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  • Simple hysteresis loop model for rock magnetic analysis
    Stud. Geophys. Geod. (IF 1.293) Pub Date : 2020-01-10
    Carlos A. Vasquez, Sabrina Y. Fazzito

    Abstract A simple phenomenological model founded on Lorentzian functions is evaluated on the first derivative of magnetic hysteresis loops from several artificial samples with iron oxide/oxyhydroxide mixtures imitating natural sediments. The approach, which shows that hysteresis loops can be described by elementary analytical functions and provides estimates of magnetization parameters to a satisfactory degree of confidence, is applied with the help of standard data analysis software. Distorted hysteresis loops (wasp-waisted, goose-necked and pot-bellied shaped) from simulations and artificial samples from a previous work are reproduced by the model which allows to straightforwardly unmix the ferromagnetic signal from different minerals like magnetite, greigite, haematite and goethite. The analyses reveal that the contribution from the ferrimagnetic fraction, though present in a minor concentration (≤2.15 wt%), dominates the magnetization.

    更新日期:2020-01-11
  • Use of the radiocarbon method for dating of skeletal remains of a mass grave (Brno, the Czech Republic)
    Stud. Geophys. Geod. (IF 1.293) Pub Date : 2020-01-10
    Kateřina Vymazalová, Lenka Vargová, Ladislava Horáčková, Jiří Kala, Michal Přichystal, Ivo Světlík, Kateřina Pachnerová Brabcová, Veronika Brychová

    The dating of skeletal remains in archaeology is difficult, especially at findings without burial equipment. In this case, apart from literary and iconographic sources, anthropological and palaeopathological analyses, the radiocarbon dating method can also be used. We present an example where we used this procedure in the dating of the skeletal remains of an anonymous recent mass grave, found in the cellars of one of the houses in Brno (Czech Republic). On the basis of an assessment of the archaeological and anthropological context, in combination with radiocarbon dating, it could be concluded that the found skeletal remains were most likely of soldiers who died in the provisional military hospital as a result of injury or infection after the Battle of Austerlitz in 1805. An alternative hypothesis, that they are the remains of soldiers who died in the Battle of Hradec Králové in 1866, was excluded by radiocarbon dating.

    更新日期:2020-01-11
  • High frequency sky wave propagation during geomagnetic field reversals
    Stud. Geophys. Geod. (IF 1.293) Pub Date : 2019-12-20
    Mariano Fagre, Bruno S. Zossi, Erdal Yiğit, Hagay Amit, Ana G. Elias

    abstract The ionosphere, a plasma embedded in the Earth’s magnetic field, affects propagation of electromagnetic waves in the high frequency range since the refractive index at these frequencies depends on a combination of plasma density and magnetic field intensity and direction. In particular, the ground range of high frequency waves that reflect in the ionosphere, or sky waves, presents detectable Earth’s magnetic field effects. This field varies greatly, with the most drastic scenario being a polarity reversal. The spatial variability of the ground range during possible reversal scenarios is analyzed in the present work using numerical ray tracing. In order to isolate the magnetic field effect we exclude the effect of changing ionospheric conditions by considering a uniform ionosphere. Our results show that the ground range increases with increasing ray alignment with the field direction as well as with increasing magnetic field intensity. For the present field that is dominated by an axial dipole, the ground range is greatest for northward propagation at the magnetic equator. A similar situation occurs for a prevailing equatorial dipole with eastward propagation at the corresponding magnetic equator that here runs almost perpendicular to the geographic equator. For less dipolar configurations the ground range spatial variability becomes smaller. Although a reversal is foreseeable only in a very distant future, studying potential consequences during a reversal may highlight possible effects of dipole decrease which is already ongoing at present. In addition to the geophysical insight, our results may have applications for communication and radar systems.

    更新日期:2020-01-04
  • Application of non-stationary iterative time-domain deconvolution
    Stud. Geophys. Geod. (IF 1.293) Pub Date : 2019-12-05
    Ergun Erhan, Robert L. Nowack

    In this study, non-stationary iterative time-domain deconvolution (CNS-ITD) is investigated. The propagating wavelets are first estimated in several overlapping Gabor windows of the data. Matrix-vector operations in the time-domain are then performed by estimating a small number of columns of the wavelet matrix by interpolation within a sparse iterative estimation for the largest reflectivities. The iteration process is stopped when a minimum root mean square (RMS) residual or a maximum number of iterations is reached. Although initially formulated on the basis of work in earthquake seismology, CNS-ITD is a matching pursuit type of approach performed continuously in the time-domain for the non-stationary case. The results can then be convolved with a higher frequency wavelet in order to make the results stationary in time and to increase the resolution of the data. We first apply CNS-ITD to synthetic data with a time-varying attenuation, where the method successfully identifies the largest reflectors in the data. We then apply CNS-ITD to two observed shallow seismic datasets where improved resolution is obtained.

