Abstract: A fault slip within the Ñaña tunnel Lima, Peru has been monitored since 2012. The data are recorded using an optical-mechanical 3D extensometer, capable of providing very precise long-term three-dimensional measurements of relative displacement across discontinuities. The Ñaña tunnel has an extremely stable environment and cannot possibly be affected by gravitationally-induced mass movements. The host rock of the tunnel is an aphanitic hornblende-bearing basaltic trachyandesite. Several fault and fracture zones detected in the tunnel represent the major discontinuities of the broader surrounding of the monitored site. The recorded fault slip on the NNW-SSE and E-W striking fracture and fault, with inclinations of 76° to WSW and 78° to N respectively, appoint to compressional event (discontinuity contraction) with a maximum horizontal compression stress axis oriented approximately WSW to ENE corresponding to the direction of the Nazca and South America plates convergence. This event resulted in an aseismic slow fault slip between July 2012 and May 2013. The anticipated compression orientation matches the previously published in-situ stress measurements and fault plane solutions, as well as GPS measurements of the movements of the corresponding part of the Peruvian coast. Nevertheless, the presented monitoring results reflect only short-term fault slip dynamics and need to be considered with caution, even though they correspond to the overall tectonic activity driven by continental subduction. PubDate: 2019-02-05 DOI: 10.1007/s11200-018-2912-2

Abstract: Global geopotential models are widely used in the remove-compute-restore technique for local gravity field modeling. In this paper, a method for regional improvement of global geopotential models using GPS/Leveling data is presented. The part of the spherical harmonic expansion degrees that can be subject to the regional improvement is determined depending on the spatial resolution of the GPS/Leveling data and the size of the study region. In this method, a global geopotential model is required as the original model. Using the GPS/Leveling data corrected for the systematic errors, the geoid surface is obtained at the GPS/Leveling points. By expanding the gravity potential of the geoid surface into the spherical harmonics, a mathematical model is made to estimate the spherical harmonic coefficients of the regionally improved geopotential model. To stabilize the mathematical model, pseudo data of the gravitational potential type produced by the original model on the entire Earth’s surface are added to the GPS/Leveling data. The relative weight of the two types of the data, i.e., the GPS/Leveling data and the pseudo data, is selected based on fitting the original model to the GPS/Leveling data. As numerical tests, the regionally improved geopotential model of the USA from degree 8 to 779 and the regionally improved geopotential model of Iran from degree 12 to 339 are developed. To develop both regionally improved geopotential models, the EGM2008 model up to degree 2160 is selected as the original model. The assessments at the GPS/Leveling checkpoints show that the regionally improved geopotential model of the USA has a 23% improvement and the regionally improved geopotential model of Iran has an 8% improvement with respect to the original model. The numerical tests confirm the efficiency of the proposed method for the regional improvement of global geopotential models using the GPS/Leveling data. PubDate: 2019-01-10 DOI: 10.1007/s11200-017-1084-9

Abstract: The functions describing material parameters and structural interfaces in velocity models are frequently represented by splines. The general cubic splines differ from the natural cubic splines by the boundary conditions at the outermost gridpoints. The general cubic splines have a general curvature at the outermost gridpoints used for interpolation, whereas the natural splines have a zero normal curvature at the outermost gridpoints. It is thus very useful to employ a simple algorithm for the transformation between the general and natural splines. The transformation from the natural to general (bi–) (tri–) cubic splines is straightforward, because the natural splines represent a special case of the general splines. This paper is devoted to the algorithm of transformation from the general to natural (bi–) (tri–) cubic splines. We present the formulae necessary for the transformation together with their derivation. We illustrate the presented formulae on the example of fitting a 1–D quadratic function by natural cubic splines, and on the example of a velocity model of a layered structure with two 3–D structural interfaces. PubDate: 2019-01-01 DOI: 10.1007/s11200-018-0933-5

