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

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

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

2 Outline New datums down the road GRAV-D Program, building on GOCE data New datum, epoch for CORS soon Visualizing Geodetic control

3 What IS a datum? 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) Our vertical datum is based on differential leveling

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

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

6 EQUIPOTENTIAL SURFACES

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

11 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…”

12 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

13 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)

14 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

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16 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 – Vertical velocities are ignored for NAD83

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

18 Worldwide Tectonic Horizontal Motions

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

20 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

21 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

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

23 Preliminary GRAV-D Results

24 Gravity/geoid as measured by GOCE satellite

25 1. Earth is a slightly flattened sphere - it is ellipsoidal in shape 2. Goce senses tiny variations in the pull of gravity over Earth 3. The data is used to construct an idealised surface, or geoid 4. It traces gravity of equal 'potential'; balls won't roll on its 'slopes' 5. It is the shape the oceans would take without winds and currents 6. So, comparing sea level and geoid data reveals ocean behaviour 7. Gravity changes can betray magma movements under volcanoes 8. A precise geoid underpins a universal height system for the world 9. Gravity data can also reveal how much mass is lost by ice sheets

26 New datum, epoch for CORS Current: ITRF2000, Near end of year: ITRF2008, and NAD83 (“CORS96A”), for CORS only No change to passive monumentation, eg, NAD83 (NSRS2007), About 1000 CORS nationwide – Those with >2 years of data – Changes on the order of mm, but a few outliers are showing several decimeters – List will be prepared, showing amount of change

27 Visualization of NGS Geodetic Control Geodetic advisor website, located at Caltrans Office of Land Surveys webpages /geodetic – Google Earth kmls – Google Maps online – Shapefiles DSWorld, NGS partner software

28 /geodetic/geodetic_control.html

29 Kml’s and shapefiles downloadable

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32 /geodetic/geodetic_control.html

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34 Using NGS DSWORLD software and Google Earth to get any vintage geodetic data from NGSIDB Start by downloading “Google earth” at: Click here

35 Mouse-over the “TOOLS” button Click on “DOWNLOAD PC SOFTWARE” Open the NGS main page at

36 Click here Click on the link: “User Contributed Software is also available…..”

37 Next, click on the DSWORLD (Version *.**) link. A “file download” window will appear. Choose to save the file where you can easily find it. It will be a zip file, so you will need to unzip it and then double click on the setup.exe file. That will install the program for you. For additional information or assistance, please contact your NGS State Geodetic Advisor

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


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