Showing papers in "Acta Geodaetica Et Geophysica Hungarica in 2020"
TL;DR: In this paper, anomalies in the Radon activity concentration time series recorded in five European caves (Czech Republic, Slovakia, Slovenia) are detected using three hybrid methods: (1) multiple linear regression and autoregressive integrated moving average statistical methods, (2) empirical mode decomposition with support vector regression techniques and (3) singular spectrum analysis composed with a predicting methodology.
Abstract: Anomalies in the Radon activity concentration time series recorded in five European caves (Czech Republic, Slovakia, Slovenia) are detected using three hybrid methods: (1) multiple linear regression and autoregressive integrated moving average statistical methods, (2) Empirical Mode Decomposition with Support Vector Regression techniques and (3) the Singular Spectrum Analysis composed with a predicting methodology. Results coming from the three methods are compared and the best hybrid method is selected based on statistical evaluation criteria of the uncertainty. Radon anomalies occur ± 30 days from earthquake occurrence, selected according to the Dobrovolsky’s earthquake preparation zone formula and to seismic events (with magnitude ≥ 4) occurred in the neighboring European Countries to the monitoring caves. The anomalies detection furnishes results consistent across the used methodologies, as proven by the calculation of a statistical parameter that search the presence of anomalies coming from the hybrid methods within ± 30 days from earthquake event.
25 citations
TL;DR: In this article, the authors used the particle swarm algorithm to estimate the unknown parameters of a finite two-dimensional inclined dike to interpret self potential anomalies due to a finite 2D dike.
Abstract: The self potential data interpretation is very important to delineate and trace the mineralized zones in several regions. We study how to interpret self potential anomalies due to a finite two-dimensional inclined dike using the particle swarm algorithm. However, the precise estimation of the model parameters during the inverse solution are unknown. Here, we show that the particle swarm algorithm is capable of estimating the unknown parameters with acceptable accuracy. The evaluated parameters are the polarization parameter, the depth, the inclination angle, the width, and the location of the source of the target. We found in controlled in free-noise synthetic case that the particle swarm algorithm has a remarkable capability of assessing the parameters. For a noisy case, the results also are very competitive. Furthermore, it is utilized for real mineralized zones examples from Germany and India. Our results demonstrate how the particle swarm algorithm overcomes in trapping in local minimum solutions (undesired) and go faster to the global solutions (desired). Finally, the target parameters estimated are matched with accessible geologic and geophysical information.
21 citations
TL;DR: In this article, the authors estimated Curie depths from the power spectra of 25 equally window sizes areas/points with 50% overlap extracted from high-resolution aeromagnetic anomalies of parts of lower and middle Benue Trough, Nigeria using modified centroid method based on fractal distribution of magnetic sources.
Abstract: To quantitatively understand the geodynamic process of a region, study of geothermal parameters underneath the earth surface is very paramount. Curie depth can be an alternative to delineate geothermal parameters. In the present study, we estimated Curie depths from the power spectra of 25 equally window sizes areas/points with 50% overlap extracted from high-resolution aeromagnetic anomalies of parts of lower and middle Benue Trough, Nigeria using modified centroid method based on fractal distribution of magnetic sources. Curie depths with associated uncertainties calculated from the region under study are between 11 ± 2 and 27 ± 2 km. The shallowest depth (11 ± 2) km is calculated around the area of Abakaliki whereas the deepest depth is calculated around Otukpa area of Anambra basin. The shallowest Curie depth as calculated is related with the Abakaliki anticlinorium while the deepest result is in connection with the Anambra basin. These suggest that different geological structures and magnetic anomalies (i.e. high or low magnetic anomaly) influenced the calculated Curie depth results. In the region, it is noted that lower Curie depths (14–18 km) are recorded over the basement rocks and Curie depths between 18 and 22 km within zones of volcanoes. The interpretation hypothesized presence of underplating in the crust and possibly mantle plume as a result of the Mesozoic–Cenozoic volcanic magmatism (magmatic centers) mostly basalts distributed and scattered in the region. It has also been hypothesized that the uncertainties calculated (± 0.2 to ± 5.0) in the region correlate more strongly with the geology, tectonic structures and type of anomalies than estimated Curie depths.
12 citations
TL;DR: In this article, a Gaussian smoothing method was proposed to spatially average 39 GPS sites using the long-wavelength part of GRACE solutions by Center for Space Research (CSR), GeoForschungszentrum, and Jet Propulsion Laboratory.
Abstract: The Global Positioning System (GPS) permanent stations at the equatorial and southern sub-tropical hydrobelts of South America undergo the highest seasonality on the Earth due to hydrological loadings. Fortunately, there are products that account for such variations, although some of them have not been properly evaluated. For instance, global solutions of Gravity Recovery and Climate Experiment (GRACE) are band-limited to lower frequencies; therefore, comparisons with GPS data must account for such spectral inconsistencies. It is proposed to spatially average 39 GPS sites by applying Gaussian smoothing, which allows comparisons with long-wavelength part of GRACE solutions by Center for Space Research (CSR), GeoForschungszentrum, and Jet Propulsion Laboratory. Comparisons are also carried out with loadings from Noah-driven Global Land Data Assimilation System (GLDAS) and GRACE mass concentration (mascon) solution by Goddard Space Flight Center. Results show that CSR best reduces the variances of the radial displacements considering both spatially filtered (70%) and unfiltered (53%) GPS data covering the period from Jan 2010 to Dec 2015. However, GLDAS-Noah underestimates the amplitudes of vertical loadings, which might be due to unmodeled inland water and groundwater storages. While acknowledging that a denser distribution of GPS stations is needed, the findings still shed light on the quality of the global hydrological loading products based on GRACE and GLDAS datasets, which might be of interest to the respective science teams.
