Global satellite gravity measurements provide unique information regarding gravity field distribution and its variability on the Earth. The main cause of gravity changes is the mass transportation within the Earth, appearing as, e.g. dynamic fluctuations in hydrology, glaciology, oceanology, meteorology and the lithosphere. This phenomenon has become more comprehensible thanks to the dedicated gravimetric missions such as Gravity Recovery and Climate Experiment (GRACE), Challenging Minisatellite Payload (CHAMP) and Gravity Field and Steady-State Ocean Circulation Explorer (GOCE). From among these missions, GRACE seems to be the most dominating source of gravity data, sharing a unique set of observations from over 15 years. The results of this experiment are often of interest to geodesists and geophysicists due to its high compatibility with the other methods of gravity measurements, especially absolute gravimetry. Direct validation of gravity field solutions is crucial as it can provide conclusions concerning forecasts of subsurface water changes. The aim of this work is to present the issue of selection of filtration parameters for monthly gravity field solutions in RL06 and RL05 releases and then to compare them to a time series of absolute gravimetric data conducted in quasi-monthly measurements in Astro-Geodetic Observatory in Józefosław (Poland). The other purpose of this study is to estimate the accuracy of GRACE temporal solutions in comparison with absolute terrestrial gravimetry data and making an attempt to indicate the significance of differences between solutions using various types of filtration (DDK, Gaussian) from selected research centres.
In this study, several variants create and choose of a local quasi-geoid model in Poland have been considered. All propositions have a source in European Gravimetric Geoid models -EGG2008 and EGG2015, which are purely gravimetric models of reference surface. In the course of this work, each model has been analyzed in various ways: without any corrections, by parallel shifting of residuals, by the 7-parameter conformal transformation and by fitting residuals by 4-and 5-parameter trigonometric polynomials. Eventual corrections were based on points of national GNSS/levelling networks (EUVN, EUVN_DA, POLREF, EUREF and ASG-EUPOS eccentric points). As a final result of this study, a comparison of the accuracy of selected models has been carried out by RMSE statistics and maps showing spatial distribution of residuals and histograms. Validation has shown that the maximum achievable accuracy of the EGG models is approximately 2 cm for the ETRF2000 reference system and approximately 8 cm for ETRF89. In turn, fitting with the use of different mathematical methods results in an improvement of the standard deviation of residues to the level of 1.3-1.4 cm. The conclusions include an evaluation of considerations for and against the use of models based only on EGG realizations and, on the other hand, fitted to the points of Polish vertical network. Its usefulness is strictly connected with needs of the definition of up to date quasi-geoid model for the new realization of heights system in Poland, based on EVRF2007 frame.
<p>In recent years, a significant challenge for geodesy has been the introduction of a global height reference system and the consideration of its regional or national applications. According to the Global Geodetic Observing System (GGOS) recommendations, providing and maintaining accurate and stable reference systems is highly desirable. Positioning of 3D spatial systems with regard to the reference ellipsoid is ensured by stable ITRF realisations and easily transformable local frames (e.g. ETRF). A more demanding task is the unification of vertical datums. The difficulties result from the multitude of height frames, their non-uniformity and usually missing elevation in-time change models. The uniform International Height Reference System aims to achieve an accuracy of 3 mm for heights and 0.3 mm/year for its velocities.</p><p>In this study, the authors focused on analysing the possible unification of the Polish national vertical datum (PL-EVRF2007-NH) with the IHRF. For this purpose, various global geopotential models (satellite and high-resolution GGMs) were tested. Their usefulness was checked in the context of the transition from the local system to the system related to the global geoid level recommended in IAG Resolution (No. 1). The impact of direct and indirect use of GGM to determine the normal heights of points in the IHRF frame in the national network was also examined. The first case included testing the possibility of obtaining normal heights based on height anomalies determined directly from the selected geopotential models. The second case involved the unification of systems on a national scale with a determined local &#916;W<sub>0</sub> value &#8203;&#8203;between the level of the PL-EVRF2007-NH and the W<sub>0</sub> of IHRS. To obtain reliable results, it was necessary to standardise input data with regard to the assumptions of the IHRS. In addition, a specific variant was tested in which the UELN (United European Leveling Network) points became the basis for a new realisation of the vertical datum in Poland.</p><p>The conducted analyses and numerical tests allowed for the formulation of recommendations regarding the methodology of unification of the PL-EVRF2007-NH and IHRF frames in Poland, in particular: evaluating and picking the optimal GGM model, selecting reference points for local height frame, collecting and assessing the quality of normal heights (or geopotential values) data.</p>
Purpose The purpose of this case study is to indicate discrepancies between the guidelines for aeronautical data quality requirements (DQR) and the legal regulations of surveying in Poland. Because of the possible difficulties in determining the original source of geodetic coordinates, it is possible for mistakes to be made, e.g. in aeronautical metadata. Design/methodology/approach The differences between selected reference data for the ASG-EUPOS network stations were determined and later extended to the entire country using the linear interpolation method. The values were investigated for exceeding the most restrictive limit on the DQR, i.e. 0.50 m for geodetic latitude and longitude and 0.25 m for measured height and geoid undulation. Findings The lack of an appropriate transformation of geodetic coordinates would result in an error of 0.30 m for the horizontal position, and <0.01 m for ellipsoidal heights. The discrepancies between the Earth Gravitational Model 96 (EGM96) geoid model used in aviation and Polish local quasigeoid model are up to 1 m. Practical implications Results prove that a mismatch of coordinate frames could be a severe threat to the aeronautical DQR. Providing complete information about reference systems during the data exchange, including the conversion parameters between selected geoid models, or considering a more accurate geoid model as a reference in aviation is recommended. Originality/value To the best of the author’s knowledge, this study is perhaps the first to compare data quality guidelines for surveying and aviation.
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