Abstract: The uncertainties of the geoidal heights estimated from ground gravity data caused by their spatial distribution and noise are investigated in this study. To test these effects, the geoidal heights are estimated from synthetic ground gravity data using the Stokes- Helmert approach. Five different magnitudes of the random noise in ground gravity data and three types of their spatial distribution are considered in the study, namely grid, semigrid and random. The noise propagation is estimated for the two major computational steps of the Stokes-Helmert approach, i.e., the downward continuation of ground gravity and Stokes’s integration. Numerical results show that in order to achieve the 1-cm geoid, the ground gravity data should be distributed on the grid or semi-grid with the average angular distance less than 2′. If they are randomly distributed (scattered gravity points), the 1-cm geoid cannot be estimated if the average angular distance between scattered gravity points is larger than 1′. Besides, the noise of the gravity data for the tree types of their spatial distribution should be below 1 mGal to estimate the 1-cm geoid. The advantage of interpolating scattered gravity points onto the regular grid, rather than using them directly, is also investigated in this study. Numerical test shows that it is always worth interpolating the scattered points to the regular grid except if the scattered gravity points are sparser than 5′. PubDate: 2019-01-01 DOI: 10.1007/s11200-018-1013-6

Abstract: Classical outlier detection test methods such as Baarda test and Pope test are generally preferred in geodetic problems. They depend on the Least Square Estimation (LSE) and LSE is very sensitive to the variations of the model. The capacity of the LSE changes depending on the different significance level, different type of outlier, the number of outlier, magnitude of outlier, number of observations and the number of unknowns. In statistics, the power of test is the probability of rejecting the null hypothesis when the null hypothesis is false. It is a theoretical assumption and depends on the significance level α (Type I error) and β (Type II error). The different types of the outliers, such as random or non-random, affect the results of the test methods; but the power of test is the same for all different types of the outliers. In this study, empirical estimation of the power of test is presented as Mean Success Rate (MSR). The theoretical power of test and empirical MSR have been estimated for univariate model and linear model by using Baarda test; according to the obtained results, MSR can be used as empirical value of the power of test and capacity of the test models. Also, MSR reflects more realistic results than the theoretical power of test. PubDate: 2019-01-01 DOI: 10.1007/s11200-018-1144-9

Abstract: Changes in Terrestrial Water Storage (TWS) due to seasonal changes in soil moisture, ice and snow loading and melting influence the Earth’s inertia tensor. Quantitative assessment of hydrological effects of polar motion remains unclear because of the lack of the observations and differences between various atmospheric and ocean models. We compare the effects of several hydrological excitation functions computed as the difference between the excitation function of polar motion Geodetic Angular Momentum (GAM) and joint atmospheric plus oceanic excitation functions, called geodetic residuals. Geodetic residuals are computed for different Atmospheric Angular Momentum (AAM) and Oceanic Angular Momentum (OAM) models and are analyzed and compared with the hydrological excitation function determined from the Land Surface Discharge Model. They are analyzed on decadal, interannual, seasonal and non-seasonal time scales. The equatorial components of hydrological geodetic excitation functions χ1 and χ2 are decomposed into prograde and retrograde time series by applying Complex Fourier Transform Models. The agreement between hydrological geodetic residuals and excitation functions is validated using Taylor diagrams. This shows that agreement is highly dependent on AAM and OAM models. Errors in these models affect the resulting geodetic residuals and have a strong impact on the Earth’s angular momentum budget. PubDate: 2019-01-01 DOI: 10.1007/s11200-018-1028-z

Abstract: Earth’s polar motion predictions are essential in near real-time applications including spacecraft navigation and satellite orbit determinations and are also important for geophysics studies. It has previously been demonstrated that the basic problem in predicting a polar motion time-series is to treat separately its low- and high-frequency components. In this paper, this problem is solved by the combination of wavelet transform with the least-squares (LS) extrapolation and autoregressive (AR) method. Wavelet transform is first employed to separate the deterministic low-frequency components including the Chandler and annual wobbles and irregular short-period high-frequency components of a polar motion time-series. Then the deterministic parts are predicted using LS extrapolation of models for the linear trend, Chandler and annual wobbles, while the remaining irregular parts together with LS residuals are forecasted using the AR stochastic method. The polar motion predictions are computed as a combination of the LS extrapolation and AR prediction. The results show that the polar motion predictions up to 360 days in the future obtained by this approach can be remarkably enhanced due to the use of the wavelet-based preprocessing procedure. We conclude that the separate treatment of low- and high-frequency components is of use to enhance polar motion predictions. PubDate: 2019-01-01 DOI: 10.1007/s11200-018-1026-1

