by the combination of complementary observations within a joint adjustment is a computationally expensive task. Global gravity field models are typically parameterized by a finite series of spherical harmonic base functions. The effort to compute the set of coefficients depends on the one hand on the maximum degree of the spherical harmonic expansion and on the other hand on the number of observations and their stochastic characteristics. The main result of this contribution is a computation scheme for the rigorous (i.e. avoiding computationally motivated approximations) estimation of high-degree gravity models. A conjugate gradient based iterative solver is implemented in a high performance computing environment allowing to estimate hundreds of thousands to millions of unknown parameters. To perform the computations in a reasonable time, the solver is designed to operate on thousands of computing cores. A flexible design is considered to process an arbitrary number of observation groups. For each group a variance component can be estimated to derive a data adaptive weighting factor. The combined solution results from the weighted joint inversion of all observation groups, which might be provided in terms of preprocessed normal equations (e.g. from satellite gravity field missions like GRACE or GOCE) or in terms of observations like datasets of point-wise terrestrial gravity field information. A small-scale closed-loop simulation (250000 unknowns, spherical harmonic degree and order 500) for the estimation of the Earth’s gravity field serves as proof of concept. Normal equations derived by observations from three satellite missions and 15 datasets of point-wise measurements (gravity anomalies and along-track altimetry) are combined in the gravity field adjustment. The simulation study i) verifies the implementation, ii) analyzes the computational effort of the individual steps involved and iii) leads to the main conclusion that the rigorous least-squares solution can be determined in a reasonable amount of time.
      PubDate: 2014-10-01
  • High resolution spherical and ellipsoidal harmonic expansions by Fast
           Fourier Transform
    • Abstract: Abstract High resolution transformations between regular geophysical data and harmonic model coefficients can be most efficiently computed by Fast Fourier Transform (FFT). However, a prerequisite is that the data grids are given in the appropriate geometrical domain. For example, if the data are situated on the ellipsoid at equi-angular reduced latitudes, spherical harmonic analysis can be employed and the coefficients subsequently converted by Jekeli’s transformation. This results in the spherical harmonic spectrum in the domain of geocentric latitudes. However, the data are most likely given at geodetic (ellipsoidal) latitudes which means that the FFT base needs to be shifted by latitude dependent phase lags in order to obtain the correct spherical harmonic spectrum. This requires appropriate sample rate conversion about the shifted latitudes by means of Fourier summation and cannot be treated efficiently by an FFT algorithm. In this article another solution is discussed instead. Since the variable heights between the spherical and ellipsoidal surfaces can be accurately approximated by a series of Tschebyshev polynomials, they can be convolved into the spherical basis. It will be shown how this new type of transformation to and from the ellipsoid in combination with Jekeli’s conversion of the spectra between the two surfaces allows eventually the sample rate conversion to shifted latitudes. This avoids the inexpedient Fourier summation mentioned previously. In this paper three applications for FFT in the domain of spherical and ellipsoidal surfaces, and using geocentric, reduced and geodetic latitudes are discussed. The Earth gravitational model EGM2008 of 5 arcminutes resolution has been used to demonstrate numerical results and computational advantages.
      PubDate: 2014-10-01
  • A novel scheme for solving the oblique derivative boundary-value problem
    • Abstract: Abstract The paper is devoted to a novel scheme for solving the boundary-value problem (BVP) with the oblique derivative boundary condition (BC). In this approach, the oblique derivative in the BC is decomposed into its normal and two tangential components which are approximated by means of numerical solution values. Then the numerical scheme by the finite volume method is developed and testing numerical experiments are done. The obtained numerical solutions are compared to the exact one to show that the proposed method is second order accurate. Afterwards, the algorithm is applied to solving the fixed gravimetric BVP, namely, the numerical solution is sought in a domain bounded by a part of the Earth’s surface (Himalaya region or Slovakia), four side boundaries and a corresponding upper boundary at the satellite level. On the Earth’s surface, the oblique derivative BC in the form of surface gravity disturbances from the EGM2008, DTU10-GRAV or the detailed gravity mapping is taken into account. On the upper and side boundaries, the Dirichlet BC from the EGM2008 or GOCO03s is applied. The disturbing potential as a direct numerical result is compared with the solution to the more common BVP with the Neumann BC considered on the Earth’s surface. All numerical experiments show better agreement of the solution to the BVP with the oblique derivative BC than solution to the BVP with the Neumann BC in comparison with the disturbing potential obtained by a different mathematical approach. In area of Slovakia, when applying the GPS/levelling test at 61 points, we have gained 1.7 cm improvement in favour of the standard deviation of residuals of quasigeoidal heights obtained by solving the BVP with the oblique derivative BC in comparison with the solution to BVP with the Neumann BC.
      PubDate: 2014-10-01
  • Numerical simulations for the non-linear Molodensky problem
    • Abstract: Abstract We present a boundary element method to compute numerical approximations to the non-linear Molodensky problem, which reconstructs the surface of the Earth from the gravitational potential and the gravity vector. Our solution procedure solves a sequence of exterior oblique Robin problems and is based on a Nash-Hörmander iteration. We apply smoothing with the heat equation to overcome a loss of derivatives in the surface update. Numerical results show the error between the approximation and the exact solution in a model problem.
      PubDate: 2014-10-01
  • Astrogeodetic geoid for Austria using least-squares prediction technique
           for densifying the deflections
    • Abstract: Abstract The paper presents a technique for densification of the deflection data using least-squares remove-predict-restore technique. The available deflections of the vertical have been topographically-isostatically reduced using the Airy isostatic hypothesis. The reduced deflections have been used to interpolate deflections on a dense grid covering the data window using the least-squares remove-predict-restore technique. These gridded reduced deflections have been used to compute astrogeodetic geoids for Austria using astrogeodetic geoid determination technique introduced by Helmert with different remove-restore schemes. For the sake of comparison, an astrogeodetic geoid for Austria has been computed using the topographically-isostatically reduced deflections at the data points without densification. Computed geoids have been fitted to the GPS/levelling derived geoid. The results proved that using the least-squares remove-predict-restore technique gives densified deflections with good precision. The results also showed that densifying the deflections using the least-squares remove-predict-restore technique in the framework of the Helmert astrogeodetic profile transformation gives better geoid accuracy.
      PubDate: 2014-10-01
  • Contribution of geophysical inversion theory and geostatistical simulation
           to determine geoelectrical anomalies
    • Abstract: Abstract This article is devoted to application of geoelectrical methods in the Abbasabad copper deposit, 26 km northeast of the city of Saveh, in central Iran. Geological studies, sampling, and preliminary explorations indicate that there are potential anomalies of copper bodies in the studied area. Electrical resistivity and induced polarization methods were used for qualitative and quantitative evaluations of these bodies, and also for exploring other possible potential bodies in the area. Eleven profiles were designed and performed in a region that had a great mineral potential with an array called combined resistivity sounding and profiling (CRSP). Apparent resistivity and induced polarization pseudo-sections were produced and consequently, anomalies were identified. The data were inverted using COMSOL3.5 script. Eventually, the sequential Gaussian simulation (SGS) was applied to map spatial distribution of mentioned parameters. Considering geophysical, geological and other exploration data, copper bodies were identified and, according to performed studies, four points were proposed for drilling. Few anomalies were also accompanied by pyrite.
      PubDate: 2014-08-13
School of Mathematical and Computer Sciences
Heriot-Watt University
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