    更新日期:2020-01-04
  • Estimating a combined Moho model for marine areas via satellite altimetric - gravity and seismic crustal models
    Stud. Geophys. Geod. (IF 1.293) Pub Date : 2019-12-05
    Majid Abrehdary, Lars E. Sjöberg

    Abstract Isostasy is a key concept in geoscience in interpreting the state of mass balance between the Earth’s lithosphere and viscous asthenosphere. A more satisfactory test of isostasy is to determine the depth to and density contrast between crust and mantle at the Moho discontinuity (Moho). Generally, the Moho can be mapped by seismic information, but the limited coverage of such data over large portions of the world (in particular at seas) and economic considerations make a combined gravimetric-seismic method a more realistic approach. The determination of a high-resolution of the Moho constituents for marine areas requires the combination of gravimetric and seismic data to diminish substantially the seismic data gaps. In this study, we estimate the Moho constituents globally for ocean regions to a resolution of 1° × 1° by applying the Vening Meinesz-Moritz method from gravimetric data and combine it with estimates derived from seismic data in a new model named COMHV19. The data files of GMG14 satellite altimetry-derived marine gravity field, the Earth2014 Earth topographic/bathymetric model, CRUST1.0 and CRUST19 crustal seismic models are used in a least-squares procedure. The numerical computations show that the Moho depths range from 7.3 km (in Kolbeinsey Ridge) to 52.6 km (in the Gulf of Bothnia) with a global average of 16.4 km and standard deviation of the order of 7.5 km. Estimated Moho density contrasts vary between 20 kg m-3 (north of Iceland) to 570 kg m-3 (in Baltic Sea), with a global average of 313.7 kg m-3 and standard deviation of the order of 77.4 kg m-3. When comparing the computed Moho depths with current knowledge of crustal structure, they are generally found to be in good agreement with other crustal models. However, in certain regions, such as oceanic spreading ridges and hot spots, we generally obtain thinner crust than proposed by other models, which is likely the result of improvements in the new model. We also see evidence for thickening of oceanic crust with increasing age. Hence, the new combined Moho model is able to image rather reliable information in most of the oceanic areas, in particular in ocean ridges, which are important features in ocean basins.

    更新日期:2020-01-04
  • Random noise attenuation using a structure-oriented weighted singular value decomposition
    Stud. Geophys. Geod. (IF 1.293) Pub Date : 2019-10-25
    Yankai Xu, Siyuan Cao, Xiao Pan

    Singular value decomposition (SVD) is a useful method for random noise suppression in seismic data processing. A structure-oriented SVD (SOSVD) approach which incorporates structure prediction to the SVD filter is effcient in attenuating noise except distorting seismic events at faults and crossing points. A modified SOSVD approach using a weighted stack, called structure-oriented weighted SVD (SOWSVD), is proposed. In this approach, the SVD filter is used to attenuate noise for prediction traces of a primitive trace which are produced via the plane-wave prediction. A weighting function related to local similarity and distance between each prediction trace and the primitive trace is applied to the denoised prediction traces stacking. Both synthetic and field data examples suggest the SOWSVD performs better than the SOSVD in both suppressing random noise and preserving the information of the discontinuities for seismic data with crossing events and faults.

    更新日期:2020-01-04
  • Variance-covariance component estimation for structured errors-in-variables models with cross-covariances
    Stud. Geophys. Geod. (IF 1.293) Pub Date : 2019-10-25
    Zhipeng Lv, Lifen Sui

    In this contribution, an iterative algorithm for variance-covariance component estimation based on the structured errors-in-variables (EIV) model is proposed. We introduce the variable projection principle and derive alternative formulae for the structured EIV model by applying Lagrange multipliers, which take the form of a least-squares solution and are easy to implement. Then, least-squares variance component estimation (LS-VCE) is applied to estimate different (co)variance components in a structured EIV model. The proposed algorithm includes the estimation of covariance components, which is not considered in other recently proposed approaches. Finally, the estimability of the (co)variance components of the EIV stochastic model is discussed in detail. The efficacy of the proposed algorithm is demonstrated through two applications: multiple linear regression and auto-regression, on simulated datasets or on a real dataset with some assumptions.

