1. Upcoming Changes to the National Spatial Reference System
— The Upcoming Changes in National Datums —
(and a few other related topics)
ACSM
Survey Summit 2011
Dave Minkel
National Geodetic Survey
APLS Geospatial Professional

2. NGS 10-Year Plan (excerpts)
Vision 1# Summary:
By 2018, NGS has defined a new geometric datum (classically called “horizontal”) to replace NAD 83 with its many systematic errors. The primary means of accessing this new datum is GNSS technology.
Vision #2 Summary: By 2018, a new geopotential datum (for orthometric and dynamic heights) is defined and realized through the combination of GNSS technology and gravity field modeling.
Note: Vision #2 can not happen without Vision #1.

3. NGS 10-Year Plan (more excerpts)
“NGS redefines the national horizontal datum to remove gross disagreements with the ITRF.”
“The primary means of accessing this new datum is GNSS technology. While passive control continues to be used as a secondary method to access the NSRS, such control will be “tied to”, not a “part of”, the NSRS.”
“Furthermore, NGS will provide simple transformation tools between historic and current datums and reference frames used by NGS, in four dimensions, wherever practical and possible.”
“In order to support users of NAVD 88, NGS will provide transformation tools between the new datum and NAVD 88 based predominantly on the few thousand measurements of GPS derived ellipsoid heights on NAVD 88 benchmarks.”
Underlining added for emphasis

4. Why a New Datum(s)? NAD 83 NAVD 88
non-geocentric, i.e. inconsistent with GNSS positioning
NAD 83 coordinates of the Continuously Operating Reference Station (CORS) network inconsistent with passive marks
Lack of velocities, i.e. NAD 83 does not report station motion for passive marks
NAVD 88
cross-country build up of errors (“tilt” or “slope”) from geodetic leveling
Passive marks inconveniently located and vulnerable to disturbance and destruction
A 0.5 m bias in the NAVD 88 reference surface from the geoid surface best approximating global mean sea level
Subsidence, uplift, freeze/thaw, and other crustal motions invalidate heights of passive marks, and can make it difficult to detect such motions.
Passive marks without adequate geophysical models make it difficult to reliably detect sea level change
Changes to Earth’s gravity field cause changes in orthometric heights, but NAVD 88 does not allow/account for those changes (because it is based on a static gravity model)
The gravity model and modeling techniques used to determine NAVD 88 are not consistent with those currently used for geoid modeling

5. In other words, horizontal coordinates will change.
Geometric Datum
“NGS redefines the national horizontal datum to remove gross disagreements with the ITRF.”
In other words, horizontal coordinates will change.

6. Z Y X Greenwich Meridian Equator A ECEF Coordinates (XA,YA,ZA,)
Latitude, Longitude,
& Height
(, , h)
Ellipsoid Height
Longitude
Greenwich
Meridian
GRS80 Ellipsoid
Earth Mass Center ZA
- Y
Latitude
- X YA Y X XA
Equator
- Z
Reference Frames 101

7. Z Y X “gross disagreements with the ITRF” (?) A Shift ≈ 2.2m + GRS 80
Earth Mass Center
Shift ≈ 2.2m +
GRS 80
Ellipsoid
NAD 83
Earth Mass Center Y X
TX = m
RX = – mas
DS = 0.62 X 10-9
TY = – m
RY= –9.426 mas
ITRF00 to NAD83(CORS96)
TZ = – m
RZ= – mas

8. WAMs = 4.9 ft to 2.6 ft

9. To SNARF or not to SNARF SNARF (Stable North American Reference Frame)
Most of North America does not move w/r to itself
NAD 83 is fixed w/r to the North American Plate
All continents show movement (coordinate change) in the ITRF system
Should the new geometric datum be fixed w/r to SNARF or ITRF?
Note: One could also “fix” the new datum to a particular epoch of ITRF
“And while the “stable” North American Plate is a significant portion of the CONUS region, NGS can not at this time commit itself to fixing the new geometric datum to that plate. The exact definition of this new geometric datum will be determined through a series of stakeholder feedback forums which will seek to achieve the best solution for all parties.” — NGS 10-Year Plan excerpt (emphasis added)

10. ITRF 2005 velocities with respect to NAD 83 (from Craymer, et al
ITRF 2005 velocities with respect to NAD 83 (from Craymer, et al., NAREF, 2007)
20 mm ≈ 0.8 in
If the new datum is NOT fixed to SNARF, or a particular ITRF epoch, this depicts the annual horizontal coordinate change one can expect.

11. And now….. the rest of the story.
Orthometric Heights,
a.k.a. NAVD 88 elevations

12. “NGS redefines the national horizontal datum to remove gross disagreements with the ITRF.”
In other words, ellipsoid heights will change.
“By 2018, a new geopotential datum (for orthometric and dynamic heights) is defined and realized through the combination of GNSS technology and gravity field modeling.”
In other words, orthometric heights will NOT be based on leveling data and they too will change.