11 citations
TL;DR: In this article, the Mesozoic carbonates of the Kohat Hills rang are recommended as potential aggregate resources for megaprojects like CPEC and other ongoing construction projects.
Abstract: China-Pakistan Economic Corridor (CPEC) is the ongoing mega construction project in Pakistan This project provides multi trading routes like roads, railways and fiber optics to more than 70 countries Additionally, local infrastructure and industrial zones construction in Pakistan is also the part of this project This construction needs a considerable amount of construction materials Therefore, the Mesozoic carbonates were studied in the vicinity of Kohat Hills Range, Khyber Pakhtunkhwa province, Pakistan, for the fundamental engineering assessments The Mesozoic carbonates are extensively exposed in Kohat Hills Range The petrographic observations reveal that these carbonates are dominantly composed of limestone with subordinate dolomites The limestone is well preserved and not extensively affected by diagenesis, which affects the aggregate capability, and there was not found any deleterious material which can cause alkali–silica reaction and alkali–carbonate reaction Likewise, the fundamental engineering tests were performed, which shows proper matching with petrographic observation The specific gravity, water absorption, soundness, los angeles abrasion value, unite weight, impact value, flakiness and elongation, bitumen coating, and crushing values reveal that these aggregates are well according to the specified limits of the international standards AASHTO, ASTM, and BS Based on the results obtained, the Mesozoic carbonates of the Kohat Hills rang are recommended as potential aggregate resources for megaprojects like CPEC and other ongoing construction projects
9 citations
TL;DR: In this paper, a 3D numerical model is developed under the condition of full mining, the height of CZ is calculated to be 144m and the water-conducting fractured zone (WCFZ) is estimated to be 670m.
Abstract: The height of the development of a caved zone (CZ) and a water-conducting fractured zone (WCFZ), hereinafter “CZ and WCFZ”, in mining of soft coal with a soft mine floor, hard mine roof and different thicknesses of the coal seam, hereinafter “two soft and one hard” unstable coal seam, is of interest in the long wall coal mining An observation borehole was drilled above a coal seam with an average thickness of 40 m By using borehole imagery technique and comparing the borehole images at different distances from the working face, the height of “CZ and WCFZ” at the working face is calculated under the condition of insufficient mining Based on field observations, a 3D numerical model is developed under the condition of full mining, the height of CZ is calculated to be 144 m and the height of WCFZ calculated to be 670 m The numerical model also shows changes in the vertical stresses in the overburden strata above the roof of the coal seams and it is related to the development of the “CZ and WCFZ” At the same time, based on the key strata theory and multiple linear regression, the height of WCFZ in the working face of this case study is predicted to be 670 m and 648 m respectively, which is close to the numerical simulation results At the same time, 30 groups of measured data are collected to analyze the main factors affecting the WCFZ, and the influence of different lithology characteristics of overburden strata on the WCFZ is mainly discussed The results show that the height of WCFZ is hard–hard > hard–soft > soft–hard The results provide important practical guidelines for the prevention and control of roof water hazards in coal mine thus improving the safety of mining
9 citations
TL;DR: In this paper, the improved crow search algorithm (ICSA) using Levy flight is proposed for SP data inversion in determining SP model parameters, and the experimental results demonstrate that ICSA is feasible and effective for determining model parameters and its uncertainty of mono and multi-SP anomalies.
Abstract: Fracture or fault can control several geological or geophysical events and exploration, where the fault associated with mineralization or fluid flow can be used as a source for Self-Potential (SP) anomaly. The 2-D inclined sheet can be used for modeling for fault interpretation using SP data. In this paper, the improved crow search algorithm (ICSA) using Levy flight is proposed for SP data inversion in determining SP model parameters. In order to evaluate ICSA, the ICSA is compared with standard crow search algorithm (CSA) for determining synthetic SP data that contains multiple anomalies with inclined sheet type structures. It was found that CSA is more explorative than ICSA, and both algorithms can estimate the posterior distribution model (PDM) of SP data. Using uncertainty analysis within the applied threshold in the objective function, both algorithms are reliable to determine PDM. Furthermore, ICSA is tested and implemented to both synthetic and field of SP anomalies for providing the posterior distribution model of SP parameters. The experimental results demonstrate that the ICSA is feasible and effective for determining model parameters and its uncertainty of mono- and multi-SP anomalies. Furthermore, estimating both model parameter and its uncertainty are sufficient for validation with previous researchers. Finally, the interpretation of multiple anomalies in SP anomaly crossing the Grindulu Fault in Pacitan, East Java, Indonesia, is analyzed.
