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  • 1
    Journal cover
    Springer Science + Business Media
    Online: 23(1).2010 –
    Publisher: Springer Science + Business Media
    Print ISSN: 1139-1138
    Electronic ISSN: 1988-2807
    Topics: Mathematics
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  • 2
    Publication Date: 2016-01-01
    Description: Each of the GPS time series that describes the changes of topocentric components consists of a deterministic and a stochastic part, whose character influences the errors of the deterministic parameters. As to the uncertainties of reliable velocities of permanent satellite station systems, surveys that estimate and take into account any dependencies that may affect subsequent operational efficiency are very important. For this analysis, we used 42 stations from the IGS (International GNSS Service) network from Europe, processed at the Military University of Technology EUREF Permanent Network Local Analysis Centre (MUT LAC). The deterministic part of the GPS time series was removed using the least squares method. The seasonal periods in topocentric components were determined assuming the existence of the residual Chandler oscillation (1.67 cpy), as well as the annual tropical (1 cpy) and draconitic (1.04 cpy) oscillations with their harmonics up to 4th. We assumed the character of the residue as a combination of white and powerlaw noise. The obtained results show, that in the case of the European sub-network of IGS stations we are dealing with the coloured noise between white and flicker noise with the amplitudes between 3 to 6 mm/year-k/4 for horizontal components and between 6 to 15 mm/year-κ/4 for the vertical ones, where κ is a spectral index. Finally, we showed that the amplitudes and spectral indices of noise are reduced after performing a spatio-temporal filtering. All the elicited results referred to the uncertainties of velocities by estimating them before and after filtration and the simulation of their values for different lengths of the time series. ©2015 Institute of Geophysics of the ASCR, v.v.i
    Print ISSN: 0039-3169
    Electronic ISSN: 1573-1626
    Topics: Architecture, Civil Engineering, Surveying , Geosciences , Physics
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  • 3
    Publication Date: 2016-01-01
    Description: We develop an inversion procedure using the total variation (TV) regularization method as a stabilizing function to invert surface gravity data to retrieve 3-D density models of geologic structures with sharp boundaries. The developed inversion procedure combines several effective algorithms to solve the TV regularized problem. First, a matrix form of the gradient vector is designed using the Kronecker product to numerically approximate the 3-D TV function. The piecewise polynomial truncated singular value decomposition (PP-TSVD) algorithm is then used to solve the TV regularized inverse problem. To obtain a density model with depth resolution, we use a sensitivity-based depth weighting function. Finally, we apply the Genetic Algorithm (GA) to select the best combination of the PP-TSVD algorithm and the depth weighting function parameters. 3-D simulations conducted with synthetic data show that this approach produces sub-surface images in which the structures are well separated in terms of sharp boundaries, without the need of a priori detailed density model. The method applied to a real dataset from a micro-gravimetry survey of Gotvand Dam, southwestern Iran, clearly delineates subsurface cavities starting from a depth of 40 m within the area of the dam reservoir. ©2015 Institute of Geophysics of the ASCR, v.v.i
    Print ISSN: 0039-3169
    Electronic ISSN: 1573-1626
    Topics: Architecture, Civil Engineering, Surveying , Geosciences , Physics
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  • 4
    Publication Date: 2015-10-01
    Description: To extract the best possible information from geodetic and geophysical observations, it is necessary to select a model of the observation errors, mostly the family of Gaussian normal distributions. However, there are alternatives, typically chosen in the framework of robust M-estimation. We give a synopsis of well-known and less well-known models for observation errors and propose to select a model based on information criteria. In this contribution, we compare the Akaike information criterion (AIC) and the Anderson-Darling (AD) test and apply them to the test problem of fitting a straight line. The comparison is facilitated by a Monte Carlo approach. It turns out that the model selection by AIC has some advantages over the AD test. ©2015 Institute of Geophysics of the ASCR, v.v.i
    Print ISSN: 0039-3169
    Electronic ISSN: 1573-1626
    Topics: Architecture, Civil Engineering, Surveying , Geosciences , Physics
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  • 5
    Publication Date: 2015-07-01
    Description: Earth variable rotation with its complex state of motion and excitation mechanism that indicates complex overall geodynamical process of the Earth’s system, reflects interactions among the solid Earth, atmosphere and oceans, etc. Solar activity has been found to be strongly correlated with some geophysical processes in the Earth system. In order to investigate the affects of solar activity on Earth rotation using the wavelet transform technique, the yearly Earth’s length-of-day (LOD) time series spanning hundreds of years is used to investigate the presence of the 11-year periodic component. The results show obvious fluctuation in the LOD variations. We suggest that the solar activity plays an important role in the oscillation of the Earth rotation, and that there is a possible relationship between solar activity and Earth rotation on decadal time scale. ©2015 Institute of Geophysics of the ASCR, v.v.i
