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OAFAQG_LSC_2025 is a local, high-precision, high-resolution, pure-gravimetric quasigeoid model developed for the area surrounding OAFA and UNSJ, two International Height Reference Frame (IHRF) stations located in the Province of San Juan, Argentina, covering latitudes 34°S to 30°S and longitudes 70.5°W to 65.5°W, with a 0.03° grid resolution. The purpose of the model is to determine the IHRF vertical coordinate at these stations. Its computation followed Molodensky’s formulation of the Geodetic Boundary Value Problem (GBVP) and employed the remove–compute–restore (RCR) strategy. Long-wavelength components were modeled using the XGM2019e Global Geopotential Model (GGM) up to degree and order 840. Topographic contributions were modeled via Residual Terrain Modeling (RTM) using the SRTM v4.1 Digital Elevation Model (DEM). Residual height anomalies were calculated with the Least-Squares Collocation (LSC) technique. All computational steps were performed with the GRAVSOFT software package. Validation against 188 GNSS/leveling points yielded an estimated precision of 0.172 m after applying a four-parameter fit. 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.
UNPAQG_LSC_2025 is a local, high-precision, high-resolution, pure-gravimetric quasigeoid model developed for the area surrounding UNPA, an International Height Reference Frame (IHRF) station located in the Province of Santa Cruz, Argentina, covering latitudes 54°S to 50°S and longitudes 72°W to 66°W, with a 0.03° grid resolution. The purpose of the model is to determine the IHRF vertical coordinate at this station. Its computation followed Molodensky’s formulation of the Geodetic Boundary Value Problem (GBVP) and employed the remove–compute–restore (RCR) strategy. Long-wavelength components were modeled using the XGM2019e Global Geopotential Model (GGM) up to degree and order 740. Topographic contributions were modeled via Residual Terrain Modeling (RTM) using the SRTM v4.1 Digital Elevation Model (DEM). Residual height anomalies were calculated with the Least-Squares Collocation (LSC) technique. All computational steps were performed with the GRAVSOFT software package. Validation against 81 GNSS/leveling points yielded an estimated precision of 0.094 m after applying a four-parameter fit. 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.
UNSAQG_LSC_2025 is a local, high-precision, high-resolution, pure-gravimetric quasigeoid model developed for the area surrounding UNSA, an International Height Reference Frame (IHRF) station located in the Province of Salta, Argentina, covering latitudes 26.5°S to 24.5°S and longitudes 66°W to 64°W, with a 0.03° grid resolution. The purpose of the model is to determine the IHRF vertical coordinate at this station. Its computation followed Molodensky’s formulation of the Geodetic Boundary Value Problem (GBVP) and employed the remove–compute–restore (RCR) strategy. Long-wavelength components were modeled using the XGM2019e Global Geopotential Model (GGM) up to degree and order 800. Topographic contributions were modeled via Residual Terrain Modeling (RTM) using the SRTM v4.1 Digital Elevation Model (DEM). Residual height anomalies were calculated with the Least-Squares Collocation (LSC) technique. All computational steps were performed with the GRAVSOFT software package. Validation against 51 GNSS/leveling points yielded an estimated precision of 0.124 m after applying a four-parameter fit. 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.
RIO2QG_LSC_2025 is a local, high-precision, high-resolution, pure-gravimetric quasigeoid model developed for the area surrounding RIO2, an International Height Reference Frame (IHRF) station located in the Province of Tierra del Fuego, Argentina, covering latitudes 56°S to 51°S and longitudes 71°W to 64°W, with a 0.03° grid resolution. The model’s purpose is to determine the IHRF vertical coordinate at this station. Its computation followed Molodensky’s formulation of the Geodetic Boundary Value Problem (GBVP) and employed the remove–compute–restore (RCR) strategy. Long-wavelength components were modeled using the XGM2019e Global Geopotential Model (GGM) up to degree and order 700. Topographic contributions were modeled via Residual Terrain Modeling (RTM) using the SRTM v4.1 Digital Elevation Model (DEM). Residual height anomalies were calculated with the Least-Squares Collocation (LSC) technique. All computational steps were performed with the GRAVSOFT software package. Validation against 41 GNSS/leveling points yielded an estimated precision of 0.066 m after applying a four-parameter fit. 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.
