GPS-levelling Data Research Articles

Validation of high-resolution global geopotential models over Sri Lanka using ground gravity & GPS-levelling data

Validation of high-resolution global geopotential models over Sri Lanka using ground gravity & GPS-levelling data

Quantifying the individual contributions of GOCE gradients for regional quasi-geoid modeling in a relatively rough topography

Gravity field and steady-state Ocean Circulation Explorer (GOCE) is the first satellite mission that measures the gravity gradients (GGs) in space with primary objective of determining the gravity field of the Earth with maximum spatial resolution and accuracy. GOCE GGs have been used for the computation of global gravity field models (GGMs) represented by the surface spherical harmonics for about 10 years. However, they may potentially improve the regional quasi-geoid solutions computed from terrestrial gravity and a Global Geopotential Model (GGM) particularly in mountainous areas with rough gravity field. This study exploits the full signal content in the GOCE Level-2 GGs given in Local North-Oriented Frame for improved regional quasi-geoid modeling in Auvergne test area located in France. The least squares collocation method is used in single-input and single-output (SISO) mode where the input is the residual terrestrial gravity data corrected for GGM contribution and residual terrain modeling effects, and also in multiple-input and single-output mode (MISO) where the terrestrial data input is augmented with the four precise GOCE GGs or their combinations. The single outputs for both modes are the quasi-geoid heights at 75 GPS collocated leveling benchmarks distributed in the central area and at 7857 Digital Elevation Model (DEM) points covering the whole area. The combination of the terrestrial gravity with the GOCE along-track gradient, having a lower noise level than the others, gives the best results when a single gradient is used. The further incorporation of the off-diagonal gradient to the along-track gradient results in the best MISO solution showing improvements with respect to the SISO solution only at GPS/leveling benchmarks near a large data gap. Intercomparison of the best MISO and SISO solutions at the DEM points suggests substantial quasi-geoid differences up to 13.6 cm in areas of sparse or no gravity data near the Alps where these results could not be assessed due to the lack of GPS-leveling data.

Empirical comparison between stochastic and deterministic modifiers over the French Auvergne geoid computation test-bed

Since 2006, several different groups have computed geoid and/or quasigeoid (quasi/geoid) models for the Auvergne test area in central France using various approaches. In this contribution, we compute and compare quasigeoid models for Auvergne using Curtin University of Technology’s and the Swedish Royal Institute of Technology’s approaches. These approaches differ in many ways, such as their treatment of the input data, choice of type of spherical harmonic model (combined or satellite-only), form and sequence of correction terms applied, and different modified Stokes’s kernels (deterministic or stochastic). We have also compared our results with most of the previously reported studies over Auvergne in order to seek any improvements with respect to time [exceptions are when different subsets of data have been used]. All studies considered here compare the computed quasigeoid models with the same 75 GPS-levelling heights over Auvergne. The standard deviation for almost all of the computations (without any fitting) is of the order of 30–40 mm, so there is not yet any clear indication whether any approach is necessarily better than any other nor improving over time. We also recommend more standardisation on the presentation of quasi/geoid comparisons with GPS-levelling data so that results from different approaches over the same areas can be compared more objectively.

Numerical Simulation Study on the Influence of Branching Structure of Longmen Shan Thrust Belt on the Nucleation of Mw7.9 Wenchuan Earthquake

