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  • 51. Norin, Dab
    et al.
    Johansson, Jan M.
    Mårtensson, Stig-Göran
    Eshagh, Mehdi
    University West, Department of Engineering Science, Division of Natural Sciences and Electrical and Surveying Engineering.
    Geodetic activities in Sweden 2010–20142015Report (Other (popular science, discussion, etc.))
  • 52.
    Novak, Pavel
    et al.
    University of West Bohemia, NTIS–New Technologies for Information Society, Faculty of Applied Sciences, Univerzitní 22, 30614 Plzeň, .
    Tenzer, Robert
    University of Otago, National School of Surveying, Division of Sciences, 310 Castle Street, Dunedin, New Zealand.
    Eshagh, Mehdi
    Royal Institute of Technology, Division of Geodesy and Geoinformatics,.
    Bagherbandi, Mohammad
    Royal Institute of Technology, Division of Geodesy and Geoinformatics,.
    Evaluation of gravitational gradients generated by Earth's crustal structures2013In: Computers & Geosciences, ISSN 0098-3004, E-ISSN 1873-7803, Vol. 51, p. 22-33Article in journal (Refereed)
    Abstract [en]

    Spectral formulas for the evaluation of gravitational gradients generated by upper Earth's mass components are presented in the manuscript. The spectral approach allows for numerical evaluation of global gravitational gradient fields that can be used to constrain gravitational gradients either synthesised from global gravitational models or directly measured by the spaceborne gradiometer on board of the GOCE satellite mission. Gravitational gradients generated by static atmospheric, topographic and continental ice masses are evaluated numerically based on available global models of Earth's topography, bathymetry and continental ice sheets. CRUST2.0 data are then applied for the numerical evaluation of gravitational gradients generated by mass density contrasts within soft and hard sediments, upper, middle and lower crust layers. Combined gravitational gradients are compared to disturbing gravitational gradients derived from a global gravitational model and an idealised Earth's model represented by the geocentric homogeneous biaxial ellipsoid GRS80. The methodology could be used for improved modelling of the Earth's inner structure.

  • 53.
    Pitonak, Martin
    et al.
    University of West Bohemia, NTIS—New Technologies for the Information Society, Faculty of Applied Sciences, Technicka´ 8, 306 14 Plzen, Czech Republic.
    Eshagh, Mehdi
    University West, Department of Engineering Science, Division of Mathematics, Computer and Surveying Engineering.
    Sprlak, Michal
    University of Newcastle, School of Engineering, Faculty of Engineering and Built Environment, Callaghan, NSW 2308, Australia.
    Tenzer, Robert
    The Hong Kong Polytechnic University, Department of Land Surveying and Geo-informatics, 181 Chatham Road South, Hung Hom, 999077 Kowloon, Hong Kong.
    Novak, Pavel
    University of West Bohemia, NTIS—New Technologies for the Information Society, Faculty of Applied Sciences, Technicka´ 8, 306 14 Plzen, Czech Republic.
    Spectral combination of spherical gravitational curvature boundary-value problems2018In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 214, no 2, p. 773-791Article in journal (Refereed)
    Abstract [en]