8 citations
TL;DR: In this paper, the authors presented a new approach for forecasting NAO index (NAO index) based on predictions of sea level anomalies (SLAs) using a linear regression model.
Abstract: The objective of this paper is to present a new approach for forecasting NAO index (NAOi) based on predictions of sea level anomalies (SLAs). We utilize significant correlations (Pearson’s r up to 0.69) between sea surface height (SSH) calculated for the North Atlantic (15–65°N, basin-wide) and winter Hurrell NAOi, as shown by Esselborn and Eden (Geophys Res Lett 28:3473–3476, 2001).
We consider the seasonal and monthly data of Hurrell NAOi, ranging from 1993 to 2017. Weekly prognoses of SLA are provided by the Prognocean Plus system which uses several data-based models to predict sea level variation. Our experiment consists of three steps: (1) we calculate correlation between the first principal component (PC1) of SSH/SLA data and NAOi, (2) we determine coefficients of a linear regression model which describes the relationship between winter NAOi and PC1 of SLA data (1993–2013), (3) we build two regression models in order to predict winter NAOi (by attaching SLA forecasts and applying coefficients of the fitted regression models). The resulting 3-month prognoses of winter NAOi are found to reveal mean absolute errors of 1.5 or less. The choice of method for preparing SLA data for principal component analysis is shown to have a stronger impact on the prediction performance than the selection of SLA prediction method itself.
7 citations
TL;DR: In this paper, a new method of numerically solving ordinary differential equations is presented, based on the Gaussian numerical integration of different orders, using two different orders for numerical integration, an adaptive method is derived.
Abstract: In this paper a new method of numerically solving ordinary differential equations is presented. This method is based on the Gaussian numerical integration of different orders. Using two different orders for numerical integration, an adaptive method is derived. Any other numerical solver for ordinary differential equations can be used alongside this method. For instance, Runge–Kutta and Adams–Bashforth–Moulton methods are used together with this new adaptive method. This method is fast, stable, consistent, and suitable for very high accuracies. The accuracy of this method is always higher than the method used alongside with it. Two applications of this method are presented in the field of satellite geodesy. In the first application, for different time periods and sampling rates (increments of time), it is shown that the orbit determined by the new method is—with respect to the Keplerian motion—at least 6 and 25,000,000 times more accurate than, respectively, Runge–Kutta and Adams–Bashforth–Moulton methods of the same degree and absolute tolerance. In the second application, a real orbit propagation problem is discussed for the GRACE satellites. The orbit is propagated by the new numerical solver, using perturbed satellite motion equations up to degree 280. The results are compared with another independent method, the Unscented Kalman Filter. It is shown that the orbit propagated by the numerical solver is approximately 50 times more accurate than the one propagated by the Unscented Kalman Filter approach.
6 citations
TL;DR: In this article, the authors estimate physical height changes over the area of Turkey using 6 GRACE-based global geopotential models and WaterGAP (Water-a Global Assessment and Prognosis) Global Hydrology Model products as well as load Love numbers from the Preliminary Reference Earth Model.
Abstract: Gravity Recovery and Climate Experiment (GRACE) satellite mission had provided gravity data for ca. 15 years, completed its mission in 2017 and handed over to GRACE Follow-On. During its active life, GRACE contributed to the understanding of temporal variations of geoid/quasigeoid heights as well as vertical and horizontal displacements of the Earth’s surface induced by mass loading, and thereby the physical height (e.g. the orthometric/normal height) changes. The main objective of this research is to estimate physical height changes over the area of Turkey. The release 6 GRACE-based global geopotential models and WaterGAP (Water—a Global Assessment and Prognosis) Global Hydrology Model products as well as load Love numbers from the Preliminary Reference Earth Model were used as input data. Physical height changes over Turkey were estimated using three different approaches: the GRACE-based Global Geopotential Models, the Green’s function, and the Terzaghi’s principle. The estimated physical height changes were analysed and modelled by means of the seasonal decomposition method and the Principal Component Analysis/Empirical Orthogonal Function method. The main findings reveal that physical height changes over Turkey reach the level of a few centimetres during years 2004–2010.
6 citations
TL;DR: The experimental result proves that through the CRIEKF-based UWB/IMU fusion robot positioning method, a mean positioning accuracy of around 0.21 m can be achieved in NLOS environments.
Abstract: In a non-line-of-sight (NLOS) environment, high accuracy ultra-wideband (UWB) positioning has been one of the hot topics in studying indoor positioning. Aiming at the UWB and inertial measurement unit (IMU) fusion vehicle positioning, a constraint robust iterate extended Kalman filter (CRIEKF) algorithm has been proposed in this paper. It has overcome the innate defect of the extended Kalman filter against non-Gaussian noise and the shortcoming of the robust extended Kalman filter algorithm, which has just processed the non-Gaussian noise solely based on the prior information. Our algorithm can update the observation covariance based on the posteriori estimate of the system in each iteration, and then update the posteriori distribution of the system based on the obtained covariance to significantly reduce the influence of non-Gaussian noise on positioning accuracy. Also, with the introduction of motion constraints, such as zero velocity, pseudo velocity and plane constraints, it can achieve a smoother positioning result. The experimental result proves that through the CRIEKF-based UWB/IMU fusion robot positioning method, a mean positioning accuracy of around 0.21 m can be achieved in NLOS environments.