On the Longmen Shan thrust belt (LMS) on the eastern margin of Tibet Plateau, the Mw7.9 Wenchuan earthquake occurred in 2008. As for the dynamic cause of the Wenchuan earthquake, many scholars have studied the rheological difference and terrain elevation difference on both sides of the fault. However, previous studies have simplified the LMS as a single listric-reverse fault. In fact, the LMS is composed of four faults with different dip angles in the shallow part, and the faults are Wenchuan-Maoxian fault (WMF), Yingxiu-Beichuan fault (YBF), Guanxian-Jiangyou fault (GJF) and Range Front Thrust (RFT) from west to east. However, the control of the branching structure of these faults on the distribution and accumulation of stress and strain during the seismogenic of the Wenchuan earthquake has not been discussed. In this paper, four viscoelastic finite element models with different fault numbers and combination structures are built to analyze the effect of fault branching structures on the stress distribution and accumulation during the seismogenic of Wenchuan earthquake, and we use geodetic data such as GPS and precise leveling data to constrain our models. At the same time, we also study the influence of the existence of the detachment layer, which is formed by the low-resistivity and low-velocity layer, between the upper and lower crust of the Bayan Har block and the change of its frontal edge position on the stress accumulation and distribution. The results show that the combinations of YBF and GJF is most conducive to the concentration of equivalent stress below the intersection of the two faults, and the accumulated stress on GJF is shallower than that on YBF, which means that more stress is transferred to the surface along GJF; and the existence of a detachment layer can effectively promote the accumulation of stress at the bottom of YBF and GJF, and the closer the frontal edge position of the detachment layer is to the LMS fault, the more favorable the stress accumulation is. Based on the magnitude of stress accumulation at the bottom of the intersection of YBF and GJF, we speculate that the frontal edge position of the detachment layer may cross YBF and expand eastward.

A refined slip distribution of the 2013 Mw 6.7 Lushan, China earthquake constrained by GPS and levelling data

SUMMARYThe 2013 Lushan Mw 6.7 earthquake is the largest blind thrust event ever occurred on the southern segment of the Longmen Shan fault system. It has attracted extensive attention since it occurred 5 yr later following the 2008 Mw 7.8 Wenchuan destructive earthquake in this region. However, its slip distribution is still on debate due to the complex tectonic settings and limited near-field observations. In this study, we added some near-field GPS data, together with previously published GPS data and levelling data, and take consideration of possible coseismic and post-seismic effects caused by the 2008 Wenchuan earthquake, to construct a more accurate horizontal and vertical coseismic surface displacement field associated with the 2013 Lushan earthquake with a better spatial coverage. Then we invert for a refined slip distribution based on a flat-ramp-flat fault suggested by the relocated aftershock sequence and seismic imaging. Our preferred fault plane is striking southwest with 211° and dipping at varying angles of 4°, 35° and 12° separately for such a flat-ramp-flat geometry. The main rupture is roughly characterized by two asperities, including a round disk on the ramp with larger slips and an adjoining oval asperity on the shallow flat with smaller slips. The maximum slip is 1.2 m at 14.3 km focal depth, located at ∼20 km to the northwest of the GCMT epicentre. The released geodetic moment is 1.50 $\ \times $ 1019 Nm, equivalent to a Mw 6.7 earthquake. The slips on the fault plane clearly illustrate that this event is dominated by the thrusting and minor striking, which is consistent with its tectonic settings. Furthermore, if we assume the 2013 Mw 6.7 Lushan event to be the characteristic earthquake on the southern section of the Longmen Shan thrust zone, the accumulated strain should not be fully released by this strong event, and a potential seismic risk still exists in this region.

Performance Comparison of Geoid Refinement between XGM2016 and EGM2008 Based on the KTH and RCR Methods: Jilin Province, China

The selection of an appropriate global gravity field model and refinement method can effectively improve the accuracy of the refined regional geoid model in a certain research area. We analyzed the accuracy of Experimental Geopotential Model (XGM2016) based on the GPS-leveling data and the modification parameters of the global mean square errors in the KTH geoid refinement in Jilin Province, China. The regional geoid was refined based on Earth Gravitational Model (EGM2008) and XGM2016 using both the Helmert condensation method with an RCR procedure and the KTH method. A comparison of the original two gravity field models to the GPS-leveling benchmarks showed that the accuracies of XGM2016 and EGM2008 in the plain area of Jilin Province are similar with a standard deviation (STD) of 5.8 cm, whereas the accuracy of EGM2008 in the high mountainous area is 1.4 cm better than that of XGM2016, which may be attributed to its low resolution. The modification parameters between the two gravity field models showed that the coefficient error of XGM2016 model was lower than that of EGM2008 for the same degree of expansion. The different modification limits and integral radii may produce a centimeter level difference in global mean square error, while the influence of the truncation error caused by the integral was at the millimeter level. The terrestrial gravity data error accounted for the majority of the global mean square error. The optimal least squares modification obtained the minimum global mean square error, and the global mean square error calculated based on XGM2016 model was reduced by about 1~3 cm compared with EGM2008. The refined geoid based on the two gravity field models indicated that both KTH and RCR method can effectively improve the STD of the geoid model from about six to three centimeters. The refined accuracy of EGM2008 model using RCR and KTH methods is slightly better than that of XGM2016 model in the plain and high mountain areas after seven-parameter fitting. EGM2008 based on the KTH method was the most precise at ± 2.0 cm in the plain area and ± 2.4 cm in the mountainous area. Generally, for the refined geoid based on the two Earth gravity models, KTH produced results similar to RCR in the plain area, and had relatively better performance for the mountainous area where terrestrial gravity data is sparse and unevenly distributed.

