Authors:Roghayeh Shamshiri; Hossein Nahavandchi; Gholamreza Joodaki Pages: 1 - 14 Abstract: We derive the mass balance of Greenland ice sheet from the Gravity Recovery and Climate Experiment (GRACE) for the period January 2003–October 2014. We have found an ice mass loss with peak amplitude of −15 cm/yr in the southeastern and northwestern parts, and an acceleration of −2.5 cm/yr2 in the southwestern region. Global warming is a well-known suspected triggering factor of ice melting. We use MODIS-derived Ice Surface Temperature (IST), and continuous and cross wavelet transforms have been determined to investigate the common power and relative phase between GRACE derived time-series of ice mass changes and IST time-series. Results indicate a high common power between the two time-series for the whole study period, but with different time patterns. PubDate: 2018-03-01 DOI: 10.1007/s40328-017-0198-4 Issue No:Vol. 53, No. 1 (2018)

Authors:K. Szokoli; L. Szarka; M. Metwaly; J. Kalmár; E. Prácser; S. Szalai Pages: 15 - 30 Abstract: We have studied a slowly moving loess landslide along the River Danube in South Hungary. In contrast with other efforts, we aimed to determine its fracture system. Due to the homogeneous composition of the loess, it seems to be the only possibility to get information about the landslide and its further evolution. Beside of the well-known Electrical Resistivity Tomography (ERT) the so-called Pressure Probe (PreP) method was applied to characterise the supposedly dense fracture system. This method was developed to detect and characterise mechanically weak zones, which may not visible from the surface, and may occur e.g. due to landslides. Fracture zones had been especially well localised by the ERT, enabling the prediction of the positions of future rupture surfaces and thus also the delineation of the endangered zones. PreP was able to give a very detailed image about the surface projection of the fractures. Both methods proved to be good to characterise the fracture system of such a landslide area. Geophysical predictions have been verified also in reality: the mass movements occurred about 1½ years after the measurements. Therefore, to provide early risk warnings and to avoid damage to constructions or endangering human life, the application of the ERT and PreP methods is highly recommended. PubDate: 2018-03-01 DOI: 10.1007/s40328-017-0199-3 Issue No:Vol. 53, No. 1 (2018)

Authors:Vahid Mahboub; Mohammad Saadatseresht; Alireza A. Ardalan Pages: 31 - 44 Abstract: We noticed that if INS data is used as system equations of a Kalman filter algorithm for integrated direct geo-referencing, one encounters with a dynamic errors-in-variables (DEIV) model. Although DEIV model has been already considered for observation equations of the Kalman filter algorithm and a solution namely total Kalman filter (TKF) has been given to it, this model has not been considered for system equations (dynamic model) of the Kalman filter algorithm. Thus, in this contribution, for the first time we consider DEIV model for both observation equations and system equations of the Kalman filter algorithm and propose a least square prediction namely integrated total Kalman filter in contrast to the TKF solution of the previous approach. The variance matrix of the unknown parameters are obtained. Moreover, the residuals for all variables are predicted. In a numerical example, integrated direct geo-referencing problem is solved for a GPS–INS system. PubDate: 2018-03-01 DOI: 10.1007/s40328-017-0201-0 Issue No:Vol. 53, No. 1 (2018)

Authors:Zhang Gang; Tuo Xianguo; Wang Xuben; Gao Song; Li Huailiang; Yu Nian; Liu Yong; Shen Tong Pages: 45 - 60 Abstract: Valid interpretations require precise and accurate determination of magnetotelluric impedance. Although remote reference magnetotellurics has been extensively investigated, majority of these studies have focused on the non-correlation between noise and signal or between the noise in the base station and that in the reference station. Few works have explored the correlation between magnetic signals in the base station and in the reference station. This study analyzes the effects of remote reference magnetotellurics on the sounding curve under different noise intensities in the base station. Results showed that regular remote reference magnetotellurics induce a limited quality-improving effect on the sounding curve and fail to satisfy the further data processing requirements at a low signal-to-noise ratio (SNR), suggesting that regular remote reference magnetotelluric methods cannot obtain an accurate transfer function under a low SNR for a time series. Comparison of various magnetic field data revealed that a strong correlation exists among magnetic signals 60 km apart at the Longmenshan area. Thus, the remote reference magnetotelluric method based on the magnetic field correlation between the base and reference stations is proposed to screen the power spectrum and undo the noise. The effectiveness and correctness of the proposed method are validated by the results of the theoretical and field data processing and of the intermediate data analysis, further proving that the remote reference magnetotelluric method based on magnetic field correlation is superior to the regular remote reference magnetotelluric method. PubDate: 2018-03-01 DOI: 10.1007/s40328-017-0203-y Issue No:Vol. 53, No. 1 (2018)

