József Ádám

Calibration/validation of GOCE data by terrestrial torsion balance observations

One promising method for the external validation and calibration of the upcoming GOCE satellite mission data is the use of ground gravity field data continued upward to satellite altitude. There is a unique situation for Hungary in this respect since surface gravity gradients are available at 20143 points over an approximately 48700 km2 area, measured by the classical E6tv6s torsion balance. The concept of this contribution is to test the usability of these point gravity gradient observations for upward continuation to the GOCE satellite orbit in combination with different geopotential models and other gravity field information.

Towards a cm-geoid for Hungary: Recent efforts and results

Abstract Some steps were taken recently for Hungary aiming at the determination of geoid heights with a cm-accuracy. The present HGTUB98 gravimetric solution was based on terrestrial gravity data, height data and the EGM96 geopotential model, and was computed with the 1D Spherical FFT method. The gravity data were used in the area 45.5 ° ≤ϑ ≤ 49 °, 16 ° ≤ λ ≤ 23 °, the resolution of the grid was 30″ × 50″. The DTM used had a resolution of 1 km × 1 km. Our solution was evaluated using GPS/levelling data at 340 and 308 points respectively and at 138 vertical deflection points. We have compared our solution to the European EGG97 geoid solution, the gravimetric solution HGR97B developed by A. Kenyeres and the litospheric geoid solution by G. Papp. We have correlated our recent HGTUB98 solution to the Moho model of Central Europe. The comparison with GPS/levelling yielded respectively an accuracy of ±8.7 cm and ±4.4 cm (in terms of standard deviation) when a linear trend was removed. The comparison of the 1D planar FFT solution for the deflections of the vertical with 138 astrogeodetic deflections yielded an accuracy (in terms of standard deviation) of ±0.62″ and ±0.52″ for ξ and η, respectively.

Gravity field modelling by torsion balance data — a case study in Hungary

Two test areas with different characteristics of the terrain were selected in Hungary to model the gravity field. We have used point gravity gradients, their terrain effects and geopotential information to model geoid heights by numerical integration using kernel functions for specific gradient and curvature combinations which arise from the solution of the corresponding overdetermined geodetic boundary value problem. The truncation characteristics of these kernel functions were also taken into account. We have compared our results with the collocation solution as well

Status and development of the European height systems

After a break of ten years, the work on the United European Levelling Network (UELN) resumed in 1994 under the name UELN-95. The objectives of the LJELN-95 project are to establish an unified vertical datum for Europe at the one decimeter level with the simultaneous enlargement of UELN as far as possible to include Central and Eastern European countries. More than 3000 nodal points were adjusted linked to the reference point of LTELN-73 (gauge Amsterdam). The new heights in the system UELN-95/98 are available for more than 20 participating countries.

Space-VLBI: Potential applications in geodynamics

Abstract A unique characteristic of space-VLBI for geodynamic studies is pointed out: space-VLBI provides a direct connection between the Conventional Inertial Reference System of extragalactic radio sources and geocentric reference systems of extragalactic radio sources and geocentric reference systems defined by dynamical methods respectively. New satellite projects (Quasat, Radioastron) are in preparation requiring precise orbits; different satellite tracking methods are discussed for this purpose.

Geodesy Demonstration Experiment (Gedex) For Space VLBI: State of the Art and Software Development

The aim of the GEDEX, which is being designed by an international team of scientists, is to explore the feasibility of Geodetic & Geodynamic applications of Space VLBI. In this paper, the outline of this experiment has been presented. A brief description of the Space VLBI technique has been provided, followed by a summary of the significant theoretical developments. Salient features of the VSOP mission. and an overview of the various aspects of GEDEX have been presented. The state of the art of software for Geodetic SVLBI has been outlined, and the different steps in software development for the GEDEX have been described in detail. Conclusions drawn from the work done so far, and recommendations for future work have been presented.

The Hungarian Contribution to the Determination of a Precise European Reference Geoid

Currently the European Geoid Project is on-going aimed at the determination of a Precise European Reference Geoid [Torge, 1992; Denker and Torge, 1993]. In Hungary we are strongly interested in the success of this effort toward a new European quasigeoid solution improved in spatial resolution and accuracy. Therefore appropriate gravity data and elevations from Hungary have been made available for use in the computations. In exchange the resulting geoid solution for the area of Hungary will be provided. This geoid surface will be very important for a check of the individual local quasigeoid solutions determined by Hungarian institutions.

Space-VLBI: A New Technique for Unification of Reference Frames

In the next decade — the 90-es — dedicated radio telescopes will be launched into Earth orbit and will be integrated in the ground based Very Long Baseline Interferometry (VLBI) networks. Space-VLBI an emerging new observational technique will be with us.

Test Computations for a Local Quasigeoid in Hungary Using FFT

The Fast Fourier Transform (FFT) technique is an efficient and practical tool in geodesy for solving local gravity field approximation problems, among others for local geoid (quasigeoid) determination. In the future we plan to use the FFT procedure for its efficiency in computing a detailed gridded set of height anomalies for Hungary.

Recent Developments in Space VLBI Geodesy Demonstration Experiment (GEDEX)

The unique radio astronomical technique of Space Very Long Baseline Interferometry (SVLBI) is an extension of the ground-based VLBI into the space. It has some important potential applications in geodesy and geodynamics, including the definition, practical realization, and interconnection of different reference frames, determining the geocentric positions of VLBI stations, estimation of the gravity field of the Earth, and satellite orbit determination using the delay and delay rate observables. With the launching of the first SVLBI satellite of the VLBI Space Observatory Programme (VSOP) of Japan, in February 1997, this technique has become a reality. An international team of scientists, working under the auspices of the FOMI Satellite Geodetic Observatory, Hungary, has designed the GEDEX, for the purpose of exploring the feasibility of the geodetic applications of SVLBI.