00254260 Kiamehr¡ Ramin Geodesy. amp;006090060301 Testing The Iranian Gravimetric Geoid, /Ramin Kiamehr; Supervisor: Prof. Petr Vanicek. 100p., Tab., Chart, Map DISS Status: Finished, Date: 11-4-1995 dissertation(MSc.)--; K.N. Toosi University of Technology, Department of Surveying¡ 1995. <br>To test the accuracy of the Iranian gravimetric geoid computed by the IfAG group, I used 55 points of Global Positioning System (GPS) network with stations of Iranian first order leveling network, chosen in different parts of the country. In order to study the effect of topography and gravity data coverage on geoid accuracy I also select five traverses in different part of the country from these points. According to the results of this research the absloute accuraccy of IfAG computed geoid is estimated as 1.56 m; similary, for the five selected frofiles I get respectivly accuracy with the range of 0.90 m to 1.92 m . The best results are seen in the west and center of country ( 0.90 and 0.91 m respectively ) and the worst in the north and south-east ( 1.92 and 1.27 respectively ). It can be clearly shown that in these areas have the greatest lack of gravity points . To test the relative accuracy of the geoid, I computed relative geoidal undulations for all possible baselines and seperately for the five above selected profiles. The average relative accuracy of the IfAG computed geoid is 36 ppm for all possible baselines (using 55 poins) and 21.3 - 57.7 ppm for the five selected profils for average basline length. Agains I get the worst results in the north and south-east of country ( 35.2 and 57.7 ppm ). <br><br>In order to absorb the effect of the long-wavelength errors of geopotential model s, bad gravity coverage (the north and south-east of the countury are not well covered), bad elevation datum for the gravity observations (since barometric leveling was mostly used), systematic errors in the differential leveling and problems in the GPS datum, a simple datum shift is determined by a regression. The results improve slightly : the RMS of geoids fits reduce from 1.38 m to 0.99 m and I get the average accuracy of the geoid equal to 1.17 m. It is noted that the cooresponding datum shift parameters are of the order of 4 to 15 m and are therefore unrealistic as a true datum shift. But the shift seems useful for absorbing the long-wavelength geoid erorrs.<br><br> In testing any gravimetric geoid it is usual to test its internal estimate of accuraccy against another independent approach such as GPS/leveling. In this reseach however I can not get any reliable values from the IfAG groups. According to a personal feeling of one members of the IfAG group it can't be much better than about 1 m. the results of this research should that even the expected value of 1 m is rejected against 1.56 m ( my external estimation of absloute accuracy). <br> <br> ŽÆæÆíÏ ÌÇÐÈí geoid, GPS, leveling Vanicek¡ Prof. Petr, ÇÑ K.N. Toosi University of Technology, Department of Surveying K.N. Toosi University of Technology, Department of Surveying