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

8Since the beginning of the 1990’s, asystematic inventory/updating of thenetwork is continuously performed.The work with implementing RH 2000among other authorities in Sweden is inprogress. 106 of the 290 Swedishmunicipalities have, in co-operationwith Lantmäteriet, started the processof analysing their local networks, withthe aim to replace the local heightsystems with RH 2000. So far, 33municipalities have finalised thereplacement for all activities, which is29 more than by the time for the lastNKG General Assembly four years ago.1.8 Geoid modelsThe national Swedish geoid model,SWEN08_RH2000 was released in thebeginning of 2009. It has beencomputed by adapting the Swedishgravimetric model KTH08 to thereference systems SWEREF 99 andRH 2000 by utilising a large number ofgeometrically determined geoidheights, computed as the differencebetween heights above the ellipsoiddetermined by GNSS and levellednormal heights above sea level. In thisstep, a correction has been applied forthe postglacial land uplift and fordifferences in permanent tide systems.A smooth residual surface is used tomodel the GNSS/levelling residuals(residual interpolation).The standard uncertainty ofSWEN08_RH2000 has been estimatedto 10-15 mm everywhere on theSwedish mainland with the exceptionof a small area in the north-west notcovered by the third precise levelling,see Figure 1.8. The standarduncertainty is larger in the latter areaand at sea, probably around 5-10 cm.706968676665646362616059585756555410 12 14 16 18 20 22 240.0480.0460.0440.0420.040.0380.0360.0340.0320.030.0280.0260.0240.0220.020.0180.0160.0140.0120.010.008Figure 1.8: Expected accuracy (standarduncertainty) for the geoid modelSWEN08_RH2000 (metre).The underlying gravimetric model,KTH08, has been computed by thetechnique called LSMSA 23 . This workhas been made in co-operation withProfessor Sjöberg and his group atKTH 24 in Stockholm (Ågren et al., 2009).Another geoid related activity duringthe last four years has been theevaluation of EGM 2008 25 (Ågren, 2009).Presently Lantmäteriet investigateswhat is required of the national gravitysystem and gravity data to be able tocompute a more accurate geoid model23LSMSA = Least Squares Modification of Stokes Formulawith Additive Corrections24KTH = Royal Institute of Technology (Kungliga TekniskaHögskolan), Stockholm25EGM2008 = Earth Gravitational Model 2008