Geodesy Group, Royal Institute of Technology, SE -100 44 Stockholm, Sweden and Department of Geomatics, Zanjan University, 313, Zanjan, Iran
Since 1986, several gravimetric geoid models have been published in the Iran region. It was found that the standard deviation of fitting between these models versus GPS/levelling data in most cases was worse than the currently available global geopotential models. A new hybrid gravimetric geoid model computed (IRG04) by using the least squares modification of Stokes formula based on the recent published GRACE based global geopotential model, the high-resolution Shuttle SRTM global digital terrain model and a new Iranian gravity anomaly database. The absolute and relative accuracies of the new geoid model tested versus the GPS/levelling points and they are estimated about 0.27 m and 3.8 ppm, respectively. Additional comparison between the IRG04 and the recent published gravimetric geoid models shows that the relative accuracy of the IRG04 is almost 4 times better than the most recent published models in this area.