Authors:Georgios S. Vergos; Bihter Erol; Dimitrios A. Natsiopoulos; Vassilios N. Grigoriadis; Mustafa Serkan Işık; Ilias N. Tziavos Pages: 61 - 79 Abstract: The unification of local vertical datums (LVDs) at a country-wide scale has gained significant attention lately due to the availability of GOCE-based global geopotential models (GGMs) and the unprecedented geoid height accuracies offered. Within a single country, several LVDs may be used, especially in the case of islandic nations. Therefore, the unification of all of them to a single nation-wide LVD is of utmost importance. The same holds for neighboring countries, where the unification of their vertical datums is necessary as a tool of engineering, cross-border collaboration and environmental and risk management projects. The aforementioned set the main scope of the present study, which focuses on the use of GOCE and GOCE/GRACE GGMs in order to investigate the offsets between the Greek and Turkish LVDs. First an evaluation of the latest release 5 GOCE GGMs is carried out, either to their maximum degree or through spectral enhancement with EGM208 and topographic effects. Then, the geopotential value for the Greek and Turkish LVDs is performed, along with different estimates for the marine area of the Aegean Sea where several islands and isles exist with each one realizing its own LVD. The relative offset between the two LVDs was determined and used to provide a direct link between the Greek and Turkish LVDs with the IAG conventional value recently proposed as a global WHS. From the results achieved it was concluded that the spectrally enhanced GOCE GGMs reduce the standard deviation of the differences with GPS/levelling data by 2–4 cm over Turkey and 2 cm for mainland Greece. In terms of the zero-level geopotential determination, the LVD of the Greek mainland is 64.9 cm below the IAG conventional value, while that of Turkey is 9.6 cm above. Finally, it is concluded that in practice each Greek island realizes its own LVD with offsets between them as large as 35 cm. Despite that fact, the spectrally enhanced GOCE GGMs and in particular GOCO05s provides the overall smallest height residuals over the islands, hence the \( \widehat{W}_{o}^{LVD} \) based on that can be recommended as the best estimate. In that way, relative offsets with the LVD of mainland Greece can be computed for each island, ranging between −23.8 and 15.5 cm. PubDate: 2018-03-01 DOI: 10.1007/s40328-017-0204-x Issue No:Vol. 53, No. 1 (2018)

Authors:Dimitrios Ampatzidis; Christian Gruber; Vasileios Kampouris Pages: 81 - 92 Abstract: Besides the methodology of triangulation and geodetic networks nowadays, the permanent stations of satellite receivers exist, giving extra asset to geodetic daily practice. Permanent stations perform observations incessantly for the visible satellites. However, the coordinates of these stations are often changing over time due to geophysical and tectonic processes. Consequently, these changes are perceived to modern observations. So, along with the coordinates of geodetic points in a given epoch, their changes over time (e.g. the velocities of their movements) are also considered. Furthermore, any change to the reference system definition or/and to the network’s geometry can significantly impact the estimated coordinates and velocities. This paper investigates the reference datum definition problem (or datum problem, or zero order design problem) in a such network over time, which is later generalized for the study of the deformation control-networks. Emphasis is given to techniques of time-dependent 2D transformation models, with numerical tests on a simulation network. PubDate: 2018-03-01 DOI: 10.1007/s40328-017-0205-9 Issue No:Vol. 53, No. 1 (2018)