13. The Relationship of Heights

14. WAMs = ft to ft

15. GPS Bench Marks (GPSBMs)
(USGG09) H
(NAVD 88)
NAVD 88 (GEOID09)
Errors in NAVD 88 :
~50 cm average, 100 cm CONUS tilt,
1-2 meters average in Alaska
Geoid (USGG09)

16. WAMs = ft to ft

17. GPS-derived orthometric heights Warning #1 H ≈ h - N
NAVD 88 height ≈ NAD 83 ellipsoid height - GEOID03
NAVD 88 height ≈ NAD 83 ellipsoid height - GEOID09
Provide, to client(s), datum & realization, ellipsoid heights, geoid model used, methodology (e.g. OPUS or adjusted survey), along with orthometric heights.
GPS-derived orthometric heights Warning #2
H ≈ h – N
The Hybrid GEOID model is defined with respect to a particular realization of NAD 83.
GEOID09 should only be used with NAD 83(NSRS 2007)
GEOID03 should only be used with NAD 83(1992 aka HARN)
NAD 83(HARN) – NAD 83(NSRS2007) in Arizona:
Heights -> min = cm, max = 11.5 cm, avg = -2.4 cm
WAMs = ft to ft

18. NAVD 88 “Slope”

19. GRAV-D
Gravity for the Redefinition of the American Vertical Datum – an NGS program to collect high-resolution gravity data across the US and its territories.
$38.5 M
7 – 10 Years

20. How much will “elevations” change?
I can’t tell you, we don’t know…yet.
Geopotential value for “zero” to be determined in consultation with our neighbors.
How the NAVD 88 slope will be “taken out” not yet determined.

21. OPUS Orthometric Height Estimate
An ESTIMATE of height on the NEW vertical datum
Found at the bottom of OPUS extended output
Do NOT use this estimate for anything “serious”, i.e. do not start using/recording these heights
W0 has not been selected
W0 is the geopotential value (geopotential number) that defines 0 (zero) height in the new datum
Selection of W0 is not just a technical decision

22. Related “stuff” i.e. Multi-year CORS Solution & 2011 National Adjustment

23. Multi-Year CORS Solution
When? – coming “Real Soon” (July)
How? – probably as an alternate set of CORS coordinates & OPUS solutions for interested folks
How Much Shift? - An analysis for the Arizona area was performed utilizing a “combined” survey of all Height Modernization style surveys performed in AZ. The combined survey is being used for a vertical adjustment using GEOID09.
Caveat Emptor (performed “solo” - without verification)
More on this later

24. Multi-Year CORS Solution Why?
Longer data spans
Absolute antenna calibrations
satellite transmitting and ground receiving antennas
most significant change
New network design—added redundancy
Delaunay triangulation over global sites and CORS backbone
tie remaining CORS to backbone as stars
IERS 2003 Conventions generally implemented
Updated model for station displacements due to ocean tidal loading
Updated models for troposphere propagation delays
Use current frame; first attempt to obtain a full history of products in a fully consistent framework

29. National Adjustment of 2011

30. NAD 83(2011) Epoch:
Q: Will there be another national adjustment, i.e. a new realization of NAD 83, before the new geometric datum is released?
A: Yes; it’s currently underway at NGS HQ; EOY goal.
Why?
Better agreement between CORS and passive control
Better ellipsoid heights & positions on passive control
Better transition to new datum(s)
Q: Transformation Tool between NAD 83 realizations?
A: Good question – I’m not sure. NGS is beginning an evaluation of possible solutions.

31. How to get to the New Geometric Datum
“Furthermore, NGS will provide simple transformation tools between historic and current datums and reference frames used by NGS, in four dimensions, wherever practical and possible.”
There is no NGS-sanctioned transformation from NAD 83(HARN) to NAD 83(NSRS2007). Therefore, if your data are on a realization prior to NAD 83(NSRS2007) you will either have to get them on NSRS2007 (or 2011) or ignore the position shift and transform them to the new datum. NGS’s OPUS may be the answer for you.
Shift from HARN to NSRS2007
Tucson, AZ

32. Future Milestones of the NSRS
Multi-Year CORS solution –
Completed (for all intents and purposes)
National Adjustment (geometric) of passive control
In planning stage, completed by end of 2011(?)
Hybrid Geoid Model using new ellipsoid heights
In preparation stage, completed 2012?
National Adjustment (vertical) of GPS passive marks
Under consideration
This not adjusting the leveling network
Adoption of new datums
Geometric, could happen any time
Vertical, requires completion of GRAV-D

33. How to Plan for the Future
Move to a contemporary realization of NAD 83
No NAD 83(HARN) <-> NAD 83(NSRS2007) tool
Obtain precise ellipsoid heights on NAVD 88 bench marks (OPUS, contact NGS Geodetic Advisor(s))
Improves hybrid geoid models and provides “hard points” in new vertical datum
Move off of NGVD 29 to NAVD 88
Understand the accuracy of VERTCON in your area
Move away from passive marks to GNSS
Especially move off of classical passive control
Require/provide complete metadata for all mapping contracts
How did they get the positions/heights?
Arizona Spatial Data Accuracy and Georeferencing Standards

34. Questions? A Question for You:
What is good enough with respect to the NSRS, i.e. have we reached a level of precision and accuracy where further realizations (adjustments) are unnecessary?
Dave Minkel

35. Dave Minkel dave.minkel@noaa.gov 602-542-1569
Questions?
Dave Minkel