Did the new geopotential models improve the fit of gravimetric quasigeoid in Poland to GPS/levelling data?

The choice of global geopotential model used in remove-restore technique for determination of regional quasigeoid from gravity data may affect the solution, in particular when the accuracy is supposed to reach a centimetre level. Global geopotential model plays also an important role in validating height anomalies at GPS/levelling sites that are used for the estimation of the external accuracy of quasigeoid models. The quality of the quasi97b quasigeoid model for Poland developed in 1997 with use of available terrestrial gravity data and EGM96 geopotential model was estimated at sub-decimetre level using GPS/levelling data at 360 stations of the POLREF network. Since then new data became available as well as new geopotential models were developed. In the framework of the project on the determination of a centimetre geoid in Poland with the use of geodetic, astronomical, gravimetric, geological and satellite data, that became operational in 2003, a number of new quasigeoid models for Poland were developed with the use of six different global geopotential models: EGM96, EIGEN-CH03S, GGM01S, GGM02S, GGM02C and GGM02S/EGM96. Three kinds of numerical tests with the use of terrestrial gravity data and GPS/levelling height anomalies at the POLREF and densified EUVN network stations were conducted. The first one concerned comparison of height anomalies at GPS/levelling sites in Poland with the corresponding ones computed from various global geopotential models. In the second one the terrestrial gravity anomalies in Poland and neighbouring countries were compared with the corresponding gravity anomalies computed from global geopotential models. Finally the quasigeoid models obtained from gravity data with use of different global geopotential models were verified against corresponding height anomalies at GPS/levelling sites in Poland. Data quality was discussed and best fitting global geopotential model in Poland was specified. It was shown that the quality of the present solutions of POLREF and EUVN networks does not allow for quantifying the improvement of quasigeoid models due to the use of newly developed geopotential models. 1. Gravity data (47oN-57oN; 11oE-26oE) used Gravity data available at the area of interest are not uniform both in terms of quality and coverage. Terrestrial gravity data used for quasigeoid modelling consists of 2 × 2 km grid of free-air gravity anomalies generated from inhomogeneous set of point and mean gravity anomalies of different spatial resolution, acquired within last 50 years (Fig. 1). They differ in geodetic datums, gravity systems, normal gravity formulae, atmospheric corrections. Fig. 1. Distribution of terrestrial and marine gravity data. Different data sets including those from different marine gravity surveys in Baltic Sea are distinguished with different colours and patterns There is still a shortage of information needed for full unification of gravity data; complete information is only available for gravity data from Poland. It can be specified as follows over 800 000 point data, almost uniformly distributed, form gravity surveys conducted for geological prospecting since 1951, measurements with Ascania GS-11, Sharp or Worden gravimeters in two hours loops, drift eliminated by linear interpolation with respect to the time between the control stations, _______________________________________________________________________________________________________________________________________________________________ 1 Jan Krynski, Institute of Geodesy and Cartography, 27 Modzelewskiego St, PL 02-679 Warsaw, Fax: +48 22 3291950, Tel.: +48 22 3291904, Email: [email protected] 2 Adam Lyszkowicz, University of Warmia and Mazury, Heweliusza 12, PL 10-724 Olsztyn, Fax: +48 89 5234878, Tel.: +48 89 5234579, E-mail: [email protected]; Space Research Centre PAS, 18A Bartycka St, PL 00-710 Warsaw, Fax: +48 22 8403131, Tel.: +48 228403766, Email: [email protected]