Authors:Juni Ildikó; Rózsa Szabolcs Abstract: The tropospheric wet delay is a significant systematic error of GNSS positioning, nevertheless it carries important information to meteorologists. It is closely related to the integrated water vapour that is the upper limit of precipitable water. The zenith wet delay can be converted to the integrated water vapour using a simple conversion factor. This conversion factor can be determined with the empirical formulae derived from radiosonde observations. In the past decades, numerous models were derived for this purpose, but all of these models rely on radiosonde observations stemming from a limited area of the globe. Although these models are valid for the area, where the underlying radiosonde observations were measured, there are several examples that these empirical formulae are used to validate GNSS based integrated water vapour estimations all over the globe. Our aim is to create a global model for the conversion of the zenith tropospheric delay to the integrated water vapour for realtime and nearrealtime applications using globally available Numerical Weather Models (NWM). Thus our model takes into consideration the fact that the model parameters strongly depend on the geographical location. 10 years of monthly mean ECMWF (European Center for Medium-Range Weather Forecast) dataset were used for the derivation of the model parameters in a grid with the resolution of 1° × 1°. The empirical coefficients of the developed models depend on two input parameters, namely the geographical location and the surface temperature measured at the station. Thus, the new models can be used for both realtime and near-realtime GNSS meteorological applications. The developed models were validated using 6 years of independent global ECMWF monthly mean analysis datasets (2011–2016). The results showed, that the application of the original models outside the area of the underlying radiosonde data sets can result in a relative systematic error of 7–8% in the estimation of the conversion factor as well as the estimated IWV values. PubDate: 2018-04-19 DOI: 10.1007/s40328-018-0215-2

Authors:Zoltán Gráczer; AlpArray Working Group; Gyöngyvér Szanyi; István Bondár; Csenge Czanik; Tibor Czifra; Erzsébet Győri; György Hetényi; István Kovács; Irene Molinari; Bálint Süle; Eszter Szűcs; Viktor Wesztergom; Zoltán Wéber Abstract: In the last few decades dense large-scale seismic networks showed their importance in studying the structure of the lithosphere and the upper mantle. The better understanding of the Apennines–Alps–Carpathian–Dinarides system is the main target of the AlpArray European international initiative in which more than 50 institutes are involved. The core of AlpArray is the AlpArray Seismic Network (AASN). With its \(\sim \) 600 broadband seismic stations ( \(\sim \) 280 of which are temporary) the AASN is, so far, the largest passive seismic experiment in Europe. The MTA CSFK Geodetic and Geophysical Institute, as a Core Member of the AlpArray project, contributes to the AlpArray Seismic Network with its entire permanent network as well as with 11 temporary broadband seismic stations deployed in Western Hungary. Three additional station equipment were provided by the Swiss-AlpArray SINERGIA program. The average station distance together with the permanent stations is around 40 km in the area of interest. The temporary network has been installed between December 2015 and July 2016 and the planned operation period is 3 years. In this paper we describe the characteristics of the 29 permanent and temporary stations, introducing not only the equipment, but the location, housing and geological setting, as well. We present median power spectral density curves in order to characterise the noise conditions at each station. PubDate: 2018-03-20 DOI: 10.1007/s40328-018-0213-4

Authors:Fei Wu; Kazhong Deng; Guobin Chang; Qianxin Wang Abstract: This study employs a combination of weighted least-squares extrapolation and an autoregressive model to produce medium-term predictions of polar motion (PM) parameters. The precisions of PM parameters extracted from earth orientation parameter (EOP) products are applied to determine the weight matrix. This study employs the EOP products released by the analysis center of the ‘International Global Navigation Satellite System Service and International Earth Rotation and Reference Systems Service’ needs to be modified to ‘International Global Navigation Satellite System Service (IGS) and International Earth Rotation and Reference Systems Service (IERS)’ as primary data. The polar motion parameters and their precisions are extracted from the EOP products to predict the changes in polar motion over spans of 1–360 days. Compared with the combination of least-squares and autoregressive model, this method shows considerable improvement in the prediction of PM parameters. PubDate: 2018-03-19 DOI: 10.1007/s40328-018-0214-3