    更新日期:2020-01-04
  • Determination of the local tidal parameters for the Borowiec station using Satellite Laser Ranging data
    Stud. Geophys. Geod. (IF 1.293) Pub Date : 2019-09-05
    Marcin Jagoda, Miłosława Rutkowska

    Abstract The values of regional tidal parameters h2, l2 associated with the tidal variations of ground stations were estimated for the Polish Satellite Laser Ranging (SLR) station Borowiec using SLR data. The study is based on satellite observations taken by the global network of ground stations during the period from January 1, 1999 until January 1, 2019 for monthly orbital arcs of the satellites LAGEOS-1 and LAGEOS-2. The adjusted regional values for h2 equalling 0.7308 ± 0.0008 and l2 equalling 0.1226 ± 0.0003 are discussed and compared with the nominal values of h2 and l2 given in the the International Earth Rotation and Reference Systems Service (IERS) standards and with other estimations of these parameters. Furthermore, the influence of the tidal parameters changes on estimation of the Borowiec station coordinates in the ITRF2014 reference frame was investigated. The analysis was carried out in two variants. The first one consisted in the determination of the Borowiec station coordinates with the use of the nominal values of the tidal parameters: h2 = 0.6078 and l2 = 0.0847 (IERS recommended values). In the second one, the Borowiec station coordinates were determined using the local tidal parameters estimated in this paper (h2 = 0.7308 ± 0.0008 and l2 = 0.1226 ± 0.0003). The differences between X, Y ,Z for Variant 1 and Variant 2 are −3.5, 3.3 and 4.2 mm, respectively.

    更新日期:2020-01-04
  • On the role of diffractions in velocity model building: a full-waveform inversion example
    Stud. Geophys. Geod. (IF 1.293) Pub Date : 2019-09-05
    Sergius Dell, Ivan Abakumov, Pavel Znak, Dirk Gajewski, Boris Kashtan, Andrey Ponomarenko

    Abstract Imaging of small-scale heterogeneities is important for the geological exploration in complex environments. It requires a processing sequence tuned to high-resolution model building. Conventional methods which use refractions or reflections might face problems in resolving small-scale features since they are visually close to the resolution of the reflection images. Additional information or an unconventional technology, which supports the reflection imaging, is thus of great interest. An unconventional method based on seismic diffractions naturally complements specular reflection imaging. Diffracted waves represent a direct seismic response from small-scale subsurface heterogeneities, such as inclusions with a characteristic size of the prevailing wavelength, or discontinuities in geological interfaces, such as faults and fractures. We investigate the rule of diffracted part of the wavefield on velocity model building using a full-waveform inversion (FWI) example. In order to best acknowledge refracted and reflected parts of the wavefield in FWI, we chose a synthetic data example which mimics the ocean-bottom nodes acquisition survey as it provides almost perfect conditions for FWI of diving waves, a standard tool for high-resolution model building. We show, that FWI using diving waves produces a well-resolved anomaly. Including other part of the wavefield, reflected waves, further improves the resolution of the velocity anomaly but also leads to a gentle overfitting due to missing illumination from the very steep anomaly flanks. Considering diffracted events in FWI improves the model resolution even further resulting in a detailed velocity model and correctly imaged anomaly in both vertical and lateral directions.

    更新日期:2020-01-04
  • Lithospheric strength of the Caroline Islands and its tectonic implications
    Stud. Geophys. Geod. (IF 1.293) Pub Date : 2019-10-25
    Mingming Wang

    The Caroline Islands are located in a broad zone near plate boundaries in southwestern Pacific. Accumulating evidence suggests that the hotspot origin alone cannot completely explain the formation of the Caroline Islands. To investigate the tectonic setting of their formation, we calculated the effective elastic thickness (Te) of the lithosphere beneath the Caroline Islands from an analysis of bathymetry and free-air gravity anomaly data by the admittance method. A synthetic model based on the actual bathymetry data of the Caroline Islands was developed for the finite window size biasing correction. The results show that the Te values of the Caroline Islands (4.5–11.5 km) are significantly lower than the Te expected for a normal oceanic lithosphere (23–50 km), and that the Te values can be approximated by the depth to the 150 ± 100°C isotherm. The low Te values indicate that the strength of the lithosphere beneath the Caroline Islands has been weakened by geological process. The thermal anomalies related to the Ontong Java Plateau and the South Pacific Isotopic and Thermal Anomaly, and the lithospheric fractures induced by interaction of plates are probable causes of the lithospheric strength reduction of the Caroline Islands.

