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

Outline History/background Current situation Rationale for new datums GRAV-D Program  Google Earth displays of geodetic control

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)

ELLIPSOIDS used in the US (More than 60 have been used around the world) CLARKE 1866 (1879 – 1986) a = 6,378,206.4 m 1/f = GEODETIC REFERENCE SYSTEM (GRS 80) ( Present) a = 6,378,137 m 1/f = WORLD GEODETIC SYSTEM (WGS 84) a = 6,378,137 m 1/f = BESSEL 1841 (1848 – 1879) a = 6,377, m 1/f =

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

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

H + H t + V E + V Et ITRF00 ( ) Evolution of Geodetic Datums in U.S. from NAD27/NGVD29 to NAD83/NAVD88 to ?/ ? H + V , 29 H + V (86), 88 H + V E + V O (92), 88 GPS +VELOCITIES (time) H + H t + V E + V O (07)+HTDP, 88 ?

EQUIPOTENTIAL SURFACES

GEOID09 published in Sept 09 In California, GEOID03 considered 567 bench marks with GPS data (ellipsoid heights), and kept 549 In GEOID09, there were 833 considered; 747 were included, a 36% increase

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

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

Rationale for new Geodetic Datums Terminology – Horizontal becomes GEOMETRIC – Vertical becomes GEOPOTENTIAL When?2020, if GRAV-D program is complete Why? But why?! 1.Primarily need a better vertical datum for “vertical” data(geoid, ortho ht) not obtained by traditional leveling

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…”

Rationale for new Datums Terminology – Horizontal becomes GEOMETRIC – Vertical becomes GEOPOTENTIAL When?2018, if GRAV-D program is complete Why? But why?! 1.Primarily need a better vertical datum for “vertical” data(geoid, ortho ht) not obtained by traditional leveling 2.Geodetic Data collection relies upon navigation (GNSS) satellites orbiting around the mass center of the Earth – NAD83 reference frame/datum is not geocentric

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

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

Rationale for new Datums Terminology – Horizontal becomes GEOMETRIC – Vertical becomes GEOPOTENTIAL When?2018, if GRAV-D program is complete Why? But why?! 1.Primarily need a better vertical datum for “vertical” data(geoid, ortho ht) not obtained by traditional leveling 2.Geodetic Data collection relies upon navigation (GNSS) satellites orbiting around the mass center of the Earth – NAD83 reference frame/datum is not geocentric 3.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

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

Worldwide Tectonic Horizontal Motions

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

H + H t + V E + V Et ITRF00 ( ) Evolution of Geodetic Datums: from NAD27/NGVD29 to NAD83/NAVD88 to ?/ ? H + V , 29 H + V (86), 88 H + V E + V O (92), 88 GPS +VELOCITIES (time) H + H t + V E + V O (07)+HTDP, 88 + GRAVITY (geoid model) H + H t + V E + V Et GEOMETRIC (V E +G)[+V Et ] + G t GEOPOTENTIAL

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 – 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

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

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

Preliminary GRAV-D Results

/geodetic/geodetic_control.html

Datums available in VDATUM

Caution: Must Convert fr WGS84/ITRF## to NAD83 and then apply GEOID##

Anything Else?! ftp://ftp.ngs. ftp://ftp.ngs noaa.gov/pub/marti