TL;DR: Wang et al. as discussed by the authors proposed a new noise suppression framework based on improved PSO-SVM to improve the signal to noise ratio (SNR) of the field seismic data.
Abstract: As one of the major regions of carbonate rock oil–gas exploration in western China, Tazhong area of the Tarim Basin has severe environment and complex ground surface conditions, hence the signal to noise ratio (SNR) of the field seismic data is extremely low. To improve the SNR of desert seismic data is a crucial step in the following work. However, the random noise in desert seismic characterizes by non-stationary, non-gaussian, non-linear and low frequency, which are very different from the random Gaussian noise. In addition, the effective signals of desert seismic generally share the same frequency band with strong random noise. These all make some traditional denoising methods cannot suppress it well. Therefore, a new noise suppression framework based on improved PSO–SVM is proposed in this paper. First, we extract the correlation of noisy desert seismic data to form feature vector. Subsequently, the model of improved PSO–SVM was built to classify the extracted feature, thereby identifying the position of the seismic events. Finally, second-order TGV filter was applied for obtaining denoised results. We perform tests on synthetic and field desert seismic record and the denoising results show that the proposed method can effectively preserve effective signals and eliminate random noise.
TL;DR: In this paper, a singular spectrum analysis (SSA) method was proposed to correct and denoise superconducting gravimetry (SG) data and then the harmonic analysis method was used to precisely extract the gravity tides from SSA-denoised SG data.
Abstract: Superconducting gravimetry is one main technique to determine the gravity tides. In superconducting gravimeter (SG) measurement, the gravity tides is affected by the gross errors (including spikes and severe deviations and mainly caused by instrument problems and earthquakes) and noise (caused due to the internal structure of SG instrument and measurement environment) in SG data. The singular spectrum analysis (SSA) method was proposed to correct and denoise SG data. Then the harmonic analysis method is used to precisely extract the gravity tides from SSA-denoised SG data. The SG data at Wuhan station of China are used in the case study. The results show that the accuracies of tidal amplitude factors, phase differences and amplitudes of most wave groups determined from SSA-denoised SG data by the harmonic analysis were improved significantly. The standard deviation of residuals between the synthetic gravity tides obtained by harmonic analysis of SSA-denoised SG data and theoretical gravity tides is 0.0096 μGal (1 μGal = 10−8 m s−2), and is 0.1772 μGal while replacing the SSA-denoised SG data from the un-denoised SG data. The Akaike’s Bayesian Information Criterion value of harmonic analysis on SSA-denoised SG data is better than that from un-denoised SG data, which indicates that SSA denoising on SG data can improve the accuracy of harmonic analysis results. The root mean square of gravity residuals obtained by harmonic analysis of SSA-denoised SG data is 0.0019 μGal, and is 0.2275 μGal when replacing the SSA-denoised SG data from the un-denoised SG data. The result shows that SSA can effectively eliminate most of gross errors and noise existing in the SG data, and improve accuracy of the gravity tides with the harmonic analysis.
TL;DR: In this article, the relative velocity between fluid and solid and their relative acceleration via Darcy permeability and the coupling factor, respectively, are used to quantify stress between the phases in Biot theory.
Abstract: In Biot theory, the relative velocity between fluid and solid and their relative acceleration, via Darcy permeability and the coupling factor, respectively, are used to quantify stress between the phases. In this paper, the relative velocity via variable permeability is used to improve the quantification of the stress. The modeling quantities are the S-wave velocity ratio of brine saturated Berea sandstone to the dry sandstone and the (viscous-flow-induced) attenuation. Although skeleton shear modulus depends on differential pressure (the confining pressure minus pore pressure), the two quantities are conservative at small differential pressures. The modeling results reveal that Berea sandstone has a permeability of 0.02–0.03 Darcy for S-wave at 1 MHz, much smaller than Darcy permeability (0.075 Darcy). The cause is that with the increase of frequency, the thinning of Stokes boundary layer decreases permeability. Moreover, the total porosity of 0.23 is better than the effective porosity of 0.20 in the simulation, because S-wave does not discriminate connected pores or occluded pores.
TL;DR: In this paper, the authors investigated the occurrence of tracking failure and effects on the positional accuracy of the NavIC L5-band and S-band system under direct exposure of X2.2 and X9.3 solar flares.
Abstract: The solar flares and geomagnetic storms are considered a potential threat for the upcoming Indian Regional Navigation Satellite System or Navigation with Indian Constellation (NavIC). Therefore, we investigated in detail the occurrence of tracking failure and effects on the positional accuracy of the NavIC L5-band and S-band system under direct exposure of X2.2 and X9.3 solar flare on September 6, 2017, X9.3 is the strongest event since the NavIC signals are in the service. The regional NavIC data (5–6 September 2017) from the equatorial region Trivandrum station and the Equatorial Ionization Anomaly area in India (Surat, Bombay, Hyderabad and Gandhinagar stations), are collected using the accord NavIC dual-frequency (L5-band and S-band) receivers. We have shown that the 1G NavIC signals remain in loss of lock condition for 1 h on September 6, 2017 (X2.2 and X9.3 solar flares), and as a result, positioning accuracy deviated on September 6, 2017. Hence, the solar flare event considered a potential threat for future NavIC based autonomous navigation technologies.
