O estudo e a compreensão dos aspectos geodinâmicos no planeta requerem referenciais geodésicos globais com uma ordem de acurácia melhor do que a magnitude dos efeitos e com confiabilidade. These stations may contribute to increase the density of reference points in the International Terrestrial Reference Frame, which is being researched and implemented by the International Association of Geodesy. The results indicate that the geopotential value needs to be monitored and determined with the time-dependent component on the three Vietnamese permanent GNSS stations for a vertical datum. The purpose is to monitor deformation of the vertical datum.
Define the gridded reference guide grg series#
Based on time series of the vertical component derived from the GNSS observations as well as InSAR data, temporal variations in geopotential are also estimated on these permanent GNSS stations.
Finally, the geodetic boundary value problem approach was used to determine the geopotential on the surface of three GNSS-CORS stations in Vietnam. Then, the mean zero-height gravity potential of the Vietnam local vertical datum is estimated equal to $$ = 62,636,846.69 m2/s2 with STD of 0.70 m2/s2 based on the proposed approach. The systematic cumulative errors in levelling data can be modelled and removed using a third-order polynomial model. The indirect bias term on the disturbing potential can be safely neglected by using a GOCE global gravity field model for degrees higher than 60 for this study region. This effect was eliminated using high-resolution terrestrial gravity data employing the remove-compute-restore technique. The results calculated on the GNSS/levelling points show that the effect of the GOCE DIR-R5 (up to degree/order 260) omission error on the offset potential value is quite significant.
These errors affect the estimated geopotential value. First, the effects of the GOCE global gravity field model omission error, the indirect bias term on the disturbing potential and the systematic cumulative errors in levelling data are estimated. This determination is carried out on the GNSS-CORS stations towards the realisation of the International Height Reference System in Vietnam. In this study, the geodetic boundary value problem approach is applied for direct determination of the gravity potential value using a GOCE global gravity field model enhanced with terrestrial gravity data. In the realization of the International Height Reference System, the determination of the geopotential value and its variations in time plays an important role. 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. 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. 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. the establishment of the International Height Reference Frame (IHRF). Accordingly, this study focuses on the strategy for the realisation of the IHRS i.e. 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. Coordinates of points or objects close to or on the Earth’s surface are given by geopotential numbers C ( P ) referring to an equipotential surface defined by the conventional value W 0 = 62,636,853.4 m ² s ⁻², and geocentric Cartesian coordinates X referring to the International Terrestrial Reference System (ITRS). The IHRS is a geopotential reference system co-rotating with the Earth. In 2015, the International Association of Geodesy defined the International Height Reference System (IHRS) as the conventional gravity field-related global height system.
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