Abstract: Aeolian loess is carried by wind and undergoes pedogenesis after deposition. Therefore, both detrital components from the source region and soil pedogenic components contribute to the magnetic properties of the loess. The pedogenic component can be identified by analyzing the coercivity spectra of loess with different degrees of pedogenesis. We used isothermal remanent magnetization acquisition curves to analyze the coercivity spectra of loess in China and Siberia and defined the low (<30 mT), medium (60–100 mT) and high (>100 mT) coercivity components, i.e., components 1, 2, and 3, respectively. In the arid region of Xinjiang, Northwest China, the Bole section, with negligible soil development has loess with only component 2 centered at ∼80 mT. In semiarid central China, the Xifeng section has both loess and paleosols with three coercivity components centered at ∼26 mT, ∼82 mT, and ∼960 mT. Component 1 has a pedogenic origin, and the remanence contribution increases in a positive linear relationship with the intensity of pedogenesis. In the humid region of Siberia, the Kurtak section has three coercivity components are centered at ∼23 mT, ∼78 mT, and ∼1014 mT. The remanence contribution of component 1 shows a low correlation with the intensity of pedogenesis. Component 3 is characterized by high-coercivity minerals and its remanence contribution is related to the intensity of pedogenesis. The soil development in the semi-arid Xifeng section tends to produce massive fine-grained ferromagnetic minerals, so the remanence contribution of component 1 is positively correlated with the intensity of pedogenesis. The humid pedogenic environment of the Kurtak section is prone to form high-coercivity minerals and destroys fine-grained ferromagnetic minerals, so the remanence contribution of component 3 increases with the degree of pedogenesis. PubDate: 2019-01-01 DOI: 10.1007/s11200-018-0915-7

Abstract: The paper presents the results of coordinates determination for some satellite laser ranging (SLR) stations in the new ITRF2014 system based on LAGEOS-1 and LAGEOS-2 satellite data. The analysis was conducted in two variants. In the first one, coordinates of the SLR stations were estimated with the use of the nominal values of the tidal parameters: h2 = 0.6078 and l2 = 0.0847 (i.e. the standard International Earth Rotation and Reference Systems Service recommended values). In the second, coordinates of the SLR stations were calculated with the use of values of the tidal parameters estimated in the author’s previous paper: h2 = 0.6140 and l2 = 0.0876 (determined from the LAGEOS-1 and LAGEOS-2 data). The influence of the tidal parameters changes on the computation of the stations’ coordinates was investigated. The maximum differences (X, Y, Z(Variant 1) — X, Y, Z(Variant 2)) of about 4 mm, were achieved for Z component for Yarragadee (station ID 7090) and Monument Peak (7110) and of about 3 mm for Y component for Yarragadee (7090) and Changchun (7237) stations. All calculations related to determining the satellite orbits and the SLR stations’ coordinates were carried out with the use of the GEODYN II NASA/GSFC software. PubDate: 2019-01-01 DOI: 10.1007/s11200-018-1174-3

Abstract: The paper is motivated by the role of boundary value problems in Earth’s gravity field studies. The discussion focuses on Neumann’s problem formulated for the exterior of an oblate ellipsoid of revolution as this is considered a basis for an iterative solution of the linear gravimetric boundary value problem in the determination of the disturbing potential. The approach follows the concept of the weak solution and Galerkin’s approximations. The solution of the problem is approximated by linear combinations of basis functions with scalar coefficients. The construction of Galerkin’s matrix for basis functions generated by elementary potentials (point masses) is discussed. Ellipsoidal harmonics are used as a natural tool and the elementary potentials are expressed by means of series of ellipsoidal harmonics. The problem, however, is the summation of the series that represent the entries of Galerkin’s matrix. It is difficult to reduce the number of summation indices since in the ellipsoidal case there is no analogue to the addition theorem known for spherical harmonics. Therefore, the series representation of the entries is analyzed. Hypergeometric functions and series are used. Moreover, within some approximations the entries are split into parts. Some of the resulting series may be added relatively easily, apart from technical tricks. For the remaining series the summation is converted to elliptic integrals. The approach makes it possible to deduce a closed (though approximate) form representation of the entries in Galerkin’s matrix. The result rests on concepts and methods of mathematical analysis. In the paper it is confronted with a direct numerical approach applied for the implementation of Legendre’s functions. The computation of the entries is more demanding in this case, but conceptually it avoids approximations. Some specific features associated with function bases generated by elementary potentials in case of the ellipsoidal solution domain are discussed. PubDate: 2019-01-01 DOI: 10.1007/s11200-017-1083-x