TL;DR: In this article, the authors used amplitude ratio, complexity and continuous wavelet transform (CWT) methods to determine the source of seismic quakes in the Eastern Marmara Region which also included two branches of western part of the North Anatolian Fault Zone.
Abstract: The aim of this study is to determine the source of seismic quakes is whether natural or artificial in the Eastern Marmara Region which is also included two branches of western part of the North Anatolian Fault Zone. It is known as one of the most seismically hazardous region in Turkey and 1999 Izmit and Duzce Earthquakes were occurred inside this area. In addition, it has geothermal springs, lots of mining areas, tunnel, bridge and road construction points. Under these conditions, it is seismologically important to make a study about the discrimination of the natural and artificial events. 611 seismic events with Ml ≤ 2.5 which has occurred between 2017 and 2019, recorded by 11 seismic stations that are being operated by Republic of Turkey Prime Ministry Disaster and Emergency Management Authority Presidential of Earthquake Department were analyzed. Amplitude ratio, complexity and continuous wavelet transform (CWT) methods were performed; linear and quadratic discriminant functions (LDF, QDF) were used for statistical processes to all waveforms and their results. All waveforms were identified by significant manual investigation that P wave first motion polarity, no or low amplitude S wave recording, the vision of coda wave decay and Rg phase detection and it called as a first determination. The results were compared to first determination and the final decisions were gained with the combination of their all. Besides with the all methods, CWT analyze could give more reliable results than the others and amplitude ratio method can serve better results than complexity. Otherwise, LDF could classify the events better than QDF. Through the final decision, 395 earthquake and 182 blast recordings were clearly discriminated with the accuracy of 94.44% and the source types of 34 seismic events could not be identified. The obtained discriminant functions for each station are useful to determine the source types of the events and they could clarify the contaminated earthquake catalogues. Increasing the reliability of the final results would be related with using these methods together.
TL;DR: In this article, a model of a concealed collapse column is constructed according to its diameter and the finite difference method is used to simulate it using an acoustic equation, and the seismic record characteristics of the collapse column are analyzed.
Abstract: A collapse column is a geological structure formed by the dissolution of a soluble rock layer under certain hydrogeological conditions. This forms a cavity, which is filled by the overburden. Collapse columns have a great impact on coal mining safety. In this work, a model of a concealed collapse column is constructed according to its diameter, and the finite difference method is used to simulate it using an acoustic equation. The seismic record characteristics of the collapse column are analyzed. In the seismic section, the attributes of the reflected wave of the concealed collapse column in the coal seam are small and undetectable, and the reflected wave of the auxiliary horizon (the upper interface of Ordovician limestone) is in-phase axis. It is difficult to artificially identify concealed collapse columns with small diameters when twisting or dislocation occurs. However, the reflected wave properties clearly indicate an annular anomaly on the horizon property plane, which helps to identify the concealed collapse column. Finally, the seismic attributes of reflected waves at the interface between the 10# coal seam and Ordovician limestone roof in the BY mining area of TY mine are identified using high-density three-dimensional seismic data to verify the effectiveness of the proposed method in identifying concealed collapse columns.
TL;DR: A global source model constructed with the help of machine learning (and deep learning) is proposed to mitigate issues, in particular the uncertainties caused by vigorous convection and small scale fields.
Abstract: A summary of methods yielding information about the generation and configuration of the geomagnetic main field is presented with special focus on complications concerning these methods. A global source model constructed with the help of machine learning (and deep learning) is proposed to mitigate these issues, in particular the uncertainties caused by vigorous convection and small scale fields.
TL;DR: In this paper, a Maximum Minimum Eigen (MME) detector was used to identify the ionosphere induced errors in the GPS Aided Geo Augmented Navigation (GAGAN) signals.
Abstract: The ionospheric anomalies are often responsible for compromising the accuracy and performance of Global Navigation Satellite System (GNSS). GPS Aided Geo Augmented Navigation (GAGAN) is the autonomous Space Based Augmentation System of India which serves to provide timely error detection and correction for the corrupted GNSS signals in aircrafts. This paper discusses a Maximum Minimum Eigen (MME) detector to identify the ionosphere induced errors in the GNSS signals. Data has been collected from 24 different GAGAN receivers spread over the length and breadth of India from January to December, 2015. The climatology of ionospheric anomaly over India, has been established using the MME detector. This paper discusses the spatio-temporal dependence of ionospheric anomalies over India. The observations indicate an increased ionospheric activity in the course of equinoxes and a comparitively quiet ionosphere in the course of solstices. A higher number of ionospheric disturbance incidents have been noticed closer to the anomaly crest. The results from the MME detector have been verified against the Rate of Total Electron Content (TEC) Index (ROTI) values and S4 observations for the year 2015 at the 24 GAGAN TEC stations. The disturbance climatology obtained from MME detector, ROTI and S4 exhibit a high correlation. However, the outcome of the MME detector clearly shows that it is capable of picking up even small irregularities in the ionospheric TEC.
