Computation of the Gravimetric Quasigeoid Model over Uganda Using the KTH Method
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Date
2015
Journal Title
Journal ISSN
Volume Title
Publisher
Sofia Bulgaria
Abstract
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 quasigeoid 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.
Description
Keywords
Geoid, Quasigeoid, Quasigeoid-to Geoid Separation, GNSS
Citation
Ssengendo, R., Sjöberg, L., & Gidudu, A. (2015). Computation of the gravimetric quasigeoid model over Uganda using the KTH method. In FIG Working Week 2015 17-21 May, 2015 Sofia Bulgaria (pp. 1-17).