AGGOQG_LSC_2025 is a local, high-precision, high-resolution, pure-gravimetric quasigeoid model developed for the area surrounding AGGO and LPGS, two International Height Reference Frame (IHRF) stations located in the Province of Buenos Aires, Argentina, covering latitudes 36°S to 31°S and longitudes 61°W to 55°W, with a 0.03° grid resolution. The purpose of the model is to determine the IHRF vertical coordinate at these stations. Its computation followed Molodensky’s formulation of the Geodetic Boundary Value Problem (GBVP) and employed the remove–compute–restore (RCR) strategy. Long-wavelength components were modeled using the XGM2019e Global Geopotential Model (GGM) up to degree and order 600. Topographic contributions were modeled via Residual Terrain Modeling (RTM) using the SRTM v4.1 Digital Elevation Model (DEM). Residual height anomalies were calculated with the Least-Squares Collocation (LSC) technique. All computational steps were performed with the GRAVSOFT software package. Validation against 111 GNSS/leveling points yielded an estimated precision of 0.063 m after applying a four-parameter fit. 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 ETH-GM21 model is a gravimetric geoid of 2'x2' spatial resolution developed over Ethiopia. This model has been computed using terrestrial and airborne gravity data together with the EIGEN-6C4 GGM and the SRTM3 digital elevation model. The ETH-GM21 model has been determined by using the remove-compute-restore procedure and the least-squares collocation method, obtaining geoid undulations referred to WGS84. With the use of geometric geoid heights obtained from 46 GNSS/levelling data distributed over Ethiopia, the accuracy of the ETH-GM21 gravimetric geoid model has been estimated to ±13 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 DRUKGEOID2015 model is a geoid of Bhutan, covering the area from 88.5°E to 92.5°E in longitude and from 26.5°N to 28.5°N with a grid resolution of 0.02°. It is referred to the GRS80 ellipsoid and it is based on a set of 255 points with both GNSS and gravity, collected in the framework of this project. Gravity observations were observed by the National Land Commission (NCL) using two CG5 gravimeters. As for the GNSS observations, the positions were computed using the differential GNSS approach for points in the proximity of Permanent Reference Stations (PRS). The Precise Point Positioning (PPP) technique were employed. The DRUKGEOID2015 model was computed by applying the remove-restore procedure, where the used global geopotential model was EIGEN-6C4 and the topography information was taken from the Shuttle Radar Topography Mission (SRTM) model. After the removal step, gravity residual were converted into residual height anomalies using the Least-Squares Collocation (LSC) approach. After the restoring step, height anomalies were converted into geoid undulations using the algorithm by Flury and Rummel (2009) and the SRTM topography. It was decided to fix the resulting gravimetric geoid to the fundamental benchmark at NLC headquarters in Thimphu (TH01). At this point the GNSS ellipsoidal height with respect to the DRUKREF03 system (ITRF2000 at epoch 2003.87) minus the geoid undulation is equal to the official orthometric height. Comparison of 27 GNSS/levelling benchmarks with DRUKGEOID15 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 local geoid for Madeira was computed using strapdown airborne gravimetry measurements taken on 27 and 31 August 2010 as part of the GEOMAD campaign. The inertial measurements were acquired with an iXsea IMU. The observations made during the turns of the aircraft were disregarded and a decimation to a 50 second sampling was applied. The geoid determination was based on the standard remove-restore technique with EGM2008 as reference global geopotential model and SRTM for the computation of the residual terrain correction. The Least-Squares Collocation approach was used to convert the residual gravity disturbances at flight level into height anomalies at sea level. The subsequent conversion of height anomalies into geoid undulations was based on the corrections provided with the EGM2008 model. The datum of the local geoid model is WGS84, given in the tide-free system. According to the Least-Squares Collocation procedure the errors are around 5 cm, however a more realistic estimate of the uncertainty is of the order 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.
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