    更新日期:2020-01-04
  • Simultaneous interpolation and denoising based on a modified thresholding method
    Stud. Geophys. Geod. (IF 1.293) Pub Date : 2019-10-25
    Jingjie Cao, Shangxu Wang, Wenquan Liang

    Abstract Seismic interpolation can provide complete data for some multichannel processing techniques such as time lapse imaging and wave equation migration. However, field seismic data often contains random noise and noisy data interpolation is a challenging task. A traditional method applies interpolation and denoising separately, but this needs two workflows. Simultaneous interpolation and denoising combines interpolation and denoising in one workflow and can also get acceptable results. Most existing interpolation methods can only recover missing traces but fail to attenuate noise in sampled traces. In this study, a novel thresholding strategy is proposed to remove the noise in the sampled traces and meanwhile recover missing traces during interpolation. For each iteration, the residual is multiplied by a weighting factor and then added to the iterative solution, after which the sum in the transformed domain is calculated using the thresholding operation to update the iterative solution. To ensure that the interpolation and denoising results are robust, the exponential method was chosen to reduce the threshold values in small quantities. The curvelet transform was used as sparse representation and three interpolation methods were chosen as benchmarks. Three numerical tests results proved the effectiveness of the proposed method on removing noise in the sampled traces when the minimum threshold values are correctly chosen.

    更新日期:2020-01-04
  • An optimized method to transform the Cartesian to geodetic coordinates on a triaxial ellipsoid
    Stud. Geophys. Geod. (IF 1.293) Pub Date : 2019-07-02
    Cheng Chen, Shaofeng Bian, Songlin Li

    A general triaxial ellipsoid is suitable to represent the reference surface of the celestial bodies. The transformation from the Cartesian to geodetic coordinates on the triaxial ellipsoid becomes an important issue in geodesy. In the literature, the vector iterative method and the Newton’s iterative method for solving the nonlinear system of equations or an algebraic fraction equation is applied to compute the geodetic coordinates, but may lead to the non-convergence regions. In this work, the universal algorithm including the Newton’s iterative solutions of an algebraic sextic equation for the points outside the equatorial plane and the analytic solutions for the points inside the equatorial plane are used to compute the geodetic coordinates. The numerical experiments show the algorithm is fast, highly accurate and well convergent. The algorithm is valid at any point inside and outside the celestial bodies including the points near the celestial bodies’ center and in the singular elliptical disc.

    更新日期:2020-01-04
  • Response of the electron density profiles to geomagnetic disturbances in January 2005
    Stud. Geophys. Geod. (IF 1.293) Pub Date : 2019-07-02
    Rumiana Bojilova, Plamen Mukhtarov

    Abstract The ionospheric response to geomagnetic storms is usually investigated by considering the variability of the critical frequency of the F2-layer (foF2) or the total electron content (TEC) because these two parameters are directly measured by the ionosonde stations and the Global Navigation Satellite Systems (GNSS). In the present paper, however, the reaction is explored by using the vertical profiles of the electron density, N(h), reconstructed by manually scaled ionosonde measurements at the station Sofia (42.4°N, 23.2°E). The mid-latitude ionosheric response to three geomagnetic storms that occurred in January 2005 is presented as this period has been selected because no major sudden stratospheric warming occurred during this month, and the winter 2005 is given in the literature as an example of a “normal” year. Hence the observed ionospheric response to the considered geomagnetic storms can be attributed mainly to the external forcing. Besides the traditional parameters foF2 and TEC, a particular attention is paid to the variability of the peak electron density height (hmF2). This study reveals for the first time that the main contribution to the response of the midlatitude ionosphere to moderate/intense winter geomagnetic storms is associated with significant enhancements of short-period quasi-diurnal oscillations with period of 6–7 hours observed in both foF2 and hmF2. An explanation of the main mechanisms responsible for the distortion of the diurnal ionospheric variability during these storms is offered. This result is especially important for the ground-based HF radio communications.