    Print ISSN: 0039-3169
    Electronic ISSN: 1573-1626
    Topics: Architecture, Civil Engineering, Surveying , Geosciences , Physics
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  • 6
    Publication Date: 2015-07-01
    Description: We study a land-based gravity reduction technique for tracking near surface massdensity anomalies. For this purpose, we apply the residual terrain modeling (RTM) technique accompanied by a global geopotential model to provide a high-frequency reference gravity field. The proposed reference gravity field includes all required corrections for the corresponding gravity reduction; hence, it is subtracted from landbased gravity data to provide a kind of gravity anomaly that depends mainly on the massdensity anomalies of the near surface geological targets. As a case study, we examine the proposed reduction method to detect horizontal locations of some of known salt diapirs within the Zagros region. The numerical results indicate that the reduced gravity anomalies are sufficiently sensitive to locations of the salt diapirs. ©2015 Institute of Geophysics of the ASCR, v.v.i
    Print ISSN: 0039-3169
    Electronic ISSN: 1573-1626
    Topics: Architecture, Civil Engineering, Surveying , Geosciences , Physics
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  • 7
    Publication Date: 2015-07-01
    Description: GNSS antenna electrical phase center variability is a source of errors in precise geodetic measurements, particularly in reference frame maintenance, satellite precise levelling, deformation monitoring, the establishment of geodetic control networks, geodynamic research, etc. It has a considerable influence on the precision and accuracy of the resulting coordinates. Previous research shows that changing the antenna on the monitored point often results in a considerable bias in the derived height coordinate component. In theory, if electrical phase center is sufficiently modeled, antenna changes should have negligible effect on coordinates. We present the analysis of the influence of the GPS antenna models on the resulting marker position. Numerical tests are based on field measurements. The GPS data collected at the test baseline were processed using Bernese GPS Software Version 5.0. The research shows that the IGS and NGS phase center variation models for some types of the surveying (rover) antennas are still imperfect and are contaminated by constant errors, which may exceed even ± 5 mm for horizontal coordinates components and ± 25 mm for vertical ones. ©2015 Institute of Geophysics of the ASCR, v.v.i
    Print ISSN: 0039-3169
    Electronic ISSN: 1573-1626
    Topics: Architecture, Civil Engineering, Surveying , Geosciences , Physics
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  • 8
    Publication Date: 2015-01-01
    Description: 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. ©2014 Institute of Geophysics of the ASCR, v.v.i
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    Electronic ISSN: 1573-1626
    Topics: Architecture, Civil Engineering, Surveying , Geosciences , Physics
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  • 9
    Publication Date: 2015-01-01
    Description: We discuss the parallel computational solution to the modified fixed gravimetric boundary-value problem (MFGBVP). In our approach, the computational domain is a finite space bounded by two spatial boundaries. The boundaries represent an approximation of the Earth’s surface and an approximation of the chosen satellite orbit. Then the MFGBVP consists of the Laplace equation for unknown disturbing potential with the Neumann and Dirichlet boundary conditions. Solution of such elliptic boundary-value problem is understood in a weak sense, so it always exists and is unique. As a numerical method for our parallel approach, the finite volume method (FVM) has been designed and implemented. The FVM is a method for solving elliptic equations and it leads to a solution of the sparse linear system of equations with an appropriate structure for parallel implementation concerning memory costs. The parallel implementation of FVM algorithms using MPI and NUMA procedures is also described. Several numerical experiments are discussed. In the first testing experiment, we show that the proposed approach is second-order accurate. Then we test a convergence of the FVM solution to the EGM2008 Earth gravitational model when refining the grid. In this case all boundary conditions (BCs) are generated from this model. Finally we present high-resolution global gravity field modelling using input data generated from the DTU10 gravity field model and the GOCO03S satellite-only geopotential model. It combines information from the GRACE and GOCE satellite misions prescribed on the upper boundary with the altimetryderived and terrestrial gravity data available on the Earth’s surface. The obtained global gravity field model is compared with the EGM2008. ©2014 Institute of Geophysics of the ASCR, v.v.i
    Print ISSN: 0039-3169
    Electronic ISSN: 1573-1626
    Topics: Architecture, Civil Engineering, Surveying , Geosciences , Physics
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  • 10
    Publication Date: 2014-10-01
    Description: 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. ©2014 Institute of Geophysics of the ASCR, v.v.i
    Print ISSN: 0039-3169
    Electronic ISSN: 1573-1626
    Topics: Architecture, Civil Engineering, Surveying , Geosciences , Physics
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