TL;DR: An adaptive iterative convergence on low-rank decomposition algorithm based on synchrosqueezed wavelet transform (SWT) is performed and the effectiveness of the proposed method can be applied to the denoising of desert seismic data.
Abstract: Elimination of random noise is crucial in seismic data processing. Especially in desert area, field record generally has problems of weak effective reflection wave and strong noise due to its special surface factors. Besides, desert noise has characteristics of low-frequency, non-stationary and non-Gaussian. Thus, it is difficult to separate the effective signal from desert noise in low-frequency band. In order to solve these problems, this paper proposes an iterative low-rank denoising method based on synchrosqueezed wavelet transform (SWT). The algorithm first transforms seismic signal into time–frequency domain by SWT, then the signal is decomposed by iterative low-rank decomposition. Different from a traditional low-rank algorithm, this paper performs an adaptive iterative convergence on low-rank decomposition algorithm. When the error of decomposition reaches the predetermined range, the effective low-rank component is extracted. In the end, the low-rank matrix is converted back to time domain by inverse SWT to achieve the denoising. The results of the synthetic and field records verify the effectiveness of the proposed method so that it can be applied to the denoising of desert seismic data. In addition, the surface waves in real desert seismic record have obvious suppression effects and the advantages of the algorithm are shown in the comparison experiments.
TL;DR: In this paper, a decision model for the ZTD blind model (DMZBM), which is a new strategy of dealing with ZTD in PPP when using blind ZTD models, was proposed.
Abstract: In precise point positioning (PPP), the zenith hydrostatic delay (ZHD) is traditionally treated as a priori value from the ZHD model but the zenith wet delay (ZWD) is treated as an unknown parameter to estimated. For some near real-time PPP tasks, priori ZHD from the blind ZHD models are often used because external meteorological measurement or information about atmospheric pressure or ZHD can not be obtained in such conditions. On the other hand, a priori ZHD errors can project into GNSS height estimates errors in the PPP analysis, because unmodeled part of the ZHD is usually absorbed into the estimated ZWD while there is the difference between the hydrostatic mapping function and the wet mapping function. In this study, we found the errors of the ZHD seasonal models are not always less than those of the ZWD seasonal models, which implies that the traditional strategy for treating ZTD (priori ZHD and estimated ZWD) is not always the best choice when using the blind zenith tropospheric delay (ZTD) models. A decision model for the ZTD blind model (DMZBM), which is a new strategy of dealing with ZTD in PPP when using blind ZTD models, was proposed. For most cases, the traditional strategy works while for some exception cases, it is recommended that priori ZWD from the blind ZWD model was set but ZHD is treated as an unknown parameter to estimated. The DMZBM can directly reduce ZHD–ZWD mutual absorption errors which potentially reduce GNSS height estimates errors due to the difference between the hydrostatic mapping function and the wet mapping function. The results show that there are significant reductions of ZHD–ZWD mutual absorption errors in polar regions when using the new ZTD-treating strategy.
TL;DR: Results show that the multipath model based on first-order regularization can improve the RMS of carrier phase residuals by approximately 49.8% compared with the solution without multipath mitigation.
Abstract: Integer ambiguity resolution is critical for achieving positions of high precision and reliability of precise point positioning (PPP). However, as an important error source in global navigation satellite system (GNSS), multipath interference limits the ability of PPP in high-accuracy GNSS positioning applications. Thus, to guarantee the performance of PPP ambiguity resolution techniques in a multipath environment, a sidereal filtering technique based on sparsity promoting regularization is adopted to mitigate the multipath error. The key idea of the proposed strategy emphasizes the use of the L1 norm to extract multipath from noisy carrier phase residuals. The classical single-difference between-satellites method is used to fix PPP with the estimated phase clocks/bias products for obtaining carrier phase residuals in the previous period. Two GPS datasets are adopted to assess the denoising effect of the multipath model and the performance of the proposed strategy. The carrier phase residuals of static PPP ambiguity resolution and the positioning accuracy of kinematic float PPP after the application of the multipath model are used to reflect the final filtering performance. Results show that the multipath model based on first-order regularization can improve the RMS of carrier phase residuals by approximately 49.8% compared with the solution without multipath mitigation. In kinematic float PPP, a mean coordinate improvement of 49.7% for day of year (DOY) 273 and 57.8% for DOY 275 in 2017 could be achieved.
TL;DR: In this paper, the results of the two experimental ways are quite different and the appropriate choice of the method which can get accurate rock electrical parameters is important, which will provide support for future development of gas-bearing tight sandstone.