Authors:Janusz Bogusz; Severine Rosat; Anna Klos; Artur Lenczuk Abstract: The inter-comparison of ground gravity measurements and vertical surface displacements enables to better understand the structure, dynamics and evolution of the Earth’s system. Within this research we analyzed the Global Positioning System vertical position time series acquired in the vicinity of the superconducting gravimeters. We estimated of noise character of GPS and SG by comparison of the satellite and terrestrial measurements collected at 18 globally distributed neighboring sites. The comparable results were provided by applying the appropriate and corresponding models of geophysical phenomena to obtain residual time series, and by unifying the sampling rate since the noise characteristics may depend on it. The deterministic part of the series was assumed to follow the Polynomial Trend Model and was subtracted prior to noise analysis. Then, a combination of power-law and white noise was presumed and the Maximum Likelihood Estimation implemented in the Hector software to investigate the stochastic part was applied. Within the paper, we show that the spectral indices for all SG time series fall in the area of fractional Brownian motion (− 2 < κ < − 1), while GPS data are best characterized by fractional Gaussian noises (− 1 < κ < 0). The estimated ratio between spectral indices of GPS and SG is stable worldwide with a global median value of about 0.5. Concerning the power-law amplitudes, these are very consistent worldwide for the GPS position time series and fluctuate around 15 mm/year−κ/4, while in the case of SG records they spread between 60 and 300 nm/s2/year−κ/4. The fraction of power-law noise employed in the assumed combination is equal to 100% for almost all SG stations, while in case of GPS it varies between 26.1 and 99.9%. The main finding of this research is that the assumption of power-law noise is much more preferred for SG data than the assumption of a pure white noise being used until now. PubDate: 2018-01-25 DOI: 10.1007/s40328-018-0212-5

Authors:V. V. Surkov; V. A. Pilipenko; A. K. Sinha Abstract: We analyze theoretically two possible sources of co-seismic electromagnetic response to the propagation of various types of seismic waves caused either by the electrokinetic phenomena or geomagnetic inductive effect. The differences between these two generation mechanisms have been examined for different types of seismic waves (P, S, and Rayleigh-Love). Theoretical relationships describing the dependence of the co-seismic signal amplitude, polarization and apparent impedance on the earthquake seismic moment and magnitude have been derived as a function of distance. We indicate an observational possibility to discriminate seismo-electrokinetic and seismo-magnetic effects and to estimate their contribution into a recorded co-seismic electromagnetic signal. Magnitudes and polarization of these signals are shown to depend strongly on the type of seismic wave and local crust parameters, such as streaming potential coupling coefficient, conductivity, inhomogeneity, etc. Co-seismic electromagnetic signals, though not directly applied for earthquake prediction, contain a useful information on local crustal phenomena, and can be used to identify “sensitive” zones perspective for the monitoring of precursory electromagnetic disturbances. PubDate: 2018-01-18 DOI: 10.1007/s40328-018-0211-6

Authors:A. Abordán; N. P. Szabó Abstract: Factor analysis of well logging data can be effectively applied to calculate shale volume in hydrocarbon formations. A global optimization approach is developed to improve the result of traditional factor analysis by reducing the misfit between the observed well logs and theoretical data calculated by the factor model. Formation shaliness is directly calculated from the factor scores by a nonlinear regression relation, which is consistent in the studied area in Alaska, USA. The added advantage of the implementation of the Simulated Annealing method is the estimation of the theoretical values of nuclear, sonic, electrical as well as caliper well-logging data. The results of globally optimized factor analysis are compared and verified by independent estimates of self-potential log-based deterministic modeling. The suggested method is tested in two different shaly-sand formations in the North Aleutian Basin of Alaska and the comparative study shows that the assumed nonlinear connection between the factor scores and shale volume is applicable with the same regression constants in different burial depths. The study shows that factor analysis solved by the random search technique provides an independent in situ estimate to shale content along arbitrary depth intervals of a borehole, which may improve the geological model of the hydrocarbon structure in the investigated area. PubDate: 2018-01-06 DOI: 10.1007/s40328-017-0210-z

Authors:Fridrich Valach Pages: 457 - 465 Abstract: This paper presents an analysis of the magnetic storm on March 8, 1918, on the basis of a preserved analogue magnetogram that was recorded by observatory Ógyalla, present day Hurbanovo. It is inferred that much of the spectacular phenomena that were attributed to this storm, such as effects in telegraph lines, were likely caused by rapid changes of the geomagnetic field during two consecutive substorms. The storm sudden commencement that preceded the magnetic storm was probably also potent in this regard. This supports the recent findings that argue against the inevitable major role of the ring current in extreme magnetic disturbances at mid latitudes. PubDate: 2017-12-01 DOI: 10.1007/s40328-016-0177-1 Issue No:Vol. 52, No. 4 (2017)

