Beyond GEOID 12 Implementing a New Vertical Datum
Beyond GEOID 12: Implementing a New Vertical Datum for North America Daniel R. Roman, Ph. D. Neil D Weston, Ph. D.
Why isn’t NAVD 88 good enough anymore? Approximate level of error known to exist in the NAVD 88 zero elevation surface TSC 04 B: Heights, Geoid, & Gravity Paper 5691, 08 May 2012, 0900 F. I. G. Working Week 2012 6 -10 May 2012 Rome, Italy 3
Available Tide Gauges TSC 04 B: Heights, Geoid, & Gravity Paper 5691, 08 May 2012, 0900 F. I. G. Working Week 2012 6 -10 May 2012 Rome, Italy 4
SST, TBM’s and the Geoid • P, T, S ≠ constant/uniform • Geoid + SST = LMSL (as seen at tide gauge) Local MSL Geoid = “Global” MSL surface TSC 04 B: Heights, Geoid, & Gravity Paper 5691, 08 May 2012, 0900 F. I. G. Working Week 2012 6 -10 May 2012 Rome, Italy SST/MODT 5
SST (MODT) Models Foreman et al. 2004 TSC 04 B: Heights, Geoid, & Gravity Paper 5691, 08 May 2012, 0900 Thompson-Demiorov 2006 F. I. G. Working Week 2012 6 -10 May 2012 Rome, Italy 6
Tide Gauge comparisons limited to where SST models exist 62, 636, 856. 00 m 2/s 2 TSC 04 B: Heights, Geoid, & Gravity Paper 5691, 08 May 2012, 0900 F. I. G. Working Week 2012 6 -10 May 2012 Rome, Italy 7
Current GRAV-D Coverage GRAV-D: Gravity for the Redefinition of the American Vertical Datum TSC 04 B: Heights, Geoid, & Gravity Paper 5691, 08 May 2012, 0900 F. I. G. Working Week 2012 6 -10 May 2012 Rome, Italy 8
Summary • NAVD 88 is insufficient to meet cm-level needs • Must use highly accurate gravimetric geoid • New W 0 best fits most Tide Gauges – SST models remove significant variability in LMSL – Same W 0 value adopted by IAU and IERS – Neglects Arctic but also Mexico & Caribbean TSC 04 B: Heights, Geoid, & Gravity Paper 5691, 08 May 2012, 0900 F. I. G. Working Week 2012 6 -10 May 2012 Rome, Italy 9
Summary • U. S. A & Canada have agreed to use this W 0 – 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 TSC 04 B: Heights, Geoid, & Gravity Paper 5691, 08 May 2012, 0900 F. I. G. Working Week 2012 6 -10 May 2012 Rome, Italy 10
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