Abstract: Reservoir evaluation of tight sandstone involves the determination of reservoir properties from samples and logs. In the calculation of water saturation, Archie formula is an important fundamental and connection between log evaluation and petrophysics. Highly accurate parameters of Archie formula are the key to the log evaluation of gas-bearing tight sandstone. At present, there are two methods of the rock-electric experiment to measure parameters of Archie formula: water increment (imbibition) and water decrement (centrifugation). In this paper the experimental measurement of a group of tight sandstone has been designed and the results of the two experimental ways are quite different. In the experiment, the distribution of brine is a main factor affecting the electrical properties of rocks. Fluid distribution model during imbibition and drainage is used to explain the results of rock electrical experiments, and the results are verified by nuclear magnetic resonance measurement. In the end, the Pickett chart method of actual data is used to compute the ranges of the saturation exponent n approximately, then to verify the correctness of the theoretical analysis. The results demonstrate that the centrifugal method is more applicable. In the log evaluation of tight sandstone, the appropriate choice of the method which can get accurate rock electrical parameters is important. Reliable evaluation will provide support for future development of gas-bearing tight sandstone.
TL;DR: In this paper, a space-time TEC variation estimator was designed for earthquake prediction, taking advantage of the well-known predictive abilities of the Gutenberg-Richter law's b-value.
Abstract: Ionospheric anomalies have been shown to occur a few days before several large earthquakes. The published works normally address examples limited in time (a single event or few of them) or space (a particular geographic area), so that a clear method based on these anomalies which consistently yields the place and magnitude of the forthcoming earthquake, anytime and anywhere on earth, has not been presented so far. The current research is aimed at prediction of large earthquakes, that is with magnitude Mw 7 or higher. It uses as data bank all significant earthquakes occurred worldwide in the period from January 1, 2011 to December 31, 2018. The first purpose of the research is to improve the use of ionospheric anomalies in the form of TEC grids for earthquake prediction. A space–time TEC variation estimator especially designed for earthquake prediction will show the advantages with respect to the use of simple TEC values. Further, taking advantage of the well-known predictive abilities of the Gutenberg–Richter law’s b-value, a combined estimator based on both TEC anomalies and b-values will be designed and shown to improve prediction performance even more.
TL;DR: In this article, a parametric correlation model called the Matern model is used to approximate the variance covariance matrix (VCM) of the residuals by performing their empirical mode decomposition.
Abstract: The detection of deformation is one of the major tasks in surveying engineering. It is meaningful only if the statistical significance of the distortions is correctly investigated, which often underlies a parametric modelization of the object under consideration. So-called regression B-spline approximation can be performed for point clouds of terrestrial laser scanners, allowing the setting of a specific congruence test based on the B-spline surfaces. Such tests are known to be strongly influenced by the underlying stochastic model chosen for the observation errors. The latter has to be correctly specified, which includes accounting for heteroscedasticity and correlations. In this contribution, we justify and make use of a parametric correlation model called the Matern model to approximate the variance covariance matrix (VCM) of the residuals by performing their empirical mode decomposition. The VCM obtained is integrated into the computation of the congruence test statistics for a more trustworthy test decision. Using a real case study, we estimate the distribution of the test statistics with a bootstrap approach, where no parametric assumptions are made about the underlying population that generated the random sample. This procedure allows us to assess the impact of neglecting correlations on the critical value of the congruence test, highlighting their importance.
TL;DR: In this paper, the authors used GNSS data from the Egyptian permanent GNSS network (EPGN), International GNSS Service (IGS), EUthis paper Permanent Network (EPN), and Scripps Orbit and Permanent Array Center (SOPAC), for the years 2013 and 2014, were used.
Abstract: The study of climate change is an important field of research. Monitoring of atmospheric variability especially the tropospheric precipitable water vapor (PWV) is a powerful way to investigate climate change. Global navigation satellite systems (GNSS) provide a good tool for studying atmospheric parameters as GNSS signals along its path from the satellites to the ground based receivers suffer a significant delay due to the refractivity of earth’s atmosphere. GNSS signals are not only delayed but also refracted in the neutral atmosphere. The zenith wet delays (ZWD) caused by the troposphere can be estimated during the geodetic processing of GNSS signals. Since the ZWD is tightly correlated to the PWV, GNSS observations can be used to study the changes of PWV. In this study GNSS data from the Egyptian permanent GNSS network (EPGN), International GNSS Service (IGS), EUREF Permanent Network (EPN) and Scripps Orbit and Permanent Array Center (SOPAC), for the years 2013 and 2014, were used. These GNSS stations provided a good geometrical coverage over the respective region. All GNSS data were processed using Bernese V 5.2 software. The needed product from GNSS data processing is the tropospheric zenith total delay (ZTD) over each GNSS site. The ZTD is divided based on physical parameters into zenith hydrostatic delay (ZHD) and zenith wet delay (ZWD). The ZWD is the basic observable used to calculate PWV. The values of the PWV were calculated and its variation over the study area was investigated. The quality of calculated PWV values from GNSS data evaluated against traditional Radiosonde (RS) measurements. The results of GNSS PWV showed good agreement with RS PWV when the PWV values were low, but this agreement became worse at high PWV values as the differences between the two techniques increased. The correlation coefficient between RS PWV and GNSS PWV varied from 0.31 to 0.84. Standard deviation of the differences between RS PWV and GNSS PWV ranged from 2.369 to 5.973 mm. The PWV estimated from GNSS observations had annual cycle, and its cycle in 2013 was different from that in 2014. The PWV differences between the 2 years clarified that the water vapor content over the east Mediterranean in most of 2014 days was higher than that in 2013. Furthermore, PWV variations were noted on both temporal and spatial scales. The highest temporal variation value was 25.41 mm whereas the maximum value of the spatial variation was 19.67 mm. The present study illustrated the importance of using geodetic networks to provide atmospheric information.