Abstract: The application of seismic interferometry provides a new approach to obtain useful information of subsurface structures using noise data. In this study we investigate the feasibility of passive seismic interferometry in anisotropic media. We simulate long duration passive noise measurements for a model containing a transversely isotropic layer with vertical symmetry axis (VTI) using the staggered-grid finite-difference method. Then we extract the Green’s functions using the cross-correlation method. Even for VTI media, various reflections and multiples can be reconstructed, and the arrival times of these reflections correspond well with the directly modelled responses. By changing the noise source configuration and anisotropic parameters, we explore the impacts of these factors on the interferometry record. The results show that noise source configuration has considerable influence on the quality of the retrieved response, especially for S-wave reflection events. Since long time ago, passive measurements recorded from a number of noise sources provide sufficient stationary phase points to retrieve the reflections; the effect of anisotropic parameters is small. The Hess VTI model demonstrates that passive seismic interferometry is feasible to wide range of anisotropic parameters and complex subsurface structures. Moreover, a migrated image is obtained from the retrieved virtual source gathers using reverse time migration, and the subsurface structures are imaged well. The synthetic results demonstrate that passive seismic interferometry is applicable to anisotropic media and that the interferometry results can be used to image subsurface structures. PubDate: 2019-01-01 DOI: 10.1007/s11200-017-0754-y

Abstract: In many modern local and regional gravity field modelling concepts, the short-wavelength gravitational signal modeled by the residual terrain modelling (RTM) technique is used to augment global geopotential models, or to smooth observed gravity prior to data gridding. In practice, the evaluation of RTM effects mostly relies on a constant density assumption, because of the difficulty and complexity of obtaining information on the actual distribution of density of topographic masses. Where the actual density of topographic masses deviates from the adopted value, errors are present in the RTM mass-model, and hence, in the forward-modelled residual gravity field. In this paper we attempt to overcome this problem by combining the RTM technique with a high-resolution mass-density model. We compute RTM gravity quantities over New Zealand, with different combinations of elevation models and mass-density assumptions using gravity and GPS/levelling measurements, precise terrain and bathymetry models, a high-resolution mass-density model and constant density assumptions as main input databases. Based on gravity observations and the RTM technique, optimum densities are detected for North Island of ~2500 kg m−3, South Island of ~2600 kg m−3, and the whole New Zealand of ~2590 kg m−3. Comparison among the three sets of residual gravity disturbances computed from different mass-density assumptions show that, together with a global potential model, the high-resolution New Zealand density model explains ~89.5% of gravitational signals, a constant density assumption of 2670 kg m−3 explains ~90.2%, while a regionally optimum mass-density explains ~90.3%. Detailed comparison shows that the New Zealand density model works best over areas with small residual heights. Over areas with larger residual heights, subsurface density variations appear to affect the residual gravity disturbance. This effect is found to reach about 30 mGal over Southern Alpine Fault. In order to improve the RTM modelling with mass-density maps, a higher-quality mass-density model that provides radially varying mass-density data would be desirable. PubDate: 2018-10-01 DOI: 10.1007/s11200-017-0656-z

Abstract: Magnetic measurements of soils are an effective research tool in assessing soil erosion. This approach is based on detecting layers showing different magnetic properties in vertical soil profiles and lateral catenas. The objective of this research is to compile data on magnetic susceptibility (MS) of soils in Eastern Ukraine to assess the soil erosion rates. The chernozems of Tcherkascy Tishki (Kharkov Region, Ukraine) have undergone a field crop rotation without proper soil conservation technologies being applied. We conducted an intrinsic element grouping of the magnetic susceptibility values and demonstrated that they can be used as MS cartograms in soil erosion mapping. The study showed a strong correlation between the MS values and the erosion index. MS and the erosion index were found to correlate with the humus content. Magnetic mineralogical analyses suggest the presence of highly magnetic minerals (magnetite and maghemite) as well as weakly magnetic goethite, ferrihydrite, and hematite. Stable pseudosingle-domain (PSD), single-domain (SD), and superparamagnetic (SP) grains of pedogenic origin dominate in the studied chernozems. Being an effective, quick and low cost alternative, magnetic methods can be successfully used in the soil erosion investigations. PubDate: 2018-10-01 DOI: 10.1007/s11200-018-0803-1

