Upcoming Changes to the Upcoming Changes to the National Spatial Reference SystemNational Spatial Reference System

— — The Upcoming Changes in National Datums The Upcoming Changes in National Datums ——(and a few other related topics)(and a few other related topics)

Dave MinkelNational Geodetic Survey

APLS Geospatial Professional

ACSMACSMSurvey Summit 2011Survey Summit 2011

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.

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

Why a New Datum(s)?o NAD 83

o non-geocentric, i.e. inconsistent with GNSS positioningo NAD 83 coordinates of the Continuously Operating Reference Station (CORS) network

inconsistent with passive marks o Lack of velocities, i.e. NAD 83 does not report station motion for passive marks

o NAVD 88 o cross-country build up of errors (“tilt” or “slope”) from geodetic levelingo Passive marks inconveniently located and vulnerable to disturbance and destructiono A 0.5 m bias in the NAVD 88 reference surface from the geoid surface best

approximating global mean sea levelo Subsidence, uplift, freeze/thaw, and other crustal motions invalidate heights of passive

marks, and can make it difficult to detect such motions.o Passive marks without adequate geophysical models make it difficult to reliably detect

sea level changeo 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)

o The gravity model and modeling techniques used to determine NAVD 88 are not consistent with those currently used for geoid modeling

Geometric DatumGeometric Datum

“NGS redefines the national horizontal datum to remove gross

disagreements with the ITRF.”

In other words, horizontal coordinates will change.

X

Z

YXA

YA

ZA

Equator

Gre

enw

ich

Mer

idia

n

ECEF Coordinates

- X

- Y

- Z

(XA,YA,ZA,)

Longitude

Latitude

Ellipsoid Height

Latitude, Longitude,& Height

(, , h)

Earth Mass Center

Reference Frames 101

GRS80 Ellipsoid

X

Z

Y

A“gross disagreements with the ITRF” (?)

NAD 83Earth Mass Center

ITRFEarth Mass Center GRS 80

EllipsoidShift ≈ 2.2m +

WAMs = 4.9 ft to 2.6 ft

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)

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.

And now….. the rest of the story.

Orthometric Heights, a.k.a. NAVD 88 elevations

“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.

The Relationship of Heights

WAMs = -0.98 ft to -5.25 ft

Geoid (USGG09)

NAVD 88 (GEOID09)

H HH

H

GPS Bench Marks (GPSBMs)

Errors in NAVD 88 : ~50 cm average, 100 cm CONUS tilt, 1-2 meters average in Alaska

H(NAVD 88)

(USGG09)

WAMs = -1.18 ft to +1.28 ftWAMs = -1.18 ft to +1.28 ft

GPS-derived orthometric heights Warning #1H ≈ 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 #1H ≈ 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 #2H ≈ 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 = -20.1 cm, max = 11.5 cm, avg = -2.4 cm

GPS-derived orthometric heights Warning #2H ≈ 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 = -20.1 cm, max = 11.5 cm, avg = -2.4 cm

WAMs = -0.49 ft to +0.72 ftWAMs = -0.49 ft to +0.72 ft

NAVD 88 “Slope”

GRAV-DGravity 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 M7 – 10 Years

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.

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

Related “stuff”i.e. Multi-year CORS Solution

&2011 National Adjustment

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

Multi-Year CORS SolutionWhy?

• 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

National Adjustmentof 2011

Q: Will there be another national adjustment, i.e. a new realization of NAD 83, before the new geometric datum is released?

Why?• Better agreement between CORS and passive control• Better ellipsoid heights & positions on passive control• Better transition to new datum(s)

NAD 83(2011) Epoch:2010.00

A: Yes; it’s currently underway at NGS HQ; EOY goal.

Q: Transformation Tool between NAD 83 realizations?

A: Good question – I’m not sure. NGS is beginning an evaluation of possible solutions.

“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.

How to get to the New Geometric Datum

Shift from HARN to NSRS2007Tucson, AZ

Shift from HARN to NSRS2007Tucson, AZ

Future Milestones of the NSRS

1. Multi-Year CORS solution – – Completed (for all intents and purposes)

2. National Adjustment (geometric) of passive control– In planning stage, completed by end of 2011(?)

3. Hybrid Geoid Model using new ellipsoid heights– In preparation stage, completed 2012?

4. National Adjustment (vertical) of GPS passive marks– Under consideration– This not adjusting the leveling network

5. Adoption of new datums– Geometric, could happen any time– Vertical, requires completion of GRAV-D

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

Questions?Questions?A Question for You:A Question for You:

What is good enough with respect to the NSRS, What is good enough with respect to the NSRS, i.e. have we reached a level of precision and i.e. have we reached a level of precision and

accuracy where further realizations accuracy where further realizations (adjustments) are unnecessary?(adjustments) are unnecessary?

Dave MinkelDave Minkeldave.minkel@noaa.govdave.minkel@noaa.gov

602-542-1569602-542-1569

Questions?Questions?

Dave MinkelDave Minkeldave.minkel@noaa.govdave.minkel@noaa.gov

602-542-1569602-542-1569