Local geoid model of the Western Desert in Egypt using terrestrial gravity data and global geopotential models

2021 ◽  
Vol 14 (15) ◽  
Author(s):  
Mostafa Ahmed Elwan ◽  
Ahmad Helaly ◽  
Khaled Zharan ◽  
Elsayed Issawy ◽  
Ahmed Abd El-Gawad
Keyword(s):  
Gravity Data ◽  
Western Desert ◽  
Geoid Model ◽  
Terrestrial Gravity ◽  
Geopotential Models ◽  
Local Geoid

Accuracy Assessment of Recent High-Degree Global Geopotential Models Using Geodetic Control Points and Terrestrial Gravity Data in Turkey

2021 ◽  
Author(s):  
Muhammed Raşit Çevikalp ◽  
Bihter Erol ◽  
Bilal Mutlu ◽  
Serdar Erol
Keyword(s):  
Gravity Data ◽  
Geopotential Model ◽  
Geoid Model ◽  
Terrestrial Gravity ◽  
Practical Applications ◽  
Geopotential Models ◽  
Vertical Datum ◽  
Height System ◽  
Orthometric Heights ◽  
Height System Unification

<p>The maintenance of leveling benchmark is both laborious and costly due to distortions caused by geodynamic activities and local deformations. It is necessary to realize geoid-based vertical datum, which also enables calculation from ellipsoidal heights obtained from GNSS to orthometric heights that have physical meaning. It can be considered as an important step for height system unification as it eliminates the problems stem from the conventional vertical datum. The ongoing height modernization efforts in Turkey focus to improve quality and coverage of the gravity data, eliminate errors in existing terrestrial gravity measurements in order to achieve a precise geoid model. Accuracy of the geopotential model is crucial while realizing a geoid model based vertical datum as well as unifying the regional height systems with the International Heights Reference System. In this point of view, we assessed the accuracies of recently released global geopotential models including XGM2019e_2159, GECO, EIGEN-6C4, EGM2008, SGG-UGM-1, EIGEN-6C3stat, and EIGEN-6C2 using high order GNSS/leveling control benchmarks and terrestrial gravity data in Turkey. The reason for choosing these models in the validations is their relatively higher spatial resolutions and improved accuracies compared to other GGMs in published validation results with globally distributed terrestrial data. The GNSS/leveling data used in validations include high accuracy GNSS coordinates in ITRF datum with co-located Helmert orthometric heights in regional vertical datum. 100 benchmarks are homogeneously distributed in the country with the benchmarks along the coastlines. In addition, the terrestrial gravity anomalies with 5 arc-minute resolution were also used in the tests. In order to have comparable results, residual terrain effect has been restored to the GGM derived parameters. Numerical tests revealed significant differences in accuracies of the tested GGMs. The most accurate GGM has the comparable performance with official regional geoid model solutions in Turkey. The drawn results in the study were interpreted and discussed from practical applications and height system unification points in conclusion.</p>

scholarly journals DEVELOPMENT OF A LOCAL GEOID MODEL AT THE FEDERAL DISTRICT, BRAZIL, PATCH BY THE REMOVE-COMPUTE-RESTORE TECHNIQUE, FOLLOWING HELMERT'S CONDENSATION METHOD

2017 ◽  
Vol 23 (3) ◽  
pp. 520-538 ◽  
Author(s):  
Giuliano Sant’Anna Marotta ◽  
Roberta Mary Vidotti
Keyword(s):  
Gravity Data ◽  
Accurate Determination ◽  
Gravity Anomalies ◽  
Federal District ◽  
Geoid Model ◽  
Condensation Method ◽  
Digital Terrain ◽  
Geopotential Models ◽  
Elevation Data ◽  
Local Geoid

Abstract: There are several techniques for determining geoid heights using ground gravity data, the geopotential models, the astro-geodetic components or a combination of them. Among the techniques used, the Remove-Compute-Restore (RCR) technique has been widely applied for the accurate determination of the geoid heights. This technique takes into account short, medium and long wavelength components derived from the elevation data obtained from Digital Terrain Models (DTM), ground gravity data and global geopotential models, respectively. This technique can be applied after adopting the procedures to compute gravity anomalies and, then, the geoid model, considering the integration of different wavelengths mentioned, and their compatibility with the vertical datum adopted. Thus, this paper presents the procedures, involving the RCR technique, following Helmert's condensation method, and its application to compute one local geoid model for the Federal District, Brazil. As a result, the local geoid model computed for the studied area was consistent with the available values of geoid heights derived from geometrical levelling technique supported by GNSS positioning.