    Four solutions of the spherical gravitational curvature boundary-value problems can be exploited for the determination of the Earth’s gravitational potential. In this paper we discuss the combination of simulated satellite gravitational curvatures, that is, components of the third-order gravitational tensor, by merging these solutions using the spectral combination method. For this purpose, integral estimators of biased-and unbiased-types are derived. In numerical studies, we investigate the performance of the developed mathematical models for the gravitational field modelling in the area of Central Europe based on simulated satellite measurements. First, we verify the correctness of the integral estimators for the spectral downward continuation by a closed-loop test. Estimated errors of the combined solution are about eight orders smaller than those from the individual solutions. Second, we perform a numerical experiment by considering the Gaussian noise with the standard deviation of 6.5 x 10(-17) m(-1) s(-2) in the input data at the satellite altitude of 250 km above the mean Earth sphere. This value of standard deviation is equivalent to a signal-to-noise ratio of 10. Superior results with respect to the global geopotential model TIM-r5 (Brockmann et al. 2014) are obtained by the spectral downward continuation of the vertical-vertical-vertical component with the standard deviation of 2.104 m(2) s(-2), but the root mean square error is the largest and reaches 9.734 m(2) s(-2). Using the spectral combination of all gravitational curvatures the root mean square error is more than 400 times smaller but the standard deviation reaches 17.234 m(2) s(-2). The combination of more components decreases the root mean square error of the corresponding solutions while the standard deviations of the combined solutions do not improve as compared to the solution from the vertical-vertical-vertical component. The presented method represents a weight mean in the spectral domain that minimizes the root mean square error of the combined solutions and improves standard deviation of the solution based only on the least accurate components.

  • 54.
    Romeshkani, Mohsen
    et al.
    Islamic Azad University, Qazvin branch, Qazvin, Iran .
    Eshagh, Mehdi
    University West, Department of Engineering Science, Division of Land Surveying and Mathematics.
    Deterministically-modified integral estimators of tensor of gravitation2015In: Boletim de Ciências Geodésicas, ISSN 1413-4853, E-ISSN 1982-2170, Vol. 21, no 1, p. 189-212Article in journal (Refereed)
    Abstract [en]

    The Earth's global gravity field modelling is an important subject in Physical Geodesy. For this purpose different satellite gravimetry missions have been designed and launched. Satellite gravity gradiometry (SGG) is a technique to measure the second-order derivatives of the gravity field. The gravity field and steady state ocean circulation explorer (GOCE) is the first satellite mission which uses this technique and is dedicated to recover Earth's gravity models (EGMs) up to medium wavelengths. The existing terrestrial gravimetric data and EGM scan be used for validation of the GOCE data prior to their use. In this research, the tensor of gravitation in the local north-oriented frame is generated using deterministically-modified integral estimators involving terrestrial data and EGMs. The paper presents that the SGG data is assessable with an accuracy of 1-2 mE in Fennoscandia using a modified integral estimatorby the Molodensky method. A degree of modification of 100 and an integration cap size of for integrating terrestrial data are proper parameters for the estimator.

  • 55.
    Seif, M. R.
    et al.
    Arak University of Technology, Department of Surveying Engineering, Arak, Iran.
    Sharifi, M. A.
    University of Tehran, School of Surveying and Geospatial Engineering, College of Engineering, Tehran, Iran.
    Eshagh, Mehdi
    University West, Department of Engineering Science, Division of Mathematics, Computer and Surveying Engineering.
    Polynomial approximation for fast generation of associated Legendre functions2018In: Acta Geodaetica et Geophysica, ISSN 2213-5812, Vol. 53, no 2, p. 275-293Article in journal (Refereed)
    Abstract [en]

    Today high-speed computers have simplified many computational problems, but fast techniques and algorithms are still relevant. In this study, the Hermitian polynomial approximation is used for fast evaluation of the associated Legendre functions (ALFs). It has lots of applications in geodesy and geophysics. This method approximates the ALFs instead of computing them by recursive formulae and generate them several times faster. The approximated ALFs by the Newtonian polynomials are compared with Hermitian ones and their differences are discussed. Here, this approach is applied for computing a global geoid model point-wise from EGM08 to degree and order 2160 and in propagating the orbit of a low Earth orbiting satellite. Our numerical results show that the CPU-time decreases at least two times for orbit propagation, and five times for geoid computation comparing to the case where recursive formulae for generation of ALFs are used. The approximation error in the orbit computation is at a sub-millimeter level over two weeks and that the computed geoid 0.01 mm, with a maximum of 1 mm