Surface modelling by geoid determination for flood control of Ewekoro limestone deposit (Nigeria)

Purpose. To determine the geoid heights from various control points of the quarry located in the northern and southern zones of the limestone deposit of the Lafarge WAPCO Cement Ewekoro in Ogun State, Nigeria. Methodology. The GPS and levelling data were used to determine the geoid heights from various control points of the quarry located in the northern and southern zones of the limestone deposit. The geoid heights obtained from GPS-Levelling data were used for three surface models which are polynomial regression model, inverse distance model and nearest neighbour model. These models were used to crossvalidate the geoid heights for the control points. Findings. The result shows that the deviations of the geoid heights for the GPS/Levelling and models are between 0.03 and 0.01m respectively. The models were used to generate contour maps that reveal the better location where the flood can be channelled. Originality. The results can be compared to the data obtainable during operations carried out in the quarry. Practical value. The flood in the quarry face will be better controlled by creating a sump at the lowest point on the elevation maps and controlled drilling to give better aeration.

Audit of stored strain energy and extent of future earthquake rupture in central Himalaya

The deadly 25 April 2015 Gorkha earthquake (Mw = 7.8) and aftershocks have partially released the accumulated interseismic strain along the Main Himalayan Thrust (MHT). Postseismic deformation associated with this earthquake is mainly confined to the north of the rupture. This suggests possible occurrence of future large events towards west or south, where MHT is locked. Asperities arising due to heterogeneity in the stress-strain patterns are believed to play a major role in controlling the coseismic rupture propagation. We determine interseismic coupling along the MHT and spatial variations in total strain rate using two decades of GPS, InSAR and sprit leveling data. Further, b-values derived from the seismicity data are used to identify zones of stress accumulation. We demonstrate that the 2015 earthquake ruptured an asperity which hosted high strain and stress accumulation prior to the event. A similar asperity towards west of the epicenter with unreleased strain energy is identified. This could spawn a future large earthquake akin in magnitude to the 2015 Gorkha event. These findings compel a revisit of the seismic hazard assessment of the central Himalaya.

Present-day crustal deformation and strain transfer in northeastern Tibetan Plateau

The three-dimensional present-day crustal deformation and strain partitioning in northeastern Tibetan Plateau are analyzed using available GPS and precise leveling data. We used the multi-scale wavelet method to analyze strain rates, and the elastic block model to estimate slip rates on the major faults and internal strain within each block. Our results show that shear strain is strongly localized along major strike-slip faults, as expected in the tectonic extrusion model. However, extrusion ends and transfers to crustal contraction near the eastern margin of the Tibetan Plateau. The strain transfer is abrupt along the Haiyuan Fault and diffusive along the East Kunlun Fault. Crustal contraction is spatially correlated with active uplifting. The present-day strain is concentrated along major fault zones; however, within many terranes bounded by these faults, intra-block strain is detectable. Terranes having high intra-block strain rates also show strong seismicity. On average the Ordos and Sichuan blocks show no intra-block strain, but localized strain on the southwestern corner of the Ordos block indicates tectonic encroachment.

