The gravimetric geoid model xGGM23 was computed at the University of New Brunswick, Canada, with the aim to update the national geoid for Mexico, as well as to contribute to the construction of the regional geoid for North and Central America. Terrestrial gravimetry collected up to year 2020 was processed in spectral combination with the satellite-derived geopotential model GOCO06s (up to degree and order 230) using the UNB’s Stokes-Helmert technique. The geoid model is purely gravimetric, corresponds to the regional standard reference gravity potential for North America (Wo=6263656.0 m2/s2), tide-free gravity concept, and covers latitudes from 10° N to 40° N and longitudes from 125° W to 80° W, with a grid resolution of 2.5 arc minutes. This resolution is coherent with the densification of terrestrial gravity data collected inside Mexico. The accuracy of geoidal height is estimated as 10 cm inside Mexico and 5 cm in the southern US. 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 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 IndGG-LSMSA2021 is the Indian Gravimetric Geoid model developed using the Royal Institute of Technology (KTH) method of Least Squares Modification of the Stokes formula with Additive corrections (LSMSA). The method was used to calculate the quasigeoid model, which was converted to the geoid model by applying the geoid-quasigeoid separation term calculated using the method by Flury and Rummel (2009). Data used are terrestrial gravity anomalies from GETECH, satellite-altimeter derived marine gravity anomalies, MERIT digital elevation model, EGM2008 and GO_CONS_GCF_2_DIR_R5 global geopotential models. The LSMSA method was used with various combinations of modification degree and integration radius. This gravimetric geoid model was obtained with the modification degree of 300 and an integration radius of 1°. The IndGG-LSMSA2021 model extends from 7° N to 37° N latitude and 68° E to 98° E longitude with a grid spacing of 0.02°×0.02° and it is referred to the GRS80 ellipsoid. On validation with the available GNSS/levelling data, mean±STD (in m) for India is -0.14±0.43. However, on cluster-wise validation in the four regions of the country, Uttar Pradesh West, Uttar Pradesh East, Hyderabad, and Bangalore, mean±STD (in m) are -0.58±0.13, -0.49±0.10, 0.14±0.16, and 0.79±0.03, respectively. 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.
DRUKGEOID2022 is the official geoid model of Bhutan, covering the area from 88.5°E to 92.5°E in longitude and from 26.5°N to 28.5°N in latitude with a grid resolution of 0.02°. It is an update of the previous DRUKGEOID2015 model, that was changed by a bias of 0.8761 m. This update was due to the change of the reference benchmark from the TH01 station at NLC headquarters to the more reliable THIZ station belonging to the national zero-order GNSS/levelling network. In this way, the resulting geoid can be used for the conversion from ellipsoidal heights in the DRUKREF03 system (ITRF2000 at epoch 2003.87) to orthometric heights in the national vertical datum, which is in turns connected to the Indian mean sea level through the neighboring benchmarks in the Indian states of West Bengal and Assam. Comparison of 27 GNSS/levelling benchmarks with DRUKGEOID2022 showed a standard deviation of 0.55 m. 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 gravimetric quasi-geoid model for the State of Minas Gerais covers the longitude range of -38º to -53º and the latitude range of -12º to -25º, with a resolution of 5 arc minutes. A total of 49,067 terrestrial gravity values were utilized to compute Molodenski's gravity anomalies. The quasi-geoid model was computed by the Least Squares Collocation method. The XGM2019 geopotential model up to degree and order 300 was employed to represent the long-wavelengths of the gravity field. The digital terrain model SRTM15+ was selected for the RTM computation, while the DTU17 gravity field model was used in oceanic areas. The quasi-geoid model was validated against 136 GNSS/leveling stations, yielding a bias of 23 cm and a standard deviation of 11 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 ColUNBSH-GSI2019 gravimetric geoid model has been computed by the Geospatial Information Authority of Japan (GSI) in cooperation with the Technical University of Denmark (DTU). 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 109°W ≤ longitude ≤ 103°W, 36°N ≤ latitude ≤ 39°N with a grid spacing of 1' in both latitude and in longitude. Terrestrial and airborne gravity data are combined and gridded by least-squares collocation with the planar logarithmic covariance model. The resulting grid of free-air gravity anomalies is converted into Helmert gravity anomalies by applying the spherical topographic reduction and the analytical downward continuation with Helmert's second method of condensation. The computation method is based on the remove-compute-restore technique, using XGM2016 up to degree and order 719 as the reference global gravity model. In particular, the geoid model is computed by Stokes integration of residual Helmert gravity anomalies with the hybrid Meissl-Molodensky modified spheroidal Stokes kernel (UNB Stokes-Helmert scheme). The accuracy of the geoid model, when compared against GSVS17 GPS/leveling, is equal to 2.9 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 ColFFTDB-CGS2019 gravimetric geoid model has been computed by the Canadian Geodetic Survey (CGS), Natural Resources Canada. 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 110°W ≤ longitude ≤ 102°W, 35°N ≤ latitude ≤ 40°N with a grid spacing of 1' in both latitude and in longitude. The solution is based on the Stokes-Helmert method, which is used with the degree-banded Stokes kernel modification (Huang and Véronneau, 2013). A band-wise spectral scheme is developed to combine the global model, airborne and surface gravity data, contributing to low-, medium- and high-degree bands of the geoid, respectively. In particular, the global gravity model provides entirely the low-degree band up to degree 150 from where it goes into transition with the surface gravity data up to degree 210. The surface gravity data complete the geoid frequencies up to degree 10800 with complement information from SRTM 3″ digital terrain model. As for the GRAV-D airborne gravity data, they provide corrective values directly to the geoid model, contributing between degrees 210 and 790 with smooth transition at each end. The geoid computation is performed by Fast Fourier Transform (FFT) numerical integration. The accuracy of the geoid model, when compared against GSVS17 GPS/leveling, is equal to 2.0 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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