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The official Uruguayan geoid model, called IGM110, was calculated by the Military Geographic Institute (IGM) in 2023 and consists of a grid of 1´ x 1´ geoidal undulations with a total of 151,981 points. The geodetic reference system is SIRGAS ROU-98 (the reference ellipsoid is GRS80). The extent is from 29.5° S to 35.5° S in latitude, and 52.5° W to 59.5° W in longitude, covering parts of Argentina and Brazil. The model is a combination of the EIGEN-6C4 geopotential model up to degree and order of 720, 10,429 land gravimetric stations plus 10,089 free air gravity anomalies in marine areas, based on the DTU13 model. The terrain data at the final 90 m resolution was taken from a 2017 Lidar survey in Uruguay with a 2.5 m initial resolution and SRTM (V2) for the external terrestrial data. The DT18 bathymetry model was used for the marine areas. Due to the total terrain data points (about 104 million), the overall area was divided into 4 overlapped blocks in the framework of the remove-compute-restore procedure. The reduced height anomalies were computed from the reduced gravity anomalies with Stokes 1D FFT and Wong Gore´s kernel modification (170-180 degrees). After adding back the residual terrain model effects and the contribution of the global geopotential model, the obtained quasi-geoid was transformed into a geoid model via Bouguer anomalies, even if the difference between the two models is just a few mm. A comparison with 51 GNSS/levelling stations shows a standard deviation of 10 cm. The resulting geoid was also adapted by a bias and a tilt to the national vertical system, Cabildo 1948, by fitting GNSS/levelling observations, with a mean of 1 cm and a standard deviation of 7 cm. The geoid model is provided in ISG format 2.0 (ISG Format Specifications), while the file in its original data format is available at the model ISG webpage.
The Uruguayan gravimetric geoid model UruGeoide110 was calculated by the Military Geographic Institute (IGM) in 2023. The extent is from 29.5° S to 35.5° S in latitude, and 52.5° W to 59.5° W in longitude, covering parts of Argentina and Brazil, with a grid resolution of 1´ x 1´. The geodetic reference system is SIRGAS ROU-98 (the reference ellipsoid is GRS80). The model is a combination of the EIGEN-6C4 geopotential model up to degree and order of 720, 10,429 land gravimetric stations plus 10,089 free air gravity anomalies in marine areas, based on the DTU13 model. The terrain data at the final 90 m resolution was taken from a 2017 Lidar survey in Uruguay with a 2.5 m initial resolution and SRTM (V2) for the external terrestrial data. The DT18 bathymetry model was used for the marine areas. Due to the total terrain data points (about 104 million), the overall area was divided into 4 overlapped blocks in the framework of the remove-compute-restore procedure. The reduced height anomalies were computed from the reduced gravity anomalies with Stokes 1D FFT and Wong Gore´s kernel modification (170-180 degrees). After adding back the residual terrain model effects and the contribution of the global geopotential model, the obtained quasi-geoid was transformed into a geoid model via Bouguer anomalies, even if the difference between the two models is just a few mm. A comparison with 51 GNSS/levelling stations shows a standard deviation of 10 cm. The geoid model is provided in ISG format 2.0 (ISG Format Specifications), while the file in its original data format is available at the model ISG webpage.
The Uruguayan gravimetric quasi-geoid model UruQGeoide110 was calculated by the Military Geographic Institute (IGM) in 2023. The extent is from 29.5° S to 35.5° S in latitude, and 52.5° W to 59.5° W in longitude, covering parts of Argentina and Brazil, with a grid resolution of 1´ x 1´. The geodetic reference system is SIRGAS ROU-98 (the reference ellipsoid is GRS80). The model is a combination of the EIGEN-6C4 geopotential model up to degree and order of 720, 10,429 land gravimetric stations plus 10,089 free air gravity anomalies in marine areas, based on the DTU13 model. The terrain data at the final 90 m resolution was taken from a 2017 Lidar survey in Uruguay with a 2.5 m initial resolution and SRTM (V2) for the external terrestrial data. The DT18 bathymetry model was used for the marine areas. Due to the total terrain data points (about 104 million), the overall area was divided into 4 overlapped blocks in the framework of the remove-compute-restore procedure. The reduced height anomalies were computed from the reduced gravity anomalies with Stokes 1D FFT and Wong Gore´s kernel modification (170-180 degrees) and the quasi-geoid model was finally obtained by adding back the residual terrain model effects and the contribution of the global geopotential model. The geoid model is provided in ISG format 2.0 (ISG Format Specifications), while the file in its original data format is available at the model ISG webpage.