  • 56.
    Sjöberg, Lars E.
    et al.
    Royal Institute of Technology (KTH) Division of Geodesy and Geoinformatics.
    Eshagh, Mehdi
    Islamic Azad University, Shahr-e-Rey Branch Department of Surveying Tehran Iran.
    A theory on geoid modeling by spectral combination of data from satellite gravity gradiometry, terrestrial gravity and an Earth gravitational model2012In: Acta Geodaetica et Geophysica Hungarica, ISSN 1217-8977, E-ISSN 1587-1037, Vol. 47, no 1, p. 13-28Article in journal (Refereed)
    Abstract [en]

    In precise geoid modelling the combination of terrestrial gravity data and an Earth Gravitational Model (EGM) is standard. The proper combination of these data sets is of great importance, and spectral combination is one alternative utilized here. In this method data from satellite gravity gradiometry (SGG), terrestrial gravity and an EGM are combined in a least squares sense by minimizing the expected global mean square error. The spectral filtering process also allows the SGG data to be downward continued to the Earth's surface without solving a system of equations, which is likely to be ill-conditioned. Each practical formula is presented as a combination of one or two integral formulas and the harmonic series of the EGM.Numerical studies show that the kernels of the integral part of the geoid and gravity anomaly estimators approach zero at a spherical distance of about 5°. Also shown (by the expected root mean square errors) is the necessity to combine EGM08 with local data, such as terrestrial gravimetric data, and/or SGG data to attain the 1-cm accuracy in local geoid determination.

  • 57.
    Sprlak, Michal
    et al.
    University of West Bohemia, NTIS - New Technologies for the Information Society, Faculty of Applied Sciences, Plzeň, Czech Republic.
    Eshagh, Mehdi
    University West, Department of Engineering Science, Division of Computer, Electrical and Surveying Engineering.
    Local recovery of sub-crustal stress due to mantle convection from satellite-to-satellite tracking data2016In: Acta Geophysica, ISSN 1895-6572, E-ISSN 1895-7455, Vol. 64, no 4, p. 904-929Article in journal (Refereed)
    Abstract [en]

    Two integral transformations between the stress function, differentiation of which gives the meridian and prime vertical components of the sub-crustal stress due to mantle convection, and the satellite-to-satellite tracking (SST) data are presented in this article. In the first one, the SST data are the disturbing potential differences between twin-satellites and in the second one the line-of-sight (LOS) gravity disturbances. It is shown that the corresponding integral kernels are well-behaving and therefore suitable for inversion and recovery of the stress function from the SST data. Recovery of the stress function and the stress components is also tested in numerical experiments using simulated SST data. Numerical studies over the Himalayas show that inverting the disturbing potential differences leads to a smoother stress function than from inverting LOS gravity disturbances. Application of the presented integral formulae allows for recovery of the stress from the satellite mission GRACE and its planned successor. © 2016 Šprlak and Eshagh.

  • 58.
    Sundararajan, Narasimman
    et al.
    Sultan Qaboos University, Department of Earth Sciences, Muscat, Oman.
    Eshagh, MehdiUniversity West, Department of Engineering Science, Division of Mathematics, Computer and Surveying Engineering.Saibi, HakimUnited Arab Emirates University,Abu Dhabi, United Arab Emirates.Meghraoui, MustaphaUniversité de Strasbourg, Strasbourg, France.Al-Garni, MansourKing Abdulaziz University, Jeddah, Saudi Arabia.Giroux, BernardCentre Eau Terre Environnement,Institut National de la Recherche Scientifique, Québec, Canada.
    On Significant Applications of Geophysical Methods: Proceedings of the 1st Springer Conference of the Arabian Journal of Geosciences (CAJG-1), Tunisia 20182019Collection (editor) (Other academic)
    Abstract [en]

