Olga Bjelotomić

HRG2009: New High Resolution Geoid Model for Croatia

Using an updated Earth´s gravity field data set widely available and applying the least square collocation calculation technique, a new Croatian geoid model HRG2009 was calculated. Significant accuracy improvements have been achieved regarding the previous national geoid model HRG2000; four times better resolution and 69 % better absolute accuracy of the model. The following data sets were used: great number of new measured terrestrial gravity data and data obtained from satellite altimetry for the area of the Adriatic Sea, along with geoid undulations at discrete points measured by GNSS/leveling on almost 500 stations all over the mainland, futhermore long and mediumwave field structures taken from the latest detailed global geopotential model EGM2008 and high frequencies field structures modeled with the help of 3 ′′ × 3 ′′ Shuttle Radar DEM’s. Absolute accuracy assessment made on 59 GNSS/leveling control stations, that were not used in calculations, have resulted with 69 % improvement of new national geoid model regarding the previous one, with standard deviation of 3. 5 cm on overall computation area. It is significantly more reliable surface as compared to the earlier HRG2000 solution with standard deviation of 11.4 cm.The new geoid surface has been used for different purposes, primary in the precise height definition using modern GNSS technology. Therefore, the Croatian Positioning System CROPOS was upgraded in 2011 with the new service which enables the real time transformation of ellipsoidal heights to the (normal) orthometric heights using HRG2009 geoid GRID and Trimble Transformation Generator software for more than 440 surveying and geoinformation companies in Croatia.