Assessment of the GOCE-Based Global Gravity Models in Canada

GEOMATICA ◽  
2012 ◽  
Vol 66 (2) ◽  
pp. 125-140 ◽  
Author(s):  
E. Sinem Ince ◽  
Michael G. Sideris ◽  
Jianliang Huang ◽  
Marc Véronneau
Keyword(s):  
Great Lakes ◽  
Rocky Mountains ◽  
Spherical Harmonic ◽  
Gravity Models ◽  
Geopotential Model ◽  
Third Generation ◽  
Combined Models ◽  
Gps Leveling ◽  
Global Gravity Models ◽  
Geoid Undulations

The aim of this study is to test the first, second and third generation GOCE geoid solutions, obtained from the first 2, 8 and 18-month observations, respectively. These solutions are assessed over Canada and for two sub-regions (the Great Lakes and Rocky Mountains). The Canadian GPS/leveling-derived geoid heights are used as independent control values in the assessment of the GOCE geoid models. The study is conducted in two steps. First, the geoid models are computed from satellite-only models and truncated to different spherical harmonic degrees. These models are compared with the GPS/leveling geoid heights which are reduced to the same spectral band as the satellite models by EGM2008 predicted frequency components higher than the truncation degrees. The results suggest that the GOCE models show a full power of signal up to about spherical harmonic degree 180. Moreover, the second and third generation GOCE models (with the exception of the direct approach models) provide better agreement with the GPS/leveling-derived geoid undulations than the first generation models due to the longer observation period. The second step involves the combination of the two third generation GOCE models with terrestrial data. These models are tested against to the GPS/leveling-derived geoid undulations in full spectrum. EGM2008 global geopotential model and Canadian gravimetric geoid model CGG2005 are also included in the comparisons to measure improvement provided by the GOCE models. The GOCE-combined models yielded GPS/leveling results that are comparable with those obtained from EGM2008 and CGG2005 models. The best comparative results with the combined models give standard deviations of 4.8 cm, 6.0 cm and 12.2 cm for the Great Lakes, Rocky Mountains and Canada, respectively. These results indicate that the third generation GOCE models conform to the Canadian terrestrial gravity data from degrees 90 to 180. The new generation models show evident improvement over the first and second generation models.

scholarly journals Evaluation of GGMs Based on the Terrestrial Gravity Data of Gravity Disturbance and Moho Depthin Afar, Ethiopia

2021 ◽  
Vol 56 (3) ◽  
pp. 78-100
Author(s):  
Eyasu Alemu
Keyword(s):  
Gravity Data ◽  
Gravity Models ◽  
Moho Depth ◽  
Equal Distribution ◽  
Terrestrial Gravity ◽  
Global Gravity ◽  
Gravity Disturbances ◽  
Combined Models ◽  
Global Gravity Models ◽  
Best Fit

Abstract To estimate Moho depth, geoid, gravity anomaly, and other geopotential functionals, gravity data is needed. But, gravity survey was not collected in equal distribution in Ethiopia, as the data forming part of the survey were mainly collected on accessible roads. To determine accurate Moho depth using Global Gravity Models (GGMs) for the study area, evaluation of GGMs is needed based on the available terrestrial gravity data. Moho depth lies between 28 km and 32 km in Afar. Gravity disturbances (GDs) were calculated for the terrestrial gravity data and the recent GGMs for the study area. The model-based GDs were compared with the corresponding GD obtained from the terrestrial gravity data and their differences in terms of statistical comparison parameters for determining the best fit GGM at a local scale in Afar. The largest standard deviation (SD) (36.10 mGal) and root mean square error (RMSE) (39.00 mGal) for residual GD and the lowest correlation with the terrestrial gravity (0.61 mGal) were obtained by the satellite-only model (GO_CONS_GCF_2_DIR_R6). The next largest SD (21.27 mGal) and RMSE (25.65 mGal) for residual GD were obtained by the combined gravity model (XGM2019e_2159), which indicates that it is not the best fit model for the study area as compared with the other two GGMs. In general, the result showed that the combined models are more useful tools for modeling the gravity field in Afar than the satellite-only GGMs. But, the study clearly revealed that for the study area, the best model in comparison with the others is the EGM2008, while the second best model is the EIGEN6C4.