    更新日期:2020-01-04
  • Using magnetic susceptibility measurements to differentiate soil drainage classes in central Iran
    Stud. Geophys. Geod. (IF 1.293) Pub Date : 2019-08-02
    Majid Gholamzadeh, Shamsollah Ayoubi, Fatemeh Sheikhi Shahrivar

    We examine the potential of magnetic susceptibility measurements to discriminate different soil drainage classes in the Gandoman region, central Iran. Four soil drainage classes, comprising poorly drained (PD), somewhat poorly drained (SPD), moderately well drained (MWD) and well drained (WD), were identified, and a total number of 48 soil profiles were excavated and studied. The soil samples were collected from all studied profiles from the genetic horizons individually. Magnetic susceptibility was measured at both low (0.46 kHz) and high (4.6 kHz) frequencies. The crystallized and amorphous iron forms were also measured using citrate-bicarbonate-dithionite solution and oxalate-ammonium extracts, respectively. The highest magnetic susceptibility was observed in WD soils, whereas the lowest susceptibility was observed in PD soils. The results of the predictor models developed by discriminate analysis showed that the use of magnetic susceptibility and iron forms could correctly predict about 90.9, 78.6, 85.7 and 88.9% of all profiles in WD, MWD, SPD and PD classes, respectively. Overall, the results indicate that magnetic susceptibility could be applied as a marker for the discrimination of drainage classes in the study area. Magnetic susceptibility is thus a quickly accessible and low-cost indicator for soil drainage classes for landownerships and subsequent analyses.

    更新日期:2020-01-04
  • Robustness of M split(q) estimation: A theoretical approach
    Stud. Geophys. Geod. (IF 1.293) Pub Date : 2019-07-02
    Robert Duchnowski, Zbigniew Wiśniewski

    Msplit(q) estimation is a development of M-estimation which is based on the assumption that a functional model of observations can be split into q competitive ones. The main idea behind such an assumption is that the observation set might be a mixture of realizations of different random variables which differ from each other in location parameters that are estimated. The paper is focused on the robustness of Msplit(q) estimates against outlying observations. The paper presents derivatives of the general expressions of the respective influence functions and weight functions which are the main basis for theoretical analysis. To recognize the properties of Msplit(q) estimates in a better way, we propose considering robustness from two points of view, namely local and global ones. Such an approach is a new one, but it reflects the nature of the estimation method in question very well. Thus, we consider the local breakdown point (LBdP) and the global one (GBdP) that are both based on the maximum sensitivities of the estimates. LBdP describes the mutual relationship between the “neighboring” Msplit(q) estimates, whereas GBdP concerns the whole set of the estimates and describes the robustness of the method itself (in more traditional sense). The paper also presents GBdP with an extension, which shows how an outlier might influence Msplit(q) estimates. The general theory proposed in the paper is applied to investigate the squared Msplit(q) estimation, the variant which is used in some practical problems in geodesy, surveying, remote sensing or geostatistics, and which can also be applied in other geosciences.

    更新日期:2020-01-04
  • Suitable gravity interpolation technique for large data gaps in Africa
    Stud. Geophys. Geod. (IF 1.293) Pub Date : 2019-08-02
    Hussein A. Abd-Elmotaal, Norbert Kühtreiber

    Abstract The gravity database for the IAG African Geoid Project contains significantly large data gaps. These large data gaps affect the interpolation precision of the reduced gravity anomalies needed for the determination of the gravimetric geoid for Africa. Our aim is to develop a suitable interpolation technique that can be used for a proper gravity interpolation within large data gaps. A gap of 10° × 5° in the latitude and longitude directions, respectively, located at the high lands of Ethiopia has been artificially created within the gravity data set for Africa. The rest of the data set has been used to interpolate the gravity values at the gap points; then a comparison between the interpolated and the actual data values at the artificial data gap has been carried-out to determine the accuracy of the used interpolation technique. The unequal weight least-squares prediction (with the optimum curvature parameter at the origin) with an underlying grid at the gap areas computed by the satellite-only GO CONS GCF 2 DIR R5 model till degree and order 300, has been proposed as the developed interpolation approach. For comparison purpose, the Kriging interpolation technique has also been tested. Both the classical residual terrain modeling reduction and the window technique, suggested earlier by the authors to get rid of the double consideration of the topographic-isostatic masses within the data window in the framework of the remove-restore technique, have been used for the reduction process. A comparison between the data and interpolated values of the gravity at the gap points has been carried out. The results show that the developed interpolation technique gives better interpolation accuracy at the artificial data gap.