Authors:A. A. Lyubushin Pages: 467 - 478 Abstract: The coherences between daily time series of four low-frequency seismic noise properties which were calculated for 78 broadband seismic stations of the network F-net in Japan and 81 broadband seismic stations in California for 13 years of observation, 2003–2015, is investigated. The studied time interval includes Tohoku mega-earthquake, M9, on March 11, 2011. The chosen noise properties are the following: minimum normalized entropy of squared wavelet coefficients, multifractal singularity spectrum support width, generalized Hurst exponent and index of linear predictability. These properties were estimated daily as median values taken over all stations of the networks. For each pair of these noise properties from Japan and California squared coherence spectrums were estimated within moving time window of the length 730 days. The maximum values of squared coherence spectra for periods more than 20 days were essentially increasing as the time window approaches the time moment of Tohoku mega-earthquake and achieved their maximum values for position of moving time window strictly before the seismic catastrophe. This fact is interpreted as a consequence of general global seismic noise synchronization before huge seismic catastrophe. PubDate: 2017-12-01 DOI: 10.1007/s40328-016-0181-5 Issue No:Vol. 52, No. 4 (2017)

Authors:Annamária Kiss; Lóránt Földváry Pages: 497 - 510 Abstract: Glacial ice mass balance of Antarctica can be observed by the twin satellites of the gravity recovery and climate experiment (GRACE). The gravity fields with monthly resolution enable efficient detection of annual, long periodic and secular variations. The present study delivers an error estimation of the long-periodic and secular variations by determining the linear trend of the observed surface mass anomaly series. Among the error sources, the error of the timing of the trend fitting, the error of the glacial isostatic adjustment correction, and the error of the atmospheric correction of the GRACE monthly solutions are discussed. The investigation concludes that apart from West Antarctica, Wilkes Land, Queen Maud Land and Enderby Land no reliable trend estimates of ice mass variation can be expected, thus any results should be treated with care. PubDate: 2017-12-01 DOI: 10.1007/s40328-016-0185-1 Issue No:Vol. 52, No. 4 (2017)

Authors:Joanna Kuczynska-Siehien; Adam Lyszkowicz; Katarzyna Stepniak; Marta Krukowska Pages: 527 - 534 Abstract: Results of three campaigns of Baltic Sea Level Project and further studies reveal the GPS and spirit levelling data possibly contain errors which affect SST and \( W_{0}^{L} \) computations. For that reason, the old data were revised and additionally, in spring 2015, the new GNNS campaign was carried out at tide gauges in Swinoujscie, Ustka and Wladyslawowo. The study concerns computation of the local average geopotential value \( W_{0}^{L} \) using water level data at the three tide gauges, geoid undulations from a global geopotential model EGM2008 and ellipsoidal heights from GNSS observations, which were obtained using revised data from three campaigns of Baltic Sea Level Project and from the new campaign conducted in 2015. Results obtained indicate that the best estimation of \( W_{0}^{L} \) was achieved from the campaign carried out in 2015, where the mean value of \( W_{0}^{L} \) calculated for three investigated tide gauge stations is equal to 62636857.45 m2 s−2. PubDate: 2017-12-01 DOI: 10.1007/s40328-016-0188-y Issue No:Vol. 52, No. 4 (2017)

Authors:Gael Kermarrec; Steffen Schön Abstract: Least-squares estimates are unbiased with minimal variance if the correct stochastic model is used. However, due to computational burden, diagonal variance covariance matrices (VCM) are often preferred where only the elevation dependency of the variance of GPS observations is described. This simplification that neglects correlations between measurements leads to a less efficient least-squares solution. In this contribution, an improved stochastic model based on a simple parametric function to model correlations between GPS phase observations is presented. Built on an adapted and flexible Mátern function accounting for spatiotemporal variabilities, its parameters are fixed thanks to maximum likelihood estimation. Consecutively, fully populated VCM can be computed that both model the correlations of one satellite with itself as well as the correlations between one satellite and other ones. The whitening of the observations thanks to such matrices is particularly effective, allowing a more homogeneous Fourier amplitude spectrum with respect to the one obtained by using diagonal VCM. Wrong Mátern parameters—as for instance too long correlation or too low smoothness—are shown to skew the least-squares solution impacting principally results of test statistics such as the apriori cofactor matrix of the estimates or the aposteriori variance factor. The effects at the estimates level are minimal as long as the correlation structure is not strongly wrongly estimated. Thus, taking correlations into account in least-squares adjustment for positioning leads to a more realistic precision and better distributed test statistics such as the overall model test and should not be neglected. Our simple proposal shows an improvement in that direction with respect to often empirical used model. PubDate: 2017-10-31 DOI: 10.1007/s40328-017-0209-5

