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A new quasi-geoid model for Hungary was determined by combining gravity data, GPS/levelling and vertical deflections. Reduction of the measurements was performed by using Earth Gravitational Model 2008 (EGM2008) and Shuttle Radar Topographic Mission (SRTM) elevation data sets. Calculation method was Least Squares Collocation (LSC) with self-consist...
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... available data sets ( Fig. 1) for quasi-geoid determination were free-air grav- ity anomalies at 1243 points, GPS/levelling observations of the Hungarian GPS Network (OGPSH) at 330 points and 138 astrogeodetic deflections of the vertical, both meridian and prime vertical components. Mean error of 0.1 mGal (1 mGal = 10 −5 ms −2 ), 0.01 m and 0.3 of the observations ...
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... sites. These differences do not show a random pattern since in the southeast part of the country they are systematically lower than the average. In order to investigate the reason of this problem the country was divided into four regions at longitude 19.5 • and latitude 47 • . The histograms of the deviation on these sub-areas are displayed in Fig. 10. Distribution of the differences cannot be described as normal especially the main problem is that levelling and GPS measurements do not refer to the same epoch. First-order polygons of the Unified National Vertical Network (EOMA) were measured in the 1970s, the OGPSH network was established in the 1990s. Furthermore, levelling of the ...
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... this GPS ob- servations were carried out using rapid measurement technology. Re-measurement of the EOMA was started in 2006 and is ongoing nowadays, and hopefully would provide more information about this suspected recent subsidence. The pure gravimetric solution shows a very good agreement with the combined solution in most parts of the country (Fig. 11). In the southeast part of Hungary a systematic discrepancy arises, the differences may reach -10 cm compared to the combined ...
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... Fig. 12 the difference between combined and pure astrogeodetic solutions is displayed. Agreement with the combined solution is not as good as when compared to the gravimetric solution. These differences are more varied, the largest differ- ences in the southeast part indicate a discrepancy among the GPS/levelling and the vertical deflections. ...
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... differences are more varied, the largest differ- ences in the southeast part indicate a discrepancy among the GPS/levelling and the vertical deflections. Figure 12 shows the astrogeodetic sites, in some part of the country the data coverage is rather poor, hence densification of the astrogeodetic stations would be desirable. ...
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Citations
... Hirt et al. [2] combined EGM2008 and data from a residual terrain model to improve the quasi-geoid computations for some mountainous areas devoid of gravity data, and pointed out from the validation of GPS/leveling data that refined quasi-geoids could be obtained. T oth and Szü cs [3] determined a new combined quasi-geoid for Hungary, using the EGM2008, topography models, and observations from other terrestrial geometric and gravimetric measurements. Odera et al. [4] developed a high-resolution geoid model for the main islands of Japan with EGM2008 and terrestrial gravity data. ...
Earth's gravity model (EGM) helps people better determine the figure of Earth, which is generally represented by a global geoid. For a considerable amount of practical applications, people use quasi-geoid to approximate the geoid, thus the quasi-geoid is also treated as an important height datum. In this study we revisit the method to directly determine regional quasi-geoid using EGM and digital elevation model (DEM), on the basis of Molodensky theory. According to the method we obtain a 5′ × 5′ quasi-geoid for Mainland China and its vicinity areas, based on the EGM2008 gravitational potential model and the Shuttle Radar Topography Mission (SRTM) DEM model. By comparing height anomalies derived from EGM2008 with observations at 70 GPS/leveling points in areas including northwest, mid-west, mid-east and southeast of China, we find that the 5′ × 5′ EGM2008 quasi-geoid well fits the GPS/leveling results, with average deviations less than 10 cm for the selected areas in east China (with mainly plain topography) and ∼20 cm for the selected areas in west China (highland or mountainous areas). We also discuss a few technical issues for directly determining height anomalies based on EGM and DEM, under the frame of Molodensky theory.
... The Earth gravity model provides the information to transfer the ellipsoid height to orthometric height or normal height [23,24]. The spherical harmonic function expansions of geoid undulation can be expressed as [25][26][27][28][29]: ...
The Continuously Operating Reference Station (CORS) technique has been widely applied in land resource management, surveying, mapping, deformation monitoring, precise navigation, etc. This article analyzed the positioning method using EGM2008 and CORS of Jilin Province, China. The vertical transformation of EGM2008 from WGS84 to China’s CGCS2000 datum and the horizontal coordinate transformation from CGCS2000 to a triangulation coordinate system were discussed. The results indicated that a local geoid with respect to CGCS2000 can be transferred from EGM2008 with the same accuracy, and the geoid correction between CGCS2000 and WGS84 varied from 0.023 m to 0.111 m. The coordinate transformation method based on the curve surface approximation method indicated that the theoretical error was less than 0.09 m in the grid within 10° longitudinal and 5° latitudinal, and less than 0.3 m in large area and 0.1 m in small area in field validation. The method proposed in this article expanded the positioning result and its application for JLCORS and other CORS with local datum.
The local geoid fluctuation is the major problem for the application of GPS survey. Algorithm for refining local geoid includes gravity method, GPS leveling method, and hybrid method. Hybrid method is widely applied due to its high precision and resolution, while high precision earth gravity model is the key for the hybrid method. The precision and resolution of EGM2008 earth gravity model is much higher than any gravity model in China. The study on its application for the refinement of local geoid has an important practical significance. We refined the geoid of the Xingcheng geophysical survey test area of Jilin University by means of hybrid method model (HMM), with using land gravity data, EGM2008, and GPS/leveling. The precision between the HMM and the model is refined by geometric method without comparision with the land gravity data(GMM). Both of the applicability of this method and EGM2008 are analyzed. The results indicate that the maximum precision of HMM in the test area is 1.2 cm with a minimum error distribution interval, and both of the precision and reliability of HMM are higher than the GMM in varied topography. High density gravity data in a much plane area may produce a high frequency disturb to EGM2008 because of its high precision, and this disturb may decrease the precision of EGM2008, which means that the spatial distribution of gravity data survey needs to be emphasized. The geoid refinement method reported in this article may be much more suitable for a complex topographic area.