The New Zealand gravimetric quasigeoid model 2017 that incorporates nationwide airborne gravimetry

A one arc-minute resolution gravimetric quasigeoid model has been computed for New Zealand, covering the region $$25^{\circ }\hbox {S}$$ – $$60^{\circ }\hbox {S}$$ and $$160^{\circ }\hbox {E}$$ – $$170^{\circ }\hbox {W}$$ . It was calculated by Wong and Gore modified Stokes integration using the remove–compute–restore technique with the EIGEN-6C4 global gravity model as the reference field. The gridded gravity data used for the computation consisted of 40,677 land gravity observations, satellite altimetry-derived marine gravity anomalies, historical shipborne marine gravity observations and, importantly, approximately one million new airborne gravity observations. The airborne data were collected with the specific intention of reinforcing the shortcomings of the existing data in areas of rough topography inaccessible to land gravimetry and in coastal areas where shipborne gravimetry cannot be collected and altimeter-derived gravity anomalies are generally poor. The new quasigeoid has a nominal precision of $$\pm \,48\,\hbox {mm}$$ on comparison with GPS-levelling data, which is approximately $$14\,\hbox {mm}$$ less than its predecessor NZGeoid09.

HUST-Grace2016s: A new GRACE static gravity field model derived from a modified dynamic approach over a 13-year observation period

The modified dynamic approach, where the observation vector and design matrix of observation equation are simultaneously filtered by empirical parameters, is implemented in this study. Using approximately 13years (spanning from January 2003 to April 2015) of Gravity Recovery and Climate Experiment (GRACE) Level 1B data published by JPL and kinematic orbits published by ITSG, we developed a new GRACE static gravity field model called HUST-Grace2016s complete to degree and order 160. To evaluate the quality of our model, other GRACE-only gravity field models including AIUB-GRACE03S, GGM05S, ITG-Grace2010s, ITSG-Grace2014s and Tongji-GRACE01, are introduced for comparison. The difference degree amplitudes in terms of geoid height of our HUST-Grace2016s relative to GOCO05c are smaller than 1mm and 1cm before degree 100 and degree 138, respectively. In terms of global gravity anomalies and geoid heights relative to GOCO05c, the RMS values of our model up to degree 140 are 4.31cm and 0.87mGal respectively, which are smaller compared to AIUB-GRACE03S, GGM05S and Tongji-GRACE01. In addition, validated with GPS-leveling data in North America and the Netherlands, the standard deviation values of our HUST-Grace2016s model are 46.56cm and 24.80cm respectively, which also performs better than AIUB-GRACE03S, GGM05S and Tongji-GRACE01.

A GOCE only gravity model GOSG01S and the validation of GOCE related satellite gravity models

We compile the GOCE-only satellite model GOSG01S complete to spherical harmonic degree of 220 using Satellite Gravity Gradiometry (SGG) data and the Satellite-to-Satellite Tracking (SST) observations along the GOCE orbit based on applying a least-squares analysis. The diagonal components (Vxx, Vyy, Vzz) of the gravitational gradient tensor are used to form the system of observation equations with the band-pass ARMA filter. The point-wise acceleration observations (ax, ay, az) along the orbit are used to form the system of observation equations up to the maximum spherical harmonic degree/order 130. The analysis of spectral accuracy characteristics of the newly derived gravitational model GOSG01S and the existing models GOTIM04S, GODIR04S, GOSPW04S and JYY_GOCE02S based on their comparison with the ultra-high degree model EIGEN-6C2 reveals a significant consistency at the spectral window approximately between 80 and 190 due to the same period SGG data used to compile these models. The GOCE related satellite gravity models GOSG01S, GOTIM05S, GODIR05S, GOTIM04S, GODIR04S, GOSPW04S, JYY_GOCE02S, EIGEN-6C2 and EGM2008 are also validated by using GPS-leveling data in China and USA. According to the truncation at degree 200, the statistic results show that all GGMs have very similar differences at GPS-leveling points in USA, and all GOCE related gravity models have better performance than EGM2008 in China. This suggests that all these models provide much more information on the gravity field than EGM2008 in areas with low terrestrial gravity coverage. And STDs of height anomaly differences in China for the selected truncation degrees show that GOCE has improved the accuracy of the global models beyond degree 90 and the accuracies of the models improve from 24 cm to 16 cm. STDs of geoid height differences in USA show that GOSG01S model has best consistency comparing with GPS-leveling data for the frequency band of the degree between 20 and 160.