Validation of the GPS leveling method through the gradient analysis of the geoidal wave. Case study of Ecuador

2021 ◽  
Vol 62 (2) ◽  
pp. 316-329
Author(s):  
Dennys Enríquez ◽  
César Leiva ◽  
Santiago Cárdenas ◽  
José Carrión ◽  
Theofilos Toulkeridis
Keyword(s):  
Geoid Undulation ◽  
Geopotential Model ◽  
Geoidal Undulation ◽  
Vertical Control ◽  
Gnss Positioning ◽  
Positioning Technique ◽  
Gps Leveling ◽  
Geoid Undulations ◽  
Gnss Observations

We validated the GPS leveling as an alternative to the traditional geometric leveling method. Validation compares the geometric slopes derived from the GNSS positioning technique, heights resulting from geometric leveling campaigns and geoid undulations extracted from the Global Geopotential Model EGM08. This analysis was performed in the Ecuadorian mainland, where we identified areas in which the gradient of the geoidal undulation is less pronounced. The spatialization of the gradient or variation-based methods allowed to analyze the performance of the GPS leveling method, under the hypothesis that less variability in geoid undulation implies less discrepancies in the GPS unevenness. GNSS observations were determined on the leveling plates belonging to the Basic Vertical Control Network. The results of the study are given based on the relative error resulting from the comparison of the traditional differential leveling method with the corresponding values obtained from the GNSS positioning, considering different distances for the spread of unevenness.

Validation of the GPS leveling method through the gradient analysis of the geoidal wave. Case study of Ecuador.

2021 ◽  
Vol 62 (2) ◽  
pp. 316-329
Author(s):  
Dennys Enríquez ◽  
César Leiva ◽  
Santiago Cárdenas ◽  
José Carrión ◽  
Theofilos Toulkeridis
Keyword(s):  
Geoid Undulation ◽  
Geopotential Model ◽  
Geoidal Undulation ◽  
Vertical Control ◽  
Gnss Positioning ◽  
Positioning Technique ◽  
Gps Leveling ◽  
Geoid Undulations ◽  
Gnss Observations

We validated the GPS leveling as an alternative to the traditional geometric leveling method. Validation compares the geometric slopes derived from the GNSS positioning technique, heights resulting from geometric leveling campaigns and geoid undulations extracted from the Global Geopotential Model EGM08. This analysis was performed in the Ecuadorian mainland, where we identified areas in which the gradient of the geoidal undulation is less pronounced. The spatialization of the gradient or variation-based methods allowed to analyze the performance of the GPS leveling method, under the hypothesis that less variability in geoid undulation implies less discrepancies in the GPS unevenness. GNSS observations were determined on the leveling plates belonging to the Basic Vertical Control Network. The results of the study are given based on the relative error resulting from the comparison of the traditional differential leveling method with the corresponding values obtained from the GNSS positioning, considering different distances for the spread of unevenness.

scholarly journals Strategy for the realisation of the International Height Reference System (IHRS)

2021 ◽  
Vol 95 (3) ◽  
Author(s):  
Laura Sánchez ◽  
Jonas Ågren ◽  
Jianliang Huang ◽  
Yan Ming Wang ◽  
Jaakko Mäkinen ◽  
...  
Keyword(s):  
Gravity Field ◽  
Reference System ◽  
International Association ◽  
Accuracy Assessment ◽  
Equipotential Surface ◽  
Precise Determination ◽  
Gravity Models ◽  
Reference Network ◽  
Global Gravity Models

AbstractIn 2015, the International Association of Geodesy defined the International Height Reference System (IHRS) as the conventional gravity field-related global height system. The IHRS is a geopotential reference system co-rotating with the Earth. Coordinates of points or objects close to or on the Earth’s surface are given by geopotential numbersC(P) referring to an equipotential surface defined by the conventional valueW0 = 62,636,853.4 m2 s−2, and geocentric Cartesian coordinatesXreferring to the International Terrestrial Reference System (ITRS). Current efforts concentrate on an accurate, consistent, and well-defined realisation of the IHRS to provide an international standard for the precise determination of physical coordinates worldwide. Accordingly, this study focuses on the strategy for the realisation of the IHRS; i.e. the establishment of the International Height Reference Frame (IHRF). Four main aspects are considered: (1) methods for the determination of IHRF physical coordinates; (2) standards and conventions needed to ensure consistency between the definition and the realisation of the reference system; (3) criteria for the IHRF reference network design and station selection; and (4) operational infrastructure to guarantee a reliable and long-term sustainability of the IHRF. A highlight of this work is the evaluation of different approaches for the determination and accuracy assessment of IHRF coordinates based on the existing resources, namely (1) global gravity models of high resolution, (2) precise regional gravity field modelling, and (3) vertical datum unification of the local height systems into the IHRF. After a detailed discussion of the advantages, current limitations, and possibilities of improvement in the coordinate determination using these options, we define a strategy for the establishment of the IHRF including data requirements, a set of minimum standards/conventions for the determination of potential coordinates, a first IHRF reference network configuration, and a proposal to create a component of the International Gravity Field Service (IGFS) dedicated to the maintenance and servicing of the IHRS/IHRF.

