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Computation of the Gravimetric Quasigeoid Model over Uganda Using the KTH Method
KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Satellite Positioning.
KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Satellite Positioning.
Makerere University.
2015 (English)Conference paper, Abstract (Other academic)
Abstract [en]

The gravimetric quasigeoid can be determined either directly by Stokes formula or indirectly by computing the geoid first and then determining the quasigeoid-to-geoid separation which is then used to determine the quasigeoid. This paper presents the computational results of the gravimetric quasigeoid model over Uganda (UGQ2014) based on the later technique. UGQ2014 was derived from the Uganda Gravimetric Geoid Model (UGG2014) which was computed by the technique of Least Squares Modification of Stokes formula with additive corrections commonly called the KTH Method.  UGG2014 was derived from sparse terrestrial gravity data from the International gravimetric Bureau, the 3 arc second SRTM ver4.1 Digital Elevation Model and the GOCE-only geopotential model GO_CONS_GCF_2_TIM_R5.  The quasigeoid-to geoid separation was then computed from the Earth Gravitational Model 2008 (EGM08) complete to degree 2160 of spherical harmonics together with the global topographic model DTM2006.0 also complete to degree 2160.

Another aim of this paper is to compare the approximate and strict formulas of computing the quasigeoid-to-geoid separation and evaluate their effects on the final quasigeoid model. Using 10 GNSS/levelling data points distributed over Uganda, the RMS fit of the quasigeoid model based on the approximate formula are 27 cm and 10 cm before and after a 4-parameter fit, respectively. Similarly, the RMS fit of the model based on the strict formula are 15 cm and 6 cm, respectively. The results show the improvement to the final quasigeoid model brought about by using the strict formula to model more effectively the terrain in the vicinity of the computation point. With an accuracy of 6 cm, UGQ2014 represents significant progress towards the computation of a final gravimetric geoid over Uganda which can be used with GNSS/levelling. However, with more data especially terrestrial gravity data and GNSS/levelling we anticipate that the accuracy of gravimetric quasigeoid modelling will improve in future.

Place, publisher, year, edition, pages
2015. 1-17 p.
Keyword [en]
Geoid, Quasigeoid, Quasigeoid-to Geoid Separation, GNSS
National Category
Geosciences, Multidisciplinary
Research subject
Geodesy and Geoinformatics
URN: urn:nbn:se:kth:diva-169470OAI: diva2:821506
FIG Working Week 2015 17-21 May, 2015 Sofia Bulgaria

QC 20150618

Available from: 2015-06-15 Created: 2015-06-15 Last updated: 2015-06-18Bibliographically approved

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Ssengendo, RonaldSjöberg, Lars
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