Authors:Branislav Hábel; Juraj Janák Abstract: GOCE Level 2 products of corrected gravity gradients in Local North-Oriented Frame were used in this study. We analyzed four accurately measured elements of the gravity tensor, which were transformed to disturbing gravitational gradients. The investigation was carried out in the restricted region of dimension 20° × 20° covering the south part of Europe. We applied several types of analytical covariance functions in a local approximation, which have the best fit to the empirical covariances calculated from the disturbing gravitational gradients in particular sub-regions. At first, we have investigated four different types of the 1-dimensional covariance function. Obtained results show that the Gaussian covariance function approximates the empirical covariances the best from tested functions. Moreover, a time stability of calculated parameters of the covariance functions was studied by assuming GOCE data from different time periods. In the second experiment, we have compared two types of the 2-dimensional covariance function, which also enables a spatial stochastic modeling. The second study revealed that the least-squares collocation using the 2-dimensional local covariance function can produce the local grid of GOCE disturbing gravitational gradients directly from GOCE Level 2 products right below GOCE orbit, which in general fits well with the recent Earth’s global gravity field models and might have some advantages. Such local grids can be useful for specific tasks, e.g. mutual comparing of GOCE data collected during particular time periods. PubDate: 2017-10-31 DOI: 10.1007/s40328-017-0208-6

Authors:Hang Yu; Jian Wang; Bin Wang; Houzeng Han; Guobin Chang Abstract: In this paper, a nonlinear dynamic errors-in-variables (DEIV) model which considers all of the random errors in both system equations and observation equations is presented. The nonlinear DEIV model is more general in the structure, which is an extension of the existing DEIV model. A generalized total Kalman filter (GTKF) algorithm that is capable of handling all of random errors in the respective equations of the nonlinear DEIV model is proposed based on the Gauss–Newton method. In addition, an approximate precision estimator of the posteriori state vector is derived. A two dimensional simulation experiment of indoor mobile robot positioning shows that the GTKF algorithm is statistically superior to the extended Kalman filter algorithm and the iterative Kalman filter (IKF) algorithm in terms of state estimation. Under the experimental conditions, the improvement rates of state variables of positions x, y and azimuth ψ of the GTKF algorithm are about 14, 29, and 66%, respectively, compared with the IKF algorithm. PubDate: 2017-10-17 DOI: 10.1007/s40328-017-0207-7

Authors:Walyeldeen Godah; Malgorzata Szelachowska; Jan Krynski Abstract: Temporal variations of geoid heights are vitally important in geodesy and Earth science. They are essentially needed for dynamic and kinematic updates of the static geoid model. These temporal variations, which substantially differ for different geographic locations, can successfully be determined using the Gravity Recovery And Climate Experiment (GRACE) mission data. So far, statistical decomposition methods, e.g. the Principal Component Analysis/Empirical Orthogonal Function (PCA/EOF) method, have not been implemented for the analysis and modelling of temporal mass variations within the Earth’s system over the area of Poland. The aim of this contribution is to analyse and model temporal variations of geoid heights obtained from GRACE mission data over the area of Poland using the PCA/EOF method. Temporal variations of geoid heights were obtained from the latest release, i.e. release five, of monthly GRACE-based Global Geopotential Models. They can reach the level of 10 mm. The PCA modes and their corresponding EOF loading patterns were estimated using two different algorithms. The results obtained revealed that significant part of the signal of temporal variations of geoid heights over Poland can be obtained from the first three PCA modes and EOF loading patterns. They demonstrate the suitability of the PCA/EOF method for analysing and modelling temporal variations of geoid heights over the area investigated. PubDate: 2017-09-25 DOI: 10.1007/s40328-017-0206-8