1. Using GNSS to establish a Height Datum on a Survey
Richard Stanaway QUICKCLOSE

2. Overview of GNSS Heighting
Height systems and Geoid models
AHD and MSL
Measuring ellipsoid Heights
Working with height datum offsets
Victorian case-study - Murray Valley LiDar

3. The Geoid
Universität Stuttgart

4. Heighting Surfaces

5. Differences between MSL and the geoid (Mean Dynamic Topography)

6. H = h - N
N = h - H

7. Australian Height Datum

8. GDA94 Ellipsoid Height

9. Ausgeoid98

10. local AHD offset (o) can computed by GNSS/GPS measurements at local PMs.
o = H(AHD) – h(GDA94) + N(Ausgeoid98)
H(AHD) = h(GDA94) - N(Ausgeoid98) + o

11. Complications….. AHD20?? – 0.1 to 0.2 m higher (sea level rise)
Regional and localised subsidence (groundwater changes)
Levelling errors and mark disturbance

12. Antenna Reference Point and Phase Centre
GNSS measurements made to phase centre (and not antenna reference point)
“trunnion axis of the GPS”
Different antennas have different phase centre offsets!!
Good advice to use phase centre heights rather than ARP heights if different antennas are used

13. Steps to get “local” AHD using GNSS/GPS
1. Determine phase centre offsets / models
Ensure correct geoid model is used (Ausgeoid98 or Ausgeoid09 in Victoria)
3. Take measurements at local high order (3rd order or higher) PMs/PSMs to compute offset (o)
(The Ausgeoid surface should be parallel with AHD over a localised area)
Apply the offset to Ausgeoid derived elevations in order to align them with local AHD
Some later GNSS systems have a local geoid builder in their software (local AHD calibration).
Alternatively, a local geoid model can be created and loaded into a GNSS controller or software

14. LiDar Ground validation - example

15. Ground Validation Points

16. Local AHD Control

17. Control Information

18. Static Data Processing - Setup

19. Network and Baselines

20. Network and Baselines

21. Baseline
solutions
Results

22. Thank You! More information at: www.quickclose.com.au/publications.htm