    更新日期:2020-01-04
  • The day-to-day effects of strong geomagnetic disturbances on the North Atlantic Oscillation in the winter periods of years 1951–2003
    Stud. Geophys. Geod. (IF 1.293) Pub Date : 2019-05-17
    Josef Bochníček, Ján Šimkanin, Pavel Hejda, Radan Huth

    The day-to-day effects of the strong geomagnetic disturbances on geopotential heights (GPH) in the winter lower atmosphere were described in many papers in the beginning of 1970s. These works focused on the North-East Pacific, while the North Atlantic was until now omitted. Our aim is therefore to investigate the possible effect of strong geomagnetic disturbances on the lower atmosphere GPH changes over the winter North Atlantic on the day-to-day time scale, represented by the daily index of the North Atlantic Oscillation (NAO). The investigated intervals are winter periods (December-March) of 1951–2003. The daily NAO average values in 3-day intervals before and after the disturbance onsets are compared. The graphs of NAO differences are complemented by the maps of GPH differences. The NAO response to geomagnetic disturbance, as registered on the day-to-day time scale, also shows a change in its behaviour around the year 1970. This response reaches its highest values in the years 1951–1969, usually 2–5 days following the onset of geomagnetic disturbances. Intensity of the response depends on the disturbance intensity (the largest differences were associated with extremely strong disturbances).

    更新日期:2020-01-04
  • Comparison of two different approaches for computing the gravitational effect of a tesseroid
    Stud. Geophys. Geod. (IF 1.293) Pub Date : 2019-05-17
    Anna Maria Marotta, Kurt Seitz, Riccardo Barzaghi, Thomas Grombein, Bernhard Heck

    Abstract Forward modelling in the space domain is a very important task in geodesy and other geosciences. From topographical or isostatic information in the form of digital terrain model (DTM) and density model, the effects of these parameters or their derivatives on the gravity potential can be evaluated for different applications. In most cases, height or height-layer models are in use, which are gridded with respect to spherical coordinates. This holds for global as well as regional or even local applications. The definition of the spherical gridlines leads immediately to the spherical volume element, that is, the tesseroid. Only in the specific case that the observation point is located on the symmetry axis of the spherical coordinate system does the Newton integral have a closed analytical solution. More specifically, the effect of a tesseroid can be determined by evaluating the analytical solution of a segment of a spherical zonal band. To apply this aspect in practice, the DTM must be transformed into the local spherical azimuthal system of the observation point (UNIPOL approach). In the general case, the Newton integral can be solved, for example, using a Taylor series expansion of the integral kernel and a subsequently applied term-wise integration (GIK approach). Within this contribution, the two fundamentally different tesseroid approaches, namely, the GIK and the UNIPOL approach are compared. This comparison is performed, in particular, with regard to the required computational time and the approximation error under different test scenarios. The numerical studies show that both approaches are equivalent in terms of accuracy for both the gravitational potential and gravity; however, the UNIPOL approach is more time consuming because, for each observation point, the whole DTM must be transformed. Small numerical differences exist between the compared approaches for special constellations regarding the source point and the observation point.

    更新日期:2020-01-04
  • Topographic effects up to gravitational curvatures of tesseroids: A case study in China
    Stud. Geophys. Geod. (IF 1.293) Pub Date : 2019-08-24
    Xiao-Le Deng, Wen-Bin Shen

    Abstract Topographic effects on gravity field modeling are important for geodesy, geophysics and related geosciences. In this study we evaluate the gravitational effects of tesseroids in spherical coordinates, including the gravitational potential (GP), gravity vector (GV), gravity gradient tensor (GGT) and especially the gravitational curvatures (GC). With the adaptive discretization stack-based algorithm by Gauss-Legendre quadrature approach, the optimized distance-size ratio values (D) of the GC components are analyzed. Numerical experiments demonstrate that the difference percentage values of the GC components (e.g., Vxxz, Vyyz and Vzzz) are larger at the range of D ∈ [0; 10] compared to those of the GP, GV and GGT components (i.e., V, Vz, Vzz). Different distance-size ratio values D = 6, 7, 14, 30, 35, 41 and 50 for the GC component Vzzz are recommended to reach the 0.1% threshold error at corresponding computational heights 260, 150, 50, 10, 8, 6 and 4 km. Moreover, the forward modeling for the gravitational effects up to GC of tesseroids based on the ETOPO1 model in China is investigated. The GC functionals could help to extend the knowledges of interior structures of the Earth and other planetary objects.