The geoid model for Taiwan, including the Kinmen and Matzu islands, covers the area 118°E–125°E and 21°N–27°N with a grid resolution of 30" x 30". The gravimetric model is based on land, shipborne and airborne gravity data, as well as marine gravity derived from satellite altimetry. After merging data by least-squares collocation, a remove-restore procedure is applied. First height anomalies are computed by 1D FFT with Wong-Gore modification of the Stokes kernel and then they are converted into the geoid heights. The reference global gravity model is EGM2008 up to degree and order 2190. The used digital terrain model is derived from several photogrammetric surveys at a resolution of 3"×3" and 9"×9" for the inner and outer zone, respectively. The gravimetric model is finally adapted to GPS/levelling data at more than 2000 benchmarks. To this aim, an interpolation based on the minimum curvature principle (GMT command) is adopted. The resulting hybrid geoid model provides the transformation surface between the conventional Taiwan Vertical Datum (TWVD2001) and Taiwan Datum 97 (TWD97). The gravimetric model fits the GPS/levelling control points with a standard deviation of 7.9 cm (and a mean difference of 21.9 cm), while the hybrid solution fits them with a standard deviation of 3.6 cm (and a mean difference of -0.9 cm). The geoid model is provided in ISG format 2.0 (ISG Format Specifications), while the file in its original data format is available at the model ISG webpage.
The geoid model for Taiwan, including the Kinmen and Matzu islands, covers the area 118°E–125°E and 21°N–27°N with a grid resolution of 30" x 30". The gravimetric model is based on land, shipborne and airborne gravity data, as well as marine gravity derived from satellite altimetry. After merging data by least-squares collocation, a remove-restore procedure is applied. First height anomalies are computed by 1D FFT with Wong-Gore modification of the Stokes kernel and then they are converted into the geoid heights. The reference global gravity model is EGM2008 up to degree and order 2190. The used digital terrain model is derived from several photogrammetric surveys at a resolution of 3"×3" and 9"×9" for the inner and outer zone, respectively. The gravimetric model fits the GPS/levelling control points with a standard deviation of 7.9 cm (and a mean difference of 21.9 cm). The geoid model is provided in ISG format 2.0 (ISG Format Specifications), while the file in its original data format is available at the model ISG webpage.
The ColFFTWG2020 quasi-geoid model is a gravimetric model and has been computed by the Laboratory of Gravity Field Research and Applications, Aristotle University of Thessaloniki. The model has been computed in the frame of the International Association of Geodesy Joint Working Group 2.2.2 "The 1 cm geoid experiment" and the so called "Colorado experiment". The area covered by the models is 108.5°E ≤ longitude ≤ 103.5°E, 36.5°N ≤ latitude ≤ 38°N with a grid spacing of 2' in both latitude and in longitude. The computation is based on the remove-compute-restore technique with XGM2106 being used as a reference field. The topographic effects were treated using a Residual Terrain Correction (RTC) by solving the spectral filter problem of RTC using Earth2014 and ERTM2160 models. The input gravity data include terrestrial and airborne data combined using Least-Squares Collocation (LSC). The final estimation was carried out using 1D FFT with Wong-Gore modification of the Stokes kernel. The accuracy of the model, when compared against GSVS17 GPS/leveling, is at 2.5 cm level. The geoid model is provided in ISG format 2.0 (ISG Format Specifications), while the file in its original data format is available at the model ISG webpage.
The ColFFTWG2020 quasi-geoid model is a gravimetric model and has been computed by the Laboratory of Gravity Field Research and Applications, Aristotle University of Thessaloniki. The model has been computed in the frame of the International Association of Geodesy Joint Working Group 2.2.2 "The 1 cm geoid experiment" and the so called "Colorado experiment". The area covered by the models is 108.5°E ≤ longitude ≤ 103.5°E, 36.5°N ≤ latitude ≤ 38°N with a grid spacing of 2' in both latitude and in longitude. The computation is based on the remove-compute-restore technique with XGM2106 being used as a reference field. The topographic effects were treated using a Residual Terrain Correction (RTC) by solving the spectral filter problem of RTC using Earth2014 and ERTM2160 models. The input gravity data include terrestrial and airborne data combined using Least-Squares Collocation (LSC). The final estimation was carried out using 1D FFT with Wong-Gore modification of the Stokes kernel. The mean accuracy of the model, when compared against GSVS17 GPS/leveling, is at 1.6 cm level. The geoid model is provided in ISG format 2.0 (ISG Format Specifications), while the file in its original data format is available at the model ISG webpage.
