National Report of Sweden to the NKG General ... - Lantmäteriet

14Figure 2.1: At the EUREF symposium inGävle June 2-5 2010, which was arrangedin co-operation between Lantmäteriet, KTHand Onsala Space Observatory, apresentation was held about a rigorousformula for the geoid-to-quasigeoidseparation. The session was chaired byMarkku Poutanen of FGI. Photo: ÖrjanZackrisson.The KTH geoid computation technique,called LSMSA 36 , is unique in the sensesthat it uses 1) least squares modificationof Stokes formula and 2) adds allcorrections for topography, atmosphereand ellipsoidal effects separately ascombined corrections.Most of this development wascompleted during 2006-2010, and themethod has proved to be the best intests, or at least not worse than anyother method, among these tests aninternational comparison of gravimetricgeoid software packages vs. GPSlevellinggeoid models. For references,see Ågren et al. (2008) and (2009), andUlotu (2009).studies dealt with a technique todetermine the geoid and orthometricheights from satellite positioning andgeopotential numbers (Sjöberg 2006a)and refinement of the conversion fromnormal to orthometric height (Sjöberg2006b). Also, Sjöberg (2009a) presenteda new method to determine Mohodepth by using Vening Meinesz-Moritzhypothesis of a global isostaticcompensation of the topography with aspherical approximation of sea level.When computing the precise geoid bystandard or modified Stokes formula(e.g. the RCR-method), the correctionfor the topographic masses is aconsiderable workload. This job is verysignificantly reduced in the LSMSAmethod, where the combinedtopographic correction is reduced tothat of the spherical Bouguercorrection, while the additional terraincorrection is eliminated. See Sjöberg(2007a), (2008a), (2009a).The KTH-method, based on LSMSA,has been applied in 3 Master’s thesisprojects to compute geoid models forGreece (Daras et al. 2008), Sudan andKazakhstan, respectively.Sjöberg and Eshagh (2009) presented anew method for geoid determinationfrom airborne gravity data. Other36LSMSA = Least Squares Modification of Stokes Formulawith Additive Corrections