TL;DR: In this paper, the results of mathematical modeling of electrical soundings with the AMNB (Schlumberger, Wenner) arrays and the proposed combined AMN+NMA array above horizontally layered medium and including a ball medium are presented.
Abstract: The results of mathematical modeling of electrical soundings with the AMNB (Schlumberger, Wenner) arrays and the proposed combined AMN + NMA array above horizontally layered medium and including a ball medium are presented. It is shown that the combined array has two main advantages: the current penetration depth is greater at the same position of outer electrodes of the considered arrays; edge effects are smaller due to bilateral measurements with respect to the central receiving electrode; a geoelectric inhomogeneity is delineated at the pseudosections of the apparent resistivity. The quantitative interpretation of the sounding curves obtained with the AMN + NMA array can be carried out by an existing software for inversing of data of the symmetric Wenner (AMNB) array with electrode spacing equal to 1/3 of supplying dipole. The results of application of the new technique of electrical soundings by the combined array in the study of state of the dam on sedimentation tank of liquid chemicals are presented. On the geoelectric sections and the pseudosections of the apparent resistivity, areas of increased electrical conductivity in body and base of the dam are detected. Filtration of water from the reservoir occurs through these areas. Soundings with the AMN + NMA array are expedient for studying of a geological medium at small depths where the medium is horizontally-heterogeneous, and also for solving of engineering-geological problems.
TL;DR: In this article, power spectra of 198 stations distributed countrywide are computed and probability density functions as well as diurnal, weekly, monthly and annual spectrogram-graphics, hence, are obtained.
Abstract: By utilizing data from the National Seismic-Monitoring Network of Turkey, operated by AFAD (Disaster and Emergency Management Presidency, Ministry of the Interior), power spectra of 198 stations distributed countrywide are computed and probability density functions as well as diurnal, weekly, monthly and annual spectrogram-graphics, hence, are obtained. Observed noise levels are the result of natural background noise, cultural noise as well as instrument installation practice and equipment defects. Countrywide noise distribution is displayed on a map and noise models for Turkey are developed in the study. Various suggestions are also given for some of the technical problems deducted from noise analyses in relation to the construction of the station, equipment faults, and defects.
TL;DR: In this article, the authors used double-difference seismic tomography to obtain the upper crustal velocity structure in Laizhou Bay and its adjacent areas (LBAA) and found that the horizontal and vertical distributions of the earthquakes after relocation in earthquake swarms are more concentrative than that before relocation.
Abstract: This study used the double-difference seismic tomography method to obtain the upper crustal velocity structure in Laizhou Bay and its adjacent areas (LBAA). We found that the horizontal and vertical distributions of the earthquakes after relocation in earthquake swarms are more concentrative than that before relocation. The lateral heterogeneity of crustal velocity structure near the surface in the LBAA is weak, and the low-velocity sedimentary caprocks are developed in most areas except for the Jiaobei uplift. The velocity structure in 5–25 km depth range is highly heterogeneity, which is closely related to different tectonic units. The local uplift tectonic units in Jiyang depression show high-velocity anomalies and should have deep crustal media properties. The high-velocity anomalies under the crust of Tancheng–Lujiang fault zone and the northern Laizhou Bay indicate the properties of upwelling mantle material media. Earthquake swarms activity in the study area are mainly concentrated in the high-velocity interlayer of the upper crust and its periphery. Compared with the relatively stable high-velocity body at the bottom crust, the location of high-velocity interlayer in the study area is more prone to earthquakes under the combined action of gravity and tectonic stress.
TL;DR: In this paper, a kind of one-step compensation downward continuation method free of iteration using the equivalent wave number domain continuation operator was reported, which will speed downward continuation compared to iterative compensation.
Abstract: As a kind of geomagnetic data processing, downward continuation of potential field plays an important role in geologic interpretation and geomagnetic localization. The inherent instability of larger distance downward continuation restricts its practical applications. In this paper, we report a kind of one-step compensation downward continuation method free of iteration using the equivalent wave number domain continuation operator, which will speed downward continuation compared to iterative compensation, and prove theoretically the convergence of the downward continuation filtering factor about one-step immune-iterative compensation. The frequency responses of the low-pass filter factor are also discussed by different damping factors, iterative numbers and continuation depths. The regularity analysis of one-step compensation method is also discussed. We use the theoretical model of magnetic bodies and real data to test experimentally the immune-iterative compensation algorithm based on the equivalent wave number domain continuation factor, respectively. The results all show high accuracy and good stability of the one-step compensation downward continuation algorithm. The performances of downward continuation including three kinds of algorithms are demonstrated by three parameters, and comparisons prove the reported algorithm has less calculated error than the generalized inverse method, and less elapsed time than the iterative compensation method.