    This edited volume is based on the best papers accepted for presentation during the 1st Springer Conference of the Arabian Journal of Geosciences (CAJG-1), Tunisia 2018. This special volume is of interest to all researchers practicing geosphysicists/seismologists, students of PG and UG in the fields of multifaceted Geoscience. Major applications with relevant illustrations presented in the volume are from Middle East. And therefore, this book no doubt would serve as a reference guide to all geoscientists and students in the broad field of Earth Science. This volume covers significant applications of gravity and magnetic methods, electrical and electromagnetic methods, refraction and reflection seismic methods besides a large number of study on earthquakes, tectonics and geological settings etc. The salient features of this volume are the interpretation and modeling of geophysical data of different nature

  • 59.
    Tenzer, Robert
    et al.
    Wuhan University, Sch Geodesy & Geomat, Key Lab Geospace Environm & Geodesy, Wuhan 430072, Peoples R China.
    Eshagh, Mehdi
    University West, Department of Engineering Science, Division of Natural Sciences and Electrical and Surveying Engineering.
    Global Sub-Crustal Stress Field2016In: Geostatistical and Geospatial Approaches for the Characterization of Natural Resources in the Environment / [ed] Raju, N. Janardhana, Springer International Publishing , 2016, p. 461-465Chapter in book (Other academic)
    Abstract [en]

    The sub-crustal stress has been traditionally computed using the Runcorn's formulae. This method allows computing the stress field only with a very limited spectral resolution. To overcome this problem, we apply a new method of computing the sub-crustal stress components based on utilizing the stress function with a subsequent numerical differentiation. This method increases the (degree-dependent) convergence domain of the asymptotically-convergent series and consequently allows evaluating the stress components to a higher spectral resolution compatible with currently available global crustal models. This method also facilitates the variable Moho geometry, instead of assuming only a constant Moho depth in the Runcorn's formulae. The crustal thickness and the sub-crustal stress are then determined directly from gravity and (seismic) crustal structure models. The numerical result reveals that the largest intensity of the sub-crustal stress occurs mainly along seismically active convergent tectonic plate boundaries, particularly along oceanic subduction zones and continent-to-continent collision zones.

  • 60.
    Tenzer, Robert
    et al.
    Wuhan University, Sch Geodesy & Geomat, Key Lab Geospace Environm & Geodesy, Wuhan 430072, Peoples R China..
    Eshagh, Mehdi
    University West, Department of Engineering Science, Division of Computer, Electrical and Surveying Engineering.
    The Sub-Crustal Stress Field in the Taiwan Region2015In: Terrestrial, Atmospheric and Oceanic Science, ISSN 1017-0839, E-ISSN 2223-8964, Vol. 26, no 3, p. 261-268Article in journal (Refereed)
    Abstract [en]

    We investigate the sub-crustal stress in the Taiwan region. A tectonic configuration in this region is dominated by a collision between the Philippine oceanic plate and the Eurasian continental margin. The horizontal components of the sub-crustal stress are computed based on the modified Runcorn’s formulae in terms of the stress function with a subsequent numerical differentiation. This modification increases the (degree-dependent) convergence domain of the asymptotically-convergent series and consequently allows evaluating the stress components to a spectral resolution, which is compatible with currently available global crustal models. Moreover, the solution to the Vening Meinesz-Moritz’s (VMM) inverse isostasy problem is explicitly incorporated in the stress function definition. The sub-crustal stress is then computed for a variable Moho geometry, instead of assuming only a constant Moho depth. The regional results reveal that the Philippine plate subduction underneath the Eurasian continental margin generates the shear sub-crustal stress along the Ryukyu Trench. Some stress anomalies associated with this subduction are also detected along both sides of the Okinawa Trough. A tensional stress along this divergent tectonic plate boundary is attributed to a back-arc rifting. The sub-crustal stress, which is generated by a (reverse) subduction of the Eurasian plate under the Philippine plate, propagates along both sides of the Luzon (volcanic) Arc. This stress field has a prevailing compressional pattern.