    更新日期:2020-01-04
  • Employing the bilateral filter to improve the derivative-based transforms for gravity and magnetic data sets
    Stud. Geophys. Geod. (IF 1.293) Pub Date : 2019-05-27
    Jun Wang, Xiaohong Meng

    In the literature, there are numerous derivative-based transforms for gravity and magnetic data sets, with which relevant features can be highlighted. However, almost all of them face the problem of instability in derivative calculation. Therefore, before applying derivative-based transforms, noise reduction is often applied to improve the quality of the data. Nevertheless, the application of conventional filters typically blurs horizontal gradients in the data, which can adversely affect subsequent transforms, for example, the sharp boundaries of the causative bodies may be obscured. To handle the above issue, this study is the first to employ the bilateral filter, used in digital image processing, for improving the derivative-based transforms for gravity and magnetic data sets. The filter replaces each data point by a weighted average of its neighbors. The established weights take into account both the geometric and amplitude closeness between the data points used. Synthetic tests indicate that the proposed method can effectively filter potential field data without distorting the structural features greatly. Thus, the performance of subsequent derivative-based transforms can be improved. The new method was applied to the magnetic data collected over the Dapai polymetallic deposit in Fujian Province, South China. This real example shows that the results obtained from the proposed method contain more pronounced features of existing faults and thus contributes to further geological interpretation.

    更新日期:2020-01-04
  • Deep lithospheric structure beneath the Polish part of the East European Craton as a result of magnetotelluric surveys
    Stud. Geophys. Geod. (IF 1.293) Pub Date : 2019-05-27
    Szymon Oryński, Wojciech Klityński, Anne Neska, Katarzyna Ślęzak

    Abstract A fundamental tectonic boundary between the Precambrian East European Craton (EEC) and the younger Phanerozoic mountain belts of Europe runs through Poland. Whereas the transition zone between both tectonical units was intensely investigated by means of electromagnetic methods in the past, the image of electric conductivity of the EEC itself has not been detailed so far. In the present study the lithospheric structure beneath the northeast of Poland is investigated by means of three parallel magnetotelluric profiles. As a result the Polish part of the craton does not appear as homogeneously highresistive as repeatedly reported. Beneath a shallow (from 2 to 4 km) sedimentary layer a less resistive structure (several hundred Ωm) under all three profiles in mid-crustal to upper mantle depth becomes apparent in the high-resistive background. It spatially coincides with a magmatic body of the Upper Proterozoic age called Śniardwy lake gabbro intrusion.

    更新日期:2020-01-04
  • IRG2018: A regional geoid model in Iran using Least Squares Collocation
    Stud. Geophys. Geod. (IF 1.293) Pub Date : 2019-05-27
    Sabah Ramouz, Yosra Afrasteh, Mirko Reguzzoni, Abdolreza Safari, Abdoreza Saadat

    The aim of this study is to determine an accurate geoid model for Iran based on the Least Squares Collocation method in the framework of the Remove — Compute — Restore technique. In areas suffering from a lack of homogeneous and accurate gravity anomaly data, as is the case of Iran, the choice of the most compatible global gravity model has a significant impact on the estimated form of the geoid. Different combined and satellite-only global gravity models were therefore analyzed for Iran, and EIGEN6C4 was selected as the best one. The Shuttle Radar Topography Mission height model was used for the residual terrain correction. The covariance modeling, a crucial step in the Least Squares Collocation method, was based on two strategies. In the first, the study area was divided into four sub-areas, and then an individual empirical covariance was computed and a covariance model fitted to each of them. In the second, an empirical covariance was computed using all terrestrial gravity data, and a unique covariance model was fitted to it. Despite some border effects, the former strategy showed slightly better performance according to the resulting statistics, and therefore it was preferred for the estimation of the geoid model called IRG2018. To remove the offset of IRG2018 with respect to GNSS/Leveling-derived geoid heights, two alternative approaches were tested: subtracting a fitting polynomial surface or directly using the GNSS/Leveling data as an input to the IRG2018 computation process. Evaluation of the results, based on an independent control set of approximately half of available GNSS/Leveling points, showed an advantage of the latter approach, with an estimated accuracy of about 20 cm in terms of RMS.

    更新日期:2020-01-04
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