Abstract: In this paper we analyze the scale of the DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite) solutions with respect to DORIS extension of the International Terrestrial Reference Frame (ITRF) for Precise Orbit Determination DPOD2014. The main goal is to explain the scale inconsistencies and to find the optimal solution reaching low-biased and consistent scale time series. Our analysis profits from 4 different strategies based only on the Geodetic Observatory Pecný analysis center solution, using DORIS exchange format data 2.2. A difference in the sequence of the solutions directly corresponds to one of the changes in the solution settings: data elevation dependent weighting, application of data validity indicators and application of phase center - reference point correction. We process multi-satellite and single-satellite solutions for the time period 2011.0–2017.0. Our analysis examines scale inconsistency issues in 2011/2012 and in 2015. The scale increment in 2011/2012 is explained as a result of the concurrence of changes in satellite constellation and change in the provider data validity standards for Cryosat-2 and Jason-2 satellites. The scale increment in 2015 is explained as the effect of change in the standards for phase center - reference center corrections for Saral, Jason-2 and Cryosat-2 satellites. Moreover, comparing the solutions with and without elevation dependent data downweighting using the same elevation cutoff (10°), we found a significant reduction of scale bias and scale variation applying the data downweighting. The data downweighting improved also the station positioning repeatability. We demonstrate that the solution, which is completely free from the additional data associated with observations in DORIS exchange format 2.2 and includes the data downweighting law, eventuates in a consistent scale time series with the lowest offset with respect to DPOD2014 (version 1.0) (12.7 ± 2.3 mm for 2011.0–2017.0). The only remaining scale issue is the part of 2011/2012 increment of around 5 mm, explained by a change in the DORIS satellite constellation. PubDate: 2018-10-01 DOI: 10.1007/s11200-018-0406-x

Abstract: The Moho information under Tibet Plateau is important for a better understanding of the geodynamic processes associated with the continental collision of the Indian and Eurasian tectonic plates and subsequent formation of Himalayan and Tibetan orogens. However, under the central and western parts of Tibet, the existing Moho models are still relatively inaccurate due to a sparse and irregular distribution of seismic surveys. To overcome this problem, the gravimetric data could be used to interpolate the Moho information, where seismic data are missing. In this study, we apply the gravimetric method for a regional Moho recovery under Tibet. Compared to existing methods that use either the gravity or gravity-gradient data, the method presented here utilizes a more generic definition based on a functional relation between the Moho depth and the gravitational potential. Since the gravity and gravity-gradient data have more regional support than the potential field, a numerical test is conducted to find an optimal data area extension that is needed to solve a regional inversion problem in order to reduce errors caused by disregarding the far-zone contribution. Our analysis shows that for the potential field such extension should be at least 25°, while 5° for the gravity and only about 1° for the gravity gradient. The comparison of our gravimetric result with the CRUST1.0 seismic model shows differences at the level of expected accuracy of the gravimetric method of about 5 km and without the presence of significant bias. PubDate: 2018-10-01 DOI: 10.1007/s11200-017-0812-5

Abstract: Simultaneous sources acquisition, also referred to as “blended acquisition”, involves recording two or more shots simultaneously. It allows for denser spatial sampling and can greatly speed up the field data acquisition. Thus, it has potential advantage to improve seismic data quality and reduce acquisition cost. In order to achieve the goal of blended acquisition, a deblending procedure is necessary. It attenuates the interference and thus improves the resolution of the pre-stack time migration image. In this paper, we propose an efficient deblending method, which applies frequency-varying median and mean filters to cross-spread azimuth-offset gathers (XSPR-AO). The method can be used with variable window sizes according to the characteristics of the interference. The effectiveness of the method is validated by a field data example. PubDate: 2018-10-01 DOI: 10.1007/s11200-017-0374-6

Abstract: The local tie vector, which connects the different space geodetic techniques at a co-located site, plays an important role in the realization of the International Terrestrial Reference Frame (ITRF). This paper presents a new method to determine the tie vector between the GNSS and very long baseline interferometry tracking points. The parameters of the local tie vector and the axes offsets are introduced into constraint equations. The parameters are then resolved using the 3D constrained least squares adjustment. With the surveying data collected at two different sites (Kunming and Urumqi) in China, the proposed method can precisely determine the local tie vectors in a geocentric frame. The root mean square error (RMSE) is (1.2, 2.3 and 1.5 mm) and (1.0, 1.5 and 1.4 mm) for the three coordinate components at the sites in Kunming and Urumqi, respectively. The offset between the primary and secondary axes of the VLBI telescopes is estimated to be 7.5 mm in Kunming’s site and 4.0 mm in Urumqi’s site, and the corresponding RMSE is 1.8 mm and 2.0 mm for the two sites, respectively. PubDate: 2018-10-01 DOI: 10.1007/s11200-017-0461-8