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

2015 ◽  
Vol 52 (10) ◽  
pp. 823-832 ◽  
Author(s):  
Ahmed Abdalla ◽  
Saad Mogren
Keyword(s):  
Saudi Arabia ◽  
Least Squares ◽  
Gravity Data ◽  
Computational Method ◽  
Gravimetric Geoid ◽  
Geoid Model ◽  
Geopotential Models ◽  
Digital Elevation ◽  
Stokes Formula ◽  
Elevation Model

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.

scholarly journals The Uganda Gravimetric Geoid Model 2014 Computed by The KTH Method

2015 ◽  
Vol 5 (1) ◽  
Author(s):  
L. E. Sjöberg ◽  
A. Gidudu ◽  
R. Ssengendo
Keyword(s):  
Gravity Field ◽  
Gravity Data ◽  
Geoid Determination ◽  
Geopotential Model ◽  
Gravimetric Geoid ◽  
Geoid Model ◽  
Satellite Mission ◽  
Terrestrial Gravity ◽  
Gravity Field Recovery ◽  
Goce Satellite

AbstractFor many developing countries such as Uganda, precise gravimetric geoid determination is hindered by the low quantity and quality of the terrestrial gravity data. With only one gravity data point per 65 km2, gravimetric geoid determination in Uganda appears an impossible task. However, recent advances in geoid modelling techniques coupled with the gravity-field anomalies from the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) satellite mission have opened new avenues for geoid determination especially for areas with sparse terrestrial gravity. The present study therefore investigates the computation of a gravimetric geoid model overUganda (UGG2014) using the Least Squares Modification of Stokes formula with additive corrections. UGG2014 was derived from sparse terrestrial gravity data from the International Gravimetric Bureau, the 3 arc second SRTM ver4.1 Digital Elevation Model from CGIAR-CSI and the GOCE-only global geopotential model GO_CONS_GCF_2_TIM_R5. To compensate for the missing gravity data in the target area, we used the surface gravity anomalies extracted from the World Gravity Map 2012. Using 10 Global Navigation Satellite System (GNSS)/levelling data points distributed over Uganda, the RMS fit of the gravimetric geoid model before and after a 4-parameter fit is 11 cm and 7 cm respectively. These results show that UGG2014 agrees considerably better with GNSS/levelling than any other recent regional/ global gravimetric geoid model. The results also emphasize the significant contribution of the GOCE satellite mission to the gravity field recovery, especially for areas with very limited terrestrial gravity data.With an RMS of 7 cm, UGG2014 is a significant step forward in the modelling of a “1-cm geoid” over Uganda despite the poor quality and quantity of the terrestrial gravity data used for its computation.

On Downward Continuing Airborne Gravity Data for Local Geoid Modeling

2020 ◽  
Author(s):  
Xiaopeng Li ◽  
Jianliang Huang ◽  
Cornelis Slobbe ◽  
Roland Klees ◽  
Martin Willberg ◽  
...  
Keyword(s):  
Gravity Data ◽  
The United States ◽  
Downward Continuation ◽  
Continuation Methods ◽  
Airborne Gravity ◽  
Spherical Harmonic Analysis ◽  
Study Group ◽  
Numerical Comparison ◽  
Geoid Model ◽  
Local Geoid