Estimation of north Tabriz fault parameters using neural networks and 3D tropospherically corrected surface displacement field

ABSTRACTIn this paper, parameters of north Tabriz fault are studied using 3D displacement field and artificial neural networks (ANNs). We provide the 3D surface displacement along the north Tabriz fault using an integration of tropospherically corrected InSAR, GPS and precise levelling data. To perform the InSAR analysis, we use the 17 ENVISAT radar acquisitions. The line of sight (LOS) displacement field was corrected using the ERA-Interim global meteorological reanalysis models. In order to calculate the 3D displacement, we use a Simultaneous and Integrated Strain Tensor Estimation from Geodetic and Satellite Deformation Measurements approach. ANNs used to estimate the parameters. 3D displacement field and ANN algorithm yields an average slip rate of 6.1 ± 0.01 mm/year with a locking depth of 13.4 ± 0.01 km. This rate is consistent with previous geodetic estimates based on recent global positioning system measurements and InSAR analysis. In addition, the length, width and dip angle of fault are about 101.2 ± 0.01 km, 25.06 ± 0.03 km and 63 ± 0.05 deg. This study demonstrates that interseismic displacement with a sub-centimetre rate can be successfully detected by integration of multi temporal InSAR techniques, GPS and precise leveling data and shows that ANN algorithm is suitable for estimating the parameters of north Tabriz fault.

Determination of geopotential value W0L at Polish tide gauges from GNSS data and geoid model

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.

Assessment of Gravity Field and Steady State Ocean Circulation Explorer (GOCE) geoid model using GPS levelling over Sabah and Sarawak

The GOCE satellite mission has significantly contributed to various applications such as solid earth physics, oceanography and geodesy. Some substantial applications of geodesy are to improve the gravity field knowledge and the precise geoid modelling towards realising global height unification. This paper aims to evaluate GOCE geoid model based on the recent GOCE Global Geopotential Model (GGM), as well as EGM2008, using GPS levelling data over East Malaysia, i.e. Sabah and Sarawak. The satellite GGMs selected in this study are the GOCE GGM models which include GOCE04S, TIM_R5 and SPW_R4, and the EGM2008 model. To assess these models, the geoid heights from these GGMs are compared to the local geometric geoid height. The GGM geoid heights was derived using EGMLAB1 software and the geometric geoid height was computed by available GPS levelling information obtained from the Department Survey and Mapping Malaysia. Generally, the GOCE models performed better than EGM2008 over East Malaysia and the best fit GOCE model for this region is the TIM_R5 model. The TIM_R5 GOCE model demonstrated the lowest R.M.S. of ± 16.5 cm over Sarawak, comparatively. For further improvement, this model should be combined with the local gravity data for optimum geoid modelling over East Malaysia.

Utilisation of Fast Fourier Transform and Least-squares Modification of Stokes formula to compile a gravimetric geoid model over Khartoum State: Sudan

We use Fast Fourier Transform (FFT) and least-squares modification (LSM) of Stokes formula to compute the geoid over Khartoum State in Sudan. The two methods (FFT and LSM) have been utilised to test their efficiency with respect to EGM08 and the local GPS-levelling data. The FFT method has many advantages, it is fast and it reduces the computational complexity. The modification of Stokes formula is widely used in geoid modelling; however, its implementation based on point-wise summation requires a considerable amount of time. In FFT, we combine the terrestrial gravity data and the global geopotential model (GGM) by means of a remove-compute-restore procedure and we successfully apply the modification of the Stokes formula in the least-squares sense. FFT and LSM geoid solutions are evaluated against EGM2008 and the GPS-levelling data. The analysis of the undulation differences shows that the LSM solution is more compatible with EGM08 and GPS-levelling data. The discrepancies of the differences are removed using a 4-parameter model, the standard deviation (STD) of the undulation differences of LSM decreased from 0.41 to 0.37 m and from 0.48 to 0.39 m for FFT solution. There is no significant impact to the LSM geoid when adding the additive corrections, while the FFT geoid solution is slightly improved when terrain correction is applied.