Abstract: The planet Earth is continuously changing in time, so there are phenomena that require continuous observation, including tidal parameters. The main goal of this study is to analyze time changes of the Love potential tidal parameters. This paper concerns an analysis of the estimated Love numbers k for the second and the third degree tides (numbers k2 and k3), associated with the tide variations of the satellite motion. The measured data used for determining the parameters k2, k3 were conducted within the period of January 1, 2014 until July 1, 2016 by LAGEOS-1 and LAGEOS-2 satellites. The results were compared with our previous determination of these parameters from LAGEOS data during the period from January 1, 2005 until July 1, 2007 to examine whether any systematic differences and time evolution occur. The adjusted values for k2 equalling 0.29842 ± 0.00008 and k3 equalling 0.0901 ± 0.0034 are discussed and compared with the nominal values given in International Earth Rotation and Reference Systems Service standards. The differences between the k2 and k3 values obtained for the time interval 2005.0–2007.5 and the results for 2014.0–2016.5 interval are –0.00288 for k2 and 0.0042 for k3. The obtained differences in the k2 and k3 values may indicate their evolution in time. PubDate: 2018-10-01 DOI: 10.1007/s11200-018-0610-8

Abstract: The western part of the Bohemian Massif hosts an intersection of two regional fault zones, the SW-NE trending Ohře/Eger Graben and the NNW-SSE trending Mariánské Lázně Fault, which has been reactivated several times in the geological history and controlled the formation of the Tertiary Cheb Basin. The broader area of the Cheb Basin is also related to permanent seismic activity of ML 3+ earthquake swarms. The Eastern Marginal Fault of the Cheb Basin (northern segment of the Mariánské Lázně Fault) separates the basin sediments and underlying granites in the SW from the Krušné Hory/Erzgebirge Mts. crystalline unit in the NE. We describe a detailed geophysical survey targeted to locating the Eastern Marginal Fault and determining its geometry in the depth. The survey was conducted at the Kopanina site near the Nový Kostel focal zone, which shows the strongest seismic activity of the whole Western Bohemia earthquake swarm region. Complex geophysical survey included gravimetry, electrical resistivity tomography, audiomagnetotellurics and seismic refraction. We found that the rocks within the Eastern Marginal Fault show low resistivity, low seismic velocity and density, which indicates their deep fracturing, weathering and higher water content. The dip of the fault in shallow depths is about 60° towards SW. At greater depths, the slope turns to subvertical with dip angle of about 80°. Results of geoelectrical methods show blocky fabric of the Cheb Basin and deep weathering of the granite bedrock, which is consistent with geologic models based on borehole surveys. PubDate: 2018-10-01 DOI: 10.1007/s11200-017-0452-9

Abstract: The aim of this research is the optimal determination of the regional geoid model of Iran based on radial basis functions (RBFs). In this case, the type and number of RBFs, their horizontal positions, depths, and unknown coefficients must be properly determined. The quality of calculations strongly depends on the correct choice of these unknown parameters. Given the precise geocentric position of any point on the Earth’s surface with the beginning of the global navigation satellite system (GNSS), the surface gravity disturbances were used to calculate the height anomaly according to Molodensky’s theory. The residual surface gravity disturbances derived by subtracting the global gravitational model EIGEN-6C4 up to degree and order 360 were applied to determine the unknown RBF parameters using the stabilized orthogonal matching pursuit (SOMP) algorithm. Based on this iterative sparse approach, non-zero components of unknown RBF parameters having the maximum recoverable energy for the desired signal were found at each iteration. The SOMP algorithm was applied for optimal determination of the proper basis functions since each unknown RBF coefficient is related to a specific basis function. Only the RBFs representing the best solution to the problem were selected at each iteration, then several new RBFs were added at suitable positions to enhance the calculation result. The new RBF-based regional geoid model entitled IRG2016 was calculated by applying the geoid-to-quasigeoid corrections to the height anomaly. The IRG2016 was fitted to 1288 GNSS/levelling control points over Iran, by applying the polynomial corrector surface. Relying on this new strategy, the calculated height reference surface shows an RMS value of approximately 0.23 m for the difference in geoidal height at the independent control points, which is comparable with the last Stokes-based geoid model. PubDate: 2018-07-01 DOI: 10.1007/s11200-016-0679-x