Development of a precise gravimetric geoid model for Argentina
Creators: name: Pinon, Diego
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 370603
subject: Geodesy
classificationCode: 370606
subject: Gravimetrics
classificationCode: 401306
subject: Surveying (incl. hydrographic surveying)

description: The main aims of physical geodesy are to study the shape of the Earth, its gravity field and the geoid which is an equipotential surface closest to the mean sea level. Precise geoid determination has been an important research topic in geodesy and geophysics in the past two decades. Scientists and government agencies all around the world have made great efforts on the development of high-accuracy geoid models. These geoid models are developed not only for scientific applications, but also for other purposes such as serving for a reference surface for mapping, sea level monitoring and natural resources exploitation and management.<br><br>A geoid model is required to define a national height or vertical datum. Precise geoid models have experienced an unprecedented demand due to the rapid development of GPS/GNSS technologies. Geoid models allow transforming ellipsoidal heights, which are relatively easily determined from GPS/GNSS observations, into physical heights, which are associated to the Earth’s gravity field, without the need for expensive and time-consuming spirit-levelling. Physical heights are used for mapping, engineering and civil engineering infrastructure since they indicate the flow direction of fluids, due to the fact that fluids are attracted by the gravity of the Earth rather than geometric height differences.<br><br>Moreover, vertical datums have been historically based on a local mean sea level surface determined by averaging tide gauge readings over a certain period of time. However, due to the sea surface topography effect, which is mainly caused by the sea dynamics and other meteorological processes, observations from different tide gauges do not commonly coincide. Therefore, when vertical datums are separated by oceans or other bodies of water, direct methods such as spirit levelling and gravity measurements are not applicable. In this case, geoid models can be used for unifying two or more vertical datums together.<br><br>This research aims to develop a new and optimal precise geoid for Argentina using all available measurements from the most state of the art technologies and the latest global geopotential models (GGMs), along with detailed digital terrain models (DTMs). The remove-compute-restore technique and the combination of an optimal GGM with 658,111 land and marine gravity observations were used for the new model determination. Several GGMs (e.g. EGM2008, GOCO05S and EIGEN-6C4) were evaluated to investigate the best GGM that fits Argentinian regional gravity field. Terrain corrections were calculated using a combination of the SRTM_v4.1 and SRTM30_Plus v10 DTMs for all gravity observations. For the regions that lacked gravity observations, the DTU13 world gravity model was utilised for filling-in the gravity voids. The residual gravity anomalies were gridded by the Kriging method and the resultant grid was applied in the Stokes’ integral using the spherical multi-band FFT approach and the deterministic kernel modification proposed by Wong and Gore in 1969. The accuracy of the new geoid was assessed by comparing its geoidal undulations over 1,904 benchmarks, which have both orthometric and ellipsoidal heights. Results showed that an accuracy of better than 10 centimetres has been achieved.