Implementation of a rigorous least-squares modification of Stokes’ formula to compute a gravimetric geoid model over Saudi Arabia (SAGEO13)

A gravimetric geoid model (SAGEO13) is computed for the Kingdom of Saudi Arabia using a rigorous stochastic computational method. The computational methodology is based on a combination of least-squares (LS) modification of Stokes’ formula and the additive corrections for topographic, ellipsoidal, atmospheric, and downward continuation effects on the geoid solution. In this study, we used terrestrial gravity data, a digital elevation model (SRTM3), and seven global geopotential models (GGMs) to compute a new geoid model for Saudi Arabia. The least-squares coefficients are derived based on the optimisation of the input modification parameters. The gravimetric solution and its additive corrections are computed based on the optimum LS coefficients. Compared to GPS-levelling data, SAGEO13 shows a fit of 18 cm (RMS) after using a 4-parameter fitting model.

Tongji-GRACE01: A GRACE-only static gravity field model recovered from GRACE Level-1B data using modified short arc approach

The modified short arc approach, where the position vector in force model are regarded as pseudo observation, is implemented in the SAtellite Gravimetry Analysis Software (SAGAS) developed by Tongji university. Based on the SAGAS platform, a static gravity field model (namely Tongji-GRACE01) complete to degree and order 160 is computed from 49months of real GRACE Level-1B data spanning the period 2003–2007 (including the observations of K-band range-rate, reduced dynamic orbits, non-conservative accelerations and altitudes). The Tongji-GRACE01 model is compared with the recent GRACE-only models (such as GGM05S, AIUB-GRACE03S, ITG-GRACE03, ITG-GRACE2010S, and ITSG-GRACE2014S) and validated with GPS-leveling data sets in different countries. The results show that the Tongji-GRACE01 model has a considered quality as GGM05S, AIUB-GRACE03S and ITG-GRACE03. The Tongji-GRACE01 model is available at the International Centre for Global Earth Models (ICGEM) web page (http://icgem.gfz-potsdam.de/ICGEM/).

Global Earth’s gravity field solution with GRACE orbit and range measurements using modified short arc approach

Traditionally, the Earth’s gravity field model is computed from GRACE orbit and range rate measurements, e.g., in a short arc approach where both the position and the velocity vectors are integrated from a force model. In this contribution, we use the GRACE orbit and range measurements to recover the Earth’s gravity field model, thus we only need to integrate the position vectors. We use the range differences between two adjacent epochs to eliminate the range ambiguities. Using GRACE Level-1B RL02 data released by Jet Propulsion laboratory, the gravity field model TJGRACE02O complete to degree and order 90 is developed from 7 years of reduced dynamic orbits covering the period 2004–2010, and the gravity field model TJGRACE02K complete to degree and order 120 is computed from 1 month of kinematic orbits and K-band range data of January. Comparing the degree geoid errors of our new models with recent gravity field models such as the CHAMP-only models EIGEN-CHAMP05S, AIUB-CHAMP03S, ULUX-CHAMP2013S and the GRACE-only models GGM05S, Tongji-GRACE01 as well as a monthly model from the ITG-GRACE2010 time series, and validating these models with GPS-leveling data sets in the USA, we can conclude that the TJGRACE02O model is more accurate than all the CHAMP-only models and TJGRACE02K is comparable in quality to the corresponding GRACE monthly model from ITG-GRACE2010.

Effect of ASTER DEM on the prediction of mean gravity anomalies: a case study over the Auvergne test region

A precise gravimetric geoid determination requires height information and terrestrial gravity data with high accuracy and resolution. The height data is utilized for predicting mean free-air gravity anomalies as well as computing the topographic, atmospheric and downward continuation effects which are fundamental components of any geoid model. Nowadays the Digital Elevation Model (DEM) obtained from the Shuttle Radar Topography Mission (SRTM) has been widely used when an accurate regional DEM does not exist. In addition the DEM generated from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) was newly released by researchers from Japan and United States. In this study the effect of ASTER DEM on the estimating mean free-air gravity anomalies in geoid determination were investigated in the Auvergne test area where one of its regions exhibits one of the most rugged topography over the world. The numerical results show that ASTER DEM gives worse statistics than SRTM DEM with respect to the accuracy of the height. Using ASTER DEM introduces discrepancies (compared to SRTM DEM) in the range of \(-\)4 to 10 mGal in the interpolation of free-air gravity anomalies. It is also proven that the geoid differences due to the use of ASTER DEM are a few centimeters, which remain below the accuracy level of the external GPS-levelling data.