The ColSHAWG-NGS2019 gravimetric quasi-geoid model has been computed by the US National Geodetic Survey (NGS). It has been worked out in the frame of the International Association of Geodesy Joint Working Group 2.2.2 "The 1 cm geoid experiment" and the so called "Colorado experiment". The area covered by the model is 251°E ≤ longitude ≤ 257°E, 36°N ≤ latitude ≤ 39°N with a grid spacing of 1' in both latitude and in longitude. The computation method is based on the spherical harmonic analysis scheme. The airborne gravity data are combined with the reference model xGEOID17RefB to produce an enhanced reference spherical harmonic model. This model is then used in a remove-compute-restore procedure, computing residual height anomalies from terrestrial gravity data by using the Wong-Gore modification of the Stokes kernel (truncation degree equal to 980), also including the g1 term because of rugged mountains. The accuracy of the quasi-geoid model, when compared against GSVS17 GPS/leveling, is equal to 2.3 cm. The geoid model is provided in ISG format 2.0 (ISG Format Specifications), while the file in its original data format is available at the model ISG webpage.
The ColSHAWG-NGS2019 gravimetric geoid model has been computed by the US National Geodetic Survey (NGS). It has been worked out in the frame of the International Association of Geodesy Joint Working Group 2.2.2 "The 1 cm geoid experiment" and the so called "Colorado experiment". The area covered by the model is 251°E ≤ longitude ≤ 257°E, 36°N ≤ latitude ≤ 39°N with a grid spacing of 1' in both latitude and in longitude. The computation method is based on the spherical harmonic analysis scheme. The airborne gravity data are combined with the reference model xGEOID17RefB to produce an enhanced reference spherical harmonic model. This model is then used in a remove-compute-restore procedure, computing residual height anomalies from terrestrial gravity data by using the Wong-Gore modification of the Stokes kernel (truncation degree equal to 980), also including the g1 term because of rugged mountains. Finally, the geoid undulations are obtained by adding the geoid/quasi-geoid separation term (based on the simple Bouguer anomalies) to the computed height anomalies. The accuracy of the geoid model, when compared against GSVS17 GPS/leveling, is equal to 2.3 cm. The geoid model is provided in ISG format 2.0 (ISG Format Specifications), while the file in its original data format is available at the model ISG webpage.
The ColFFTWG-DTU2019 gravimetric geoid model has been computed by the Technical University of Denmark (DTU), Copenhagen. It has been worked out in the frame of the International Association of Geodesy Joint Working Group 2.2.2 "The 1 cm geoid experiment" and the so called "Colorado experiment". The area covered by the model is 250°E ≤ longitude ≤ 258°E, 35°N ≤ latitude ≤ 40°N with a grid spacing of 1' in both latitude and in longitude. The computation was performed by the GRAVSOFT package in the framework of a remove-compute-restore procedure. XGM2016 was used up to degree and order 360 as global gravity model, and SRTM v4.1 was used for the residual terrain reductions at 3″ resolution for both airborne and terrestrial data, computed from a 9″ mean model. The linear Prey term approximation was applied for the harmonic correction of surface gravity points below the mean elevation surface (Forsberg and Tscherning, 1981). The reduced airborne gravity data were downward continued and gridded, together with surface gravimetry, at the terrain surface using 3D Least-Squares Collocation with planar logarithmic covariance function (Forsberg, 1987). The resulting 1'x1' grid was converted to a residual quasi-geoid by spherical FFT, using a Wong-Gore modified Stokes kernel, with a low-wavelength cut-off transition band at harmonic degrees 180-190, to keep the GOCE information unchanged up to this degree. Residual terrain effects and the XGM2016 contribution were restored to obtain the final gravimetric quasi-geoid, and the geoid was obtained by adding the classical separation term (Heiskanen and Moritz, 1967). The accuracy of the geoid model, when compared against GSVS17 GPS/leveling, is equal to 2.7 cm. The geoid model is provided in ISG format 2.0 (ISG Format Specifications), while the file in its original data format is available at the model ISG webpage.
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