  • 61.
    Tenzer, Robert
    et al.
    Wuhan University, The Key Laboratory of Geospace Environment and Geodesy, School of Geodesy and Geomatics,.
    Eshagh, Mehdi
    University West, Department of Engineering Science, Division of Computer, Electrical and Surveying Engineering.
    Jin, Shuanggen
    Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai, China .
    Martian sub-crustal stress from gravity and topographic models2015In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 425, p. 84-92Article in journal (Refereed)
    Abstract [en]

    The latest Martian gravity and topographic models derived from the Mars Orbiter Laser Altimeter and the Mars Global Surveyor spacecraft tracking data are used to compute the sub-crustal stress field on Mars. For this purpose, we apply the method for a simultaneous determination of the horizontal sub-crustal stress component and the crustal thickness based on solving the Navier–Stokes problem and incorporating the Vening Meinesz–Moritz inverse problem of isostasy. Results reveal that most of the Martian sub-crustal stress is concentrated in the Tharsis region, with the most prominent signatures attributed to a formation of Tharsis major volcanoes followed by crustal loading. The stress distribution across the Valles Marineris rift valleys indicates extensional tectonism. This finding agrees with more recent theories of a tectonic origin of Valles Marineris caused, for instance, by a crustal loading of the Tharsis bulge that resulted in a regional trusting and folding. Aside from these features, the Martian stress field is relatively smooth with only a slightly enhanced pattern of major impact basins. The signatures of active global tectonics and polar ice load are absent. Whereas the signature of the hemispheric dichotomy is also missing, the long-wavelength spectrum of the stress field comprises the signature of additional dichotomy attributed to the isostatically uncompensated crustal load of Tharsis volcanic accumulations. These results suggest a different origin of the Earth's and Martian sub-crustal stress. Whereas the former is mainly related to active global tectonics, the latter is generated by a crustal loading and regional tectonism associated with a volcanic evolution on Mars. The additional sub-crustal stress around major impact basins is likely explained by a crustal extrusion after impact followed by a Moho uplift.

  • 62.
    Tenzer, Robert
    et al.
    Wuhan Univ, Sch Geodesy & Geomat, Key Lab Geospace Environm & Geodesy, 129 Luoyu Rd, Wuhan 430079, Peoples R China, University of West Bohemia.
    Eshagh, Mehdi
    University West, Department of Engineering Science, Division of Computer, Electrical and Surveying Engineering.
    Shen, Wenbin
    Wuhan Univ, Sch Geodesy & Geomat, Key Lab Geospace Environm & Geodesy, 129 Luoyu Rd, Wuhan 430079, Peoples R China.
    The sub-crustal stress estimation in central Eurasia from gravity, terrain and crustal structure models2017In: Geosciences Journal, ISSN 1226-4806, Vol. 21, no 1, p. 47-54Article in journal (Refereed)
    Abstract [en]

    We investigate the horizontal stress field beneath crustal structures of central Eurasia. The numerical procedure applied for a simultaneous determination of the sub-crustal stress and the crustal thickness from the global gravity, terrain and crustal structure models is based on solving Navier-Stokes' problem which incorporates the inverse solution to the Vening Meinesz- Moritz's problem of isostasy. The numerical results reveal that a spatial distribution of the sub-crustal stress in this study area closely resembles the regional tectonic configuration comprising parts of the Eurasian, Indian and Arabian lithospheric plates. The maximum shear stress intensity is generated by a subduction of the Indian plate beneath the Tibetan block. The intra-plate tectonic configuration is marked by the stress anomalies distributed along major active strike-slip fault systems and sections of subduction which separate the Tibetan and Iranian blocks from the rest of the Eurasian plate. The most pronounced intra-plate stress anomalies are related with a subduction of the Eurasian plate beneath the Tibetan block. We also demonstrate that a prevailing convergent orientation of stress vectors agree with the compressional tectonism of orogenic formations (Himalaya and Tibet Plateau, Than Shan, Zargos and Iranian Plateau), while the extensional tectonism of continental basins (Tarim, Ganges-Brahmaputra, Sichuan) is manifested by a divergence of stress vectors.

12 51 - 62 of 62
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