Who Needs New Datums? NGS Says…

1. Who Needs New Datums?NGS Says… Marti Ikehara California Geodetic Advisor, Sacramento ftp://ftp.ngs.noaa.gov/pub/marti

2. Outline • New datums down the road • GRAV-D Program • New datum, epoch for CORS soon • Visualizing Geodetic control • VDATUM

3. What IS a datum? • It is NOT the same (concept) as a “projection”, which controls how maps are represented or “look” on paper or on a screen. • It is a reference, a basis, for coordinates, so a datum has an origin and/or ‘zero’. • “Underlying” a horizontal datum system is an ELLIPSOID, that represents the global shape of the earth; a DATUM is the ‘continental’ shape as realized with physical marks (passive or active)

4. NGVD29 The National Geodetic Vertical Datum of 1929 was referenced to 26 tide gauges in the US and Canada

5. NAVD88 The North American Vertical Datum of 1988 is referenced to a single tide gauge in Canada

6. EQUIPOTENTIAL SURFACES

8. GEOID09 compared to GEOID03 09: teal, good; yellow: State advisor-rejected; red: analysis-rejected 03 (underlying dots): dk blue, kept; orange: rejected

9. From Helmer’s article in Winter 09/10 issue of California Surveyor

10. 2009 National Research Council Report “…uniform national standards for FEMA flood maps cannot be met until an improved orthometric height datum and geoid model exist…”

11. Rationale for new Datums • Terminology • Horizontal becomes GEOMETRIC • Vertical becomes GEOPOTENTIAL • When? 2018, if GRAV-D program is complete • Why? But why?! • Primarily need a better vertical datum for “vertical” data(geoid, ortho ht) not obtained by traditional leveling • Geodetic Data collection relies upon navigation (GNSS) satellites orbiting around the mass center of the Earth • NAD83 reference frame/datum is not geocentric

12. Z Earth-Centered Earth-Fixed (ECEF) Coordinate System XA, YA,ZA (not NAD83) -Y -X Greenwich Meridian Earth Mass Center X, Y, Z = 0 Y X GRS 80 Ellipsoid -Z

13. Simplified Concept of NAD 83 vs. ITRF00 (or WGS84) h83 h00 Earth’s Surface ITRF 00 Origin 2.2 meters Identically shaped ellipsoids (GRS80) a = 6,378,137.000 meters (semi-major axis) 1/f = 298.25722210088 (flattening) NAD 83 Origin

14. Rationale for new Datums • Terminology • Horizontal becomes GEOMETRIC • Vertical becomes GEOPOTENTIAL • When? 2018, if GRAV-D program is complete • Why? But why?! • Primarily need a better vertical datum for “vertical” data(geoid, ortho ht) not obtained by traditional leveling • Geodetic Data collection relies upon navigation (GNSS) satellites orbiting around the mass center of the Earth • NAD83 reference frame/datum is not geocentric • Earth is not stable in all directions; reference frame must account for this to be as geodetically accurate as possible • NAD83 is not defined to include vertical velocities

15. Horizontal Velocities, relative to ‘stable’ NA tectonic plate, are reflected in HTDP model

16. Worldwide Tectonic Horizontal Motions

17. CORS Data allows for Monitoring Vertical Crustal Motion Vertical velocities associated with Glacial Isostatic Adjustment (rebound)

18. Evolution of Geodetic Datums: from NAD27/NGVD29 to NAD83/NAVD88 to ?/ ? GPS H + V 2 + 1 27, 29 H + V 2 + 1 83(86), 88 H + VE+ VO 2 + 1 + 1 83(92), 88 +VELOCITIES (time) H + Ht+ VE +VO 2 + 2 + 1+ 1 83(07)+HTDP, 88 H + Ht+VE+ VEt 2 + 2 + 1+ 1 GEOMETRIC (VE+G)[+VEt] + Gt 1 + 1 GEOPOTENTIAL H + Ht+VE+ VEt 2 + 2 + 1+ 1 ITRF00 (2002.00) + GRAVITY (geoid model)

19. The Future of Height Mod: GRAV-D Gravity for the Redefinition of the American Vertical Datum • GRAV-D • Airborne gravity surveys (taking 10 years) • Coastal areas surveyed first • All USA states and territories • www.ngs.noaa.gov/GRAV-D • GOAL: • Orthometric heights-”elevations” – to be good to 2 cm anywhere, anytime with an excellent ellipsoid height from GNSS technology. Currently this takes 3-4 hours at 15-second recording and dual-frequency GPS • Height changes much more easily monitored than by leveling, using new technology – GNSS heights and gravity values • Spot-checking/monitoring gravity changes with portable field units

20. “CONUS” Alaska Guam / Northern Marianas Hawaii Puerto Rico / Virgin Islands American Samoa Planned GRAV-D Coverage

21. Status of GRAV-D in early 2010 As of Jan 2010: 6.7% of planned areas have been flown NGA funded NRL plane USACE funded

22. Preliminary GRAV-D Results

23. New datum, epoch for CORS • Current: ITRF2000, 2002.00 • Near end of year: ITRF2008, 2008.00 • NAD83 (“CORS96A”), 2010.00 • No change to passive monumentation, eg, NAD83 (NSRS2007), 2007.00 • About 1000 CORS nationwide • Those with >2 years of data • Changes on the order of mm, but some outliers are showing closer to decimeters • List will be prepared, showing amount of change

24. http://www.dot.ca.gov/hq/row/landsurveys/geodetic/geodetic_control.htmlhttp://www.dot.ca.gov/hq/row/landsurveys/geodetic/geodetic_control.html

27. http://www.dot.ca.gov/hq/row/landsurveys/geodetic/geodetic_control.htmlhttp://www.dot.ca.gov/hq/row/landsurveys/geodetic/geodetic_control.html

29. Datums available in VDATUM

30. www.vdatum.noaa.gov

35. Anything Else?! • Marti.ikehara@noaa.gov • 916-227-7325 • ftp://ftp.ngs. noaa.gov/pub/marti