Ramin Kiamehr

The new gravimetric quasigeoid model KTH08 over Sweden

Abstract The least squares modification of Stokes formula has been developed in a series of papers published in Journal of Geodesy between 1984 and 2008. It consists of a least squares (stochastic) Stokes kernel modification with additive corrections for the topography, downward continuation, the atmosphere and the ellipsoidal shape of the Earth. The method, developed at the Royal Institute of Technology (KTH) will here be denoted by the abbreviated name the KTH method. This paper presents the computational results of a new gravimetric quasigeoid model over Sweden (the KTH08 model) by employing the KTH method. Traditionally the Nordic Geodetic Commission (NKG) has computed gravimetric quasigeoid models over Sweden and other Nordic countries; the latest model being NKG 2004. Another aim of this paper is therefore to compare KTH08 and NKG 2004 quasigeoid models and to evaluate their accuracies using GNSS/levelling height anomalies. The rms fit of KTH08 in 196 GNSS data points distributed over Sweden by using a 1(4)-parameter transformation is 22 (20) mm. It is concluded that KTH08 is a significant step forward compared to NKG 2004.

A New Height Datum for Iran Based on the Combination of the Gravimetric and Geometric Geoid Models

A new geoid model for Iran (IRG04) is computed based on the method of least squares modification of Stokes formula based on the most recent gravity anomaly database, SRTM high resolution Digital Elevation Model (DEM) and GRACE GGM02 Global Geopotential Model. In order to define a new height datum for Iran, we attempt to combine this high resolution gravimetric geoid model with GPS/levelling data by using a corrective surface idea. The corrective surface is constructed based on 224 GPS/levelling points and then evaluated with 35 independent points. Different interpolation techniques were tested for the creation of the corrective surface; among them the Kriging method gives the minimum RMS and noise level versus the suggesting that GPS/levelling data. The RMS of fitting the new combined geoid model versus GPS/levelling data is 0.09 m, it is near 4 times better accuracy compared with the original gravimetric geoid model. Comparing the later model, the new surface should be more convenient and useful in definition of the new height datum, specifically in engineering and GPS/levelling projects.