1. Beyond GEOID12: Implementing a New Vertical Datum for North America
Daniel R. Roman, Ph.D.
Neil D Weston, Ph.D.

2. Outline Why isn’t NAVD 88 good enough anymore?
Selection of a datum surface (W0)
Tide gauges
SST/MODT
Aerogravity coverage
Summary
TSC04B: Heights, Geoid, & Gravity Paper 5691, 08 May 2012, 0900
F.I.G. Working Week 2012
6-10 May Rome, Italy

3. Why isn’t NAVD 88 good enough anymore?
This map reflects the sort of height changes that users could expect if NAVD 88 were replaced with a geoid-based vertical datum. This is only a large scale approximation and should not be used as an absolute guide.
Approximate level of error known to exist in the NAVD 88 zero elevation surface
TSC04B: Heights, Geoid, & Gravity Paper 5691, 08 May 2012, 0900
F.I.G. Working Week 2012
6-10 May Rome, Italy 3

4. Available Tide Gauges
TSC04B: Heights, Geoid, & Gravity Paper 5691, 08 May 2012, 0900
F.I.G. Working Week 2012
6-10 May Rome, Italy

5. SST, TBM’s and the Geoid P,T,S ≠ constant/uniform
Geoid + SST = LMSL (as seen at tide gauge)
SST/MODT
Local MSL
Geoid = “Global” MSL surface
TSC04B: Heights, Geoid, & Gravity Paper 5691, 08 May 2012, 0900
F.I.G. Working Week 2012
6-10 May Rome, Italy

6. SST (MODT) Models Foreman et al. 2004 Thompson-Demiorov 2006
TSC04B: Heights, Geoid, & Gravity Paper 5691, 08 May 2012, 0900
F.I.G. Working Week 2012
6-10 May Rome, Italy

7. Tide Gauge comparisons limited to where SST models exist
62,636, m2/s2
TSC04B: Heights, Geoid, & Gravity Paper 5691, 08 May 2012, 0900
F.I.G. Working Week 2012
6-10 May Rome, Italy

8. Current GRAV-D Coverage
GRAV-D: Gravity for the Redefinition of the American Vertical Datum
TSC04B: Heights, Geoid, & Gravity Paper 5691, 08 May 2012, 0900
F.I.G. Working Week 2012
6-10 May Rome, Italy

9. Summary NAVD 88 is insufficient to meet cm-level needs
Must use highly accurate gravimetric geoid
New W0 best fits most Tide Gauges
SST models remove significant variability in LMSL
Same W0 value adopted by IAU and IERS
Neglects Arctic but also Mexico & Caribbean
TSC04B: Heights, Geoid, & Gravity Paper 5691, 08 May 2012, 0900
F.I.G. Working Week 2012
6-10 May Rome, Italy

10. Summary U.S.A & Canada have agreed to use this W0
Will serve as Canadian Vertical Datum in 2013
It is the likely value for U.S. in 2022
GRAV-D aerogravity will bridge gap
Satellite gravity models will provide unification
Surface gravity & DEM’s give high frequency
Aim is for cm-level accuracy in geoid and GNSS
TSC04B: Heights, Geoid, & Gravity Paper 5691, 08 May 2012, 0900
F.I.G. Working Week 2012
6-10 May Rome, Italy