| dc.description.abstract | Norway is about to realize a new vertical datum NN2000, which is supposed to replace the present datum NN1954. Norwegian Mapping Authority (NMA) is also realizing a new geodetic reference frame ITRF09, with focus mainly on vertical accuracy. The present geodetic reference frame EUREF89 was realized as a horizontal frame. Norwegian Mapping Authority has earlier calculated geoid-type surfaces for converting ellipsoidal heights in EUREF89 to normal heights in NN1954. In this study, we have calculated geoid-type surfaces for the new vertical datum NN2000, by fitting the gravimetric quasigeoid model NKG2004 to Global Navigation Satellite System (GNSS)/leveling data in a test area in eastern Norway. The calculations were carried out by the geodetic gravity field modeling programs GRAVSOFT, where the fitting process to GNSS-levelling data are done by least squares collocation or weighted mean methods. The results from calculations show that the new vertical datum NN2000 yields improved accuracy compared to NN1954. Assessment of the geoid-type surface models computed from EUREF89/NN2000 and EUREF89/NN1954 shows Standard Deviations (SD) of 15 mm and 20 mm, respectively. Standard deviation of 20 mm for EUREF89/NN1954 is in accordance with empirical values of latest model calculated by NMA. Analogous fitting process to ITRF09/NN2000 gives standard deviation of 23 mm, indicating that ITRF09 does not yield improved accuracy. However, ITRF09 coordinates used in the calculations where preliminary, so final coordinates are expected to give more accurate geoid-type surfaces. Fitting to GNSS/leveling data is tested by varying number of GNSS/leveling stations, indicating that increasing number of stations does not automatically yield better accuracy for the estimated geoid-type surface models in this study. The accuracy of the model is relatively stabilized for 30 GNSS/leveling stations in test area in eastern Norway. | en_US |