scholarly journals A High-Resolution Gravimetric Geoid Model for Kuwait Using the Least-Squares Collocation

2022 ◽  
Vol 9 ◽  
Author(s):  
Hamad Al-Ajami ◽  
Ahmed Zaki ◽  
Mostafa Rabah ◽  
Mohamed El-Ashquer
Keyword(s):  
High Resolution ◽  
Least Squares ◽  
Geopotential Model ◽  
Gravimetric Geoid ◽  
Least Squares Collocation ◽  
Geoid Model ◽  
Terrestrial Gravity ◽  
Digital Elevation ◽  
Elevation Model ◽  
Gps Leveling

A new gravimetric geoid model, the KW-FLGM2021, is developed for Kuwait in this study. This new geoid model is driven by a combination of the XGM2019e-combined global geopotential model (GGM), terrestrial gravity, and the SRTM 3 global digital elevation model with a spatial resolution of three arc seconds. The KW-FLGM2021 has been computed by using the technique of Least Squares Collocation (LSC) with Remove-Compute-Restore (RCR) procedure. To evaluate the external accuracy of the KW-FLGM2021 gravimetric geoid model, GPS/leveling data were used. As a result of this evaluation, the residual of geoid heights obtained from the KW-FLGM2021 geoid model is 2.2 cm. The KW-FLGM2021 is possible to be recommended as the first accurate geoid model for Kuwait.

scholarly journals Discrete Spherical Harmonic Transforms of Nearly Equidistributed Global Data

2011 ◽  
Vol 1 (3) ◽  
pp. 251-258 ◽  
Author(s):  
J. Blais
Keyword(s):  
Spherical Harmonic ◽  
Fourier Transforms ◽  
Simulated Data ◽  
Geopotential Model ◽  
Structural Constraints ◽  
Geopotential Models ◽  
Analysis And Synthesis ◽  
Comparative Results ◽  
Efficiency And Reliability ◽  
Global Data

Discrete Spherical Harmonic Transforms of Nearly Equidistributed Global DataDiscrete Spherical Harmonic Transforms (SHTs) are commonly defined for equiangular grids on the sphere. However, when global array data exhibit near equidistributed patterns rather than equiangular grids, discrete SHTs require appropriate adaptations for analysis and synthesis. Computational efficiency and reliability impose structural constraints on possible equidistribution characteristics of data patterns such as for instance with Chebychev quadratures and Fast Fourier Transforms (FFTs). Following some general introduction to discrete SHTs and equidistributions on the sphere, equitriangular (near equiareal) lattices based on the octahedron and the icosahedron are introduced for SHT analysis and synthesis. The developed formulations are described and implemented using simulated data and geopotential models such as the Earth Geopotential Model EGM 2008. Comparative results for analysis and synthesis at different levels of resolution show the potential of the spherical equitriangular approach for geodetic and other applications with nearly equidistributed global data.

scholarly journals Multiple-data-based monthly geopotential model set LDCmgm90

2019 ◽  
Vol 6 (1) ◽  
Author(s):  
Wei Chen ◽  
Jiesi Luo ◽  
Jim Ray ◽  
Nan Yu ◽  
Jian Cheng Li
Keyword(s):  
Gravity Data ◽  
Gravity Models ◽  
Geopotential Model ◽  
Satellite Mission ◽  
Stripe Pattern ◽  
Angular Momenta ◽  
Multiple Data ◽  
Model Set ◽  
Gravity Recovery

Abstract While the GRACE (Gravity Recovery and Climate Experiment) satellite mission is of great significance in understanding various branches of Earth sciences, the quality of GRACE monthly products can be unsatisfactory due to strong longitudinal stripe-pattern errors and other flaws. Based on corrected GRACE Mascon (mass concentration) gridded mass transport time series and updated LDCgam (Least Difference Combination global angular momenta) data, we present a new set of monthly gravity models called LDCmgm90, in the form of Stokes coefficients with order and degree both up to 90. The LDCgam inputs are developed by assimilating degree-2 Stokes coefficients from various versions of GRACE (including Mascon products) and SLR (Satellite Laser Ranging) monthly gravity data into combinations of outputs from various global atmospheric, oceanic, and hydrological circulation models, under the constraints of accurately measured Earth orientation parameters in the Least Difference Combination (LDC) scheme. Taking advantages of the relative strengths of the various input solutions, the LDCmgm90 is free of stripes and some other flaws of classical GRACE products.

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