K e y w o r d s: EGM08, quasigeoid heights, ellipsoidal heights, normal heights. A b s t r a c tThe paper presents the evaluation results for the new Earth Gravitational Model (EGM08) that was recently released by the US National Geospatial Intelligence Agency, using GPS and normal heights from precise levelling in the area of Poland. Detailed comparisons of quasigeoid heights obtained from the EGM08 model and other combined global geopotential models with GPS/levelling data have been performed in both absolute and relative sense. The test network covers the entire part of the Poland territory and consists of 360 sites which belong to the Polish national primary triangulation network, with direct levelling ties to the Polish vertical reference frame. The spatial positions of these sites have been determined at cm-level accuracy with respect to ETRF89 during a nation-wide GPS campaign that was organized in the frame of the EUREF activity. Additionally for relative accuracy evaluations of EGM08 model precise GPS/levelling traverse was used. Our results reveal that EGM08 offers a major improvement (more than 80%) in the agreement level among quasigeoidal, ellipsoidal and normal heights over the area of Poland, compared to the performance of previous combined geopotential models for the same area. OCENA DOKŁADNOŚCI MODELU EGM08 NA OBSZARZE POLSKI Adam ŁyszkowiczKatedra Geodezji Szczegółowej Uniwersytet Warmińsko-Mazurski w Olsztynie S ł o w a k l u c z o w e: EGM08, odstepy, odstępy quasi-geoidy, wysokości elipsoidalne, wysokości normalne.A b s t r a k t W pracy podano wyniki oceny jakości nowego modelu geopotencjału Ziemi jaki ostatnio udostępnił US National Geospatial Intelligence Agency. Ocenę bezwzględnej i względnej dokładności modelu przeprowadzono przez porównanie odstępów quasi-geoidy wyliczonych z modelu z odstępami uzyskanymi z satelitarnych pomiarów GPS i niwelacji precyzyjnej. Bezwzględna dokładność modelu była testowana na satelitarnej sieci GPS, która pokrywa równomiernie obszar kraju. Sieć ta składa się z 360 punktów należących do krajowej podstawowej sieci triangulacyjnej. Trójwymiarowe współrzędne kartezjańskie punktów tej sieci wyznaczono w układzie ETRF89 z pomiarów satelitarnych GPS podczas kampanii zorganizowanej w ramach Podkomisji EUREF. Względna dokładność modelu była testowana na precyzyjnym trawersie pomierzonym techniką GPS i dowiązanym do sieci niwelacji precyzyjnej. Uzyskane wyniki pokazują, że model EGM08 daje znacznie lepszą zgodność (ponad 80%) między odstępami quasi-geoidy, wysokościami elipsoidalnymi i wysokościami normalnymi niż poprzednie modele.
One of the fundamental problems of modern geodesy is precise defi nition of the gravitational fi eld and its changes in time. This is essential in positioning and navigation, geophysics, geodynamics, oceanography and other sciences related to the climate and Earth’s environment. One of the major sources of gravity data is satellite altimetry that provides gravity data with almost 75% surface of the Earth. Satellite altimetry also provides data to study local, regional and global geophysical processes, the geoid model in the areas of oceans and seas. This technique can be successfully used to study the ocean mean dynamic topography. The results of the investigations and possible products of altimetry will provide a good material for the GGOS (Global Geodetic Observing System) and institutions of IAS (International Altimetry Service). This paper presents the achievements in satellite altimetry in all the above disciplines obtained in the last years. First very shorly basic concept of satellite altimetry is given. In order to obtain the highest accuracy on range measurements over the ocean improved of altimetry waveforms performed on the ground is described. Next, signifi cant improvements of sea and ocean gravity anomalies models developed presently is shown. Study of sea level and its extremes examined, around European and Australian coasts using tide gauges data and satellite altimetry measurements were described. Then investigations of the phenomenon of the ocean tides, calibration of altimeters, studies of rivers and ice-sheets in the last years are given.
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