<p>The topic of downward continuation (DWC) has been studied for many decades without very conclusive answers on how different methods compare with each other. On the other hand, there are vast amounts of airborne gravity data collected by the GRAV-D project at NGS NOAA of the United States and by many other groups around the world. These airborne gravity data are collected on flight lines where the height of the aircraft actually varies significantly, and this causes challenges for users of the data. A downward continued gravity grid either on the topography or on the geoid is still needed for many applications such as improving the resolution of a local geoid model. Four downward continuation methods, i.e., Residual Least Squares Collocation (RLSC), the Inverse Poisson Integral, Truncated Spherical Harmonic Analysis, and Radial Basis Functions (RBF), are tested on both simulated data sets and real GRAV-D airborne gravity data in a previous joint study between NGS NOAA and CGS NRCan. The study group is further expanded by adding the TU Delft group on RBF and the TUM group on RLSC to incorporate more updated knowledge in the theoretical background and more in-depth discussion on the numerical results. A formal study group will be established inside IAG for providing the best answers for downward continuing airborne gravity data for local gravity field improvement. In this presentation, we review and compare the four methods theoretically and numerically. Simulated and real airborne and terrestrial data are used for the numerical comparison over block MS05 of the GRAV-D project in Colorado, USA, where the 1cm geoid experiment was performed by 15 international teams. The conclusion drawn from this study will advance the use of GRAV-D data for the new North American-Pacific Geopotential Datum of 2022 (NAPGD2022).</p>

Study of geoid–quasigeoid separation obtained from terrestrial gravity data and two geopotential models

2013 ◽  
Vol 7 (10) ◽  
pp. 4279-4290
Author(s):  
Mahmoud Mehramuz ◽  
Hossein Zomorrodian ◽  
Siamak Moazezi
Keyword(s):  
Gravity Data ◽  
Terrestrial Gravity ◽  
Geopotential Models

scholarly journals Generalized geoidal estimators for deterministic modifications of spherical Stokes' function

2010 ◽  
Vol 40 (1) ◽  
pp. 45-64 ◽  
Author(s):  
Michal Šprlák
Keyword(s):  
Gravity Model ◽  
Spherical Harmonic ◽  
Gravity Data ◽  
Surface Integral ◽  
Terrestrial Gravity ◽  
Global Gravity ◽  
Higher Derivatives ◽  
Stokes Integral ◽  
Global Gravity Model ◽  
Local Geoid

Generalized geoidal estimators for deterministic modifications of spherical Stokes' function Stokes' integral, representing a surface integral from the product of terrestrial gravity data and spherical Stokes' function, is the theoretical basis for the modelling of the local geoid. For the practical determination of the local geoid, due to restricted knowledge and availability of terrestrial gravity data, this has to be combined with the global gravity model. In addition, the maximum degree and order of spherical harmonic coefficients in the global gravity model is finite. Therefore, modifications of spherical Stokes' function are used to obtain faster convergence of the spherical harmonic expansion. Decomposition of Stokes' integral and modifications of Stokes' function have been studied by many geodesists. In this paper, the proposed deterministic modifications of spherical Stokes' function are generalized. Moreover, generalized geoidal estimators, when the Stokes' integral is decomposed in to spectral and frequency domains, are introduced. Higher derivatives of spherical Stokes' function and their numerical stability are discussed. Filtering and convergence properties for deterministic modifications of the spherical Stokes' function in the form of a remainder of the Taylor polynomial are studied as well.

scholarly journals ASSESSMENT OF RECENT GOCE-BASED GLOBAL GEOPOTENTIAL MODELS AND EGM2008 IN NIGER REPUBLIC

2019 ◽  
Vol 45 (3) ◽  
pp. 116-125
Author(s):  
Salissou Ibrahim Yahaya ◽  
Driss El Azzab
Keyword(s):  
Gravity Data ◽  
Geoid Height ◽  
Terrestrial Gravity ◽  
Terrain Model ◽  
Spectral Bands ◽  
Geopotential Models ◽  
Before And After ◽  
Gravity Database ◽  
Enhancement Method ◽  
The One

