1. A NEW HEIGHT DATUM FOR UGANDA
The 3rd Conference on Advances in Geomatics Research 6th-7th August Kampala 2015
A NEW HEIGHT DATUM FOR UGANDA
Ronald Ssengendo1,2, Lars.E. Sjöberg2, Anthony Gidudu1
1 CEDAT, Makerere University
2 Royal Institute of Technology, Division of Geodesy, SE Stockholm, Sweden

2. outline Introduction- geoid/quasigeoid, GNSS height determination
Uganda Vertical Network- current status
UGG2014 & UGQ determination & evaluation
Determination of the New height datum-UGQ2014C
Evaluation of UGQ2014C
Conclusions & way forward

3. Introduction
Need for geoid/quasigeoid model?---GNSS-HEIGHT DETERMINATION

4. Uganda Vertical Network

5. Uganda Vertical Network
Status
Number of points
Stations
Good condition 14
Buteba, Jinja, Mbarara, Kasese, Fortportal, Mabale, Mubende, Kiboga, Rhino Camp, Kabale, Ishasha, Yumbe, Pakelle, Nakalama
Partially destroyed 2
Packwach and Bukonte
Not sure 22
Dokolo, Soroti, Abella, Nakasongola, Hoima, Busunju, Hamurwa, Kikarara, Kyenjojo, Kibaliga, Tororo, Karuma, Okollo, Laropi, Pabo, Achwa, Nkonge, Mutir,Anaka, Kanungu and Koputh

6. Uganda Vertical Network

7. Uganda Vertical Network

8. Uganda Gravimetric Geoid Model 2014 (UGG2014)
UGG 2014 computed by Ssengendo et al., (2015a)-KTH Method

9. Uganda Gravimetric Geoid Model 2014 (UGG2014)
UGG 2014 computed by Ssengendo et al., (2015a)-KTH Method
Data used for the determination of the geoid model
7839 terrestrial gravity data from BGI
World Gravity Map 2012 surface gravity anomalies –BGI
SRTM3 DEM—CGIAR-CSI
GOCE-only GGM—GO_CONS_GCF_2_TIM_R5 (maximum degree=280)
10 GNSS/levelling points

10. Uganda Gravimetric Quasigeoid Model 2014 (UGQ2014)
Uganda Vertical Network – normal-orthometric heights
UGQ2014 determined indirectly from UGG2014

11. Evaluation of UGG2014/UGQ2014—GNSS/levelling
Modelling options – systematic biases

12. Evaluation of UGG2014/UGQ2014—GNSS/levelling
Results -- Statistics of residuals at 12 GNSS/levelling points (Unit: cm)
Model
Min.
Max.
Mean
Std.
RMS
UGG2014
before
-14.6
36.8
9.3
13.2
15.7
4-parameter
-15.6
13.6
0.0
9.1
8.7
5-parameter
-21.3
30.1
12.2
11.7
UGQ2014
-30.5
14.6
-8.6
12.8
14.9
-17.5
14.4
8.1
7.7
-15.7
13.4
6.7
6.4

13. Determination of the new height datum-UGQ2014C
New height datum – combination of UGQ2014 & GNSS/levelling

14. Determination of the new height datum-UGQ2014C
New height datum – corrector surface determined by the Kriging method

15. Determination of the new height datum-UGQ2014C

16. Validation of the new height datum-UGQ2014C
Absolute heights (Unit : cm) Relative heights
Model
Min.
Max.
Mean
Std.
RMS
UGQ2014
-5.2
30.5
9.0
15.4
16.1
UGQ2014C
-12.6
16.6
-1.6
12.6
11.1

17. Conclusion & way forward
Conclusions
Results satisfy the requirements for third order precise levelling
GNSS observations coupled with the new datum can be used to replace spirit levelling in most engineering applications
UGQ2014C provides a practical solution to the GNSS/levelling problem
However
heterogeneous distribution of terrestrial gravity data– to achieve the ‘1 cm geoid’
homogeneous network of GNSS/levelling benchmarks--improve the fit between the gravimetric solutions and GNSS, hence improving the new height datum

18. THANK YOU