In this study, we assessed recent GOCE-based Global Geopotential Models (GGMs) and EGM2008 in Niger. The combined GGMs EIGEN_6C4, GECO and EGM2008 were evaluated up to their maximum degree and order (d/o) 2,190 to select the one for gravity database densification. The following pure satellite GGMs were assessed for the modelling of the long and medium wavelengths in geoid computation: GGM05G, ITU_GGC16, EIGEN_6S4v2 and the fifth releases from direct (DIR5), space-wise (SPW5) and time-wise (TIM5) approaches. The GGMs are compared to terrestrial gravity data and geoid heights from GNSS/Levelling points before and after applying spectral enhancement method (SEM) by residual terrain model (RTM) for combined models and by RTM and the coefficients of selected combined GGM for pure satellite models. The agreements of combined GGMs with terrestrial gravity data and GNSS/Levelling points, in terms of root mean square (RMS) are about 4.88 to 5.02 mGal and 0.14 to 0.16 m, respectively. EIGEN_6C4 was selected as it showed the best performance in terms of geoid height differences and the probability of 3-sigma rule for gravity anomaly differences. At d/o 200, DIR5 showed a good agreement with terrestrial gravity data (5.04 mGal) and GNSS/Levelling points (0.15 m) after applying SEM, it was then retained. All GOCE-based models exhibited a good performance in long and medium wavelengths confirming the good recovery of the gravity field by the spatial gravity mission in these spectral bands.

scholarly journals Geoid Modelling of Kalimantan Island using Airborne Gravity Data and Global Geoid Model (EGM2008)

2021 ◽  
Vol 936 (1) ◽  
pp. 012029
Author(s):  
Zahroh Arsy Udama ◽  
Ira Mutiara Anjasmara ◽  
Arisauna Maulidyan Pahlevi ◽  
Anas Sharafeldin Mohamed Osman
Keyword(s):  
Standard Deviation ◽  
Gravity Anomaly ◽  
Gravity Data ◽  
Airborne Gravity ◽  
Gravimetric Geoid ◽  
Wave Component ◽  
Geoid Model ◽  
Free Air ◽  
Free Air Gravity ◽  
Local Geoid

Abstract The availability of geoids, especially in survey and mapping activities, is useful for transforming the geometric heights obtained from observations of the Global Navigation Satellite System (GNSS) into orthometric heights that have real physical meanings such as those obtained from waterpass measurements. If a geoid is available, the orthometric heights of points on earth can be determined using the GNSS heighting method. The use of modern survey and mapping instruments based on satellite observations such as GNSS is more efficient in terms of time, effort, and cost compared to the accurate waterpass method. According to the Indonesian Geospatial Information Agency (BIG) it is stated that the application of geoid as a national Vertical Geospatial Reference System has an adequate and ideal category if the accuracy is higher than 15 cm. Recent studies have shown that it is possible to generate local geoid models with centimetre accuracy by utilizing airborne gravity data. We calculate free-air gravity anomaly data is calculated by processing airborne gravity and GNSS data using the Stokes Integral method on AGR software. Next a geoid model is created by calculating the contribution of three components, namely the long wave component represented by the EGM2008 global geoid data model, the shortwave component represented by the Shuttle Radar Topography Mission (SRTM) data and the medium wave component represented by the free-air gravity anomaly data. The geoid model validation was carried out using the geoid fitting method for geoid accuracy by calculating the difference between the gravimetric geoid and the geometric geoid and comparing it with the global geoid model EGM2008 degrees 2190. As a result, the total geoid model accuracy value was determined to be 49.4 cm on gravimetric geoid undulations with a standard deviation of 7.1 cm. Meanwhile, the results of the EGM2008 geoid undulation accuracy test at 2190 degrees resulted in an accuracy of 51.9 cm with a standard deviation of 9.9 cm. These results indicate that the local geoid model from airborne gravity measurement data produces a geoid model with a higher accuracy than the global geoid model EGM2008 degrees 2190. However, the accuracy of the resulting data is still below the BIG standard of 15 cm, so further research is needed to produce a geoid model which conforms to the standard.

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